FLIGHT TEST VALIDATION REPORT – D39 · AMS (Italy) DLR (Germany) FRQ (Austria) Indra Sistemas...

TECHNICAL REPORT

CONTRACT N° : GRD1-2000-0228

PROJECT N° :

ACRONYM : MA-AFAS

TITLE : THE MORE AUTONOMOUS - AIRCRAFT IN THE FUTURE AIR TRAFFIC MANAGEMENT SYSTEM

FLIGHT TEST VALIDATION REPORT – D39

AUTHOR : QINETIQ (UK)

PROJECT CO-ORDINATOR : BAE SYSTEMS

PRINCIPAL CONTRACTORS :Airtel ATN Ltd (Ireland) QinetiQ (UK)ETG (Germany) EUROCONTROL (France)NLR (Netherlands)

ASSISTANT CONTRACTORS:Airsys ATM (France) Galileo Avionica (Italy)AMS (Italy) DLR (Germany) FRQ (Austria) Indra Sistemas (Spain) NATS (UK) SCAA (Sweden) S-TT (Sweden) Skysoft (Portugal) SOFREAVIA (France) Stasys Limited (UK)

Report Number : QINETIQ/S&E/AVC/CR031041 – D39Project Reference number :Date of issue of this report : 19 Jun 2003Issue No. 1.0

PROJECT START DATE : 01 Mar 2000 DURATION : 40 months

Project funded by the European Communityunder the ‘Competitive and SustainableGrowth’ Programme (1998-2002)

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Customer Information

Customer Reference NumberProject Title The More Autonomous-Aircraft in the

Future Air Traffic Management SystemCompany Name BAE SYSTEMSCustomer Contact A Hanna

Contract Number GRD1-2000-0228Milestone Number D39Date Due (dd/mm/yyyy) 30/06/2003

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Authorisation

Prepared by I MansfeldTitle Senior Flight Test Engineer

Signature

DateLocation QinetiQ, MoD Boscombe Down

Approved by Dr D WalkerTitle CM – Telematic Solutions

Signature

Date

Principal authorsAuthorised by Mr A Hanna

Title BAE Systems

SignatureDateName Mr A WolfeAppointment Senior ScientistLocation QinetiQ Boscombe Down

NameAppointmentLocation

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Record of changes

Issue Date Detail of ChangesA 29/04/03 DraftB 10/06/03 Revised Draft after internal reviewC 19/06/03 Completion of all chapters and additional update from reviewD 30/06/03 Minor refinements

QinetiQ/S&E/AVC/CR031041 v

List of contents

Authorisation iii

Record of changes iv

List of contents v

List of Figures vii

List of Tables viii

1 Introduction 11.1 Scope of Document 1

1.2 Programme 1

2 BAC 1-11 Validation Flights 22.1 Sortie Overview 2

2.2 Summary Table 2

2.3 Trial Routes 3

2.4 Trial Scripts 3

2.5 Sortie Details 3

3 Boscombe Down Trials 43.1 14th January 2003 4

3.2 7th February 2003 9



3.5 11th March 2003 26

3.6 14th March 2003 27

3.7 19th March 2003, Sortie No. 762. 32

3.8 19th March 2003 34

3.9 19th March 2003 39

3.10 20th March 2003 40

3.11 Summary of GBAS Approach Guidance Presented on the Primary Flight Display. 46

3.12 Summary of Boscombe Results 53

4 Rome Trials 564.1 24th March 2003 56

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4.2 25th March 2003 58

4.3 25th March 2003 62

4.4 26th March 2003 64

4.5 26th March 2003 67

4.6 28th March 2003 69

4.7 28th March 2003, Sortie No. 774. 72

4.8 Summary of Rome Results 73

5 Overall Summary of MA-AFAS Flight Trials 76

6 Conclusions and Recommendations 78

7 References 80

8 List of abbreviations 81

A Appendix 83A.1 Original QNQ1 UK Trials Route 83

A.2 UK route QNQ1 (revised) 85

A.3 Rome Route QNQ6 87

Report documentation page 89

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List of Figures

Figure 3.1-1: Route Flown for First MFMS Trial 4Figure 3.1-2 Demanded and Actual Bank Angle, 1st Circuit, 14th Jan. 03 6Figure 3.1-3 Demanded and Actual Computed Air Speed, 1st Circuit, 14th Jan. 03 7Figure 3.2-1 Route used for MFMS Flight, 7th Feb. 03 9Figure 3.3-1 Tracks for BAC 1-11 and SIM00 14Figure 3.3-2 Spacing of BAC 1-11 from SIM00 14Figure 3.3-3 Tracks of BAC 1-11 and SIM02 15Figure 3.3-4 Spacing of BAC 1-11 from SIM02 15Figure 3.3-5 Tracks of BAC 1-11 and SIM03 16Figure 3.3-6 Spacing of BAC 1-11 from SIM03 16Figure 3.4-1 GBAS Position Reports during Precision Departure 20Figure 3.4-2 Accuracy of GBAS 3D Position Data during Departure 20Figure 3.4-3 Freeze of SBAS Data within the FMS, 27th Feb. 03 22Figure 3.4-4 Tracks of BAC 1-11 and SIM04 23Figure 3.4-5 Spacing of BAC 1-11 from SIM04 23Figure 3.4-6 ADS-B Flight Data Received by EEC 24Figure 3.6-1 Tracks of BAC 1-11 and SIM03 29Figure 3.6-2 Spacing of BAC 1-11 from SIM03 29Figure 3.8-1: QNQ5 Route used for Test Flight in Rome, 19th March 03 34Figure 3.8-2 Tracks of BAC 1-11 and SIM02 for 1st Pass-Behind Manoeuvre 35Figure 3.8-3 Spacing of BAC 1-11 from SIM02 during 1st Pass-Behind Manoeuvre 35Figure 3.8-4 Tracks of BAC 1-11 and SIM02 for 2nd Pass-Behind Manoeuvre 36Figure 3.8-5 Spacing of BAC 1-11 from SIM02 during 2nd Pass-Behind Manoeuvre 36Figure 3.8-6 Plot of ADS Position Data during Rome Test Flight 38Figure 3.10-1 Precision Departure Route With Indication of GBAS Operational Mode 41Figure 3.10-2 Accuracy of GBAS Position Fix Referenced to GPS Truth Track 41Figure 3.10-3 Tracks of the BAC 1-11 and SIM02 42Figure 3.10-4 Spacing of BAC 1-11 from SIM02 42Figure 3.10-5 Approach Route with Indication of GBAS Operational Mode 44Figure 3.10-6 Accuracy of GBAS Position Fix Relative to GPS Truth Track 44Figure 3.10-7: MFMS Lateral Guidance Performance 45Figure 3.11-1: Representative STAR for Boscombe Down 46Figure 3.11-2: 7th February GBAS Approach 1 using 3º Glide Slope 47Figure 3.11-3: 7th February GBAS Approach 1 using 4.5º Glide Slope 48Figure 3.11-4: 19th February GBAS Approach using 3º Glide Slope 49Figure 3.11-5: Glide Slope Comparisons for Approaches on 14 March 51Figure 3.11-6: GBAS and MA-AFAS Glide Slope Differences 52Figure 4.2-1 Spacing during first Pass-Behind Manoeuvre, 25th Mar. 03 59Figure 4.2-2 Spacing during second Pass-Behind Manoeuvre, 25th Mar. 03 60Figure 4.4-1: Spacing Distance during Merge Manoeuvre, 26th Mar. 03 65Figure 4.6-1: Spacing of BAC 1-11 from ATTAS during Merge Behind, 28th Mar. 03 70

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List of Tables

Table 2.2-1: Flight Trials using MA-AFAS on the QinetiQ BAC 1-11 2Table 3.11-1: GBAS Guided Approaches 46Table 4.2-1: Updated VDL4 Identity Codes 58

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1 Introduction

1.1 Scope of Document

This document describes the validation flight testing of the Avionics Package (AvP),developed within the MA-AFAS project, in the QinetiQ BAC 1-11 avionics researchaircraft and the DLR VFW-614 ATTAS aircraft. The initial test flights, using only theBAC 1-11, took place from QinetiQ Boscombe Down in the UK, during the periodJanuary to March 2003. These flights were intended to verify the performance of theMA-AFAS FMS (MFMS) and the associated air/air and air/ground data linkcommunications environment. This also included the procedures developed for thedifferent Airborne Separation Assurance System (ASAS) manoeuvres, these beingcarried out in a real airborne environment. While these flight trials took place,development continued of the various MA-AFAS functional components. The flighttrials at Boscombe Down were the precursor to the main trials that took place from RomeCiampino Airport in Italy between 24th and 28th March 2003. Both aircraft participated inthese trials to investigate the performance when the ASAS manoeuvres were performedwith live aircraft in the roles of both the host aircraft and the target aircraft.

A further set of taxi management and flight trials, using additional developments of theASAS functionality, were conducted on the DLR ATTAS aircraft in May 2003. Theresults of these trials are provided in a separate document [4], Annex A to this flighttrials report. An additional document, Annex B of this current D39 report, contains adetailed summary by NATS of the performance of the Ground- and Satellite-BasedAugmentation Systems (GBAS and SBAS) that were used to support the flight trials atBoscombe Down [5]. The GBAS provided approach guidance information to the pilotduring these flights and it was intended that the MFMS would also use this system toprovide a precision approach capability. A further MA-AFAS document, D40 [6],describes the airline pilot evaluation of the MFMS and the ASAS manoeuvres conductedon the NLR simulator in Amsterdam.

Prior to the flight trials programme and in support of the continued system developmentonce it had started, ground simulation testing of the MA-AFAS components was carriedout at the different trials sites. This was intended to resolve any functional performanceproblems with the system before it was committed to the real airborne environment. Theresults of these ground tests are described in the MA-AFAS document D37 [3].

1.2 Programme

The planned flight test programme and deliverables are fully described with the MA-AFAS D32 document [1]. In particular, Annex A of document D32 refers to the flighttests that were to be carried out from Boscombe Down, Annex B refers to the testsconducted by DLR from Braunschweig and Annex C to flight tests from RomeCiampino. Finally, Annex D of D32 defined the tests that were to be performed at NLRfor the pilot evaluations.

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2 BAC 1-11 Validation Flights

2.1 Sortie Overview

The initial development sorties were all flown out of the QinetiQ Boscombe Downairfield in the southern UK. Not all of these used the entire MA-AFAS FMS (MFMS)equipment, for example when flights were dedicated to assessing problems with the VHFData Link mode 4 (VDL4) data link. Due to these data link problems, the trialsprogramme was re-arranged to allow for a one day visit to the Rome operating area sothat both the VDL4 and the proposed route could be tested prior to the final flight phase.The final week of the trials was flown out of Rome Ciampino airport, and during thisperiod the MFMS was exercised for the first time using a live ‘target’ aircraft usingADS-B via the VDL4.

2.2 Summary Table

Serial Date Location S/Wversion

Notes

1 14/01 Boscombe Down C5 Initial Shakedown using short route. Basic FMS operationonly, no ASAS.

2 07/02 Boscombe Down D2 Short route. Simulated static ASAS target used.

3 19/02 Boscombe Down D2-ER1 Long Route with simulated ASAS targets. VDL4 coverageexplored.

4 27/02 Boscombe Down D3 Long Route with added ‘loop’ for Merge. Western extentreduced for VDL4. SID flown.

5 11/03 Boscombe Down N/A VDL4 Range checks only. No MFMS.

6 14/03 Boscombe Down E1A-2 Met data introduced.

7 19/03 Boscombe Down E1A-3 Airways transit to Rome for VDL4 checks.

8 19/03 Rome Ciampino E1A-3 Rome route using simulated targets. Voice and VDL4coverage were explored.

9 19/03 Rome Ciampino E1A-3 Airways transit.

10 20/03 Boscombe Down E1A-3 The full ‘Rome’ version exercised with simulated targets

11 24/03 Boscombe Down E1A-3 Airways transit to Rome. Checks of ATTAS VDL4 link.

12 25/03 Rome Ciampino E1A-3 ATTAS target via VDL4





17 28/03 Rome Ciampino E1A-3 Airways transit

Table 2.2-1: Flight Trials using MA-AFAS on the QinetiQ BAC 1-11


2.3 Trial Routes

The trials were flown over planned routes. The initial planning for the UK trials requiredco-ordination through controlled airspace to permit the BAC 1-11 to fly on non-deviatingtracks (i.e. not to be subject to ATC tactical changes of heading or altitude). QinetiQBoscombe Down, as a part of the normal trials planning and support, carried out liaisonwith the UK Airspace Utilisation Service (AUS) to produce an Aeronautical Co-ordination Notice (ACN) [2]. This was promulgated 6 weeks before commencement ofthe trials, and is contained in Appendix A.1. The route it describes is the one referred toas ‘QNQ1’ within the MFMS.

During the development, several modifications were made to the route in order to enablethe ASAS functionality to be fully exercised. The most used version of this is shown asAppendix A.2.

For Rome trials, a similar and lengthy liaison process with ENAV was successfullyfollowed to produce the route QNQ6, promulgated by ENAV as a NOTAM (Notice toAirmen). This route is shown as Appendix A.3.

2.4 Trial Scripts

For each sortie, a comprehensive script was developed to suit both the route to be flownand the functions to be exercised .

2.5 Sortie Details

Each of these sorties will now be covered in more detail as a series of flight reports. Thesorties have been divided up to cover those associated with development of the MFMS(described in Chapter 3) and those relating to the live aircraft trials in Rome (described inChapter 4). Each flight report is presented in a series of functional groups representingthe systems that integrate to provide the overall MA-AFAS. Due to the nature of thedevelopment programme, data is not available for all sections for all of the sorties.Within each functional group, the information has been collated from that provided bythe system specialists.


3 Boscombe Down Trials

3.1 14th January 2003

3.1.1 Sortie Objectives

The primary intention of this first flight with the MFMS on-board the BAC 1-11 was toensure that the MFMS would operate correctly when integrated with the various otheravionics systems installed on the aircraft. Of greatest interest was the interaction of theMFMS with autopilot in order to confirm that the MFMS demands could be handled bythe autopilot without any significant problems in the airborne environment and that therewas smooth tracking of the transitions in the demand values by the autopilot. The otherkey factors included verification of simulation results conducted with the ground basedavionics rig to confirm that the MFMS would continue to function throughout theduration of the flight without any system failures or runtime problems.

At this stage, there was still a limitation in the basic functionality of the MFMS so thatthe system could only predict a trajectory containing climb and cruise phases, but nodescent. The FMS was also assuming zero wind conditions and an ISA temperaturegradient with altitude when predicting the aircraft's trajectory. Additionally, only thelateral version of the Navigation Display was available to the pilot at this stage of thesystem development.

Figure 3.1-1: Route Flown for First MFMS Trial


For this first flight, a short route (stored as company route BOSC02) was flown in orderto verify the basic FMS and validate experience with the ground test simulation. This isshown in Figure 3.1-1, the circular route being flown in the clockwise direction. NoVDL4 transponder was available for use on this flight.

3.1.2 MFMS Report

The FMS equipment had been installed in the cockpit of the BAC 1-11 to allow the left-hand pilot to operate the system. The right-hand pilot had the standard instrumentationavailable in order to act as the safety pilot during the flight. The MCDU had beenmounted in the centre pedestal area just aft of the throttle quadrant so that it could beviewed by both pilots and allowing the safety pilot to monitor the intended actions of theFMS. The left-hand pilot was also provided with a track-ball, mounted on the right-handarmrest that permitted the pilot to interact with the soft keys on the electronic NavigationDisplay. This display was also only available to the left-hand pilot, having been mountedin the console directly in front of the pilot.

In the cabin of the aircraft, the scientific crew that was monitoring the performance of thesystem could view a repeater of the Navigation Display. An IHTP laptop PC was alsoconnected via ethernet to the PC cards in the FMS cabinet, allowing additionalmonitoring of the system behaviour, including the emulation of the MCDU and to detectany possible problems being encountered.

For this first flight, the pilot was able to use the MCDU to initialise the FMS, includingselecting the primary navigation data source to be the inertial reference system (IRS),inputting the fuel load and zero fuel weight of the aircraft and finally selecting thecompany route. The pilot also input the required cruise altitude (in this case FL240,although the MCDU required the entry in feet) before generating the trajectory while theaircraft was still on the ground at the stand. In its current form, the FMS used zero as thetake-off time, viewing the generation in terms of an elapsed time. When predicting thelateral route, the FMS used 8nm constant radius turns. The vertical and speed profiles

The picture at leftshows the ElectronicFlight InstrumentSystem (EFIS) in theBAC 1-11. This is inthe Left Side cockpitonly, and comprisesa Primary FlightDisplay of Attitude,Speed and Altitudeon the left, and theExperimental MapDisplay on the right.The Map display isshowing the MFMSoutput during anASAS Pass-Behindmanoeuvre.


were predicted based on a set of subphases with a continuous climb from take-off to thecruise altitude. The initial en-route climb speed was defined to be 230 knots CAS with aspeed change on reaching FL100 to 250 knots CAS and a further acceleration to 260knots CAS once the aircraft was at the cruise level.

Once the aircraft had taxied to the holding point for runway 23 at Boscombe Down, afurther trajectory generation was carried out successfully. The trajectory was notactivated until after the aircraft had taken off. With the autopilot first engaged in its basicmodes, the FMS demands were then engaged by the pilot selecting the LateralNavigation (LNAV) and Profile (PRFL) modes on the autopilot control panel. Theaircraft was at about 5400ft once the FMS demands were engaged through the autopilot.The aircraft was just under 1.5nm off to the left of its originally intended track at thisstage, but the bank demand from the FMS resulted in the aircraft capturing back on totrack just at the start of the turn at waypoint B15. Lateral guidance was then maintainedthroughout the remainder of the flight until the aircraft was about 3nm (on track forrunway 05) before being overhead Boscombe Down (waypoint EGDM) when the pilotdisengaged the system in order to perform an approach to runway 23. Figure 3.1-2 showshow the autopilot was able to track the bank angle demand from the FMS, there being alatency of 1 or 2 seconds in the autopilot's response to a change in the demand. It canalso be seen that the pilot had briefly disengaged the autopilot at about 2770 seconds,although the MFMS demands were soon re-engaged again.

Figure 3.1-2 Demanded and Actual Bank Angle, 1st Circuit, 14th Jan. 03

The Profile demands were also successfully used by the autopilot, the FMS initiallydemanding a climb to FL240 at 250kts CAS and with a climb power setting of 94% HPRPM. Although the aircraft was lower than FL100 when the demands were fully engaged


with the autopilot, the MFMS, in these earlier versions, was deriving the speed demandsbased on the aircraft's position along the route. Consequently, due to the aircraft havingbeen delayed on its initial climb out from Boscombe Down, it was not as high as theMFMS had originally predicted and had passed the point on the route where the MFMShad expected it to reach FL100. Therefore the speed demand had already transitioned to250kts (see Figure 3.1-3). As seen with the ground test runs using the aircraft model rig,the FMS had occasional problems calculating the aircraft's relative position to thesubphase transition points. In this case, it was known that it did not correctly determinethe distance from the top of climb point where the aircraft was to accelerate to 260ktsCAS. Therefore this speed change did not occur, although there was a brief increase inthe speed demand during the climb itself, before returning to 250kts again. This wasdirectly related to the problem with a relative distance calculation. Once the aircraft hadreached waypoint C in the cruise, the Profile demands were disengaged from theautopilot and the pilot directly dialled in a descent to FL50 on the autopilot. The lateralbank demand from the FMS was still engaged, however

Figure 3.1-3 Demanded and Actual Computed Air Speed, 1st Circuit, 14th Jan. 03

The aircraft landed at the end of the approach to runway 23 and the FMS system wasreset in order to repeat the flight. The system behaved identically to the first flight,although there were some problems with the initial engagement of the autopilot due to ithaving not fully reinitialised after the landing (this was an issue on this first flight onlyand the problem was not encountered on any subsequent MFMS flight). The MFMSdemands were not fully engaged through the autopilot this time until the aircraft was at


about FL120. As before, the Profile demands were disengaged at waypoint C while thelateral demands were maintained until about 3nm before EGDM at FL50.

The flights showed consistency with the results obtained from the simulation runs. Theyproved that the basic FMS was functioning correctly with the other on-board systems andwas capable of using the data from these various systems such as the inertial referencesystem, the air data computer, the engine instrumentation system and the autopilot.Similarly, the autopilot was able to function properly using the demands from the FMSwith no divergent trends or other problems in tracking these demands to guide the aircraftboth in the lateral and profile modes along the predicted trajectory.


3.2 7th February 2003


For the second trials flight with the MFMS, advancements in the development of thesystem now permitted a complete flight profile to be predicted from take-off to theapproach gate altitude at the arrival airport (in this case Boscombe Down again). TheSTAR produced for this flight took the aircraft to a waypoint, DM002, just prior to theturn on to the final approach for runway 23 at a distance of about 8nm from touchdown.The gate altitude was set to be FL40 and it was intended that the predicted trajectoryshould maintain FL40 throughout the region of the STAR.

The route had also been modified (now company route BOSC06) so that the aircraftwould effectively fly the BOSC02 route in reverse, i.e. anticlockwise (see Figure 3.2-1).This was to allow a suitably long straight section of track on which to perform a pass-behind manoeuvre and also to provide a smoother feed into the STAR, which was to thesouth of the airfield. The cruise altitude was reduced to FL210 in order to permit a betterduration of cruise.

Figure 3.2-1 Route used for MFMS Flight, 7th Feb. 03

The functionality of the system had been improved and it was intended to test a pass-behind manoeuvre being performed relative to a target aircraft selected by the pilot viathe MCDU ASAS pages. In this case, a simulated target aircraft was created within theFMS that would conflict with the trajectory of the BAC 1-11. In order to ensure that thesimulated target aircraft was going to be in the correct position and at the right time tocreate a conflict, this aircraft was defined to have a ground speed of only 1kt and to be at


a position about 5nm along the leg from waypoint AGIBS to DM005. This aircraft wasalso set up to be following a north-south track, which was about 100º to the proposedtrack of the BAC 1-11.

Additional updates had been incorporated in order for the FMS to utilise the data fromthe two GPS systems, SBAS and GBAS, including the use of this data to assign UTCtime within the FMS. The FMS defaulted to using GBAS as its primary navigation datasource, the pilot being able to change this selection via the MCDU, if required.Improvements had also been made to the determination of relative distance from theaircraft to the subphase change points in order to overcome the problem where speedchanges were being triggered at incorrect points along the route.

As for the previous flight, the VDL4 transponder was not currently available for testing.

3.2.2 MFMS Report

Similar to the first flight, the pilot used the MCDU to initialise the FMS and generate atrajectory for the BOSC06 company route. As well as inserting the required cruisealtitude, the pilot also now had to input the Estimated Off-Blocks Time (EOBT) and theComputed Take-Off Time (CTOT). It was known from the ground tests with the aircraftmodel rig that the FMS was computing a descent that was far too shallow for what theaircraft would typically achieve and therefore the predicted descent was not reachingFL40 by the beginning of the STAR. The predicted location for the top of descent wassuitable, however, for achieving this required altitude within the given distance when itwas actually flown. For the purpose of this trial, this was not a significant problem.

Prior to take-off, the primary navigation source was changed from GBAS to SBAS toensure a continuous data source for the flight. As on the first flight, the trajectory was notactivated until the aircraft was airborne. After the aircraft had been cleaned up (flaps andundercarriage retracted) and the aircraft established in the climb, then the FMS lateraland profile demands were engaged through the autopilot. The initial FMS speed demandwas 230 knots CAS that was then increased to 250 knots as the aircraft passed thesubphase change point on the route. A further increase to 260 knots CAS occurred whenthe aircraft attained the cruise altitude of FL210. Prior to the demand for descent to 5900feet (final altitude of the trajectory), the FMS demanded a deceleration back to 250 knotsCAS, in accordance with the predicted flight profile.

Once into the descent, the pilot was able to enter the details for the pass-behindmanoeuvre into the FMS via the MCDU. This was to simulate the response to aninstruction from ATC to perform a manoeuvre in which ATC are delegating partialresponsibility to the pilot for ensuring the required manoeuvre spacing from the otherconflicting traffic. Having identified that the minimum separation between the twoaircraft will be compromised, ATC could request that one aircraft performs a pass-behindmanoeuvre with a defined spacing distance to be observed and to return to the originalroute at an assigned waypoint. In this case, the BAC 1-11 was to pass-behind the othertraffic, SIM01, with a minimum manoeuvre spacing of 5nm and to return to the originalroute at waypoint DM005. The traffic identity, the type of manoeuvre, the minimumspacing and the resume waypoint were all entered by the pilot through the MCDU.


The pilot was also able to select an option on the lateral Navigation Display using thetrack-ball in order to display any other traffic in the vicinity for which ADS-B reportshad been received. After entering the target aircraft's identity into the ASAS page of theMCDU, this traffic was highlighted on the Navigation Display in orange to easeidentification. A trajectory could only be generated, however, once the BAC 1-11 was ona straight leg and therefore this delayed the manoeuvre until the aircraft had completedits turn at waypoint A. The conflicting aircraft, SIM01, was now about 2nm to the rightof the leg from waypoint AGIBS to DM005. At this point, the pilot was able to use theMCDU to request the FMS to compute a trajectory incorporating the pass-behindmanoeuvre. This was successfully achieved and the trajectory activated, althoughactivation had to be performed within 15 seconds because this was the time period aheadof the aircraft that the FMS maintained current track before inserting any start of turn toavoid the conflict situation.

With the target aircraft being effectively static, the trajectory generated by the FMSdeviated the BAC 1-11 by 3.8nm to the left of its original track between AGIBS andDM005, allowing for the fact that the target aircraft was already 2nm to the right of thistrack (see Figure 3.2-1). The route distance for this pass-behind manoeuvre to itstermination at waypoint DM005 was 38.6nm, which was only about 0.5nm greater thanthat for the original route. However, this partly benefited from the fact that themanoeuvre bypassed the waypoint AGIBS at which there was 7º turn to the left towardsDM005, i.e. in the same direction as the pass-behind manoeuvre was turning the aircraft.

Since this manoeuvre had not originally been intended for use during the descent, it didhave an effect on the predicted speed during the course of the manoeuvre. The FMSmanoeuvre generator assigned time constraints to each of the track change points that itdefined to create the pass-behind. In this case, the system determined the time constraintsbased on the aircraft approximately maintaining its current ground speed. Clearly, duringthe descent, this is not the case, the ground speed continuously decreasing for a constantCAS value. Thus, the trajectory predictor computed that a higher CAS value would beneeded to ensure the time constraints were met. Hence there was an increase in the CASdemand to the autopilot to 259 knots on activation of this new trajectory. The aircraftsuccessfully followed the lateral route (the turn radii for the pass-behind manoeuvrebeing based on a bank angle of 20º) and the profile demands. The prediction had alsonow computed a descent to FL40 and therefore the aircraft continued down to thisaltitude for entry into the STAR. The profile demands were disengaged from theautopilot as the aircraft approached waypoint DM001 and then the lateral demands weredisengaged mid-way between DM001 and DM002, so that the aircraft could bepositioned for a manual approach to runway 23 using GBAS guidance signals.

Following the landing, the FMS was reset on the ground and the pilot re-initialised theinformation via the MCDU in order to perform a repeat of the first flight. Once again, thetrajectory was generated while the aircraft was on the ground with an EOBT of 1420UTC and a CTOT of 1425 UTC. The aircraft actually took-off at about 1420 UTC andthe trajectory was only activated once the aircraft was airborne and the pilots hadcompleted cleaning up the aircraft.

With the lateral and profile demands engaged through the autopilot, on this flight an in-flight trajectory generation was also performed during the climb with the aircraft on the


leg to waypoint ADSON. This was successful and on activation, it was noted that therewas no disturbance in the autopilot behaviour as the FMS started sending demands basedon this new trajectory. Effectively, there were no changes in the profile demands and nosignificant variation in the lateral demands either.

As before, the pass-behind manoeuvre was set-up by the pilot entering the target identity(SIM01), the minimum spacing distance (5nm) and the resume waypoint name (DM005)into the FMS via the MCDU. On this occasion, the FMS initially reported errorsattempting to generate the pass-behind trajectory due to trouble meeting the timeconstraints. As previously mentioned, the implementation had not originally envisagedthe use during the descent. However, a trajectory was successfully generated after a fewattempts and then activated. As for the previous run, the speed demand increased, thistime to 262 knots CAS. The aircraft correctly followed the planned lateral path that wasintended to ensure a spacing distance of 5nm from the conflicting target aircraft.

On this occasion, the conflicting aircraft, SIM01, was 1.1nm to the right of the track fromAGIBS to DM005 and the resultant pass-behind trajectory deviated the BAC 1-11 byabout 4.9nm to the left of this track leg. The total route length for this manoeuvre leadingto DM005 was 35.3nm, which was 1nm longer than the originally intended route.

Both the lateral and profile demands were subsequently disengaged from the autopilotprior to waypoint DM001, the aircraft being in level flight at FL40 and the FMS havingdemanded a speed reduction first to 250 knots CAS and then to 230 knots CAS formanoeuvring in the STAR.




For this flight, the full trials route (company route QNQ1) was to be used for the firsttime (see Appendix A.1), this provided areas where the aircraft was cleared to performASAS manoeuvres when simulating delegation being granted by the controller to thepilot. The intention was to perform four pass behind manoeuvres during the course of theflight. As for the last flight, the target aircraft were being simulated within the FMS,although this time they were moving at typical ground speeds to create a morerepresentative situation. The default turn radius used for the standard en-route trajectoryprediction had also been reduced to 5nm, since this was the value that was likely to beused in the Rome trials. This also meant that there was a longer section of straight trackfor generating the various manoeuvres.

This was the first flight of the VDL mode 4 and the primary objective was to assess therange and reliability of this data link. The designed route, QNQ1, remained within150nm of the Boscombe Down base station. This maximum route range had beendecided so as to allow suitable signal strength throughout the trial. It had also been notedthat if the transponder link was lost for a period of 2 minutes or more an MFMS CMUreset would occur which has the side effect of crashing the MFMS FMU. This was anundesirable effect for the flight so the transponder performance was observed using theSC-TT T5 viewer software.

3.3.2 MFMS Report

The pilot initialised the FMS similarly to the previous flight, although on this occasionthe company route selected was QNQ1 and the cruise altitude was FL240. This was alldone with the aircraft still at the stand and a trajectory generated for the complete flightas far as waypoint DM002, where the aircraft would capture the final approach path. Thecompany route was based on the aircraft departing from runway 23 at Boscombe Down,but, for this flight, the winds were such that the aircraft had to depart from runway 05. Toaccommodate this, after take off, the aircraft was flown through a dumb-bell turn in orderto return along the centre-line of runway 23 at about 1200ft QFE. After traversing thelength of the runway 23, the pilot activated the trajectory in the FMS and engaged thelateral FMS guidance demands through the autopilot, followed soon after by the profiledemands, once the climb had been initiated. This occurred without any problems andwith a smooth transition by the autopilot to the FMS demands.

During the climb, the FMS updated the speed demands in accordance with the plannedspeed profile for the flight so that, once established in the cruise, the aircraft was flying at260kts CAS. At this point, the pilot selected the Cockpit Display of Traffic Information(CDTI) overlay on the lateral map of the Navigation Display (ND) using the track-ball toselect the soft-keys on the map display. As the aircraft approached the turn at waypointYYY, the simulated traffic was triggered to start automatically within the FMS and thesymbols representing the location of the surrounding traffic appeared on the map. It wasnoted that, although the fore-point of the triangle symbol, representing the own aircrafton the map, indicated the position of the aircraft, it was actually the centres of thetriangular-shaped symbols representing the other traffic that indicated their positions.


This might be considered an inconsistency in the implementation, but given the scale ofthe traffic symbols, the variation in the perceived position could be small compared withthe influence of the update frequency of the ADS-B reports for the traffic.

Due to the limited length of the straight legs that could be incorporated within thecomplete route structure in order to remain within the required trials area, the method ofperforming the pass-behind manoeuvres was not entirely as might be expected in a moreoperational environment. Primarily, rather than a conflict being identified and resolvedwhen two aircraft were on converging legs, the pilot had to enter the relevant data for themanoeuvre via the MCDU on the preceding leg. This meant that a trajectory could begenerated as soon as possible after the completion of the turn on to the leg on which theconflict would occur and thus there would be sufficient airspace available to incorporatethe lateral route adjustment.

For the first pass-behind, the pilot selected the target aircraft, SIM00, and entered arequired minimum spacing distance of 5.5nm. When computing the pass-behindmanoeuvre, an additional factor of 0.25nm was applied by the FMS to the minimumspacing value in order to provide a performance buffer during the execution of themanoeuvre. The path of the other aircraft would currently result in the spacing distanceof the two aircraft being compromised while the BAC 1-11 was on the leg betweenwaypoints EEE and FFF. On this leg, the aircraft SIM00 was predicted to cross about4.9nm ahead of the BAC 1-11 on a track that was approximately 83° to that of the 1-11,passing from right to left. This intercept point between the two tracks of the aircraft was15.7nm ahead of the BAC 1-11's current position when the pilot triggered the prediction.The trajectory generated by the FMS for the BAC 1-11 to pass-behind SIM00 resulted inthe BAC 1-11 deviating about 4.4nm to the right of its original track to waypoint FFF.The extra route length created by this manoeuvre was of the order of 1nm. The tracks ofthe two aircraft are shown in Figure 3.3-1, the track of the BAC 1-11 being displayed inblue and that of the target aircraft, SIM00, in red. The BAC 1-11 was initially on a south-westerly track while the target aircraft, SIM00, was flying on a south-easterly track.

Figure 3.3-1 Tracks for BAC 1-11 and SIM00 Figure 3.3-2 Spacing of BAC 1-11 from SIM00

Following activation, the aircraft transitioned smoothly on to this new trajectory andaccurately tracked the lateral path for this manoeuvre. The initial change in track angle


for the manoeuvre was 16.5°. The speed demand remained unchanged at 260 knots CASand the height demand continued at the cruise altitude of FL240. During the course of themanoeuvre, the minimum spacing distance that was encountered between the BAC 1-11and the simulated target aircraft was actually about 5.6nm (see Figure 3.3-2). Themanoeuvre was regarded as complete once the BAC 1-11 had performed the turn atwaypoint FFF to return to the original route on the leg to waypoint GGG.

On this next leg, the pilot cancelled the selection of the target SIM00 and entered theidentity of the target aircraft for the second pass-behind manoeuvre, SIM02. Theminimum spacing distance was again set to 5.5nm (5.75nm including the performancebuffer) and the resume waypoint was entered as HHH. The track of this aircraft wouldintercept that of the BAC 1-11 on the leg between waypoints GGG and HHH. On thisoccasion, the target aircraft was flying on a track that gave a much shallower interceptangle of 40°, crossing from left to right, than had been the case for the first pass-behindsituation. The simulated aircraft, SIM02, was predicted to reach the intercept point 3.6nmahead of the BAC 1-11. At the point on the route where the pass-behind trajectory waspredicted, the BAC 1-11 was 24.3nm away from this intercept point. With the simulatedaircraft flying a track that was closer to that of the BAC 1-11, this configuration was usedto investigate whether the resultant track change required for the pass-behind would begreater than that encountered with the first example. As it was, the generated trajectorydeviated the BAC 1-11 by about 4.5nm to the left of its original track and the initial trackchange was of the order of 18° (see Figure 3.3-3). The geometry of the pass-behindmanoeuvre was therefore reasonably similar to that produced when the target aircraft hadbeen flying almost at right-angles to the track of the BAC 1-11, although in this case, thepredicted intersection in the original tracks was almost 10nm further away. The extraroute distance created by this pass-behind manoeuvre was only about 1.2nm. As before,the aircraft flew this lateral manoeuvre with no problems being encountered and thespeed and altitude demands remaining unchanged. The minimum spacing distance duringthe manoeuvre was 6.1nm compared to the defined value of 5.5nm (see Figure 3.3-4).

Figure 3.3-3 Tracks of BAC 1-11 and SIM02 Figure 3.3-4 Spacing of BAC 1-11 from SIM02

The system was then configured for a third pass-behind manoeuvre, this time to occur onthe leg between waypoints III and JJJ. The selected target aircraft was SIM03 but thistime the minimum spacing distance was defined as 8nm. This was due to the targetaircraft running earlier than had been originally planned (this was partly affected by the


delay to the BAC 1-11 caused by flying the extra 2nm created by the previous two pass-behind manoeuvres). The track of SIM03 would result in it crossing that of the BAC 1-11at an angle of 92° from left to right, the angular intercept being similar to that withSIM00, but this time with the target aircraft heading very slightly towards the BAC 1-11.With this current track geometry, the simulated aircraft would reach this intercept point6nm ahead of the BAC 1-11. The trajectory for the pass-behind manoeuvre wasgenerated when the BAC 1-11 was still 24.9nm from this intercept in the current tracks.The resultant trajectory required the BAC 1-11 to deviate by 5nm to the left of itsoriginal track to waypoint JJJ, requiring an initial track change of 18º and an extension of2.2nm to the previous route distance (see Figure 3.3-5). The minimum spacing fromSIM03 reached 7.7nm during the manoeuvre, consequently this was 0.3nm inside therequired minimum value of 8nm (see Figure 3.3-6).


During these manoeuvres, the variations from the intended lateral spacing, which equatedto the defined minimum spacing distance plus the performance buffer, can be explainedto a certain extent by the effects of the prevailing wind. The version of MA-AFAS thatwas flown assumed zero wind conditions in its prediction, but the actual wind was of theorder of 45-50 knots from a direction of about 150º. This resulted in variations in theground speed compared with the predicted value within the trajectory. For instance, forthe pass-behind of SIM03, the BAC 1-11 encountered a significant direct tail windcomponent and therefore the spacing distance achieved a value below the requiredminimum.

Towards the end of the manoeuvre to pass-behind SIM03, as the BAC 1-11 wasapproaching waypoint JJJ, a problem arose with the position data being output by theSBAS equipment. Just prior to this waypoint the SBAS receiver lost lock on thegeostationary augmentation satellite, which provided not only the differential correctionmessages but also an additional pseudorange source. Upon reacquisition, the receiverincorrectly resolved the CA code ambiguity resulting in a 600km error in themeasurement of this pseudorange to the geostationary satellite. This pseudorange wasincluded in the position solution and, possibly due to the nature of the implementation ofthe software, the error was not detected causing the solution to jump by a number of


miles. This position jump was influential on the behaviour of the FMS, which saw a stepin the aircraft's position of just under 7nm on a bearing of 168º True, the aircraftcurrently flying a track of 54º True. Ground speed values reported by the SBAS alsoshowed extremes of 1700kts. With this position data giving a cross-track deviation ofabout 5nm, the FMS demanded the maximum allowed left bank of 25º. At this point theFMS was disengaged and the aircraft manually flown to regain the trajectory. Once theprimary position source had been changed, via the MCDU, to the inertial referencesystem, a new trajectory was generated direct to waypoint ZZZ and, with sensibledemands now being produced, LNAV and PRFL were re-engaged through autopilot. Theerror with the SBAS was tracked down and the receiver reset and upon restarting normaloperation was resumed.

Due to the deviation from the route caused by this problem, it was not possible toperform the final pass-behind manoeuvre on the leg between waypoints JJJ and ZZZ.However, it had been noted that the performance of the VDL4 data link to the groundstation at Boscombe Down had not been very consistent when the aircraft had beenflying in the proximity of the furthest west point on the route (waypoint III). Therefore itwas decided to fly a further circuit to the west of the airway A25 in order to investigatefurther the performance of the VDL4 data link. At the same time, the pilot inserted theadditional waypoints GGG, HHH and JJJ into the FMS route between ZZZ and KKK onthe LEGS page of the MCDU. A new trajectory was generated and activated to providethe routing for this extra circuit. The guidance demands were not permanently engagedthrough the autopilot, though, because of a requirement on occasion to deviate theaircraft either side of the track in order to check on the effects on the data linkperformance.

The FMS demands were re-engaged, however, for the return to Boscombe Down and theFMS demanded a deceleration to 250 knots just prior to triggering a descent to FL75during the turn at waypoint CCC. The FMS was still computing too shallow a descentand therefore to overcome this problem, a further trajectory generation was carried outwhile the aircraft was in the descent, just after completing the turn at waypoint AAA.This now correctly resulted in a descent to FL40 for the STAR, the FMS demanding anadditional speed change to 230 knots CAS on reaching this altitude. In order to preparefor the approach, the Profile demands were disengaged from the autopilot as the aircraftstarted the turn at waypoint DM001 and then the lateral demands were disengaged whenthe aircraft was about 1nm from the end of the route at DM002.

3.3.3 VDL4 Report

The flight trials were performed to exercise the MA-AFAS ASAS manoeuvrecapabilities during which dynamic Aircraft Position Reports using ADS-B weregenerated and received by a ground station installed on the QinetiQ Boscombe Downairfield.

For this first flight there was no Point to Point traffic present on the link, just the positionbroadcasts from the air and ground transponders. The reporting rate of the ground stationhad been set to provide uplink reports at specific intervals in the repeated sequence of


16s, 12s and 32s. The reporting rate of the airborne transponder had been set to providedownlink broadcast reports at regular 4s intervals.

The online assessment during the flight was made very difficult in that the only availabledata was presented on a laptop PC screen within two windows. The first, a scrollingscreen of position reports, from the local transponder, at 1s intervals interspersed with theremote position report. The second window consisted of a two-line timestamped messagerepresenting the latest local and remote message data. It was noticed on the airborneviewer that aircraft speed was reported as being a factor of 10 too great. This was theopposite on the ground side as a factor of 10 too small.

Several events were noticed during the flight where the uplink data was lost for periodsapproaching 60s. One such event lost the link for 60s when at 32nm during the initialclimb. A further significant event took place as the aircraft exceeded 135nm from thebase station when the uplink messages were lost for a period of greater than 2 minutes. Afurther 3 uplinks were observed over a period whilst the aircraft range from the basestation was varied between 143nm and 68nm, the aircraft was manoeuvred to allow forany antenna interference and masking characteristics and both aircraft and groundtransponders were reset. None of these actions had any effect until the aircraft reduced itsrange to within 50nm of the base station, when the link was re-established.

Observations of the aircraft at the base station remained constant until the aircraft’s rangeexceeded 135nm when the downlinks became unreliable. However, the down link wasnot lost in the same manner as the up link and returned to normal performance when theaircraft range returned to within 135nm. It was, however, noticed that the base station logfile contained a significant number of reports where the system clock was reported asbeing 00:00:58. This would indicate that the base station was losing lock on the satellites,from which the time is derived.

As a consequence of this flight the MFMS route was re-designed to remain within 135nmof Boscombe Down airfield to allow a reliable communication link to be maintained.Further investigation was also required to determine the cause of the apparent receptionrange anomaly.




This flight was planned as a repeat of the flight carried out on the 19th February, butusing the revised version of the QNQ1 route that kept the aircraft within 135nm of theVDL4 ground station at Boscombe Down (see Appendix A.2). Once again, four passbehind manoeuvres were to be tested and the range and integrity of the VDL4 air/groundlink evaluated. In addition, a merge behind manoeuvre was to be flown for the first time.

3.4.2 MFMS Report

The modified company route QNQ1 had been inserted into the FMS in order to keep theaircraft within 135nm of Boscombe Down and therefore improve the coverageperformance of the VDL4 data link. The pilot initialised the system in the same way ason the previous flights. On this occasion, however, the trajectory was activated once theaircraft was lined-up on the runway. At this stage, the FMS would detect that the aircraftwas still on the ground and would only transmit guidance demands to the autopilot onceit had detected the aircraft was airborne and climbing away from the airfield. Uponactivation, the trajectory line on the lateral map display changed colour from light blue tomaroon in order to indicate that the FMS had acknowledged the activation of thetrajectory. Due the aircraft's very close proximity to the start point of the trajectory, theFMS was not able to consistently determine the correct 'Next Waypoint' information untilthe take off roll had begun and the aircraft had moved a few hundred metres along therunway. This problem was exacerbated by the fact that Boscombe Down was not onlythe departure but also the arrival airport and therefore the aircraft could also bedetermined to be at the end of the route as well as the start.

Although the curved precision departure route was being flown for the first time, theprimary navigation source was still set to be SBAS while data was gathered to confirmthe GBAS performance over the course of this departure route. The lateral navigationdemands were engaged through the autopilot as soon as possible prior to the start of thefirst turn, 2nm beyond the end of the runway. Profile guidance was also engaged as theaircraft entered this turn. No problems were encountered with the lateral guidancethroughout the departure route. However, since the FMS was only generating continuousclimbs, the aircraft had already reached about FL100 as it passed waypoint KATE andthis placed it in close proximity to an area of controlled airspace to the south ofBoscombe Down for which the lower altitude limit was FL95. The requirement was forthe FMS to handle height constraints during the climb, especially for the SID procedures,but this was not available in this current release. Subsequent releases would provide thiscapability and would thus allow the originally defined limit of not being above FL50 atKATE to be met and consequently would remove any problem with the neighbouringcontrolled airspace.


Figure 3.4-1 GBAS Position Reports duringPrecision Departure

Figure 3.4-2 Accuracy of GBAS 3D PositionData during Departure

The performance of the GBAS while the aircraft was flying the SID was found to beextremely consistent for the vast majority of the route up to and beyond KATE, the endof SID waypoint (see Figure 3.4-1). There was a brief period of only about 5 secondswhen the GBAS came out of differential mode. Figure 3.4-2 shows that, compared to thetruth track data, the deviation in the GBAS information was no more than about 1mlaterally and 3m vertically while in differential mode and the respective values when instand-alone mode were 4m and 20m. This demonstrated that, for use as a data source forthe FMS lateral guidance during the precision departure, the GBAS could easily providethe accuracy required in the aircraft position fix.

The climb continued to the cruise at FL240 without any further problems. Rig testing hadshown, however, that, with this version of software, while in the cruise, wherever theoutbound route crossed over the inbound route, the FMS would demand a descent (theinbound route being part of the descent at these cross-over points). For the initial circuitof the route to the east of airway A25, the FMS Profile guidance was thereforedisengaged from the autopilot in the cruise.

The first pass-behind manoeuvre was then carried out against the simulated targetaircraft, SIM00. For this and all subsequent flights, the standard minimum spacingdistance that was to be used was now 6nm, but still with an additional 0.25nmperformance buffer applied. This was to allow some flexibility from the minimumseparation of 5nm permitted by ATC during the trials in Rome when these manoeuvreswould be flown against a real aircraft. The geometry of this conflict situation wasessentially identical to that experienced on the flight on the 19th February, although thistime the BAC 1-11 was 9.8nm from the predicted intercept point when the pass-behindtrajectory was generated. Although the minimum spacing distance had been increased by0.5nm, the deviation of the BAC 1-11 from its original track to waypoint FFF was5.5nm, about 1nm greater than that on the previous flight, and the initial track changewas now 23.5º. This resulted in an extension of 1.8nm to the to tal route length. Theactual minimum spacing from SIM00 achieved during the manoeuvre was 5.8nm. TheFMS was still not utilising forecast or actual wind information in its prediction andconsequently this could influence the spacing at the closest point of approach. However,the overall execution of this manoeuvre was successfully accomplished.


With the profile guidance re-engaged once the aircraft was clear of the airway A25, thedata for the next pass-behind manoeuvre was entered by the pilot. The simulated aircraft,SIM02, was flying an identical track to that on the previous flight hence the geometry ofthe conflict remained similar, although significantly, the target aircraft would now crossthe track of the BAC 1-11 about 4.5nm ahead of the BAC 1-11 rather than 3.6nm. Thiswas due to the extra 1nm required for the first pass-behind manoeuvre. A trajectory wasgenerated for the pass-behind manoeuvre for a 6nm spacing, this occurring when theBAC 1-11 was 23.9nm from the predicted intercept between the two aircraft's tracks. Theoffset distance from the original track for this manoeuvre was 4.1nm with an initial trackchange of 17º. With this extended spacing distance, but the target aircraft now slightlyfurther ahead of the BAC 1-11, the additional route length amounted to 1.3nm, whichwas comparable to the change on the previous flight.

Activation of this pass-behind manoeuvre was successful and the aircraft started tofollow the required track. However, a problem then occurred within the FMS itself withregard to the SBAS position information that it was reading from the Arinc data bus. Thenavigation data being used by the FMS froze at 1452:37 (UTC), soon after the aircrafthad completed the initial turn off from the original track to start the pass-behindmanoeuvre. Although the navigation data, including time, was no longer changinginternally to FMS, other data was updating correctly and it was not immediately apparentthat a problem had occurred. However, it was noted that the aircraft was not appearing toprogress along the route on the map display relative to the next waypoint. The impressionof movement was still given, though, by the progress of the target aircraft symbol acrossthe map and therefore the sense that the own aircraft was no longer moving was not soapparent with this display configuration. Once it had been recognised that the navigationdata was not changing, the primary navigation source was altered to be the inertialreference system. The aircraft was now beyond the start of the next turn, so it wasmanually flown back on to the correct track while the FMS problem was investigated. Itwas determined that the SBAS was still functioning correctly and later it was confirmedthat the data was also updating correctly on the Arinc channel from the SBAS equipment.Therefore the problem was internal to the FMS, either the Arinc card had developed afault reading the data from this channel or the problem existed in the access of this databetween the Arinc card and the main FMS processor. Figure 3.4-3 shows how the timereference became frozen within the FMS along with the position data until the positiondata source was changed.


Figure 3.4-3 Freeze of SBAS Data within the FMS, 27th Feb. 03

Once the aircraft was back on track, a new trajectory was generated and activated, but bynow the simulated target aircraft, SIM03, for the next pass-behind manoeuvre wasbeyond the point where a sensible trajectory could be generated and therefore this wasomitted. Consequently the system was configured for a pass-behind the simulated traffic,SIM04. This aircraft would cross the westerly track of the BAC 1-11 on the leg betweenwaypoints JJJ and ZZZ, the track of the target aircraft being 118º to that of the BAC 1-11and passing from right to left. This geometry meant that the conflicting traffic had areasonable component of track that was towards the BAC 1-11. This traffic was predictedto reach the intercept point between the two aircraft about 12.5nm ahead of the BAC 1-11, but with the aircraft converging towards one another, the spacing distance would stillbe reducing after the target aircraft had passed this point. Hence, a trajectory wasgenerated with a minimum spacing distance set at 8nm with the BAC 1-11 only having todeviate by 2.7nm to the right of its original track, the generation taking place when theBAC 1-11 was 20nm from the original intercept point (see Figure 3.4-4). This smalldeviation in the track resulted in less than 0.5nm increase in the route length with aninitial track change of 9.5º. The pass-behind manoeuvre was successfully flown and theminimum spacing that occurred between the two aircraft was approximately 8.2nm(comparable to the 8.25nm used by the FMS in its manoeuvre computation).



For this flight, the FMS was also tested with regard to a merge behind manoeuvre. In thiscase, the ATC controller would define the distance that the own aircraft is required toattain behind another aircraft at a set waypoint. At this waypoint, both aircraft should beflying a common lateral path and the own aircraft would maintain the required spacingfrom this point onwards, either to a defined end point or until the controller issues achange in instruction. The current version of the software did not perform this latterfunction, however, so the manoeuvre would be complete when the BAC 1-11 hadreached the merge waypoint. Due to the problem in ensuring that the simulated traffic isin the right place for the initiation of this merge manoeuvre, a stream of five aircraft hadbeen pre-defined to follow the same route, 10nm apart. These aircraft were set on a trackfrom waypoint ZZZ to RRR (the merge waypoint) and then continued on the same pathas the BAC 1-11 to SSS.

The selected target aircraft was SIM06 and the spacing distance entered was 6nm. Asalready noted, the waypoint at which the merge was to be complete was RRR. As for thepass-behinds, the pilot entered this data via the ASAS pages on the MCDU. A trajectorywas generated once the aircraft was on the leg to waypoint QQQ, effectively flying aparallel track at that moment to the target aircraft, SIM06. Although the new trajectorynow took the BAC 1-11 on a direct track to waypoint RRR, there was no updated speeddemand computed by the FMS, so the demand to the autopilot remained at 260kts CAS.Hence the spacing distance had not been achieved by the time the BAC 1-11 reachedRRR.

The primary navigation source, which had been set to the IRS since the SBAS dataproblem, was now changed to be GBAS for the remainder of the flight. A furthertrajectory was generated and activated when the BAC 1-11 was on the leg to waypointTTT in order to correct the next waypoint information that was being displayed on theND and the MCDU. Both the lateral and profile demands were disengaged from theautopilot on reaching waypoint DM001 within the simulated STAR at Boscombe Down.

The taxi map was used after landing and provided a reasonable display of the aircraft'sposition on the airfield as it taxied back to the stand. The use of white to block in thetaxiways as well as for the aircraft symbol did cause a problem in being able to locate theaircraft on the map. Although the position did give an element of situation awareness to


the pilot of the aircraft's location, with the weather being very clear and the pilot'sextreme familiarity with the airfield, there is little that can be determined about theeffectiveness of the display.

3.4.3 VDL4 Report

In the first flight of VDL mode 4, the link had been observed to lose contact with theBoscombe Down ground station at an approximate range of 135nm. This loss of link wasprimarily in the uplink direction and was re-established at approximately 50nm range. Asno explanation of the reception range difference could be discovered in the timeavailable, a second route was devised whose maximum range would not exceed 135nmfrom the Base Station.

Flight trajectory

50.2

50.4

50.6

50.8

51

51.2

51.4

51.6

-6 -5 -4 -3 -2 -1 0

Boscombe Down

1st Pass Behindmanoeuvre

2nd Pass Behindmanoeuvre

3rd Pass Behindmanoeuvre

4th Pass Behindmanoeuvre

Curved Departure

Figure 3.4-6 ADS-B Flight Data Received by EEC

The reporting rate of the ground station was set to provide uplink reports at specificintervals in the repeated sequence of 16s, 12s and 32s. The aircraft transponder reportswere set to 4s intervals. Data recordings were made using the T5 viewer software at bothends of the link. The ground system was also configured to send the ADS-B data to EECBretigny. A plot of the data received at EEC is shown in Figure 3.4-6. After take-off theoutbound performance was observed to be comparative with previous experience withuplink data being received at intervals not exceeding 60 seconds. Beyond 100nm rangefrom the ground station gaps in the uplink data exceeding 1 minute became common.The first 2 minute gap in data was observed at a range of 135nm whilst in the turn atwaypoint H. The link remained intermittent along the leg H – M - J but recovered afterwaypoint J at a range of 124nm. The link remained consistent with the first loop all the


way around the second loop only exhibiting reliability when the range became less than100nm.

The VDL4 performance was judged as being acceptable for ADS broadcasts. Noexperience has been gained yet on requirements for the Point to Point capability.

The ground VHF voice link was not maintained to 135nm range and if needed as a datalink backup and technical link will need further attention.


3.5 11th March 2003


This flight was to check the range and performance of the modified SAAB VDL4transponder, using part of the modified QNQ1 route (see Appendix A.2), then followedby a range check to 200nm. The first part of this flight consisted of a climb to FL240 inthe region of VLN to join the route at waypoint F for an airway crossing to G, then to H,M, J, Z. This was to confirm that the revised unit will work at the shortened range of135nm. If this was satisfactory, it was then required to check that the VDL4 would workwithin the full box size of 200nm that had initially been allocated for the trials at Rome.

Two hand flown 4.5º approaches from 2500ft using the GBAS guidance were also to beincluded at the end of the flight.

The MFMS was not used for this flight.

3.5.2 VDL4 Report

SC-TT have analysed the flight data from the 19th Feb. flight and advised that thetransponders should be changed. SC-TT supplied 2 new transponders, both engineeringdevelopment models, with revised hardware for improved frequency stability. Thetransponders replaced both the air and the ground systems. The estimated, but un-proved,range of the new transponders is 150nm. This flight was conducted to verify the reliabletransponder range to allow a route to be designed with its coverage area.

The transponder data was monitored using the SC-TT supplied T5viewer software.

Pre-flight the ground transponder was configured and observed to be transmitting in asequence of 4s, 4s, 8s, 4s, 4s, 8s … The airborne transponder was reporting position atregular 2s intervals.

After take-off the T5 recorder was started. Ground speed was observed as being a factorof 10 too great, as per previous flights, both track and distance to the base-station agreedwith the IRS and Trimble GPS systems onboard the aircraft.

The aircraft flew around the new short route with no significant loss of data. The aircraftcontinued on a modified second loop which extended west until the air/ground link waslost. A plan had been prepared which allowed for the aircraft to extend to 200nm fromBoscombe Down. However the link was lost at a base station range of 143nm. Theaircraft continued on for a further 22nm before turning back to test where the link wouldbe re-gained. Re-establishment of the link occurred at 132nm initially with sporadicreports being received. A regular ground report was not recovered until the aircraft camewithin 122nm from base. The aircraft returned to its standard routing and returned toBoscombe Down.

On the basis of this flight a decision was made to continue with the new shortened routeas this would enable aircraft operation with the best air/ground link available.


3.6 14th March 2003


This flight was based on the same company route, QNQ1, as flown on the 27th February(see Chapter 3.4.1). One significant change from the previous flights was that the FMSnow utilised forecast meteorological data in its trajectory predictions. This data was inthe form of the forecast air temperature, wind speed and wind direction for variouspressure levels at different grid points covering the area traversed by the route. Thisshould have provided a more accurate time profile for the aircraft’s predicted trajectorywhich would be important for merge manoeuvre in which the FMS aimed to meet a timeconstraint at the merge waypoint in order to be at the necessary spacing behind the otheraircraft.

Additional improvements since the last flight included the handling of height constraintswithin the SID, allowing the precision departure routing to be flown properly and notinfringe the neighbouring controlled airspace. The problem encountered on the previousflight relating to the crossover points between the inbound and outbound routes, andresulting in premature demands for the descent being sent to the autopilot, had beenfixed. Finally, the descent prediction had been improved to produce a steeper descentprofile, more comparable to that flown by the BAC 1-11.

3.6.2 MFMS Report

The prevailing winds at Boscombe Down meant that the BAC 1-11 had to depart againfrom runway 05 rather than runway 23 for which the precision departure route wasconfigured. Therefore, once again a dumb-bell turn was performed directly after take-offso that the aircraft could be flown at 500ft above runway 23 in order to simulate a takeoff from this runway. Activation of the trajectory was performed by the pilot as theaircraft passed the far threshold of runway 23 allowing the FMS lateral demands to beengaged through the autopilot as soon as possible. Since the aircraft had already beencleaned up, the FMS profile demands could also be engaged soon after trajectoryactivation. The SID was flown without any problems, the FMS initially demanding aclimb to FL50 for the duration of the SID until demanding a climb to the cruise at FL240.The FMS sent this demand for the climb about 1.5nm before waypoint KATE providingsufficient anticipation time for the autopilot to make the transition from level flight to theclimb. Throughout the SID, the FMS was using the GBAS as its primary position source,however, once passed KATE, the SBAS was selected as the source for the en-routesection of the flight. Transitions between the data from these two sources caused nodiscontinuity in the FMS guidance performance.

It was noted that upon activation of this trajectory, all the waypoint ETA values on theND and the MCDU were being shown as 0314:00. This had been seen before during thetesting with the aircraft model rig, but the exact cause of this had not been fullyidentified. Although this did not cause any problem with the FMS’s ability to generatethe guidance demands for the autopilot in order to follow the trajectory, it was decided toperform an in-flight generation and activation in case the erroneous times influenced the


generation of the pass-behind manoeuvres. This was done once the aircraft was in cruiseon the leg to waypoint DDD and now all the times were correctly set.

As normal, the first pass-behind was set up with SIM00 selected as the target aircraft anda minimum spacing distance of 6nm entered. The generation of this trajectory failed,however, with the FMS reporting a problem trying to meet the time constraints that itsmanoeuvre generator function had applied to the various waypoints that it had definedfor the pass-behind manoeuvre. The reason for the system applying time constraints tothese inserted lateral waypoints was to try and ensure that the spacing of the two aircraftcould be determined in relation not only to position but to time as well. The spacingdistance was changed to 8nm, but a trajectory could still not be computed. Finally, 5nmwas tried and this time the generation was successful. The tracks of the two aircraft priorto the activation of this pass-behind manoeuvre had been the same as on the previousflights, although the problem in generating a trajectory meant that the BAC 1-11 was12.2nm from the intercept point when a valid trajectory was eventually predicted. Thetarget SIM00 had been predicted to pass 4.9nm ahead of the BAC 1-11. On this occasion,the resultant track change for the BAC 1-11 was 17° and its maximum deviation from itsoriginal track was 2nm. The speed demand for the first part of manoeuvre up to theestimated point of closest approach was 220kts CAS, while beyond this point, it revertedback to 250kts CAS. This change in speed was a result of the time constraints inserted bythe manoeuvre generator and the application of the forecast meteorological data,resulting in variations in ground speed dependent on the air speed and track angle. It latertranspired that there was a problem with the forecast meteorological data due to an extracontrol character having appeared at the end of each line in the file during the transferprocess. This affected the way the MFMS interpreted the data from the file and caused agreater variation in the forecast values used by the trajectory prediction function than wasactually the case. During the execution of this pass-behind manoeuvre, the actual spacingfrom SIM00 at the closest point of approach was 5.4nm.

The second pass-behind manoeuvre, using the target aircraft SIM02, was unchanged interms of the conflict geometry from the previous flight, the target being predicted tocross 3nm ahead of the BAC 1-11. On this occasion, a trajectory was successfullygenerated with an assigned minimum spacing distance of 6nm, resulting in the BAC 1-11deviating by 5.7nm from its original track with an initial track change of 28.5°. Onceagain, on trajectory activation the speed demand to the autopilot was reduced to 220ktsCAS until passing the closest point of approach where the demand went back 250ktsCAS. This time, the minimum spacing that was achieved was 7.6nm, compared to thepermitted value of 6nm. This was because the ground speed predicted in the trajectorywas over 50kts greater than that actually achieved for the demanded air speed. Althoughtesting had shown that the FMS was correctly applying the forecast wind information topredict the effect on the aircraft's ground speed, it was later determined that there wasproblem in the derivation of true air speed by the FMS. This only existed when the FMSwas using the forecast meteorological data and although a fix was subsequentlyproduced, it was too late to implement and test prior to the aircraft departing for the trialsin Rome. Hence this problem had an influence on the results of the various pass-behindand merge manoeuvres, but not to such a degree that it significantly compromised themanoeuvres that were being flown. This particular pass-behind manoeuvre wascompleted without problems and without any transients affecting the guidanceperformance.


The third pass-behind with the simulated target SIM03 was also successfullyaccomplished. This was the first time that this particular manoeuvre had been flown sinceit had not been possible on the last flight due to the navigation data problems and theroute had been updated since the flight on the 19th February. The geometry for the twoaircraft had the target aircraft, SIM03, following a track 113° relative to that of the BAC1-11, passing from left to right and thus SIM03 had a small component of its track beingtowards the BAC1-11 (similar to SIM04). When the pass-behind manoeuvre wasgenerated, SIM03 was predicted to cross the track of the BAC 1-11 5.7nm ahead. At thepoint of generation, the BAC 1-11 was still 18nm from this intercept point. The newtrajectory was based on a defined minimum spacing distance of 6nm and resulted in theBAC 1-11 deviating 3.3nm to the left of its original track, the initial track change being15°. Figure 3.6-1 shows the tracks of the two aircraft, The BAC 1-11 (blue line) havingbeen on a northerly heading and SIM03 (red line) on a south-easterly heading. At theclosest point of approach (see Figure 3.6-2), the BAC 1-11 was 6.5nm from SIM03, theCAS demand having this time reduced to 224kts and the actual ground speed being about25kts less than that determined by the prediction for this air speed.

Figure 3.6-1 Tracks of BAC 1-11 and SIM03 Figure 3.6-2 Spacing of BAC 1-11 fromSIM03

The final pass-behind manoeuvre took place on the leg between waypoints JJJ and ZZZ.This configuration was as per the previous flight with the target aircraft, SIM04,predicted to cross the track of the BAC 1-11 about 3.1nm ahead of it. The minimumspacing distance was again set as 6nm and the pass-behind manoeuvre was successfullygenerated when the BAC 1-11 was 20.4nm from the predicted intercept point betweenthe two tracks. The manoeuvre deviated the BAC 1-11 by 5nm to the right of its originaltrack and required an initial track change of 19°. As with the other pass-behinds on thisflight, there was a change in the speed demand from the FMS to 220kts until past theclosest point of approach. Consequently, the actual minimum spacing distance thatoccurred during the manoeuvre was 6.8nm due to the predicted ground speed beinggreater than that achieved for the demanded air speed.

Having completed the last pass-behind, the BAC 1-11 now followed the additional loopsection that had been inserted for testing the merge behind manoeuvre. When the aircraftwas on the leg to waypoint PPP, the pilot entered the selected target aircraft identitySIM05 into the MCDU along with the merge waypoint name RRR. A spacing distance of6nm was used again and once the BAC 1-11 was on track to waypoint QQQ, a trajectory


was predicted. At this point the target aircraft SIM05 was 19nm from the BAC 1-11 andtherefore the predicted trajectory needed to close the distance between the two aircraft byincreasing the speed demand for the BAC 1-11. The algorithm that was implemented forthe merge with spacing manoeuvre applied an additional tolerance of 0.25nm to thespacing value entered via the MCDU. This was to create a buffer region to cater forerrors that might arise from the prediction and guidance processes and to preventunwanted alerts possibly being generated as the aircraft attempted to maintain therequired spacing distance.

On activation of this trajectory, the speed demand did increase to 268kts CAS, whichresulted in a ground speed of 354kts. The aircraft SIM05 was, however, flying at aconstant ground speed of 356kts and therefore the BAC 1-11 was only just matching thespeed of the target without closing the distance. The reason was the same as for theprevious pass-behind manoeuvres where the predicted ground speed was an over-estimation of the actual ground speed that was achieved for the demanded air speed.Hence, by the end of the manoeuvre, when the BAC 1-11 reached waypoint RRR, theaircraft SIM05 was still approximately 18nm ahead. The other aspect that was notedabout the manoeuvre was that the transition in the aircraft’s track on to the direct path towaypoint RRR was too abrupt for the BAC 1-11 to follow smoothly. The predictionassumed a direct track from the aircraft’s current position to the merge waypoint, butinserted an S-bend manoeuvre to capture this track. However, with the manoeuvregenerator configured to use 25° of bank in its lateral computations, it was not possible forthe BAC 1-11 to transition fast enough from 25° of right bank to 25° of left bank in orderto maintain the aircraft exactly on the lateral path. The aircraft subsequently drifted wideon the second section the S-turn and would then have to make a significant correction inorder to capture back on to the track towards waypoint RRR. A smoother lateraltransition in track, similar to that used for the pass-behind manoeuvres would havegreatly improved this aspect of the performance, but the principal aspect of the merge isbased on the speed change.

An additional merge manoeuvre was attempted once the BAC 1-11 had completed itsturn on to the track towards waypoint TTT. In this case, a stream of five target aircraft,10nm apart, were flying on a track from a point just north of waypoint HHH to waypointZZZ (the next waypoint on the BAC 1-11’s route after TTT). The target aircraft SIM12had been selected with the merge waypoint set as ZZZ and a required spacing distance of6nm. When the merge manoeuvre was predicted, the target aircraft, SIM12, was over22nm away and was also 41.5nm from waypoint ZZZ, while the BAC 1-11 was still61nm from ZZZ. Activation of this trajectory resulted in a similar lateral over-correctionto capture the track to ZZZ as seen on the first merge manoeuvre. The speed demandincreased to 267kts CAS and this gave a ground speed of 392kts compared to the 356ktsof SIM12. This was insufficient to make up the necessary distance to achieve a 6nmspacing, the actual spacing being 16nm when the BAC 1-11 reached the waypoint ZZZ.

The top of descent point that was predicted by the trajectory generator was located withinthe airway A25, which the route crossed to return towards Boscombe Down. Therefore,the profile guidance was deliberately disengaged while traversing the airway and re-engaged in the turn at waypoint CCC. The altitude demand from the FMS was zero,however, rather than the expected FL40. Attempts were made in the descent to regeneratethe trajectory to correct this altitude demand but these were not successful, so the profile


demands were disengaged from the autopilot again as the aircraft passed FL105. Lateralguidance was retained until the aircraft was approaching waypoint DM002, at whichpoint the pilots configured the aircraft for performing the manual approaches using theGBAS guidance signals.

3.6.3 VDL4 Report

This trial used the new transponders supplied by SC-TT. It was not intended to connectthe VDL4 into the MFMS but to monitor multiple transponders and record the groundspeed observed by the laboratory transponder during the flight. This was to be the firstexperience in MA-AFAS of data being received by another aircraft transponder and thuswould be an indication of the data expected when operating with the ATTAS aircraft.Two transponders, the Base Station and a laboratory test transponder, were configured asfollows:

• Old Fire Station transponder was configured as a base station. The antenna wasmounted on the building roof;

• Transponder in Building 414 laboratory was configured as an airborne station butwould remain stationary. The antenna was positioned on the ground outside thelaboratory, as roof access was not possible. With the antenna in this position, realisticground-air range was not expected. However, reported ground speed could bedetermined over a significant portion of the flight.

The transponder data was monitored using the SC-TT supplied T5viewer software.

During a pre-flight ground test both stationary transponders were observed on the T5viewer status screen. All links were maintained during the take-off and initial departure.

The laboratory transponder link was maintained outbound to a range of 80nm fromBoscombe, this reduced range was as expected. The base station transponder link wasmaintained throughout the flight to a range of 135nm, with only short outages atmaximum range as the aircraft was manoeuvred. As soon as the aircraft returned tostraight and level flight, the air/ground link was automatically re-established. During thereturn legs the laboratory transponder was re-acquired at a range of 45nm. Two passesdown the runway were used to calibrate the ground speed observed by the laboratorytransponder.

As both ground transponders were stationary, a zero ground speed was recorded at alltimes on the airborne status display. However, on the ground transponder, the aircraftspeed was reported as being 10 times too small, which would cause problems whenASAS manoeuvres were performed against the real ATTAS target.

For the MA-AFAS trials SC-TT had supplied three transponders for use by both QinetiQand DLR. After this flight the QinetiQ base station transponder was required for theRome flight tests so no further VDL4 activity was available for the remaining Boscombetests.


3.7 19th March 2003, Sortie No. 762.


For the transit to Rome, the MFMS was to be used to provide lateral guidance for themajority of the route (company route BOSROM). For the initial and final parts of theroute, where the aircraft was likely to be vectored by ATC to first join the airwayssystem and later to pick up the approach into Ciampino Airport, the aircraft would beflown manually. The VDL4 transponder was also connected to the FMS for the first timeduring a flight since it was to be checked that the FMS could successfully communicatewith the ground stations at Rome. It was also intended to check the range performance ofthe VDL4 data link relative to the ground stations at Rome that would be involved in theMA-AFAS trials.

The flight planned route was:

EGDM-SAM-MID-XAMAB-BAMES-RBT-PTV-NEV-LERGA-LATAM-KURIR-RETNO-KOLON-DIVUL-SODRI-BTA-ELBA-GILIO-MEDAL-GILET-OST-LIRA.

3.7.2 MFMS Report

A trajectory was generated while the aircraft was still on the ground at Boscombe Down,the cruise altitude having been set as FL270. This trajectory was then activated once theaircraft had lined up on runway 23.

The FMS now contained a full navigation data base for the European region so that, ifchanges were required to the route during the flight, these could be applied by editing thewaypoint list on the LEGS page of the MCDU. Entering a waypoint name into theMCDU scratchpad and then pressing the line select key beside the point in the list wherethis waypoint was to be inserted, would accomplish this task. The FMS would extract theposition data for the waypoint from the navigation data base and, in the case of duplicatewaypoints existing with the same name, the pilot was presented with the options to selectthe correct one. The pilot could also easily delete waypoints from the current list.

Additionally, a Go-Direct function was available to the pilot on the MCDU's VNAVpage. Entering a waypoint name into the appropriate location on this page would result inthe FMS automatically generating a trajectory direct to this waypoint from the aircraft'scurrent position, providing the waypoint existed in the current route. This was theprimary function used by the pilot during the transit flight as ATC provided occasionalclearances to waypoints further along the route, by-passing the current route leg.

Initially the aircraft was vectored by ATC until it was cleared to join the airways andproceed along its planned route. It had also been noted that the FMS was missing the datasource from the Engine Instrumentation Unit (EIU), due to a power supply fault with thislatter piece of equipment. Once this power fault had been rectified and the aircraft wasestablished on its route, a new trajectory was generated direct to waypoint BAMES, afew miles after the aircraft had passed Midhurst (MID). The lateral and profile demandswere engaged through the autopilot and the lateral guidance was maintained forremainder of the flight until just prior to waypoint MEDAL as the aircraft levelled at3800ft and 230kts CAS. At this point, the aircraft was to be vectored by the Rome


controllers for capturing the approach to Ciampino Airport. The profile guidance hadbeen disengaged from the autopilot when the aircraft reached the cruise level FL270 inorder for the pilots to fly a different speed profile than that predicted by the FMS. Itwould normally have been possible for the pilots to update the cruise speed via theMCDU pages, but this facility had been disabled recently while overcoming a separateissue affecting the speed profile produced for the merge manoeuvres.

During the course of the transit flight, the FMS lateral guidance, in conjunction with theautopilot response to these demands, had resulted in a mean Flight Technical Error valuefor the cross-track deviation of 110m (approximately 0.05nm), with a standard deviationof 91m. This is the measurement of lateral error from the predicted route as determinedby the FMS itself and therefore is not the overall performance error term since it does notaccount for navigation system performance. The maximum cross-track deviation thatoccurred while using the FMS lateral demands was 815m (about 0.44nm). The positiondata source used throughout the flight by the FMS was the SBAS equipment. It shouldalso be noted that the FMS was configured in preparation for the trials sortie in Romeand was therefore using 5nm as the default turn radius for all the waypoints. With theaircraft flying at 320kts CAS, the correspondingly high ground speed resulted in the FMSdemanding its maximum permissible bank angle of 25º in order to follow the path of theturns and, in some cases, this was not quite sufficient. This was the cause of theoccasional larger spike in the cross-track deviation while performing a turn. The meanvalue was also influenced by the BAC 1-11 not flying exactly in trim, generally requiringabout 1º of left bank in order to maintain a constant track. A stable condition wastherefore achieved when the FMS was demanding this level of bank angle. For theground speed of the aircraft during the cruise, this equated to a cross-track deviation ofaround 80m.

3.7.3 VDL4 Report

This sequence of three flights on the 19th March was arranged to test the VDL4 and voicecommunications range in the proposed Rome flight trials area. For these flight tests theaircraft transponder was required to be re-configured to operate on the Rome VDL4approved frequency of 136.95MHz. As this frequency was not approved for use in UKand French airspace, the transponder remained switched off until the aircraft was insideItalian airspace. This was the first time that the transponder had been used in flight whilstconnected to the MFMS. The switch on process did not cause any problems to theMFMS and after a short start-up delay the BAC 1-11’s own transponder position, shownas a traffic symbol, overlaid the current aircraft position on the Navigation Display (ND)when “TRAFFIC” was selected on. The BICCA code of ASEQA and current groundspeed, although 10 times too great, were also displayed next to the traffic symbol,together with the altitude offset (in hundreds of feet) from the host aircraft.

It was noted that the ND would be too cluttered with the own-ship transponderinformation displayed and a request was made to remove this unnecessary extra trafficsymbol. During the approach to Ciampino airport, further transponders were displayedsuccessfully on the ND. These transponders equated to ground test transpondersidentified with BICCA codes of HORIA and CQAIA. At this stage the groundtransponder installed for MA-AFAS at Ciampino was not observed.


3.8 19th March 2003


This flight would verify the route that was to be flown the following week for the trialswith the ATTAS aircraft. This route was referred to as QNQ5 (see Figure 3.8-1) andincorporated two pass behind and one merge manoeuvre within the assigned trials area.The cruise level for this flight was FL210. On this occasion, the ATTAS aircraft was tobe simulated within the FMS using the same process as for the flights at BoscombeDown. The triggering for the start of the simulation was to be done manually, however,when the BAC 1-11 was 4nm before the waypoint LUNAK. The VDL4 transponderrange would also be checked during the flight to ensure adequate coverage could beachieved with the ground station over the entire route.

Figure 3.8-1: QNQ5 Route used for Test Flight in Rome, 19th March 03

3.8.2 MFMS Report

With the departure and arrival airports entered as LIRA (Ciampino) on the MCDU andthe company route QNQ5 selected, a trajectory was generated with the cruise altitude setto FL210. The SID that was used was based on the published departure route OST5A forrunway 15. At this point the route continued to follow the airway L5 to VALMA, atwhich point the aircraft would turn left into the trials area. For the return to Ciampino, aSTAR had been set up within the supplementary data base of the FMS in order to providea routing from OST to the approach to runway 15. The trial itself would be finished by


the time the aircraft reached OST on the return leg, however this STAR was requiredprimarily to complete a trajectory profile that would lead on to the approach path.

The primary navigation data source was again set to be the SBAS. Having activated thetrajectory after lining up on the runway, the FMS started to transmit guidance demandsonce the aircraft had climbed through 150ft after take off. The lateral demands wereengaged through the autopilot for the initial turn, but the profile demands were notengaged until the aircraft was established on track towards waypoint OST, this being aprecaution in case there were any system problems after take off.

The FMS guided the aircraft along the trajectory and the simulated target aircraft,SIM02, was started on its own route when the BAC 1-11 was 4nm before LUNAK inorder to co-ordinate the timings around the route. This target aircraft flew a fixed route ata constant ground speed of 287kts. For the first pass-behind manoeuvre, the targetidentity was entered on to the ASAS page of the MCDU with a minimum spacingdistance of 6nm and the resume waypoint specified as B3. Once the BAC 1-11 hadcompleted the turn at VALMA, a trajectory was generated, the aircraft SIM02 beingpredicted to cross ahead of the BAC 1-11 by only 0.3nm on a track that was at 79º (i.e.almost at right-angles) to that of the BAC 1-11. With the aircraft estimated to convergealmost exactly at the intercept point, the resultant trajectory for the pass-behind requiredthe BAC 1-11 to perform significant track change of 36º at the start of the manoeuvre,deviating from the original track by 6.6nm. Figure 3.8-2 shows the tracks of the twoaircraft during the pass-behind manoeuvre, the BAC 1-11 originally on a southerly trackand SIM02 moving approximately due east.

Figure 3.8-2 Tracks of BAC 1-11 and SIM02 for1st Pass-Behind Manoeuvre

Figure 3.8-3 Spacing of BAC 1-11 from SIM02during 1st Pass-Behind Manoeuvre

The trajectory that had been produced by the FMS was not complete, however, despitebeing presented on the ND to the pilot for activation. The trajectory only consisted of thefirst half of the pass-behind manoeuvre, the remaining points in the trajectory beingduplicates of the same point, the trajectory containing 128 points in total, the maximumpermissible by the system. This problem had been seen occasionally during the rigtesting, but its exact cause was not known, although in the past it had been linked to theprediction being incomplete for the STAR. The trajectory was activated and the aircraftfollowed the pass-behind manoeuvre to beyond the point of closest approach, theminimum spacing achieved being 6.2nm (see Figure 3.8-3). To create a new trajectory


for the remainder of the route, the pilot successfully generated direct to the next waypointB3 and activated this trajectory, as seen in Figure 3.8-2.

The two routes then converged again on the leg between B4 and B5. Once again theminimum spacing distance was set to 6nm and the resume waypoint was B5. This time,the simulated target aircraft, SIM02, was on a track that cut that of the BAC 1-11 at anangle of around 50º. When the pass-behind trajectory was generated, SIM02 wasestimated to cross 3.1nm ahead of the BAC 1-11. This trajectory, activated by the pilot,had an initial track change of 24º and the deviation from the original leg to B5 was 6.3nm(see Figure 3.8-4). The FMS speed demand to the autopilot increased to 267kts CAS, inaccordance with the prediction. As seen on the previous flight trial at Boscombe Down,however, this predicted air speed was greater than was actually required for the desiredground speed. Hence the minimum spacing distance that was achieved during thismanoeuvre was 5.7nm compared with the originally defined value of 6nm, as shown inFigure 3.8-5. The application of a speed change during the lateral pass behind was notconsidered as an ideal solution for this type of manoeuvre and it was only really intendedif there was an additional time constraint that had been imposed further along the route.

Figure 3.8-4 Tracks of BAC 1-11 and SIM02 for2nd Pass-Behind Manoeuvre

Figure 3.8-5 Spacing of BAC 1-11 from SIM02during 2nd Pass-Behind Manoeuvre

A merge manoeuvre was also performed with the target aircraft SIM02. The simulatedtarget followed a route from waypoint A5 to MMP and then to waypoint A6, while theplanned route for the BAC 1-11 was initially on a track from B7 to B8 that paralleled thetrack of SIM02 from A5 to MMP. After B8, the BAC 1-11's route went to MMP andthen, like SIM02, to A6. Once the turn at B7 was completed, a trajectory for the mergemanoeuvre was generated, the merge waypoint being MMP and the required spacing wasset to 20nm. Although a trajectory was successfully predicted, upon activation the speeddemand to the autopilot remained at 267kts CAS, despite the trajectory having apredicted speed of 272kts CAS for the duration of the merge manoeuvre. The lateralelement of the trajectory was carried out with the aircraft turning on to a track towardsMMP, this change in track being about 10º. The trajectory still consisted of an S-shapedturn for capturing this direct track and therefore there was an initial overshoot of thesecond part of the turn, as seen in the trials at Boscombe Down. The spacing between thetwo aircraft at the start of manoeuvre had been 31nm, with the BAC 1-11 56nm fromwaypoint MMP. By completion of the initial part of the merge manoeuvre, i.e. when theBAC 1-11 passed the merge waypoint MMP, the spacing from SIM02 was around 21nm.


The speed demand was still unchanged, however, and at this stage the aircraft in trail, i.e.the BAC 1-11, should now have adjusted its speed demand to match the ground speed ofthe lead aircraft, i.e. SIM02. Therefore, despite being about 1nm from the requiredspacing from SIM02, this had not really been achieved directly from the trajectoryprediction, but was more a result of the BAC 1-11 already flying at a suitable groundspeed for closing the distance on the target aircraft.

The MFMS guidance was disengaged at waypoint MMP since the aircraft was thenflown towards upper left corner of the trials area in order to verify the VDL4 coverage inthis region where the DLR's ATTAS aircraft was to pass through on its planned route.

Once the aircraft had landed back at Ciampino, the taxi map was selected on the ND.This revealed an offset in the FMS position data and the reference of the taxi map. Theposition data source being used by the FMS was the SBAS equipment. The FMS hadautomatically selected the Ciampino airport map, but the map showed the aircraft to bedisplaced about 200m to the left of its position on runway 15. Similarly, by the time theaircraft had reached its stand position on the apron, the position displayed on the mapindicated that the aircraft was on the runway. The inference was that there was a positionreference problem with the map display co-ordinates.

3.8.3 VDL4 Report

On power up, the Ciampino ground transponder was observed, located at N41° 48.2050’E012° 35.0136’ 131.06m and identified with BICCA code JKAAA. It was transmittingin the interval sequence 4s, 4s, 8s, 4s, 4s, 8s, etc. and it was noted during this initial testthat the ground transponder in use was an old type. AMS had experienced problems withthe new transponder, transferred from the Boscombe Down ground station site. Theaircraft transponder status was monitored using the T5 monitor software rather thanconnecting to the MFMS. This would allow the MFMS to conduct ASAS manoeuvreswith simulated targets and provide a more reliable record of VDL4 performance in thetrials area.

The VDL4 link was maintained throughout three MFMS ASAS manoeuvres to themaximum route range of 108nm from Ciampino as shown in Figure 3.8-6. The aircraftroute also explored the area where the ATTAS aircraft would be operating. At amaximum range of 90nm the VDL4 link was still reliable. However, it was noted that thevoice communication at the southerly and north-western ends of the route had becomebroken and at times unreadable.


Ciampino

VDL mode 4Ground stations

1st Pass BehindManoeuvre

2nd Pass BehindManoeuvre

Start of MergeManoeuvre

Part of ATTAS route

Figure 3.8-6 Plot of ADS Position Data during Rome Test Flight

The result of this flight declared the VDL4 ground/air link range performance to beacceptable for the Rome trials. Unfortunately, due to network problems, the air/grounddata could not be received at the ENAV Shadow control workstation.


3.9 19th March 2003


For the transit back to Boscombe Down, the VDL4 transponder was again connected tothe FMS in order to ensure that the data exchange with the transponder was functioningcorrectly and that no data errors could occur that might affect the FMS performance. Aswith the outbound transit flight, the FMS was to be used to provide lateral guidance tothe autopilot during the majority of the flight.


LIRA-OST-MEDAL-GILIO-ELBA-DOBIM-AKUTI-PIGOS-BARSO-OKTET-GIPNO-BULOL-ARDOL-CHABY-LAULY-BRY-CLM-KOPOR-KOMEL-GUBAR-GURLU-SAM-EGDM.

3.9.2 MFMS Report

With the MFMS lateral guidance demands being used for nearly 2 hours of the flight, themean cross-track deviation during this period was 108m with a standard deviation valueof 269m. The reason for this larger standard deviation compared with the transit flightout to Rome is primarily due to the way two trajectories were generated and activated.For instance, ATC cleared the aircraft to go-direct to waypoint GIPNO just as it wasapproaching the turn at PIGOS. A trajectory was generated and activated about 4 secondslater. The trajectory predictor, however, would generate direct from the aircraft's currentposition to the new waypoint and therefore did not compensate for the turn required toget the aircraft on to the direct track. With a track change of just under 40º and a groundspeed of over 460kts, the result was that, for a maximum bank angle of 25º, the aircraftdeviated from the new track by a maximum of 2900m. before recovering back on to newroute leg. This deviation was the principal cause of the larger standard deviation. With abetter estimate of the route transition from the previous track to the new one, there wouldhave been little difference in the data from the outbound flight.

3.9.3 VDL4 Report

On power up for the third flight test in this sequence the ground based targets (BICCAcodes of CH9SK, CQAIA, HORIA and JKAAA) were observed on the NavigationDisplay (ND) as being similar to the inbound test flight. The transponder was again usedwith the MFMS with no problems observed. The aircraft transponder was switched offbefore leaving Italian airspace.

It was noted that the latest version of transponder software had not uploaded correctly.This was remedied for the Rome trials, moving the software version to 1.4.5.


3.10 20th March 2003


Updated software was available for this flight in order to restrict the need for speedchanges during the pass-behind manoeuvres when the forecast meteorological data wasbeing used and also to improve the determination and execution of the speed changes forthe merge manoeuvres. The flight profile itself was a repeat of that carried out on the 14th

March using the company route QNQ1 and engaging the FMS demands as soon aspossible after take off in order to follow the precision departure route, SID23.

A total of four pass behind and two merge behind manoeuvres were to be performedduring the course of this flight using simulated traffic generated in the same way as onthe previous trials flights from Boscombe Down.

3.10.2 MFMS Report

As usual, the FMS was initialised while the aircraft was still at the stand and 4Dtrajectory predicted from take off to the final approach path. With the position datasource set to the GBAS equipment, the aircraft taxied out to the holding point for runway23 with the taxi map selected on the ND. As a situational awareness aid, the map workedreasonably well with the aircraft position being shown correctly for the taxiway that itwas on at any time, but with a displacement of the order of 20 metres from the aircraft'sexact location.

A further trajectory generation was performed at the holding point and this was activatedonce the aircraft was on the runway. Following take off, the lateral guidance demandsfrom the FMS were engaged through the autopilot to ensure a smooth tracking of theprecision departure route. Once the aircraft was clean, the profile demands were alsoengaged, the aircraft levelling at FL50 as required until completion of the departure routeat waypoint KATE. No problems were encountered during this part of the profile. TheFMS was still using the GBAS equipment as the primary position source and this wasmaintained throughout the departure route. Figure 3.10-1 shows that for about 15seconds, while the aircraft was on the leg between waypoints WOLFE and INGLE, theGBAS dropped out of differential mode, probably due to masking from the groundstation situated near the touchdown point of runway 23. A comparison of the GBAS datato the GPS truth track system during the departure segment of the flight (see Figure3.10-2) reveals that, while taxiing the lateral error in the GBAS data was less than 2.5m.However, once airborne, this figure reduced to being about 0.75m when the GBAS wasin differential mode. For the short period when the GBAS was in stand-alone mode (nodifferential corrections), the lateral error only increased to 2m. Similarly, the error in thevertical axis was less than 2.5m while GBAS was in differential mode, increasing to 16mfor the stand-alone condition. This level of accuracy would provide a significantcontribution towards meeting requirements for achieving the capability of an RNP of0.5nm.


Figure 3.10-1 Precision Departure Route WithIndication of GBAS Operational Mode

Figure 3.10-2 Accuracy of GBAS Position FixReferenced to GPS Truth Track

Once the aircraft had passed waypoint KATE and initiated its climb to the cruise altitudeof FL240, the primary position source was reverted to SBAS for the en-route section. Asmooth transition occurred when the change in position source was made with nosignificant lateral adjustment taking place. During the climb, ATC instructed that theclimb should stop at FL220, so the autopilot was disengaged from the FMS profiledemands. After being re-cleared to FL240 by ATC, the profile demands were re-engagedand the FMS demanded a continuation of the climb to FL240, the FMS recognising thatthe planned climb had not yet been completed.

As per normal on these sorties now, the pilot entered the conditions for the first pass-behind manoeuvre into the MCDU, the target aircraft being SIM00, the minimum clearedspacing distance was 6nm and the resume waypoint was FFF. When the trajectory for thepass-behind manoeuvre was generated, the aircraft SIM00 was predicted to cross thetrack of the BAC 1-11 4.8nm ahead. The resultant trajectory deviated the BAC 1-11 by amaximum of 3.3nm from its original track with an initial required track change of 23º,extending the route by 0.6nm. The FMS speed demand remained unchanged at 250ktsCAS. The minimum spacing that was actually encountered during the manoeuvre was6.4nm. The manoeuvre was completed successfully by waypoint FFF.

The second pass-behind was set-up using the target aircraft SIM02, still using aminimum permitted spacing of 6nm, resuming the original route at waypoint HHH.Generating after the turn at GGG, the target aircraft, SIM02, was predicted to cross thetrack of the BAC 1-11 in 3.3 minutes time, at which point it would be 3.7nm ahead of theBAC 1-11. The resultant trajectory required an initial change of 25º in the track of theBAC 1-11, causing a maximum deviation of 5.1nm from the original track and anextension to the route distance of 1.9nm (see Figure 3.10-3). At the closest point ofapproach during the manoeuvre, the spacing between the two aircraft was 5.9nm (seeFigure 3.10-4). In this case, the point of closest approach was almost exactly on theminimum spacing ring around the target aircraft. Thus, as the BAC 1-11 began to turndirectly after passing this point, the spacing distance between the two aircraft remainedrelatively constant for about 30 seconds at around 5.9 to 6.0nm until the BAC 1-11 wason its new track for its recovery route back towards HHH.


Figure 3.10-3 Tracks of the BAC 1-11 andSIM02

Figure 3.10-4 Spacing of BAC 1-11 from SIM02

For the third pass-behind manoeuvre, the selected target aircraft was SIM03, with aminimum cleared spacing of 6nm, to resume the original route at waypoint JJJ. When thetrajectory was generated, the aircraft SIM03 was 2.5 minutes from intersecting the trackof the BAC 1-11, at which point it was predicted to be 4.9nm ahead of the BAC 1-11.This therefore required a smaller track change of only 15º as compared to the previousmanoeuvre, while the maximum deviation from the original track for the BAC 1-11 was3.3nm., which extended the route by 1.3nm. Once again, there was no change in the FMSspeed demand in association with this predicted manoeuvre and the minimum spacingthat was achieved relative to SIM03, during execution of the pass-behind, was 6.1nm.

The pilot entered details for the final pass-behind on this flight using the MCDU,selecting the simulated aircraft SIM04 and a 6nm minimum spacing for the manoeuvre,intending to resume the planned route again at waypoint ZZZ. On this occasion, when thepass-behind trajectory was generated, the FMS predicted that the conflicting aircraftSIM04 would cross the track of the BAC 1-11 in 3 minute's time and at that point itwould be 2.8nm ahead of the BAC 1-11. For this manoeuvre, the predicted trajectoryrequired a track change of 19º and resulted in maximum deviation of 5nm from originalroute. The extension in the route length was of the order of 1.1nm. No speed change waspredicted and as the BAC 1-11 followed the new trajectory, at the closest point ofapproach, the spacing from SIM04 was again approximately 5.9nm. As with the other 3pass-behind manoeuvres on this flight, there were no problems encountered during theexecution of the manoeuvre and the lateral transitions were all implemented smoothlythrough the autopilot.

The two merge manoeuvres were then attempted using the FMS during the second loop,west of the airway A25. As the BAC 1-11 approached waypoint PPP, the pilot selectedthe aircraft SIM09 and then entered the details into the MCDU for the merge. Therequirement was to be 12nm behind SIM09 by the time the BAC 1-11 reached waypointRRR. A trajectory was generated first time, after the BAC 1-11 had completed its turn atPPP and was on track towards QQQ. At this point, the SIM09 was 24.9nm from the BAC1-11 on a bearing of 28º relative to the BAC 1-11's current track to QQQ. A trajectorywas generated direct to waypoint RRR to merge behind SIM09, this trajectory beingactivated within 5 seconds of generation. The FMS speed demand increased from 250kts


CAS to 300kts CAS, in accordance with the predicted trajectory. Although 300kts CASwas the maximum value that the trajectory predictor was permitted to use for the cruisephase, the resultant trajectory estimated the BAC 1-11 would arrive within 3 seconds ofthe time constraint applied to waypoint RRR to ensure a spacing of 12nm from SIM09.To allow some flexibility in the prediction process, a time window of ±10 seconds wasset-up around the time constraint and if the prediction was inside this window, then theconstraint was assumed to have been met.

For this manoeuvre, the aircraft SIM09 was 33.4nm from waypoint RRR and waspredicted to get there at a time of 1611:57 (time at start of prediction was 1606:20). Thesystem then predicted the time it would take SIM09 to travel a further 12nm (the requiredspacing distance) and this was added to the previous time in order to obtain the time atwhich the BAC 1-11 needed to arrive at RRR. It later transpired that the calculation ofthis additional time was incorrectly using the CAS value for the target aircraft rather thanits ground speed and thus, in this case, the estimated time at which SIM09 would be12nm beyond RRR was 1614:48 rather than 1613:58. Over these extra 50 seconds, thetarget aircraft SIM09 would cover an extra 5nm. The trajectory that was subsequentlypredicted for the BAC 1-11 estimated that it would reach RRR at 1614:45. The speedprofile was designed so that, when it reached RRR, it should be at the correct spacingwhile its ground speed should match that of SIM09. Therefore, a waypoint was insertedalong the route just prior to RRR where the BAC 1-11 would start to change speed tomatch that of the target aircraft. Although the trajectory was successfully generated tomeet the assigned time constraints, there was a flaw in the derivation of the true air speedfrom the computed air speed and consequently this affected the predicted ground speed.The result was the actual ground speed achieved for CAS demand of 300kts was not408kts as predicted, but was actually 442kts. The BAC 1-11 consequently arrived about33 seconds earlier than predicted at waypoint RRR. Along with the prediction being 3seconds earlier than the original constraint, the effect was that the aircraft SIM09 wasonly about 14 seconds ahead of where it needed to be for a spacing of 12nm. This extradistance was therefore of the order of 1.4nm and, given that the FMS assumed a point-to-point route for the target aircraft, the final spacing distance between them was actuallydetermined to be 13.1nm.

With the FMS speed demand returning to 250kts CAS when the BAC 1-11 reached RRR,the aircraft continued along the route and the system set-up for the second mergemanoeuvre. For this one, the selected target aircraft was SIM10 and the merge waypointwas to be ZZZ. The required spacing distance at this merge waypoint was to be 18nm. Atrajectory was generated once the BAC 1-11 had completed the turn at SSS and was ontrack to waypoint TTT. SIM10 was currently 23.5nm from the BAC 1-11 on a relativebearing of 30º from the BAC 1-11's current track. The direct distance from the BAC 1-11to the waypoint ZZZ was 63.1nm. A trajectory was generated first time and this predicteda CAS of 298kts to meet the defined time constraints at ZZZ for achieving the requiredspacing. As previously, this time constraint had been incorrectly derived with regard tothe time it would take SIM10 to fly the extra 18nm beyond ZZZ. The result was a timeconstraint to be met by the BAC 1-11at ZZZ of 1630:54, which should have been1630:21.

The predicted trajectory for this second merge manoeuvre did not entirely conform withthe expected speed profile in which the speed changed to that of the target aircraft at the


inserted manoeuvre waypoint prior to ZZZ. In this case, the change in speed was notpredicted to occur until the waypoint ZZZ itself and the CAS value estimated for thetarget aircraft from its ground speed data was 303kts, which was significantly in excessof the correct value. This should have been in the range of 260 to 270ktsCAS. It ispossible that data from the first merge behind manoeuvre was influencing the predictionof the second or a limit had been reached within the FMS with regard to the total numberof new subphases that could be created throughout a flight.

The FMS guidance function successfully followed this new trajectory followingactivation of it. As before, the actual ground speed for a CAS of 298kts was greater(398kts) than the predicted value (354kts). In this case, the difference was 44kts and theBAC 1-11 arrived at the merge waypoint not only 1 minute earlier than predicted, butalso 27 seconds before the simulated aircraft SIM10 had reached a distance of 18nmfrom ZZZ on the track to the next waypoint KKK. In 27 seconds, SIM10, at groundspeed of 357kts, would cover about 2.8nm and this agrees with the actual distancebetween the positions of the two aircraft at this point being 15.2nm (compared with theplanned spacing of 18nm). Once passed ZZZ, the FMS reverted to its normal cruisespeed demand of 250kts CAS.

Figure 3.10-5 Approach Route with Indicationof GBAS Operational Mode

Figure 3.10-6 Accuracy of GBAS Position FixRelative to GPS Truth Track

For this flight, the FMS lateral guidance was maintained through the autopilot until theaircraft was actually in the turn between waypoints DM002 and DM003, bringing theaircraft on to the final approach path. This was partly to determine how well thewaypoints had been defined to be in line with the localiser path that was being generatedby the GBAS equipment (the GBAS was already known to be aligned with the airfieldsILS localiser). Earlier, with the aircraft already in the STAR, the primary position sourcefor the FMS had been changed from the SBAS to the GBAS. The FMS was able tomaintain the aircraft on the defined lateral path throughout this final turn, but the positionof DM003 was determined to be a few hundred metres to the right of the localiser centreline. Therefore, as the aircraft passed through the centre line, the pilots disengaged thesystem to ensure a suitable capture was made of the approach. Figure 3.10-5 shows theapproach route up to the end of the FMS lateral guidance at DM003, along with regionsduring this phase where the GBAS was operating in differential mode (highlighted ingreen). Figure 3.10-6 indicates the accuracy of the GBAS position data (relative to a GPS


truth track system) during the period that the FMS was using it as the primary positionsource. It can be seen that laterally, when in differential mode, the error was a fraction ofa metre and vertically it was 1 to 2m.The actual lateral guidance performance throughoutthe flight is indicated in Figure 3.10-7, which shows the cross-track error derived by theMFMS. This demonstrates that the flight technical error for the lateral guidance of theMFMS was typically no more than about 150m (or 0.08nm) when controlling to the routeand for all of the pass behind manoeuvres. The exact figures for this flight were a meanerror of 70m with a standard deviation of 154m. The spikes that can be seen in thedeviation are related to the go-direct function used for the merge behind manoeuvres and,as explained previously, result from the aircraft being unable to react sufficiently quicklyto follow the second part of the predicted S-shaped path. A smoother predicted tracktransition, similar to that employed for the pass behinds would resolve this and shouldmean that the same level of performance would be achievable throughout the flight.

Figure 3.10-7: MFMS Lateral Guidance Performance


3.11 Summary of GBAS Approach Guidance Presented on the Primary Flight Display.

In preparation for the auto-coupled approach trials of the MFMS, GBAS guidanceinformation was displayed on the primary flight display (PFD) on the left-hand side ofthe cockpit. The aim of this was to give the flight crew experience of the anticipatedauto-coupled approaches and the steeper approach angle (4.5°) that was to be used duringsome of the later auto-coupled approach work. A summary of the flights on which GBASinformation was used for manual approaches is given in Table 3.11-1:

Date Number of Approaches Glideslope

7 Feb 2 1 @ 3º, 1 @ 4.5º

19 Feb 1 3º

27 Feb 2 3º

11 Mar 2 4.5º

14 Mar 2 4.5º

20 Mar 1 3º

Table 3.11-1: GBAS Guided Approaches

The quality of the GBAS information will be assessed on a flight-by-flight basis and willbe presented in terms of the percentage full-scale deflection (FSD) of the guidancedeviations. Also shown on the graphs will be the equivalent FSD of the guidancedeviations derived from the post-processed GPS truth source.

The approaches were conducted after following representative STAR procedures, anexample of which is given in Figure 3.11-1.

Figure 3.11-1: Representative STAR for Boscombe Down


3.11.1 7th February

This flight was divided into two separate circuits with a full stop landing and FMS resetin between. At the end of the first circuit a 3º approach was flown, with the GBASproviding guidance. At the end of the second circuit the approach was conducted at 4.5º.

During both of these approaches the GBAS coverage remained constant with no drop-outs observed and the guidance displayed to the pilot was seen to be good.

It can be seen in Figure 3.11-1 that there is a small divergence between the GBAS andtruth glide slope data with approximately half a mile to go to touchdown during the firstapproach. This divergence was found to be approximately 1m in both the glide slope andlocaliser deviations. The reason for the start of the glide slope trace being at –100% FSDis due to the fact that the aircraft was flying level below the glide slope prior to capture atapproximately 8nm to go.

Figure 3.11-1: 7th February GBAS Approach 1 using 3º Glide Slope

The data for the second approach (see Figure 3.11-2) shows a similar pattern to the firstapproach, the only difference being that the divergence in the glide slope is more gradualfrom about one and a half miles to go. The corresponding difference between the GBASand truth glide slope deviation was found to increase by 1.5m.


Figure 3.11-2: 7th February GBAS Approach 1 using 4.5º Glide Slope

3.11.2 19th February

During this flight, a problem developed with the GBAS equipment during the downwindleg prior to the approach. The reacquisition of the GBAS VHF broadcast had beenachieved during the descent and, as the aircraft passed the AGIBS waypoint, theequipment reported a non-differential operating mode. At first it was thought that thiswas just caused by masking of the VHF transmission as had been seen before and that thetransmission would be reacquired in due course. As the flight progressed it appearedmore and more apparent that the signal would not be reacquired, and eventually theGBAS approach was aborted. It can be seen from Figure 3.11-1 that the difference inguidance between the post-processed GPS truth track and the non-differential GBAS ismost marked in the glide slope due to the nature of the uncorrected errors in the standalone GPS system.

Analysis of the logged GBAS data showed that there had been no differential messageslogged from the aircraft VHF receiver after the AGIBS waypoint. The reason for this isunknown, but could be caused by a communications breakdown between the GBASprocessing unit and VHF receiver or by an integrity failure of one of the components ofthe ground system.


Figure 3.11-1: 19th February GBAS Approach using 3º Glide Slope

3.11.3 27th February

The GBAS equipment performed in a similar fashion to that seen before, with patchycoverage on the downwind leg, probably due to masking of the VHF transmission. Onceagain there is a small divergence between the GBAS and truth glide slope guidance dataevident on both approaches corresponding to a difference in linear deviation ofapproximately 1m.

During the first approach the pilots commented on an observed two dot jump in thedisplayed guidance, but a distinct jump is not evident on the trace of the internallyrecorded data.

The second approach was conducted with good guidance and no data anomalies wereseen.

3.11.4 11th March

During this flight the GBAS coverage was again patchy during the downwind leg, withseveral outages observed in the VHF transmission. During this flight the first approachhad to be aborted due to problems with the display of GBAS guidance data. This problemappeared to be related to the analogue guidance signal provided by the equipment fordisplay on the PFD. During the aborted approach, guidance computations were occurringand appropriate numerical deviations were being displayed on the GBAS equipment inthe aircraft cabin. The guidance bugs on the PFD (and repeater in the cabin), which aredriven by analogue outputs from the GBAS equipment, were seen to remain centred andred. This approach was broken off with 5nm to go and the GBAS equipment reset while


the aircraft repositioned for further approaches. The cause of the fault was not isolated,but resetting the GBAS equipment cleared the error.

The first successful approach of the sortie was achieved after the GBAS equipment hadbeen restarted. The fault observed previously where the guidance bugs did not move wasnot re-observed and the approach was conducted to a low overshoot. Good agreementbetween the GBAS and truth-derived guidance was observed.

3.11.5 14th March

During this flight the GBAS coverage was again patchy during the downwind leg andalso for part of the base turn, where outages were observed in the VHF transmission.During this flight the first approach again had to be aborted due to problems with theanalogue guidance data preventing the bugs from becoming active on the PFD. While theaircraft repositioned for another approach the GBAS equipment was again reset torecycle the hardware.

The first approach after the reset was successful with good guidance provided to thepilots and no observed dropouts.

The second approach was also successfully conducted with good agreement between theGBAS and truth data.

3.11.6 20th March

After the problems observed during the previous approaches, the GBAS equipment wasrestarted before the aircraft passed the AGIBS waypoint. No problems were encounteredduring the approach with the guidance bugs on the PFD.

The guidance supplied to the pilot was generally good, although when the aircraft waswithin 4nm of touchdown there were some jumps in the differences between the GBASand truth glide slope guidance of the order of 1 to 1.5m. These differences wereessentially undetectable on the guidance displayed on the PFD.

3.11.7 Summary

The guidance information provided by the GBAS equipment was, on the whole, reliableand of sufficient accuracy to enable the pilots to follow the beam bars on both a 3.0º and4.5º glide slope approaches.

The source of the problems with the analogue guidance was independent of the GBASsignal-in-space, and most probably caused by an intermittent hardware fault within thereceiver or somewhere else in the signal path between the GBAS equipment and theaircraft displays.

The loss of the GBAS link during the downwind leg should not have an impact on theoperational deployment of the system. It is envisaged that the coverage of airport GBASinstallations should be similar to that of an ILS and not be based on an omni-directionalantenna similar to that used in the experimental installation at Boscombe Down.


3.11.8 Summary of MA-AFAS Glide Slope Guidance Compared to GBAS

For the later phases of the MA-AFAS project where precision curved approaches wereplanned, the MFMS would have to provide glide slope guidance commands to theautopilot during the initial curved section of the approach, the autopilot transitioning toGBAS-derived approach guidance once the aircraft had captured the localiser. To test thecomputation of these guidance commands, comparisons were made between the GBASguidance data and the MFMS glide slope guidance data. At this stage of the developmentof the MFMS precision approach function, there was still some refinement to be done tothe algorithms, but this test was to verify that the MFMS was capable of using actualGBAS position solution information to determine a reasonable glide slope deviationvalue.

Figure 3.11-1: Glide Slope Comparisons for Approaches on 14 March

It can be seen in Figure 3.11-1 that there is a difference between the two deviation traces(the GBAS-derived deviation is shown red whilst the MFMS-derived value is in blue),which on closer inspection appears to be constant.


Figure 3.11-2: GBAS and MA-AFAS Glide Slope Differences

It can be seen from Figure 3.11-2 that the offset appears constant at about 5% FSD(equivalent to 0.00875 DDM) when the guidance bugs are active. Close comparison ofthe two traces also shows that the MA-AFAS-derived information is noisier than theGBAS. The exact reason for this is unknown but was possibly related to the way theArinc data from the GBAS was handled by the MFMS, which consequently couldinfluence the derivation of the distance to go to the touchdown point. With the positioninformation from the GBAS being split between coarse and fine components over theArinc data bus, if these components were not exactly matched on each iteration, then thismight result in some background noise affecting the solution.


3.12 Summary of Boscombe Results

The flight trials that took place at Boscombe Down and the single check flight at Romeachieved the aim of developing the MFMS to a sufficient level of performance that itcould be used in the subsequent trials at Rome with two live aircraft. None of the flightshad to be aborted due to system failures and the MFMS was demonstrated to be capableof meeting the general objectives of each flight within any limitations imposed by itsdevelopmental progress at that stage. This also vindicated the process of ground testingand validation that was being followed during the trials period before systemimprovements were tested in the airborne environment. In the majority of situations, thetype of performance experienced with the MFMS during these flight trials wascomparable to that which had been determined from the ground testing.

The initial couple of flights had primarily proved the compatibility of the MFMS with thevarious other avionics systems to which it was interfaced onboard the BAC 1-11. Thekey system in this respect was the autopilot, which was demonstrated to operate withoutany serious problems when using the demands from the MFMS. These first flights werealso important in verifying the basic FMS functionality of the system for predicting a 4Dtrajectory for the aircraft and generating the necessary autopilot demands for guiding theaircraft around the planned flight profile. There had been added emphasis on this aspectdue to the project having been forced into producing a complete FMS from scratch,which had not been the original plan.

With the main baseline FMS functionality in place, it was possible to start flight testingthose components of the ASAS delegated manoeuvres that had been implemented. Theseessentially consisted of the pass behind and merge behind manoeuvres. All these flighttrials used simulated aircraft targets within the MFMS against which these ASASmanoeuvres could be generated.

The main route used for the Boscombe Down trials incorporated four pass behindsituations, with different configurations in the relative tracks of the two aircraft wherethey crossed. These included a shallower intercept where the two aircraft were flyingcomparable tracks and two situations where the simulated aircraft had a component oftrack that was in direct opposition to that of the BAC 1-11. In practically all of thesetests, the simulated aircraft was timed to reach the intercept point ahead of the BAC 1-11in order to replicate the condition that would require the BAC 1-11 to be the selectedaircraft to manoeuvre around the simulated one. Apart from when problems arose withthe position data being used by the MFMS, the trajectory predictor was always able togenerate a lateral pass behind manoeuvre. The one exception to this had been the firstpass behind during the check flight in Rome, when a separate problem prevented thepredictor from creating a complete trajectory.

A total of 17 pass behind manoeuvres were flown against simulated target aircraft. Thegeometry of the route meant that typically, the BAC 1-11 was less than 3.5 minutes fromthe intercept point when the pass behind was predicted. Assuming a standard separationdistance of 5nm, then this separation would likely have been compromised anything upto 1 minute before the BAC 1-11 had reached the track intercept point. Although itshould be noted that the pilots had been requested to activate the trajectory as soon asthey were satisfied with it on the lateral map display, the time between the pilot


requesting the MFMS to generate the manoeuvre and then activating it was often within5 seconds. The MFMS was allowing a 15-second period over which the aircraft wasassumed to be maintaining its currently planned profile before any new turn was inserted,so this comfortably covered the response times that were being encountered.

All the lateral manoeuvres were predicted within the standard performance limits used bythe MFMS for normal generations of en-route flight profiles. For the situations where a6nm minimum spacing was defined, the maximum deviation of the BAC 1-11 from itsoriginally planned track was 6.6nm, although the situations were that the target aircraftwas always passing ahead of the BAC 1-11. Although there was insufficient data to makea definitive statement, the magnitude of this deviation from the original track tended tobe dependent more on the relative time difference between the two aircraft passing theintercept point in their tracks, rather than the relative difference in the track anglesthemselves.

The flight trials from Boscombe Down were also used to test the ability of the MFMS tomerge the BAC 1-11 to be a specified distance behind a simulated target aircraft. Moreproblems were encountered with this function than with the lateral pass-behind. This wasprimarily due to the need to add in additional speed change subphases, theimplementation of which was not initially being handled correctly. It was not really untilthe flight on the 20th March that the insertion of the speed change subphases wasfunctioning more as expected and the true behaviour of the merge behind process itselfcould be investigated. The results on the 20th March revealed that, although the systemwas producing speed demands to modify the spacing distance between the two aircraft,the magnitude of these demands was not quite correct to achieve the specified distance. Itwas clear that the trials were demonstrating the feasibility of the concept, but notnecessarily an error-free implementation. However, with the equipment needing to bepackaged ready for transportation to Rome for the live aircraft trials directly followingthis flight, further evaluation of the system and the testing of additional softwaremodifications could not be carried out prior to the start of the Rome trials themselves.

The flight trials had shown that the MFMS was able to guide the aircraft to the predictedflight profile for both the pass behind and merge behind manoeuvres. Since the MFMSused the standard FMS trajectory prediction functions in the determination of thesemanoeuvres, the level of guidance performance was essentially unchanged from thatachieved under normal en-route conditions.

The en-route navigation performance was predominantly dependent on the use of theSBAS as the primary position source. When compared against a GPS truth track, theSBAS was shown to be in error laterally by only 1.3m. With the MFMS itself exhibitinga flight technical error of the order of 70m (data from the flight on 20th March), then thiswould demonstrate that such a system could provide the capability of meeting RNP 1performance. The trials, however, also highlighted the need for back-up systems toprovide a means of cross-checking the integrity of the position solution.

Some performance data was obtained for the GBAS equipment to consider its ability tosupport precision departure and arrival operations using the MFMS. Relative to the truthtrack system, the GBAS was seen to be capable of providing a position solution with alateral error of less than 1m and a vertical error within 3m while in differential mode.


FMS guidance could be maintained through the departure and arrival routes, althoughsystem development was not sufficient to perform in-flight precision approach trials withthe FMS providing initial glide path guidance to the autopilot.

During these flight trials at Boscombe Down, the VDL4 data link communications testswere concentrating on range and integrity performance of the system. The initialtransponders that were used were found to lose the communication link with the groundstation at the extremities of the original trials route (a range of around 150nm). Thisresulted in the update to the route that ensured the aircraft remained within reliable linkcoverage range of 135nm from the ground station at Boscombe Down. Revised versionsof the transponders also improved the performance of the system, not in range but withregard to the speed at which the link could be re-established in situations where data linkcommunications were briefly lost. Only the ADS-B component could be tested duringthese trials while the point-to-point communications for CPDLC continued to be groundtested. The trials also indicated that the air-to-ground link performed more reliably thanthe ground-to-air link, when the VDL4 ground station at Boscombe Down was in use.Additionally, the operation of a second airborne transmitter on the ground during oneflight had provided a level of confidence that the air-to-air ADS-B reports would besuccessfully exchanged between the two live aircraft during the flight trials in Rome. Ithad also been possible to connect the transponder at the ground station to the air/groundrouter and to the Broadcast Application Ground Server (BAGS) in order to relay ADS-Bdata to a simulated ATC position at the Eurocontrol Experimental Centre (EEC) atBretigny, France. There were some issues with the validity of some of the recorded ADS-B data (altitude and speed) which were subsequently investigated in the lab but were notfully resolved.


4 Rome Trials

4.1 24th March 2003


This was the transit flight by the QinetiQ BAC 1-11 to Ciampino Airport in Rome inpreparation for the MA-AFAS trials that would be taking place here during this week. Aswith the transit flights to and from Rome during the previous week for the practice sortie,the MFMS was to be used to provide lateral guidance demands to the autopilot for themajority of this flight.


EGDM-SAM-MID-XAMAB-BAMES-RBT-PTV-NEV-LERGA-LATAM-KURIR-RETNO-KOLON-DIVUL-SODRI-BTA-ELBA-GILIO-MEDAL-GILET-OST-URB-LIRA.

The FMS was also to be coupled to the VDL4 transponder with the intention ofinvestigating whether air-to-air broadcast data could be successfully received from DLR'sATTAS aircraft, which was due to arrive at Rome shortly before the BAC 1-11. Theairborne transponder had been reset to the Rome trials frequency and therefore was notcleared to be powered outside of the Italian FIR.

4.1.2 MFMS Report

Having initialised the FMS on the ground as usual, the aircraft took off and once ATChad vectored the aircraft to join the airways system, a new trajectory was generated byperforming a go-direct to waypoint HAWKE, this trajectory then being activated. TheFMS lateral guidance was subsequently engaged through the autopilot.

While transiting across France, ATC deviated the aircraft from its original pre-plannedroute using airway UM728 on to a neighbouring airway UL612. This occurred about12nm before reaching Pithiviers (PTV) and consequently the FMS lateral guidance wasdisengaged from the autopilot while the pilot was receiving heading instructions from thecontroller. After some negotiation with the controller, the aircraft was permitted to returnto its original route, rejoining on the leg from Nevers (NEV) to the waypoint LERGA.Although FMS lateral guidance was re-established, it appears from the post-flightanalysis that the FMS source had been changed from the MFMS to the secondary lateralguidance system onboard the BAC 1-11, which was being used as a backup to the MA-AFAS equipment. This was corrected, but not until much later in the flight and thereforethere is only about 40 minutes of this flight for which cross-track deviation data can beconsidered as valid. From this data, the flight technical error related to the cross-trackdeviation term shows a mean value of 40m with a standard deviation of 29m and amaximum offset of 206m.

Once in Italian airspace, the VDL4 transponder was activated. The ADS-B reports fromthe ATTAS were successfully received by the VDL4 transponder and this data passed to


the FMS. An aircraft symbol was displayed on the lateral map of the ND to indicate theposition and track of the ATTAS, the CDTI overlay having been selected by the pilotusing the trackball and the soft keys on the display. The identity code for the ATTASwas also shown alongside the symbol with the ground speed of the ATTAS and its heightoffset (in hundreds of feet) relative to the BAC 1-11. The identity code was indicated asIOEAA while the height offset appeared to be valid as both aircraft were descendingtowards Rome. The ground speed data for the ATTAS was, however, about 10 times toolarge (displayed as 2430kts), consistent with the results that had been seen on the 19th

March concerning the ADS-B data for the BAC 1-11. The other observation frommonitoring the CDTI data on the ND was that there were occasional instances of theground speed and track angle data being zero. Along with the magnitude of the groundspeed data, these zero values would need to be corrected, or at least filtered out, beforethe main trials began at Rome, in case these affected the trajectory prediction process forthe pass-behind and merge manoeuvres.


4.2 25th March 2003


This was to be the first proper test of the MA-AFAS system in which two live aircraft,the BAC 1-11 and the VFW-614 ATTAS, would perform delegated ASAS manoeuvreswith air-to-air broadcast data being provided via the VDL4 data link. The routes flownby the two aircraft in the assigned trials area are shown in Appendix A.3. Both aircraftwere at FL210, with the ATTAS cruising at 210kts CAS and the BAC 1-11 at 250ktsCAS, although this could be modified to co-ordinate the timings during the flight. TheBAC 1-11 was to take-off 10 minutes after ATTAS aircraft in order to arrive in the areaof the first pass behind manoeuvre at the right time. A total of two pass behind and onemerge behind manoeuvres were to be tested. The BAC 1-11 would carry out thesemanoeuvres while the ATTAS maintained its planned track. The trials scenarios wereplanned to not reduce aircraft separation below the standard 5nm. A dedicated radiocommunications link was provided on P134.900, S129.000 in order to allow co-ordination of the trial between the various participants.

Updates had been made to the FMS surveillance database software with regard to thehandling of the ADS-B reports received from the VDL4 transponder. The ground speeddata was now divided by an additional power of 10 to ensure that the manoeuvreprediction process used the correct speed. The reports were also filtered to remove anythat contained zero track or ground speed values, while those reports relating to the ownaircraft were ignored so that this data would not be displayed on the CDTI overlay. It hadbeen noted that the identity information had also been decoded incorrectly, so this hadbeen revised as well, the new codes that were expected are listed in Table 4.2-1.

Aircraft/Ground Station VDL4 IdentityBAC 1-11 AAEQJATTAS AAEEH

Ciampino AAAJI

Table 4.2-1: Updated VDL4 Identity Codes

The route that had been used on the practice flight on the 19th March had also beenmodified to allow a little extra route distance beyond the merge waypoint (in this caseMMP). The FMS company route that was selected by the pilot was now QNQ6. TheSTAR that was selected related to an approach to runway 33 at Ciampino, although itwas expected to be runway 15 that would be used. This was an initial precaution in casethe short STAR used for runway 15 had caused some of the manoeuvre predictionproblems encountered on the 19th March.

As the ground tests of the VDL4 communications network in Rome were not able toproduce a reliable Point to Point capability, the fall back position of using voicecommunication for the ATC control of the delegated ASAS manoeuvres was adopted.

4.2.2 MFMS Report

With the flight profile data entered into the FMS, a trajectory was generated while theBAC 1-11 was still on the ground at Ciampino, the aircraft taking off, as planned, 10


minutes after the ATTAS aircraft had departed. With the trajectory having been activatedwhile the BAC 1-11 lined up on the runway, the FMS guidance demands startedautomatically once the aircraft was airborne and lateral guidance could be engagedthrough the autopilot prior to the start of the first turn at SOT15. FMS profile guidancedemands were not engaged through the autopilot until the aircraft was on track towardsOstia (OST) at about FL60. The aircraft climbed under FMS control to the cruise atFL210, accelerating as planned from 230kts to 250kts CAS as it reached FL100.Meanwhile, the ATTAS aircraft was also at FL210, but flying at 210kts CAS.

Once the BAC 1-11 had entered the trials area and passed waypoint B2, a manoeuvrewas generated to pass-behind the ATTAS aircraft (code AAEEH) with a minimumallowed spacing of 6nm, resuming the original route at waypoint B3. This was inresponse to the instructions via R/T from the trials ATC controller to select this targetaircraft, which had to be first confirmed by the pilot, before the further instruction wasreceived defining the requirements for the manoeuvre itself. The current tracks of the twoaircraft would intercept one another at waypoint P1, the ATTAS crossing at an angle of80º to the track of the BAC 1-11. At the point when the pass-behind manoeuvre wasgenerated at 0914:25, the ATTAS was predicted to reach P1 at 0917:00, approximately30 seconds before the BAC 1-11. With the ground speed of the BAC 1-11 being 42ktsgreater than that of the ATTAS aircraft, the estimated separation by the time the BAC 1-11 was at P1 would have been 2.4nm.

Figure 4.2-1 Spacing during first Pass-Behind Manoeuvre, 25th Mar. 03


The resultant trajectory for the first pass-behind required an initial track change for theBAC 1-11 of 26º, the aircraft deviating by 4.9nm from its original track beforerecovering back to waypoint B3. The duration between the pilot triggering the trajectoryprediction and then activating it was around 5 seconds. During the course of themanoeuvre, the actual minimum spacing that was achieved relative to the ATTAS was6.4nm (see Figure 4.2-1).

Having cleared the ATTAS aircraft, the pilots increased the speed of the BAC 1-11 to280kts for about 3.5 minutes to try and reduce the time difference between thepredictions of when the two aircraft would arrive at waypoint P2 for the second pass-behind manoeuvre. The ATTAS would cross the path of the BAC 1-11 at P2 when the 1-11 was on the leg from B4 to B5, the ATTAS being on a track that was 50º to that of theBAC 1-11. At 0923:51, a trajectory was generated at the first attempt with the FMSpredicting that the ATTAS would reach waypoint P2 at about 0927:04, 25 seconds beforethe BAC 1-11. The BAC 1-11 would be approximately 2.2nm from P2 when the ATTASreached this waypoint. The pass-behind manoeuvre generated by the FMS required aninitial track change of 27º and would deviate the BAC 1-11 by 7.3nm from its originaltrack in order to ensure a 6nm minimum spacing. Once again, there was a 5-secondperiod between the start of the prediction process and the trajectory being activated. Themanoeuvre was carried out successfully and the BAC 1-11 resumed its previous route atwaypoint B5, having passed the ATTAS at a minimum distance of 6.1nm.

Figure 4.2-2 Spacing during second Pass-Behind Manoeuvre, 25th Mar. 03


For the merge manoeuvre, a spacing distance of 20nm was entered into the MCDU andthe merge waypoint was defined as MMP. No software modifications had beenimplemented since the flight on the 20th March. This was due to there having been noavailable time to identify the problems, apply the necessary software modification andground test using the aircraft model rig before all the equipment had had to be loaded onto the aircraft in preparation for the detachment to Rome. Thus the same basicperformance problems still existed as previously described for the flight on the 20th

March at Boscombe Down. However, the principle of the merge manoeuvre could betested. With the system configured for the merge behind, a trajectory was predicted at0941:59. At this point, the BAC 1-11 was currently 32.9nm from the ATTAS while thewaypoint MMP was 66.9nm on a direct track from BAC 1-11's current position. Atrajectory was generated and activated about 4 seconds after the pilot initiated theprediction. Although the aircraft turned on to the direct track to MMP, there was nochange in the speed demand from the FMS. Post-flight analysis revealed that there hadbeen a problem with part of the ADS-B surveillance data used by the FMS to predict theflight path of the target aircraft, i.e. the ATTAS. The manoeuvre generator process usedthe height rate from the ADS-B report for the target aircraft to estimate the aircraft stateconditions for this aircraft at the merge waypoint, MMP. The height rate data was notproviding any sensible information, however, the value being set to 9999m/s, and thiscaused incorrect data to be derived for the speed and time of the ATTAS at MMP. Sincethe manoeuvres were all being executed in level flight, this parameter was set to alwaysbe zero in the surveillance database and thus allow this process to function better.

Throughout the flight, the ADS-B reports had been received from the ATTAS via theVDL4 transponders and processed by the FMS giving sufficiently continuous updatesthat allowed the position of the ATTAS to be monitored successfully on the lateral mapof the ND. This information remained on the display and it was not noted that itdisappeared at any time. The ATTAS, however, had had problems obtaining the ADS-Breports from the BAC 1-11 when the two aircraft were at the same altitude.


4.3 25th March 2003


In the afternoon, the BAC 1-11 and the ATTAS repeated their flights from the morning,but with the FMS surveillance database now always setting the height rate within thetarget aircraft reports to be zero. Otherwise the FMS was set up identically to themorning's flight, although with the latest meteorological forecast file loaded.

4.3.2 MFMS Report

The departure of the BAC 1-11 was delayed by about 2 minutes due to another aircraftbeing on the approach at the 10-minute mark after the ATTAS had taken off. TheATTAS was therefore requested over the trials R/T frequency to delay its progress toallow the BAC 1-11 to catch up. Consequently, the ATTAS slowed down in order to co-ordinate the arrival times of the aircraft at waypoint P1.

With the trajectory activated after lining up on the runway, the output of the FMSguidance demands was triggered after take off and the lateral demands engaged throughthe autopilot before the first turn. The profile demands were also engaged earlier than onthe previous flight, the aircraft being at about 2500ft. As the aircraft reached the cruise atFL210, degradation in the performance of the SBAS started to occur. It is believed thatthere was some source of interference in the area that was affecting the reception of theGPS signals. With the SBAS being unable to maintain lock on to the signals fromsufficient GPS satellites, it was decided to change the primary position source for theFMS to be the IRS. This was done without any problem to the flight itself.

By the time the first pass-behind manoeuvre was to be carried out, both aircraft were attheir originally planned cruise speeds of 250kts CAS for the BAC 1-11 and 210kts CASfor the ATTAS. The position source for the FMS on the BAC 1-11 had also beenreverted back to the SBAS after clearing the area of GPS interference. The configurationof the pass-behind was unchanged from the previous flight, the minimum permittedspacing distance being 6nm. A trajectory was predicted at 1419:30, the FMS estimatingthat the ATTAS would reach waypoint P1 at 1421:39, approximately one and a quarterminutes before the BAC 1-11, so that by the time the BAC 1-11 had reached P1, thedistance to the ATTAS would be 6.1nm. The trajectory that was produced for the pass-behind manoeuvre only required a 7º change in track for the BAC 1-11, which resulted ina total deviation from the original track of 2.1nm. The time between initiation of theprediction and activation of the trajectory was just 4 seconds and the spacing between thetwo aircraft at the closest point of approach during the manoeuvre was 6.4nm.

Once clear of the ATTAS, the speed of the BAC 1-11 was increased to try and make upsome of the earlier delay and to co-ordinate the ETAs of the two aircraft at waypoint P2for the second pass-behind manoeuvre. An additional region of GPS interference wasencountered shortly before carrying out this pass-behind so the IRS was selected asposition source until completion of the manoeuvre. With the BAC 1-11 back to 250ktsCAS, the next pass-behind was generated at 1429:20, the FMS predicting that theATTAS would arrive at P2 at 1431:38, 38 seconds ahead of the BAC 1-11, indicating aseparation of 3nm when the BAC 1-11 had reached P2. This pass-behind manoeuvre


required an initial track change of 26º for the BAC 1-11, the deviation from the aircraft'soriginally planned track being 5.9nm. The time from triggering the trajectory predictionto activating this trajectory was 4 seconds again. While following this trajectory, theachieved minimum spacing of the BAC 1-11 from the ATTAS aircraft was 6.3nm.

Once the BAC 1-11 had completed the turn at waypoint B7, the merge manoeuvre wascalculated with the merge waypoint defined as MMP and the required spacing behind theATTAS set to be 15nm. At 1446:13, when this new trajectory was predicted, the ATTASwas 31.6nm from the BAC 1-11 and had a ground speed of 295kts. The direct distancefrom the BAC 1-11 to the merge waypoint MMP was 67nm, while the ATTAS wascurrently 36.3nm from MMP and already on a track towards it. The trajectory for thismerge behind manoeuvre was activated 6 seconds after the prediction process hadoriginally been triggered. A new speed demand of 286kts was output by the FMS to theautopilot. This provided a reasonable closure rate for the BAC 1-11 relative to theATTAS, although by the time the BAC 1-11 had reached the waypoint MMP, it wasactually 14.2nm behind the ATTAS. Prior to MMP, the FMS speed demand changed to229kts CAS, which was intended to match the speed of the target aircraft, i.e. theATTAS, which was actually flying at around 210kts CAS. The report on the flight on the20th March details why there were problems with the prediction of the speeds for mergemanoeuvre. The predicted wind for this flight in Rome was 189º/8kts, while that actuallyencountered during execution of the merge manoeuvre was 187º/18kts. Since this wasvery much a tail wind for this part of the flight, it would have resulted in the groundspeed of the BAC 1-11 being about 9kts greater than predicted. However, the differencebetween the predicted ground speed from the trajectory and the actual ground speed,when flying at 286kts CAS, was of the order of 44kts, so the problem of the conversionto true air speed was resulting in an error of around 35kts. In this case, a CAS demand ofaround 275kts may have been more suitable for meeting the set spacing distance of15nm.

Having passed MMP, the CAS demand reverted to the standard cruise value of 250kts.The aircraft then departed the allocated trials area after passing waypoint A6 and thecontrol was taken over by the pilot in order to follow ATC instructions for returning toCiampino airport.


4.4 26th March 2003


The plan for this sortie was the same as that for the previous day with the BAC 1-11following the QNQ6 route and the ATTAS acting as the target aircraft for two passbehind and one merge manoeuvre to be performed by the BAC 1-11. The FMS remainedin the same state as for the previous flight, but with the latest meteorological forecast filehaving been loaded. The co-ordination between the two aircraft had worked well on theday before and therefore the timings were left unchanged.

4.4.2 MFMS Report

Initialisation of the flight details in the FMS was carried out by the pilot and the BAC 1-11 took off at 0900, 10 minutes after the ATTAS. No problems were encountered afterthe FMS guidance demands were engaged through the autopilot as soon as practicableafter take off. Towards the top of the climb, the interference that affected the GPSsystems was experienced again and consequently the pilot selected the IRS as theprimary position source for the FMS until the aircraft had cleared this region ofinterference. A couple of hundred feet before the BAC 1-11 reached the cruise altitude ofFL210, the thrust demand from the FMS reduced to flight idle, causing the aircraft tolevel a fraction early and start to descend. The profile guidance demands weredisengaged and the autopilot was used directly to complete the climb to FL210. Thecause of this was that the FMS had detected that the conditions were correct for thetransition to the cruise mode, for which there is no requirement for a thrust demand (onlyheight and speed demands). On this occasion, the transition point determined by the FMSwas prior to the autopilot starting its flare to the cruise level and therefore the autopilotcontinued to react to any changes in the FMS thrust demand. After the flight, anadjustment to the flare to level anticipation parameter used by the FMS ensured that thiswould not reoccur on any subsequent flights.

The first pass-behind manoeuvre was performed as planned when the BAC 1-11 hadpassed waypoint B2, the pilot responding to the R/T instructions from the trials ATCstation for a minimum permitted spacing of 6nm. The FMS trajectory was generated at0916:04 with the ATTAS predicted by the FMS to reach the intercept point P2 at0918:30, 53 seconds before the BAC 1-11, and resulting in a predicted separation of4.5nm at P1. This new trajectory required a track change of 16º for the BAC 1-11 andproduced a maximum offset distance from its original route of 3.2nm. Activation of thenew trajectory was selected by the pilot 3 seconds after the prediction was made. At thepoint of closest approach during the manoeuvre, the spacing between the BAC 1-11 andthe ATTAS aircraft was 6.6nm.

The interference that had been affecting the reception of the GPS signals for the SBASequipment had disappeared earlier on during the pass-behind manoeuvre and so theSBAS was reselected as the primary navigation data source for the remainder of theflight. The second pass-behind also took place without any problems. At the time of thetrajectory prediction (0925:29), the ATTAS was being predicted by the FMS to arrive atP2 at 0928:16, which was now 62 seconds prior to the BAC 1-11 reaching P2. However,with the ground speed of the BAC 1-11 being 65kts greater than that of the ATTAS at


this point, the separation distance would have been down to 5nm by the time the BAC 1-11 was at P2. The trajectory to pass-behind the ATTAS required a track change of only7º and consequently, the BAC 1-11 would only deviate by 2.5nm to the left of itspreviously planned track. The time between prediction and activation of this trajectory bythe pilot was again 4 seconds, while this time the spacing at the point of closest approachwas 6.3nm.

The conditions input for the merge behind manoeuvre were to be a distance of 15nmbehind the ATTAS on reaching waypoint MMP. A trajectory was computed at 0943:24when the BAC 1-11 was on track towards waypoint B8. At this point, the ATTASaircraft was 30.2nm from the BAC 1-11 with 37.2nm to run before reaching the mergewaypoint MMP. Meanwhile, on a direct bearing, the BAC 1-11 was a distance of 66.5nmfrom MMP. Activation of the predicted trajectory was within 3 seconds of the predictionand the new speed demand from the FMS was 272kts. The BAC 1-11 reached thewaypoint MMP at 0954:28, by which point it was 15.4nm behind the ATTAS (see Figure4.4-1). Prior to MMP, the FMS speed demand had reduced to 228kts CAS in order tomatch the predicted ground speed of the ATTAS. The subsequent determination of theproblem with the conversion to true air speed with the forecast meteorological datashowed that there was a combination of effects that resulted in the BAC 1-11 being closeto the required spacing. However, as shown by the 228kts CAS demand, which shouldhave been 210kts CAS to match the ATTAS, the predicted speed profile from the FMSwas not deriving the correct values, although the sense of the speed changes was correct.

Figure 4.4-1: Spacing Distance during Merge Manoeuvre, 26th Mar. 03

Profile guidance was disengaged at MMP in order to follow the height and speedclearances from Rome ATC. The pilot changed the STAR in the FMS to be appropriateto runway 15 rather than runway 33 and generated a new trajectory, which was activated


successfully. Lateral guidance was maintained until reaching Ostia (OST), whereuponATC heading instructions required the disengagement of the FMS bank demands.


4.5 26th March 2003


A further trial flight was performed in the afternoon on the 26th March with the systemremaining unchanged from the morning apart from including the latest forecastmeteorological data and the modification to the FMS flare to level anticipation parameter(to overcome the problem seen on the morning flight). The planned sortie profileremained the same as that flown in the morning.

4.5.2 MFMS Report

Initialisation of the FMS and trajectory prediction was carried out as per the earlierflights, the BAC 1-11 taking off approximately 10 minutes after the ATTAS aircraft.Lateral guidance demands from the FMS were engaged through the autopilot as soonafter take off as possible, with the profile demands engaged as the aircraft passed about2000ft.

During the climb, ATC restricted the BAC 1-11 to FL160 for a while before clearing itall the way to the cruise level of FL210. This resulted in the BAC 1-11 being partlydelayed and was thus further behind the ATTAS than had been planned. The interferenceof the GPS signals was encountered in the same place again, so the IRS was selected asthe primary navigation data source until completion of the first pass-behind manoeuvre.

This first pass-behind was executed successfully, with the trajectory being predicted at1416:06, after the BAC 1-11 had completed the turn at waypoint B2. A minimumspacing distance was still being used (this being the value passed by the trials ATCcontroller), although the FMS predicted that the ATTAS was going to reach P1 66seconds (about 6.3nm) ahead of the BAC 1-11. The actual point of closest approachwould be approximately when the BAC 1-11 reached P2, the separation at this pointbeing down to around 5.6nm. Consequently, the pass-behind manoeuvre that wasgenerated consisted of only a small offset, the initial track change being just over 9º witha maximum deviation distance of 1.9nm from the aircraft's previous track. The timebetween requesting prediction of the trajectory and its activation by the pilot was 5seconds, similar to the other flights. During the manoeuvre, the closest distance that wasactually achieved was just under 6.5nm.

As on the previous flight, the speed of the BAC 1-11 was adjusted, after havingcompleted the first pass behind, in order to co-ordinate the time difference between thetwo aircraft at the next intercept point P2. The navigation data source was also changedback to SBAS for the second pass-behind manoeuvre. The minimum permitted spacingwas again 6nm and, when the pass-behind trajectory was generated at 1424:35, the FMSpredicted that the ATTAS would reach P2 at 1427:31, which was 47 seconds prior to theBAC 1-11. By the time the BAC 1-11 had reached P2, it was estimated that the twoaircraft would be 3.9nm apart. Hence the resultant trajectory required a track change of8º, but this time the deviation distance from the original track was 3.9nm. It took lessthan 5 seconds from initiating the trajectory prediction to activating it and at the closestpoint of approach during the manoeuvre, the two aircraft were 6.4nm apart.


Generation of the merge manoeuvre took place at 1442:00, after the BAC 1-11 wasestablished on track to waypoint B8, the intention being to achieve a spacing of 15nmbehind the ATTAS by the time MMP had been reached. The ATTAS was currently30.4nm from the BAC 1-11 and 37.1nm from MMP. At the point when the trajectory forthe merge manoeuvre was generated, the direct distance from the BAC 1-11 to the MMPwaypoint was 66.7nm. The pilot quickly activated this trajectory (4 seconds after thegeneration had been initiated) and the new CAS demand derived from this trajectory was266kts. By the time (1453:32) that the BAC 1-11 arrived at the merge waypoint MMP, itwas still approximately 18nm behind the ATTAS. This is partly because the actualground speed of the BAC 1-11 was only 16kts greater than the predicted value for thesection when it was flying at 266kts CAS. Therefore, although the BAC 1-11 reachedMMP about 35 seconds earlier than predicted, this had not compensated sufficiently forthe error in the predicted time for the ATTAS to fly the extra 15nm, the error in this termbeing of the order of 55 seconds. The difference of 20 seconds would account for about1.5nm in the spacing distance from the ATTAS. In the calculation of the mergemanoeuvre for the BAC 1-11, the FMS estimated a time of about 1449:59 for arrival ofthe ATTAS at MMP and this proved to be very close to the actual arrival time of1449:57. Consequently, in this respect, the forward estimation of the target's movementwas very accurate. The merge manoeuvre was regarded as complete once the BAC 1-11had passed MMP.


4.6 28th March 2003


This was the final trials flight to be carried out from Rome. For this flight, an update hadbeen incorporated into the software to correct for the determination of time for the targetaircraft to fly the additional spacing distance beyond the merge waypoint (previously ithad been based on the target's derived CAS value rather than its ground speed). A newtaxi map had also been received for testing. This was to overcome the displacementbetween the aircraft's position on the map and its actual location on the airport that hadbeen seen with the previous version. No other changes had been implemented and theroute remained the same as for the other trials flights.

4.6.2 MFMS Report

With the latest meteorological forecast file loaded into the FMS, the FMS was initialisedas normal and the trajectory predicted prior to departure from the stand. The taxi mapnow gave a more representative indication of the aircraft's position on the airport,although the aircraft was shown towards the edge of the taxiway rather than followingthe centre line.

The BAC 1-11 was held by ATC prior to take-off due to landing traffic and therefore itsactual departure time was about 13 minutes after the ATTAS aircraft, rather than the 10minutes that had been planned. In order to allow the BAC 1-11 to catch up, the ATTASslowed down during the initial part of its cruise. Similarly, once the BAC1-11 had alsoreached the cruise altitude, its speed was increased to reduce the difference in the ETAsof the two aircraft at P1, the intercept point for the first pass-behind manoeuvre.Although this had been achieved to certain extent, when the trajectory was generatedusing a minimum spacing distance of 6nm, the FMS predicted that no lateral offset wasrequired. At this stage, the FMS predicted that the ATTAS aircraft would reach P1 at0919:54 (actual time of arrival was 0919:54), around 98 seconds before the BAC 1-11.By the time the BAC 1-11 was expected to have passed P1, the ATTAS would be 7.9nmaway. A spacing distance of 8nm was used instead and this time a lateral route changewas predicted with a track deviation of 14º and lateral displacement of 3nm from theoriginal route. Due to the delay in having to generate a second trajectory with thisdifferent spacing value, the BAC 1-11 was only 15nm from P1 at the time the trajectorywas activated. During the manoeuvre itself, the two aircraft were 8.5nm apart at theclosest point of approach.

A further speed adjustment was carried out to try and further reduce the time differenceat the next intercept waypoint P2. When the pass-behind trajectory was generated0927:16, the MFMS was predicting that the ATTAS aircraft would be at P2 by 0929:54(actual arrival time was 0929:53), while the ETA for the BAC 1-11 was some 62 secondslater. The estimated separation at the time when the BAC 1-11 was predicted to reach P2was 4.9nm. This meant that a trajectory could be generated for the pass-behindmanoeuvre using the normal 6nm minimum spacing distance. With an initial trackchange of 8º, the BAC 1-11 was required to deviate by a cross-track distance of 3.3nm


from its original route. The actual minimum spacing from the ATTAS aircraftencountered by the BAC 1-11 during the manoeuvre was 6nm.

Figure 4.6-1: Spacing of BAC 1-11 from ATTAS during Merge Behind, 28th Mar. 03

With this software having been modified for determining the correct time at which theBAC 1-11 should arrive at the merge waypoint to achieve the required spacing (15nmagain), a trajectory was generated once the BAC 1-11 was on track towards waypoint B8.This occurred at 0944:01, when the ATTAS was 29.1nm from the BAC 1-11 and 38.6nmfrom reaching MMP, the merge waypoint. The trajectory was activated within 4 secondsof the generation being triggered. When computing the conditions for the mergemanoeuvre, the FMS determined that the ATTAS would pass MMP at 0951:54 (actuallypassed this waypoint at 0951:51) and consequently would take a further 184 seconds tocover the additional 15nm. The prediction for the BAC 1-11 to merge behind the ATTASdetermined that the BAC 1-11 would reach MMP about 8 seconds ahead of the timewhen the spacing would be exactly 15nm. This 8 seconds would equate to just over0.6nm at the ground speed of the ATTAS aircraft. The predicted CAS for the manoeuvrewas 300kts and the BAC 1-11 actually arrived at MMP approximately 46 seconds earlierthan predicted. This was a direct result of the error in the true air speed calculation thatmanifested itself in an under-estimated ground speed value for the selected CAS.Consequently, on reaching the merge waypoint, the spacing of the BAC 1-11 behind theATTAS aircraft was 11nm (see Figure 4.6-1), which can be related to the distancecovered by the ATTAS in 46 seconds being of the order of 3.5nm. In order to haveachieved a more appropriate ground speed for the manoeuvre, a CAS of between 280 and285kts would probably have been better suited.


As encountered on the previous trials flights from Rome, interference had once againaffected the SBAS and GBAS equipment towards the top of the climb to FL210. On thisoccasion, the FMS had detected the degradation in the SBAS performance status and ithad automatically reverted to using the IRS as the position data source. After region ofinterference had been passed and the SBAS started to indicate that it had a reliable fixagain, the FMS automatically re-selected it as the position source. This transition gave noproblems to the FMS guidance function.


4.7 28th March 2003, Sortie No. 774.


Airways transit from Ciampino back to Boscombe Down. As for the other transit flights,the MFMS was to be used to provide lateral guidance and, where possible, profileguidance as well. The system was in the same state as for the trials flight in the morningapart from updating the default cruise speed to be 320kts CAS. The MA-AFAS companyroute for this flight, ROMBOS, was selected by the pilot via the MCDU and the cruisealtitude was set to be FL260. The VDL4 transponder was to be operated for monitoringpurposes while the aircraft remained in the ROME FIR


LIRA-OST-MEDAL-GILIO-ELBA-DOBIM-AKUTI-PIGOS-BARSO-OKTET-GIPNO-BULOL-ARDOL-CHABY-LAULY-BRY-CLM-KOPOR-ABUDA -GUBAR-GURLU-SAM-EGDM.

4.7.2 MFMS Report

After departure, the aircraft was initially vectored by ATC until it was cleared to godirect to waypoint MEDAL. At this point, an in-flight generation was carried out and theresultant trajectory activated, allowing the lateral and profile guidance demands from theFMS to be engaged through the autopilot. This guidance was maintained for the majorityof the remainder of the flight until the profile demands were disengaged prior to the topof descent. Lateral guidance was re-instated for periods after this, dependent on theclearances that were currently being issued by ATC for the recovery into BoscombeDown.

The lateral guidance demands from the FMS were used for nearly 1.75 hours of thereturn flight to Boscombe Down. Over the course of its use, in terms of the flighttechnical error determined by the FMS, the mean cross-track deviation that was achievedwas 84m with a standard deviation of 77m. The maximum magnitude of deviation was410m and this, as mentioned before, was principally due to the tight default turn radii(5nm) that the FMS was set to use. With the high ground speed of the aircraft whenoperating at 320kts CAS, the FMS was demanding the maximum available bank angle of25º in order to complete the various turns and this was not always sufficient to track thelateral path exactly. Similarly, the transitions into and out of the turns resulted in peaks inthe cross-track deviation value caused by the need to apply an anticipation factor to thedemand to cater for the roll response performance of the autopilot. Normally, the FMSwould have been configured with a larger default turn radius for en-route waypoints andthis would have reduced the peaks in the cross-track error. The use of the go-directfunction could also result in a localised increase in the cross-track deviation until the newtrack had been captured.

These values of cross-track error that were experienced while using the MFMS wereessentially, however, very small and demonstrated an accurate capability for tracking adefined lateral path, suitable for the reduced values of RNP that are intended for futureoperations.


4.8 Summary of Rome Results

The Rome flight trials demonstrated that ASAS delegated manoeuvres could beperformed between two live aircraft using the functionality developed for the MFMS andthe aircraft state data received via the ADS-B reports using the VDL4 communicationssystem. When the two aircraft arrived in Rome at the start of the trials week, this was thefirst time that a full check of the ADS-B report data could be carried out using anotheractual aircraft as the data source. The air-to-air broadcast provided by the VDL4 systemproved to be robust and neither the transponders nor the MFMS CommunicationsManagement Unit (CMU) needed to be reset during any of the flights. With the VDL4system operating successfully for Air to Air broadcast data throughout these airbornetrials, the ATTAS was therefore able to act as the target aircraft about which the BAC 1-11 performed the ASAS manoeuvres. This required the VDL4 transponder to beconnected to the MFMS for all these flights. This configuration restricted the type of datalogging that could be achieved on the aircraft and therefore it was not possible to directlydetermine performance figures for the data link.

MFMS performance would be dependent on the integrity of the data that it received fromthe ADS-B reports and, once a scaling factor for the ground speed data had been revised,this proved to be suitable for the requirements of the ASAS manoeuvres. With theoccasional report being filtered out that contained values of zero for ground speed ortrack angle, the frequency of valid updates being received by the MFMS on the BAC 1-11 from the ATTAS aircraft proved high enough for these trials. For each manoeuvrethat was performed, the MFMS computed a trajectory without failure and the ADS-Bdata available was typically less than 3 seconds old (the update rate of the ADS-B reportsbeing around 4 seconds). This also supported the requirements of the Cockpit Display ofTraffic Information (CDTI), allowing the execution of the manoeuvre to be monitored bythe pilot via the ND. The Ciampino ground station had been able to monitor the ADS-Breports that were received from the two aircraft as well.

The MFMS was operated successfully throughout the trials without any system failuresoccurring during the flights. It was able to predict trajectories from take-off to the finalapproach point and provided guidance to follow the Standard Instrument Departure (SID)Ostia 5A once the aircraft was airborne. With both aircraft operating at the same cruiseflight level, two pass behind and one merge manoeuvre were tested on each of the fiveflights that were undertaken. Unlike the flight trials at Boscombe Down, where thesimulated target aircraft had comparable ground speeds to the BAC 1-11, for the trials inRome, the ATTAS aircraft was cruising with a CAS 40kts below that of the BAC 1-11.This meant that there was a significant variance in the ground speeds of the two aircraftfor these manoeuvres.

The pilots were able to readily enter the relevant data into the MCDU for the pass behindmanoeuvres before generating and executing a trajectory via the MFMS, this processbeing generally comparable to setting up an FMS for more standard types of operations.The required data was provided over R/T by the trials air traffic controller. The pilots andcontrollers noted, however, that some of the phraseology that was used might need to berevised to improve the clarity and efficiency in the issuing of certain instructions. Therewas also a reasonable confidence from the pilots that the MFMS was producing sensibletrajectories for these manoeuvres due to the fact that the typical time between selecting


prediction of a trajectory and the activation of it was around 5 seconds. The estimationfor the duration of the prediction process itself is of the order of 1 to 1.5 seconds.

Apart from the 1st pass behind manoeuvre on the flight on the 28th March, which usedan 8nm minimum spacing distance, all the others employed a 6nm minimum spacing,with the MFMS adding a 0.25nm tolerance to this in its trajectory computation. In noneof these situations was the minimum specified spacing distance ever compromised at theclosest point of approach (CPA) between the two aircraft. For the seven pass behindmanoeuvres using a 6nm minimum spacing, the mean value at the CPA was 6.3nm witha standard deviation in the results of 0.2nm. On the lone occasion that an 8nm minimumspacing was used, the actual value at the CPA was 8.5nm. On average the BAC 1-11 wasabout 3.3 minutes from reaching the intercept point between the tracks of the two aircraftwhen the pass behind manoeuvre was predicted. Therefore, given the relative positionsand speeds of the two aircraft, the minimum specified spacing distance would likely havebeen compromised approximately 3 minutes ahead without any action being taken.

There is insufficient data to make too many significant conclusions on the type of lateraldeviation required to resolve the conflict. Various factors are involved, but generally, thesecond pass behind on each flight required a slightly greater deviation from the originalroute due to the ATTAS flying a track with a shallower cut angle relative to that of theBAC 1-11. However, as would be expected, the difference between their predicted timesof arrival at the track intercept point was also important in terms of the magnitude of thelateral deviation. Along with this term, the remaining time before the BAC 1-11 reachedthe intercept point would tend to determine the change in track angle that was required.For the predicted conflict conditions experienced between the two aircraft in these trials,the resultant pass behind manoeuvres required the BAC 1-11 to perform an initial trackchange of no more than 27° and in the majority of cases it was within 15°. Typically, thelateral deviation was within the normal ±5nm width of a current airway with all but oneof the pass behind manoeuvres using a spacing of 6nm. However, the ATTAS wasalways ahead of the BAC 1-11 in time and in many cases it was predicted to be of theorder of 1 minute ahead at the intercept point in the tracks of the two aircraft, hencelimiting the magnitude of the lateral deviation..

Similar to the final trial flight at Boscombe Down (on the 20th March), the mergemanoeuvre that was tested at Rome demonstrated the concept and application of thisfunction, but was lacking the complete software modifications to allow it to operate tothe required precision. The MFMS was always able to compute a trajectory to meet thetiming constraints determined by the manoeuvre generator function, but as alreadymentioned, the conversion of computed air speed to true air speed was under-estimatingthis value. Hence, the demanded CAS typically resulted in a ground speed that was toohigh for required merge manoeuvre. With the ATTAS flying at a constant CAS of 210ktsand a fixed track towards the merge waypoint, the results indicate that the MFMS on theBAC 1-11 was making a reasonably accurate estimate for the arrival time of the ATTASat this waypoint. With a fairly stable wind system over the period of the manoeuvre, theestimate could be within 2 or 3 seconds of the aircraft's actual ETA. In most cases, theATTAS was 35 to 40nm from the merge waypoint and the spacing distance wouldnormally be 15nm. For the ground speed of the ATTAS, this would equate to about 11minutes of flying time. Meanwhile the BAC 1-11 would be around 67nm from the mergewaypoint and consequently was aiming to close the distance to the ATTAS by


approximately 15nm in this time frame. The MFMS was therefore aiming for a groundspeed for the BAC 1-11 that was of the order of 80kts greater than that of the ATTASaircraft. With the ATTAS flying at 210kts CAS, then to achieve this closure rate requireda speed demand for the BAC 1-11 from the MFMS that was typically around 270ktsCAS.

During the course of these flights, the application of these pass behind and merge behindmanoeuvres were generally regarded as relatively simple procedures by the pilots andcontrollers. Having become familiar with the method of operation involved with thesemanoeuvres, the overall process placed no undue pressure on the participants and it wastypically considered in a similar context to any standard ATC instruction. The executionof the manoeuvre was also fairly benign from the user’s perspective.

During the course of the trials, it was found that there were regions of interference inwhich GPS equipment onboard the aircraft were being affected. This was important tothe MFMS because it was configured to use the SBAS as its primary source of positionand ground velocity data. This interference was located between waypoints LUNAK andVALMA and in the vicinity of waypoint B3, this latter situation influencing the aircraftbetween not only B3 and B4, but also as it approached MMP. The impact of thisinterference was to reduce the Signal-to-Noise Ratio (SNR) for the GPS satellites and tocause tracking of the geostationary (GEO) satellite to be lost briefly. Once thisinterference had been encountered on one flight, the tendency was to manually select theIRS as the primary position source for the MFMS on later flights whenever the SNRfigures started to fall. It was noted, however, that the MFMS was capable of switchingautomatically to the IRS if there was a loss of valid data from the SBAS. Additionally,the results show a drop in the SNR values of about 8dBHz soon after 0900 UTC on eachday, although the exact reason for this is unknown.


5 Overall Summary of MA-AFAS Flight Trials

The ASAS delegated manoeuvres were based on single-shot predictions using current state dataobtained for the target aircraft via either real ADS-B reports from the VDL4 data link or fromsimulated ADS-B reports generated within the MFMS itself. For the conditions under which theseflight trials took place, this aircraft state data proved sufficient for the MFMS to predict the futureflight path of the target over the time period required for the manoeuvre. This was probably moretrue for the pass behind manoeuvre, which was typically looking at the resolution of a possibleconflict 3 or 4 minutes ahead, compared with the longer term (around 10 minutes) needed tocomplete the merge manoeuvre.

The flight trials with the two live aircraft revealed that knowledge of the current state data of theother aircraft was sufficient to produce a short-term prediction for that aircraft that could beaccurate to within about 3 seconds. Clearly, the wind conditions during the Rome trials were fairlystable which assisted this process. If conditions were more variable, then the single-shot approach tothe prediction would need to be backed up by a monitoring process and modification of thetrajectory values if it is determined that the specified spacing will be compromised. This processhad been designed into the MFMS, but it had not reached a sufficient level of development that itcould be used during the flight trials themselves.

The flight trials at Boscombe Down helped to develop the MFMS and prove the functionality of thesystem in flight. These trials were all performed with simulated target aircraft and, as such, alloweda systematic approach to expand the capability of the MFMS on the aircraft itself. With variousupdates to the system being received during the period of the trials at Boscombe Down, there wasnever really a fully stable configuration that could be assessed over a series of flights. The flightsdid demonstrate, however, that the implementation of the lateral pass behind could achieve therequired spacing within the normal guidance limitations used by the FMS. A similar situationexisted with the development of the merge manoeuvre, although this encountered a few moreproblems related to the derivation of the required speed demand to achieve the defined spacing.

With the Rome flight trials occurring directly at the end of the period of testing at Boscombe Down,the MFMS was essentially in the same configuration used for the final Boscombe flight. There weretherefore known limitations in the performance, notably with regard to the merge manoeuvreneeding further refinement. Since, when the aircraft arrived at Rome, this was the first time that theair-to-air broadcast of the VDL4 data link could be tested for real, it was satisfying to find that thiswas working reliably. With the MFMS status remaining essentially unchanged during the Rometrials, it could be demonstrated that the prediction and execution of these delegated ASASmanoeuvres was repeatable for the same situation on each flight.

The HMI that had been developed to support these ASAS manoeuvres worked as principallyintended and did not prove burdensome to operate for the pilot. For these flight trials, the pilot hadto enter the conditional data for the manoeuvres via the MCDU, this data being specified by thecontroller over R/T. The use of data link to automatically supply this data to the MFMS could notbe tested and although this might reduce the work required of the pilot, it may also raise new issuesconcerning the display of information for the pilot's situation awareness. There were areas wherethe HMI could be improved. For the pass behind manoeuvre, since this was solely a lateral change,then the graphical display on the ND was generally sufficient to view the revised trajectory and


monitor progress. It may have been useful to also have a readout of the predicted minimum spacingbetween the two aircraft, which could be continually updated. This would help, along with the ringdrawn around the target aircraft, to confirm that the system was achieving the required spacing. Themerge manoeuvre involved not only a lateral modification, but a speed change as well. The pilotswere interested in having the updated air speed being more predominantly displayed when thetrajectory had been predicted so that it was not necessary to access other MCDU pages to locate it.This would provide confidence that the FMS was not going to demand an excess speed to meet thespacing requirements (the MFMS did contain speed limits for each flight phase and so it would notbe expected to exceed these). Another area that was commented upon concerned the feedback fromthe system if it could not meet the specified requirements in order to be able to clearly identifywhere any limitation might exist. This actually requires quite a bit of development to perfect andwas not a key issue within the project at this stage.

When flown on the BAC 1-11, the MFMS was typically used with the SBAS equipment as theprimary position source, although for the flights at Boscombe Down, the GBAS was used in theSID and the STAR. The SBAS itself was capable of providing a lateral fix to a mean accuracy of1.3m with a standard deviation of 0.7m, while the vertical fix had a mean of -0.9m and a standarddeviation of 2.5m. These accuracy figures were determined relative to a GPS truth track system thatcan be considered to have an accuracy of 0.5m. The typical flight technical error for the lateralguidance that was achieved by the MFMS during the flights on the BAC 1-11 was of the order 90 to100m with a standard deviation that was just over 100m. These levels of performance wouldsupport the type of accuracy required in the execution of the ASAS manoeuvres and anyimplementation of RNP 1 for en-route navigation.


6 Conclusions and Recommendations

The MA-AFAS flight trials with the QinetiQ BAC 1-11 were able to demonstrate feasibility ofincorporating into a modern FMS the functionality for performing delegated ASAS manoeuvres.This was achieved not only with simulations of other aircraft within the same airspace as the BAC1-11, but also with another live aircraft (DLR's ATTAS) during the trials in Rome. The ASASmanoeuvres that were flown consisted of a lateral pass behind and a merge behind with distanceand, during the Rome trials, it was shown that these had a consistent performance and could beapplied successfully.

The approach taken to the development and testing of the MFMS functionality leading to the Rometrials was also proved to be a successful method in terms of the efficient use of the flights. By usingaccurate ground-based simulation to determine the expected overall system performance prior toeach flight meant that no flights were actually aborted due significant system problems beingencountered while airborne. It also allowed confidence in the behaviour of the system to be built upin the limited time that became available for completing these flights. This level of confidence thatwas achieved in the expected performance of the MFMS was also vital in ensuring that all of theparticipants in the Rome trials were satisfied with operating these two live aircraft at the samealtitude and on conflicting tracks. This was especially so, since the first trials flight in Rome wasalso the first time that the complete MA-AFAS system environment had been operated as acomplete entity.

An additional key component to the success of these flight trials was the implementation of ADS-Bvia VDL4. This proved capable of satisfying the air-to-air broadcast requirements for computingthese ASAS manoeuvres by providing regular position and velocity reports for the two aircraft.There were still issues to be resolved concerning the data communication between the VDL4transponder and the MFMS. However, the proportion of valid position reports received by theMFMS was sufficiently high to not cause any disruption to the manoeuvre generation process andto allow the pilot to monitor progress via the CDTI option on the ND.

Although the use of the current aircraft state data proved adequate for these manoeuvres, it wouldtend to limit the application to those situations where the motion of the target was relativelyconstant (track, ground speed and height rate) for the duration of the manoeuvre. This was probablymore reasonable for the pass behind manoeuvres in which the look-ahead time was of the order of 3to 4 minutes, but for the merge behind, the duration of manoeuvre could be around 10 minutes.Regular monitoring by the FMS of the relative progress of the two aircraft would therefore improvethe performance. Similarly, the inclusion of additional intent data in the ADS-B report wouldincrease the accuracy of the longer-term prediction by having greater knowledge of the targetaircraft's planned profile. Both of these capabilities had been incorporated within MA-AFAS, butneither was actually operational during these particular trials, although developments continued toincrease the availability of this functionality for DLR's later flight trials (see [4]).

The operation of the systems provided to the pilot and the controller, to support the execution ofthese ASAS manoeuvres, did not prove to be a significant distraction from their normal tasks. Thetrials indicated that the pilots and controllers found the application of the pass behind and mergebehind functions to be relatively simple to perform, similar in respect to normal ATC procedures.Aspects of the HMI still need to be improved, though, before complete user acceptability is


achieved. The implication, however, is that the integration of such procedures into the operationalenvironment should not require a major transition. There is further work to be done to resolve theresponsibility and course of action for the various failure states when executing these types ofASAS manoeuvres, but this would be typical of any new procedure.

The following recommendations are made to further the work and validation of the MA-AFASsystem:• Further development of the ASAS manoeuvres in terms of types and efficiency – the project

proposed ASAS Lateral, Vertical and Longitudinal manoeuvres. In each of these categories, avariety of executions were designed. In the event, due to development time, only Pass Behindand Merge could be flight tested in this phase. The further manoeuvres should also be tested andverified to provide a complete capability (part of this was achieved in the flight trials at DLR,see [4]).

• The MFMS used an instantaneous interrogation of the target state vector to determine the extentof the ASAS manoeuvre – this was found to work for the conditions experienced during thetrials and proved effective against an aircraft not fully equipped. However, to provide a moreeffective, reliable and flexible approach to obtaining the target information, aircraft intent datashould be included in the data link messages.

• Further flight testing of the VDL4 sub-system to verify air/ground operations – the VDL4system was delivered to the flight test phase in a state where the Air/Ground Point to Point linkwas unproven. Considerable effort was expended during ground testing to prove the capabilitybut this was not capable of being used during these trials. Further work is required before thiselement of the communications chain can be implemented in an efficient manner.

• Further improvements to the HMI – although the HMI was considered, by the pilots, as beingadequate for the job a number of improvement areas were highlighted. For instance in the areaof required speed to perform the Merge manoeuvre. At present, there is no immediate indicationto the pilot of the revised speed profile for the Merge manoeuvre and of the predicted spacing atthe completion of the Merge.

• The phraseology used for the ASAS instructions needs to be revised to make them as clear andconcise as possible and avoiding unnecessary repetition.


7 References

1. The More Autonomous – Aircraft in the Future Air Traffic Management SystemSimulation and Flight Test Plan – D32 of 29 Nov 2000. Report NumberQinetiQ/FST/TR025809-D32.

2. Aeronautical Co-ordination Notice Activity No. 2003-01-0011 of 23 December2002. Aeronautical Utilisation Services, CAA, Kingsway, London, UK.

3. The More Autonomous – Aircraft in the Future Air Traffic Management SystemAir/Ground Validation Report – D37 of 30 June 2003. Report NumberQINETIQ/FST/CR032536-D37.

4. MA-AFAS D39 Annex A - Taxi trials and Flight Test Report from Braunschweig.DLR, Germany, June 2003

5. MA-AFAS D39 Annex B - Stanford Plot Evaluation of Ground and Space BasedAugmentation Systems Flight Trial Data. NATS, UK, June 2003

6. D40: Results of Pilot-in-the-Loop Simulator Trials for ASAS Spacing. NLR, TheNetherlands, June 2003


8 List of abbreviations

A/A Air to AirADS-B Automatic Dependant Surveillance – BroadcastADS-C Automatic Dependant Surveillance – ContractA/G Air to GroundAGP AOC Ground PlatformAOC Airline Operations ControlA/P AutoPilotASAS Airborne Separation Assurance SystemATTAS Advanced Technologies Testing Aircraft SystemATC Air Traffic ControlATM Air Traffic ManagementATN Aeronautical Tele-communications NetworkAvP Avionics PackageCAS Computed Air SpeedCCD Cursor Control DeviceCDTI Cockpit Display of Traffic InformationCM Context ManagementCMU Communications Management UnitCNS Communication Navigation SurveillanceCPDLC Controller Pilot Data Link CommunicationDADC Digital Air Data ComputerEFIS Electronic Flight Instrumentation SystemEIU Engine Instrumentation UnitFIR Flight Information RegionFIS-B Flight Information System – BroadcastFMS Flight Management SystemGBAS Ground-Based Augmentation SystemHMI Human-Machine InterfaceICCS Integrated Civil Cockpit SimulatorIHTP In-House Test PlatformILS Instrument Landing SystemIP Internet ProtocolIRS Inertial Reference SystemISDN Integrated Services Digital NetworkLCD Liquid Crystal DisplayMA-AFAS More Autonomous Aircraft in the Future Air traffic management SystemMCDU Multi-function Control and Display UnitMETAR Meteorological Aerodrome ReportMFMS MA-AFAS Flight Management SystemMTA Managed Terminal AreaND Navigation DisplayOOOI Out, Off, On, InPAD Precision Approach and DepartureRFS Research Flight SimulatorR/T Radio Telephony


RTAVS Real Time All Vehicle SimulatorSBAS Space-Based Augmentation SystemSID Standard Instrument DepartureSIGMET Significant Meteorological ReportSMGCS Surface Movement Guidance Control SystemSTAR Standard ArrivalTAF Terminal Area ForecastTCAS Traffic alert and Collision Avoidance SystemTIS-B Traffic Information System – BroadcastUP User PlatformUTC Universal Time Co-ordinatedVDLM4 VHF Data Link Mode 4WP Work Package


A Appendix

A.1 Original QNQ1 UK Trials Route

Waypoint list:Position orWaypoint

Lat/Long(WGS84)

S/S N5058.0 w001 47.0

A N5053.0 W02 55.0

B N51 05.0 W003 00.0

C N51 23.0 W003 00.0

D N51 23.0 W002 28.0

E N51 13.0 W002 12.0

F N50 45.0 W 003 10.0

G N50 47.0 W 003 47.0

H N50 26.0 W005 02.0

I N50 45.0 W005 38.0

J N51 23.0 W005 08.0

K N51 25.0 W003 32.0

C N51 23.0 W003 00.0

A N50 53.0 W002 55.0

S/S N5058.0 W001 47.0


J

I

H

K

F

D

A

B

C

G

E

S/S

ANNEX A TOACN 03-01-0011DATED 23 DEC 02

BOSCOMBE MA-AFAS TRIAL - ROUTE

Trial Route

Bi-directional Portion

Manoeuvring Area

Route Order:

BD - S/S - A - B - C - D- E - * - F - G - * - H - I -* - J - * - K - C - A - S/S- BD

*‘AvoidanceManoeuvring

BD


A.2 UK route QNQ1 (revised)

Waypoint list:Position orWaypoint

Lat/Long(WGS84)

Position orWaypoint

Lat/Long(WGS84)

EGDM N51 09.13 W001 44.84 PPP N51 13.0 W003 38.0

ESPIN N51 07.3 W00148.2 QQQ N50 24.5 W004 22.0

WOLF N51 04.4 W001 47.1 RRR N50 25.0 W004 39.5

INGL N51 03.2 W001 42.3 HHH N50 26.00 W005 01.80

KATE N50 58.6 W001 43.1 SSS N50 42.5 W005 11.0

XXX N50 53.63 W002 50.39 TTT N51 20.0 W004 16.0

BBB N51 04.90 W003 00.00 ZZZ N51 24.39 W003 48.26

YYY N51 23.25 W002 55.21 KKK N51 24.80 W003 32.80

DDD N51 23.00 W002 28.30 CCC N51 23.30 W003 00.00

EEE N51 12.50 W002 11.90 AAA N50 53.30 W002 55.10

FFF N50 44.60 W003 10.00 AGIBS N50 55.00 W002 20.00

GGG N50 46.60 W003 46.80 DM005 N50 59.87 W001 42.75

HHH N50 26.00 W005 01.80 DM001 N51 06.17 W001 30.74

MMM N50 50.0 W005 13.0 DM002 N51 13.10 W001 29.09

JJJ N51 23.10 W005 07.80 BD10E N51 16.21 W001 32.30

ZZZ N51 24.39 W003 48.26 EGDM N5109.13 W001 44.84


J

I

H

K

F

D

A

B

C

G

E

KATE

MA-AFAS ROUTE REVISED 26/02/03

Trial Route

MERGE Route

SID STAR

Old route not in use

Manoeuvring Area

Route Order:

EGDM-SID-KATE-X-B-Y-D-E*F- G*H-M*J*Z-P*Q*R-H-S*T*Z-K-C-A-AGIBS-DM005-STAR-EGDM

* ASASManoeuvring

EGDM

M

Z

P

QR

T

S

X

Y

AGIBS

DM002


A.3 Rome Route QNQ6

AREA 1 boundariesPosition or Waypoint Lat/Long (WGS84) Remarks

A1A N41 25.48 E011 21.50 OST 239/45, TAQ 198/50A1B N41 06.54 E010 16.56 OST 24/97, TAQ 224/93A1B1 N40 44.21 E011 27.12 PNZ 260/69, OST 208/73A1C N39 46.28 E012 00.26 PNZ 221/81, SOR 245/117A1D N40 05.32 E013 04.46 CAR 242/65, PNZ 172/49

MA-AFAS QNQ6 Route WaypointsPosition or Waypoint Lat/Long (WGS84) Remarks

OST N41 48.2 E012 14.3LUNAK N41 42.2 E011 52.3VALMA N41 34.6 E011 25.3

B2 N41 20.0 E011 26.0P1 N41 00.5 E011 29.0B3 N40 40.0 E011 31.0B4 N40 31.0 E011 36.0P2 N40 28.0 E012 10.5B5 N40 26.0 E012 37.0B6 N40 02.5 E012 43.0B7 N39 51.0 E012 02.5B8 N40 42.0 E011 21.5 Will be bypassed during execution

of merge behind manoeuvre.MMP N40 57.0 E011 24.5

A6 N41 17.5 E011 28.5ESINO N41 23.1 E011 47.7TORLI N41 35.8 E012 01.1

OST N41 48.2 E012 14.3


BAC 1-11 routeATTAS routeMerge manoeuvre legs never flownBoth aircraft after mergeCleared area boundary


Report documentation page

1. Originator's report number:

2. Originator's Name and Location: I Mansfeld 414/1 MoD Boscombe Down

3. MOD Contract number and period covered: GRD1-2000-022840 months

4. MOD Sponsor's Name and Location:

5. Report Classification and Caveats in use: 6. Date written: Pagination: References:

jUNE 2003 ix + 90

7a. Report Title: FLIGHT TEST VALIDATION REPORT - D39

7b. Translation / Conference details (if translation give foreign title / if part of conference then give conferenceparticulars):

7c. Title classification:

8. Authors: IMANSFELD

9. Descriptors / Key words: TRIALS, AIR TRAFFIC MANAGEMENT,FUTURE,

10a. Abstract. (An abstract should aim to give an informative and concise summary of the report in up to 300 words).

10b. Abstract classification: FORM MEETS DRIC 1000 ISSUE 5


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