GAINS D2.4 Electronic Conspicuity ConOps · The scope of GAINS Surveillance Concept is the use of...

GAINS D2.4 Electronic Conspicuity ConOps

Deliverable ID: D2.4

Dissemination Level: PU

Project Acronym: GAINS

Grant: 783228 Call: H2020-SESAR-2016-2

Topic: SESAR-VLD1-09-2016 Solutions for General Aviation and Rotorcraft

Consortium Coordinator: HELIOS Edition Date: 25 November 2019 Edition: 00.00.00 Template Edition: 02.00.01

VERY LARGE-SCALE DEMONSTRATION

GAINS D2.4 ELECTRONIC CONSPICUITY CONOPS

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Authoring & Approval

Authors of the document

Name/Beneficiary Position/Title Date

Julian Scarfe/AOPA Work Package 5 Leader 17/09/2019

Reviewers internal to the project


Philip Church/HELIOS SGA Coordinator 25/09/2019

Bob Darby/AOPA Work Package 4 Leader 24/09/2019

Andreia Simoes/HELIOS Project Manager 17/09/2019

Approved for submission to the SJU By - Representatives of beneficiaries involved in the project


Philip Church/HELIOS SGA Coordinator 25/11/2019

Martin Robinson/AOPA FS and LS 13/11/2019

Santiago Soley/PILDO FS and LS 13/11/2019

Marc Gerlach/FAV EC 13/11/2019

Andy Davis/TRIG FS and LS 13/11/2019

Rejected By - Representatives of beneficiaries involved in the project


Document History

Edition Date Status Author Justification

00.00.00 25/11/2019 Issued Julian Scarfe Initial issue

Copyright Statement

This document and its content is an internal deliverable of the GAINS project and may not, except with the GAINS consortia express written permission, be distributed or have its content commercially exploited. This project has received funding from the SESAR Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 783228. The opinions expressed herein reflect the author’s view only. Under no circumstances shall the SESAR Joint Undertaking be responsible for any use that may be made of the information contained herein.


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GAINS GENERAL AVIATION IMPROVED NAVIGATION AND SURVEILLANCE

This Electronic Conspicuity Concept Description is part of GAINS a VLD project that has received funding from the SESAR Joint Undertaking under the grant agreement No 783228 under European Union’s Horizon 2020 research and innovation programme. This two-year project initiated in January 2018 is overseen by a consortium from the general aviation (GA) community: AOPA UK, Pildo Labs, Funke Avionics and Trig Avionics. Aviation consultancy Helios is the project coordinator.

Abstract

This document is the Surveillance Concept Description that proposes a concept for the use of reduced integrity ADS-B ground surveillance equipment at General Aviation (GA) aerodromes within the General Aviation Improved Navigation and Surveillance (GAINS) project.


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Table of Contents

Abstract ................................................................................................................................... 3

1 Executive summary .................................................................................................... 6

2 Introduction ............................................................................................................... 7

2.1 Purpose of the document............................................................................................... 7

2.2 Scope ............................................................................................................................ 7

2.3 Intended readership ...................................................................................................... 7

2.4 Background ................................................................................................................... 7

2.5 Structure of the document ............................................................................................. 8

2.6 List of Acronyms ............................................................................................................ 8

3 Context: characteristics of GA operations at smaller aerodromes.............................. 10

4 GAINS Surveillance Concept ..................................................................................... 11

4.1 EC Equipment .............................................................................................................. 11

4.2 Airborne Mode of Use ................................................................................................. 11

4.3 Map display and information displayed ........................................................................ 12

4.4 Audio vs Visual display................................................................................................. 13

4.5 Performance requirements for traffic information ........................................................ 13

4.6 Ground Mode of Use ................................................................................................... 13

5 Benefits of the GAINS Surveillance Concept .............................................................. 16

5.1 Safety .......................................................................................................................... 16

5.2 Other benefits ............................................................................................................. 16

6 Challenges and Risks of the GAINS Surveillance Concept ........................................... 17

6.1 EC equipage proportion ............................................................................................... 17

6.2 Interoperability ........................................................................................................... 17

6.3 Performance and data quality ...................................................................................... 18 6.3.1 Accuracy .......................................................................................................................................... 18 6.3.2 Integrity ........................................................................................................................................... 19 6.3.3 Continuity ........................................................................................................................................ 20

6.4 Distraction .................................................................................................................. 21

6.5 Clutter and transmissions on the ground ...................................................................... 21

7 Comparison with SESAR Solutions ............................................................................ 22

7.1 SESAR Solution(s) addressed by VLD ............................................................................. 22 7.1.1 Deviations with respect to the SESAR Solution(s) definition .......................................................... 22

8 References ............................................................................................................... 24


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List of Tables Table 1: List of acronyms ......................................................................................................................... 9


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1 Executive summary

The objectives of GAINS are to validate, through live flying demonstrations, concepts enabled by Global Navigation Satellite System (GNSS) and EGNOS. These include a Surveillance Concept proposing an electronic conspicuity solution and a Navigation Concept proposing instrument flight procedure elements to meet the needs of GA, including both fixed wing and rotorcraft. GAINS’s Surveillance and Navigation Demonstrations aim to show the wider aviation community how improvements being developed by SESAR can be adapted to the respective Concepts enhancing GA operations without prohibitive cost or certification requirements.

The GAINS Surveillance Concept proposes the use of cost-effective Electronic Conspicuity (EC) equipment with modest performance requirements to provide traffic information, both within the cockpit and for use by ground staff at aerodromes, for operations at and near the aerodrome. It envisages (and the GAINS Surveillance Demonstrations documented in D4.4 tests) the utility of such equipment in a 100% equipage environment. The Concept suggests that the equipment may be used for Enhanced Visual Acquisition and Situational Awareness, both in the air and on the ground. This document discusses some beneficial features, such as combination of the traffic information with a moving-map display. It analyses the performance requirements of the equipment in the context of the use cases proposed and concludes that a limited accuracy requirement and no integrity nor continuity requirements are required to achieve a net safety benefit.


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2 Introduction

2.1 Purpose of the document

This document is the GAINS Surveillance Concept description for the GAINS project. It describes the Electronic Conspicuity (EC) concept that GAINS has demonstrated and tested.

2.2 Scope

The GAINS project [1] includes a Surveillance workstream and a Navigation workstream (based on a Navigation Concept described in GAINS deliverables D2.1 and D2.3 and not discussed further in this document).

The initial GAINS Surveillance Concept was sketched out in D2.2 and was the starting point for a set of exercises, the GAINS Surveillance Demonstrations. This document refines the initial concept based on the learnings from the GAINS Surveillance Demonstrations (the full results of which are documented in the Demonstration Report D4.4). The GAINS Surveillance Concept may therefore be viewed as a collection of the recommendations of the GAINS Surveillance Demonstrations into a coherent operational concept.

The scope of GAINS Surveillance Concept is the use of EC in operations at and close to aerodromes mostly used by GA traffic. Both cockpit use and ground-based use of EC are considered, and are complementary.

2.3 Intended readership

This document is intended to explain the GAINS electronic conspicuity concept to stakeholders, including pilots participating in the demonstrations, airports and ANSPs, regulators and other SESAR projects.

2.4 Background

The objectives of the GAINS project are to utilise the SESAR solutions to the extent possible, taking account of differences in the navigation and surveillance equipage for GA vs commercial air transport, and demonstrate clearly, through live flying exercises, the ability of the general aviation and rotorcraft community GA to also benefit – potentially with adaptation – and to help deliver the overall SESAR performance objectives as defined in the European ATM Masterplan. The project therefore aims to:

• demonstrate to the wider GA community the benefits of these technologies;

• collect evidence on performance of these technologies within the typical operational environments of GA;

• support regulatory adaptations with the certification authorities to enable wider deployment; and

• demonstrate the deployment of SESAR solutions, with adaptations as necessary, to enable integration of all airspace users.


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The GAINS project includes a Surveillance workstream and a Navigation workstream (based on a Navigation Concept described in a separate document, D2.3). The GAINS Surveillance Concept is based on the use of EC in operations at and close to aerodromes mostly used by GA traffic. The GAINS Surveillance Demonstration (documented in D4.4) proves the GAINS Surveillance Concept.

2.5 Structure of the document

This document is structured in eight sections.

Section 1 is the executive summary.

Section 2 is this introductory section where the relevant information about the document purpose, scope, intended readership, background, structure, glossary of terms and list of acronyms can be found.

Section 3 is a description of current operations at small aerodromes, providing a context for the GAINS Surveillance Concept.

Section 4 describes the GAINS Surveillance Concept.

Section 5 discusses the benefits of the GAINS Surveillance Concept.

Section 6 discusses the risks and challenges associated with the GAINS Surveillance Concept.

Section 7 makes a comparison with SESAR solutions for surveillance.

Section 8 lists the reference documents used to develop this document.

2.6 List of Acronyms

Acronym Definition

1090ES 1090 MHz extended squitter

A4A Airspace for All

ADS-B Automatic Dependent Surveillance - Broadcast

AGCS Air Ground Communications Service

ANSP Air Navigation Service Provider

ATC Air Traffic Control

ATS Air Traffic Services

CAA Civil Aviation Authority

CAS Controlled Air Space

CAT Commercial Air Transport

CONOPS Concept of Operations


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Acronym Definition

CS-ACNS Certification Specifications for Airborne Communications, Navigation and Surveillance

EC Electronic Conspicuity

EGNOS European Global Navigation Overlay System

EVAcq Enhanced Visual Acquisition

FIS Flight Information Service

FISO Flight Information Service Officer

GA General Aviation

GAINS General Aviation Improved Navigation and Surveillance

GNSS Global Navigation Satellite System

GPS Global Positioning System

IFR Instrument Flight Rules

MAC Mid Air Collision

NATS National Air Traffic Services

RA Resolution Advisory (TCAS function)

RT Radio Telephony

SA Situational Awareness

SSR Secondary Surveillance Radar

TCAS Traffic Collision Avoidance System

TSO Technical Standard Order

UTM Unmanned Traffic Management

VFR Visual Flight Rules

Table 1: List of acronyms


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3 Context: characteristics of GA operations at smaller aerodromes

The majority of GA and Rotorcraft flights in Europe are conducted in accordance with Visual Flight Rules (VFR) in uncontrolled airspace. This means that other aircraft are avoided visually (“see-and-avoid”).

Where traffic density is high, particularly at aerodromes, the risk of mid-air collision is higher [4] than in en-route airspace, which is typically low traffic density. To mitigate this risk, aerodromes may be provided with different levels of Air Traffic Service:

Air Traffic Control Service, under which a controller provides mandatory clearances and instructions to avoid conflicts between aircraft. Note that in some classes of airspace and for some traffic type combinations (e.g. IFR vs VFR in class C), this may achieve separation between the aircraft. In most circumstances however (class D or G airspace), separation is not formally provided, and ATC instructions provide order (for example, sequencing instructions like “you are no. 2, follow the Cessna late downwind”) and build a plan that reduces the risk of conflict. It is then for the pilot of each aircraft to achieve separation that reduces risk to an acceptable level using visual means, complemented by the instructions and information from ATC.

Aerodrome Flight Information Service, under which a Flight Information Service Operator (FISO) provides information to aerodrome traffic. Typically, the FISO will use visual techniques from a “control” room as well as pilot reports to assess aircraft positions and pass relevant traffic information to pilots. Surveillance equipment is rarely used, both because of the cost of the surveillance equipment, which is disproportionate at smaller aerodromes, and also the training required to use the surveillance equipment, which is typically used for ATC functions and therefore much more extensive than what it might be used for in a FIS environment. It is for the pilot of each aircraft in the aerodrome environment to achieve the separation that reduces risk to an acceptable level using visual means, complemented by the information from FIS.

Air-to-Ground Communication Service, under which no traffic information is provided by a ground station. Pilots are able to build a picture of other traffic through reports made on the radio.

The workload demand placed on pilots to see-and-avoid traffic, even at controlled aerodromes, is substantial, and is exacerbated by the imperfect nature of see-and avoid. Some reports [5,6] suggest that unaided see-and-avoid is effective in only about 50% of cases of random, conflicting trajectories. The orderly nature of aerodrome traffic improves the probability of successful visual acquisition by reducing closing speeds and providing an expectation of where other traffic is likely to be. However, it remains far from perfect, and collisions continue to occur even in an ATC environment, such as the fatal collision between Cessna 402C, G-EYES and Rand KR-2, G-BOLZ, near Coventry Airport on 17 August 2008 [7].

An incomplete traffic picture for ATC and FIS also contributes to the issue.


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4 GAINS Surveillance Concept

The GAINS Surveillance Concept aims to address the issues identified in the previous section. It envisages operations at GA aerodromes with 100% equipage of aircraft with interoperable electronic conspicuity devices (including in-cockpit information displays, the “IN” function), and compatible ground equipment.

Note that the GAINS Surveillance Concept is not a proposal for a mandate for equipage with EC, which would be a decision for the regulator based on cost-benefit. But by using cost-effective equipment that delivers clear benefits to users (for example by improving confidence of detecting other traffic), the GAINS Surveillance Concept should be attractive to all stakeholders.

Elements of the Concept are described in the remaining sub-sections.

4.1 EC Equipment

The GAINS Surveillance Concept envisages equipage of all aircraft operating in the aerodrome environment with:

EC OUT: broadcast of position, level and possibly other parameters from the aircraft

EC IN: reception and display/annunciation of information received from other aircraft

The GAINS Surveillance Concept does not demand particular air or ground technology, provided there is a mechanism for full and reliable interoperability. Interoperability is considered in more detail in D4.4 and 4.5 in the context of the demonstration flight participants. However, all the participants were equipped with ADS-B IN and OUT on 1090MHz. This is to a significant extent the result of a UK initiative to develop a standard (known as CAP1391) for low-cost, low-power portable ADS-B equipment transmitting on 1090MHz. We will simply note here that this enables the detection of other aircraft equipped with SSR transponders or transceivers capable of ADS-B OUT, though this is also possible with other receivers without 1090ES OUT capability. Interoperability is discussed in more detail in section 6.2.

The GAINS Surveillance Concept also envisages access of ground-based personnel (ATC, FIS or AGCS staff) to an EC IN system capable of displaying the information received from nearby aircraft. It is envisaged that the EC IN system, like the airborne EC equipment, is low-cost equipment that might not meet the performance requirements of traditional surveillance systems.

4.2 Airborne Mode of Use

Electronic conspicuity equipment in general may be used for a variety of related though distinct purposes.

Collision Avoidance is the best-known mode of EC already in operation, in the form of TCAS. Limited (because of its expense) to CAT aircraft, TCAS is used as a safety net, warning crews of imminent collision risk with other aircraft. Modern TCAS provides not only a warning but also a Resolution Advisory where available, advice on the vertical trajectory required to avoid a collision. Even without the coordination required to provide effective RAs, a collision avoidance function might be proposed


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for EC used in GA aircraft. It is important to note that the GAINS Surveillance Concept does not include such a collision avoidance function.

Conflict Alerting is the advanced warning provided by an EC IN system that aircraft on their current trajectories will come close to each other. This allows the pilots of one or both aircraft to make small modifications to the trajectory to avoid the conflict. The threshold of minimum separation for such a function would depend on the aircraft and operations involved and would not necessarily equate to standard separation distances. Conflict Alerting is typically by an alerting or annunciation function, to bring the potential conflict to the attention of the pilot. It is also important to note that the GAINS Surveillance Concept does not include such a Conflict Alerting function, even though some of the equipment used may be capable of doing so.

Situational Awareness (SA) is the use of EC IN information to build of a picture of the traffic in the vicinity of an aircraft to inform the choices made by the pilot of that aircraft.

Examples of the way in which situational awareness might be used by the pilot to mitigate risk include:

• planning entry into the traffic pattern of an aerodrome so as to avoid conflict with other aircraft already in the pattern or also joining;

• adjustment of heading or level to reduce the likelihood of conflict with, or increase separation from, another aircraft;

• sequencing arrival at a particular point (e.g. the aerodrome overhead or other standard joining location) to allow preceding aircraft to have cleared the position.

Enhanced Visual Acquisition (EVAcq) is the use of EC IN information to enhance the visual scan and includes:

• detecting other aircraft likely to come into proximity, to prioritise direction of visual scan and allow a timely see-and-avoid manoeuvre;

• locating other aircraft known to be in the aerodrome traffic pattern ahead so that they can be acquired visually and, if required, followed at a safe distance.

The GAINS Surveillance Concept proposes the use of EC for SA and EVAcq by airborne users. Note that this does not make a judgment on other uses of the same equipment for other purposes, in particular conflict detection, though the demonstration flights highlighted some relevant issues with Conflict Alerting in the busy aerodrome environment.

Note that, unlike EVAcq, use of EC information for SA may allow the pilot to change heading or level to reduce the risk of a conflict with as yet unsighted traffic. EVAcq is a short range tactical use because it depends on visual acquisition, whereas SA may be a longer range strategic use.

4.3 Map display and information displayed

An element of the GAINS Surveillance Concept is that the information on relative position and level of other traffic may be supplemented by other information, for example:

• geographical information i.e. the traffic may be displayed on a map with ground and airspace features, not simply on a relative bearing display (which might be more appropriate for collision avoidance or conflict detection); and


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• callsign information, to allow the pilot using EC for SA to reconcile aircraft depicted on the map with their radio transmissions.

Both aspects are intended to improve SA.

4.4 Audio vs Visual display

While there is no alerting aspect of the GAINS surveillance concept, traffic information may be provided on a visual display or aurally, for example by traffic being announced with relative bearing and range.

Aural traffic information has the advantage that it does not require the pilot to look at a screen in the cockpit. However, it has the disadvantage that it is more difficult to build a mental model of traffic using aural information, and updates are necessarily less frequent. It is expected that insights on the advantages and disadvantages will emerge from the demonstrations.

4.5 Performance requirements for traffic information

The equipment envisaged for use in the GAINS Surveillance Concept does not meet the same standards as some other equipment used for ATM purposes (for example, SSR transponders). It is therefore useful to look at the effect of some aspects of performance:

Accuracy: GNSS-derived information is likely to be of high accuracy, either that expected of unaided GNSS, or of GNSS with EGNOS, depending on the system. Mean position error of such systems is typically a fraction of a second of aircraft travel, even at typical GA speeds. In the demonstration flights, it was generally found that the accuracy was sufficient for the purpose of SA.

Integrity: It is unlikely that high integrity will be a feature of the positioning system of the EC system. Thus, it is more likely that significant errors in position will occasionally occur than with, for example, an ADS-B system satisfying CS-ACNS requirements. This may have an effect on the usefulness of the information.

Continuity: The EC systems envisaged in the concept may be portable, and do not have permanently installed antennae. Thus, interruptions in the transmissions are more likely than for, e.g. an installed ADS-B system satisfying CS-ACNS requirements.

The concept, explored in the demonstration flights, is that the overall performance of these uncertified, portable systems is sufficient to provide a net safety benefit. A more detailed analysis of the performance challenges and relationship to the required data quality is set out in section 6.3.

4.6 Ground Mode of Use

The GAINS Surveillance Concept includes the use of low-cost ground-based EC IN equipment that might not meet the performance requirements of traditional surveillance systems by ground personnel (providing ATC, FIS and AGCS), for purposes equivalent to EVAcq and SA. For brevity in what follows, such equipment will be described as a “GAINS traffic display”, even though no specific technology is proposed.


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All ground personnel who need to acquire and maintain visual contact with traffic may use the GAINS traffic display to direct and improve visual search, analogous to EVAcq. In some cases, such as a visual control room or aerodrome FIS, visual contact with traffic is part of the role of the ground personnel. Others, such as AGCS operators, have no responsibility to maintain visual contact with traffic but may nevertheless do so.

Ground personnel may also wish to use the information on the GAINS traffic display for situational awareness. As in the airborne context, SA in the context of ground use relates to building a picture of the traffic in the vicinity of an aerodrome to inform the choices made.

In some cases, this may involve decisions that do not affect aircraft in flight, for example, to give the fuelling crew advanced warning of the ETA of an aircraft expected inbound.

Since the ground personnel also provide a service (not necessarily an ATS) to airborne users, it is inevitable that SA may also influence the way they interact with airborne users.

The GAINS Surveillance Concept does not propose the use of the GAINS traffic display for:

• provision of separation services by ATC (to IFR aircraft in class A to E and VFR aircraft in class A to C airspace); nor

• provision of avoiding action, even at the request of the pilot.

It does propose, however, the use of the GAINS traffic display as a source of information on collision hazards. A net safety benefit is available where ground personnel can use EC-surveillance-derived information to pass traffic information. In particular:1

• Information about collision hazards from any source should be passed regardless of data quality.

• Pilots should be warned of surveillance data of lower than standard (verified) quality.

• ATS and pilots may use all information/data they have to improve situational awareness.

• Pilots accept responsibility for how they treat all information whether it is verified or not.

In the case of an ATC service or FIS, traffic information should be passed in the standard way, using a relative bearing, e.g.:

‘(Callsign) unverified traffic in your twelve o’clock range three miles’

The passing of traffic information based on the GAINS traffic display by an AGCS operator should remain generic but can be more targeted on the basis of position reports of opposing traffic:

‘(Callsign), multiple aircraft believed to be operating in the (location) area’ ‘(Callsign), traffic just reported over (location) at (height reported by joining traffic) joining down-wind left-hand for Runway (xx)’

Where traffic-display derived information indicates a variance with an ATC clearance, routing or pilot report and this is supported by one of the other tools available, ground personnel may query the discrepancy. In such instances the phraseology to be used might be:

1 The bulleted points listed were part of the conclusions of a “Pilots’ Workshop on EC in the Cockpit” held on 5th February 2019 at AOPA, with participants from AOPA UK, MOD UK, NATS and others.


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‘(Callsign) confirm your position/level/routing’

If the pilot’s report is still in discrepancy with the traffic-display derived information, ground personnel should not provide further challenge but may confirm the level of service being provided.

Where it is suspected there is a possibility an aircraft on frequency is about to infringe airspace (controlled airspace, prohibited, restricted or danger areas) without authorisation, ground personnel may advise pilots of their proximity to the airspace, enabling the pilot to resolve the situation before an actual infringement occurs:

‘(Callsign) I believe you are approaching the (airspace), confirm your intentions’.

Where it is believed that an aircraft on frequency has entered airspace (controlled airspace, prohibited, restricted or danger areas) without authorisation, ground personnel should advise pilots to contact the relevant ATS:

‘(Callsign) I believe you are within (airspace), contact (ATS Unit) immediately on (ATS Unit frequency)’

(The phraseology suggested is a modified version of that proposed for the GA Airfields ATS ADS-B Traffic Display Trial in its “Trial Safety Plan v1.0” [1], part of the A4A Project.)


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5 Benefits of the GAINS Surveillance Concept

5.1 Safety

The primary benefit of the GAINS Surveillance Concept is Safety. In particular for example:

• Better SA allows airborne users to plan their trajectories (for example, their entry point to the aerodrome traffic pattern) so as to avoid conflicts with other users.

• SA also facilitates the visual acquisition of other users in the aerodrome traffic pattern, and re-acquisition in the event that initial visual contact is interrupted. This helps to avoid errors of assumption about other airspace users’ positions.

• EC enhances the likelihood of visual acquisition of other aircraft in the aerodrome traffic pattern.

• A more comprehensive and effective FIS can be provided by ground personnel.

• A reduced risk of runway incursions, if ground personnel are permitted to warn airborne users of impending incursions.

• A reduced risk of airspace infringements, if ground personnel are permitted to warn airborne users of impending infringements.

5.2 Other benefits

Capacity is also improved, in that the benefit of the SA may lead to users having the confidence to enter a busy traffic pattern which, without SA, would present an unacceptably high risk.

Integration with unmanned systems is a potential benefit. UTM providers may be able to use the EC information acquired at the aerodrome to better coordinate flights of unmanned aircraft, though this use case is not within the scope of the GAINS project.


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6 Challenges and Risks of the GAINS Surveillance Concept

6.1 EC equipage proportion

The GAINS Surveillance Concept is built on an assumption of all participating aircraft using interoperable EC systems. Currently, equipage proportion with EC of various kinds varies strongly between locations and activities. Without 100% equipage (at least of EC OUT) in the aerodrome environment, the benefits associated with the GAINS Surveillance Concept fall off rapidly. Situational awareness relies on a complete picture in order for the pilot to build a reasonable level of trust. While there may be missing data, even in an environment with 100% equipage in principle, it must be the exception rather than the rule: for example, it is difficult to plan entry into the aerodrome traffic pattern effectively if only half of the aircraft are depicted on the visual display. Subject to interoperability considerations (see below), equipage proportion may be increased by:

• delivering a strongly positive benefit-to-cost to drive equipage;

• aerodrome-mandated EC equipage (a condition of aerodrome use, thus limited to those taking off or landing); and/or

• state-mandated EC equipage (including those in the vicinity of the aerodrome, or other defined airspace volumes).

6.2 Interoperability

The GAINS Surveillance Concept relies on all participating aircraft using interoperable EC systems. There are many EC systems available, based on different datalinks. Although fitted to some participating aircraft, datalinks other than 1090MHz were not used in the GAINS demonstration flights.

Potential datalinks include:

• 1090ES: extended squitter used by Mode S transponders.

• UAT: a datalink designed specifically for GA ADS-B, used for ADS-B in the USA.

• FLARM: a proprietary protocol used with encryption in the gliding community operating in the Industrial, Scientific and Medical band.

• P3i: a commercial but open standard used in light aircraft, also operating in the Industrial, Scientific and Medical band.

• 4G/5G: datalinks used for ground data communications that could potentially be extended for future airborne use.

Interoperability may be achieved by:

• all aircraft transmitting using the same EC datalinks, typically 1090ES.

• aircraft transmitting on a number of different EC systems but each aircraft being able to receive all of the transmissions used.

• ground-station rebroadcast of EC data on different datalinks.


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The simplest interoperability is achieved through the use by all aircraft of a 1090 MHz ADS-B system, and this was used in the demonstration flights. However, to achieve interoperability in the vicinity of an aerodrome, a rebroadcast system on the ground at the aerodrome may also be feasible. This option would not, however, give interoperability away from the aerodrome. Therefore, the risk of en-route MAC would not be mitigated by this option.

6.3 Performance and data quality

It is fundamental to safety regulation that performance requirements for equipment used for a safety-related task is consistent with the risk associated with performance in that task. Performance, particularly if proven through certification, comes at a cost. For example, TCAS II systems, used for collision avoidance by large commercial air transport aircraft, are several orders of magnitude more expensive than any device that would be suitable for typical light GA aircraft.

It is therefore helpful to examine the implications of performance in relation to the use cases identified in section 4.2 as part of the GAINS Surveillance Concept (EVAcq and SA). Note that this document does not comment on how performance is assured, i.e. whether the equipment should be certified in some way, or otherwise required to meet a particular standard.

6.3.1 Accuracy

For the EVAcq use case, the indicated position of the traffic needs to direct visual search with sufficient precision to be useful.

Where a relative bearing display is provided, for an aircraft indicated at 1800 m (about a nautical mile, a typical visual search range), a 300 m difference in relative position in the worst (tangential) case is equivalent to a 10-degree difference in relative bearing. Surveillance derived traffic information is typically given to 30 (clock hours) degree or perhaps 15-degree (30 clock minutes) precision. Thus, a device that offers an accuracy of about 300 m in relative position (which might correspond to an accuracy of about 200 m in each absolute position) is likely to be sufficient.

The GAINS Surveillance concept emphasises the use, for both EVAcq and SA, of traffic information displayed relative to navigation features or circuit positions rather than on a relative bearing display (although the equipment might also offer a relative bearing display). A typical downwind leg for a GA aerodrome traffic pattern might be 2000 m long, and 200 m accuracy would locate an aircraft within one of 10 notional sectors of such a leg. A typical GA aircraft will move at about 50 m/s, which means that 200 m is 4 seconds of motion. This is commensurate with the time taken to switch attention from a display to a directed external search, and further confirms that 200 m is a reasonable benchmark for a useful accuracy.

It therefore seems reasonable to suggest that devices with a positional accuracy of about 200 m is required. An accuracy of 20 m would probably add little extra to the efficacy of an EC device used for EVAcq and SA, while an accuracy of 2000 m would clearly be insufficient, being the typical dimension of an aerodrome traffic pattern.

It was not the objective of the GAINS Surveillance Demonstrations to assess the performance of particular EC devices quantitatively, but nearly all the devices used appeared, by inspection of track, to provide an accuracy of significantly better than 200 m (and probably better than 20 m). One device


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appeared to suffer from GPS position error of up to 0.5 nm, which may have been due to the participant putting the ADS-B device onto its side, which compromised its ability to achieve a good satellite lock.

6.3.2 Integrity

While the mean positional error is relevant to the utility of an EC device put to a particular use, the integrity is relevant to the possibility of misleading information.

With a TSO-C146() navigation system such as were used in the GAINS Navigation Demonstrations, and which are used to manage the trajectory of an aircraft in safety critical situations (within an obstacle clear area), integrity is defined by Horizontal Protection Level, exceeded with a probability less than 2 x 10-7 per approach. This is typically 5 to 20 m in EGNOS coverage.

Position sources such as those used in the EC OUT devices in the GAINS Surveillance Demonstrations, offer no such integrity. While mean accuracy is often good, it is possible for significant errors to be introduced in certain situations. This raises the question of whether a minimum level of integrity is required to deliver a net safety benefit in the EVAcq and SA use cases, and, if so, what it should be?

Safety benefit must be viewed in the context of other risk mitigations in place in a particular scenario. For example, in the case of use of ACAS II for collision avoidance in a controlled environment, risk is already mitigated by the provision of an ATC service which assures separation from other traffic. A system such as TCAS II should only replace or override the provision of separation by ATC if it can demonstrate at least an equivalent level of safety, including an assessment of the risk of it providing hazardously misleading information. Since the ATC service already provides a level of safety of the order of 10-8 accidents per flight hour, a collision avoidance system designed to allow aircrew to deviate from an ATC clearance must offer an equivalent level of safety through the integrity of the information provided, which results in a demanding certification requirement.

For the use cases that constitute the GAINS Surveillance Concept, risk factors are quite different.

The existing mitigations in the environments for which the GAINS Surveillance Concept is proposed are primarily:

• see and avoid;

• voice communication (position reporting); and

• rules of the air, including adherence to ATC clearance/instructions, if applicable.

In the EVAcq use case, the existing mitigation is unalerted see and avoid. Numerous studies (e.g. Andrews in Ref 5) have demonstrated the lack of efficacy of unalerted see-and-avoid. However, pilots do successfully operate in pure unalerted see-and-avoid environments with an acceptable level of safety.

Provided pilots remain normally vigilant, the provision of traffic information from an EC device will not decrease the efficacy of unalerted see-and-avoid where the EC device fails to provide information. Misleading information from an EC system might, in principle, cause visual search to be focused in the wrong direction, reducing the overall likelihood of detecting an aircraft on a conflicting trajectory. However, provided the information is correct more often than not, it is likely that a net safety benefit is delivered.


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In the SA use case, the pilot may, on the basis of traffic information from an EC device before visual acquisition, adjust heading or level to reduce the likelihood of conflict. One existing mitigation is the set of rules of the air that have the objective of avoiding collisions. These include, for example, turning to the right in the case of head-on convergence, conformance with the established aerodrome traffic pattern, and a requirement to obey joining traffic-pattern-instructions given by ATC at a controlled aerodrome. The rules of the air act as a set of constraints on what is otherwise the freedom to manoeuvre as desired.

Provided any trajectory adjustment initiated by the pilot on the basis of EC traffic information remains within the set of trajectories from which the pilot is free to choose without compromising the existing mitigations, then misleading or missing information will neither increase nor decrease risk. Misleading information may cause the safety benefit to be lost on a particular occasion, by encouraging an unnecessary alteration of trajectory, but that modified trajectory will, on average, be no more or less safe than any other trajectory that the pilot might have chosen.

As a result, the GAINS Surveillance Concept does not propose an integrity requirement for the EC devices used, provided that any EC-derived information is not used in a way that reduces existing mitigations. Conversely, the use for SA of EC-derived information without an appropriate level of integrity must not result in:

• flight contrary ATC clearance or instructions;

• a violation of the rules of the air (e.g. a non-conforming traffic pattern);

• flight into an environment in which unalerted see-and-avoid becomes less effective (e.g. IMC).

Voice communications, in the form of position reporting for the benefit of other traffic, is also an existing mitigation. It would be generally acknowledged the information from position reporting is of low integrity, and most pilots have witnessed situations with inaccurate, misleading or missing position reports. Nevertheless, position reporting is used by pilots for SA (to adapt trajectory before visual acquisition of a potential conflict), for example by choosing to join on one leg of the traffic pattern rather than another. Provided the reliability of EC-derived traffic information is at least comparable with the reliability of position reporting by voice communication (in practice), it should provide a net safety benefit. Further, if callsign information is displayed with EC-derived traffic information, potentially misleading information (whether displayed position or a pilot position report) may become apparent.

In summary, the GAINS Surveillance Concept proposes that no integrity requirement is necessary for the EVAcq and SA use cases envisaged.

6.3.3 Continuity

The portable and uncertified nature of the equipment proposed in the GAINS Surveillance Concept makes continuity of EC out transmissions challenging, particularly as antenna placement can be critical. Targets may at times disappear from the traffic display, and reappear sometime later, depending on the geometry. With imperfect continuity, confidence in the SA offered by a traffic display is undermined, though a net safety benefit may still be achieved.

The case that a net safety benefit is delivered even without a continuity requirement is similar to the case in section 6.3.2 about integrity. Provided EC-derived traffic information is not used as a substitute for other mitigations, no extra risk is associated with the information being missing.


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It is possible that experience of high reliability EC environments may lead to an expectation of reliability in other circumstances, and thus complacency, reducing the existing mitigation of vigilance and see-and-avoid. But a reliance and complacency argument can often be raised against any novel technology offering a safety benefit, and the effect can be dealt with by appropriate awareness of the limitations of the technology.

The relatively low current equipage rate of EC in GA tends to reduce any reliance on the technology: there is no expectation among GA pilots that all traffic will show up on a display. The time that was spent during the GAINS Surveillance Demonstrations in a 100% equipage environment was not long enough for participating pilots to develop any such reliance. It seems more likely in the short term that poor continuity performance would affect users’ confidence in an EC system, and therefore limit the uptake of the system.

It was not the objective of the GAINS Surveillance Demonstrations to test continuity performance of particular systems. However, a qualitative conclusion was that, by contrast with the other performance metrics described, improvements in continuity of the portable systems tested, for example through better antenna installation and placement, would be a cost-effective way of improving performance, and therefore confidence and uptake of the systems.

6.4 Distraction

As with any other information system in the cockpit, the introduction of a traffic display brings the risk of distraction. This is particularly the case at times of high workload, and flight in the vicinity of an aerodrome tends to be a high workload period.

Initial feedback from the demonstration flights indicates that participating pilots are quite aware of the potential for distraction by a traffic display in the cockpit at the expense of external visual lookout. It is likely that a balance can be struck between providing too little information and too much, allowing the safety benefit to be optimised. It will probably be necessary to ensure that the information on the display can be rapidly assimilated, minimising “head-down” time.

6.5 Clutter and transmissions on the ground

Fully certified Mode S transponders and ADS-B equipment have an aircraft-on-ground flag that allows other airspace users to filter out aircraft that pose no threat because they are not flying. With portable equipment, differentiating between aircraft flying and aircraft on the ground is more difficult, both because of the lack of an easy sensor input to provide that information, and also because battery powered equipment may remain on even after the aircraft electrical system is switched off.

This is a particular issue in the vicinity of an aerodrome, where stationary and moving aircraft on the aerodrome surface are likely to be encountered. While it is not expected to present insuperable issues, procedures, practices or technical amendments to the EC OUT equipment to suppress transmissions from aircraft on the ground may need to be developed to avoid clutter of traffic displays with spurious information.


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7 Comparison with SESAR Solutions

7.1 SESAR Solution(s) addressed by VLD

The SESAR solution for surveillance that is applicable to this concept of operations is:

• Solution 110: ADS-B surveillance of aircraft in flight and on the surface.

SESAR Solution #110 is relevant to the GAINS Surveillance Concept. The characteristics of the EC transceivers to be used in GAINS are similar in intention to Solution #110. The opening statement of the Contextual Note for Solution #110 states “The ADS-B Surveillance of aircraft in flight and on the surface addressed by the SESAR projects consists of the ADS-B Ground station and the Surveillance Data Processing and Distribution (SDPD) functionality”.

The use of ground surveillance data in solution #110 supports operational use for separation and flight conformance monitoring both of which should increase the safety and capacity of operations. The GAINS Surveillance Concept does not support separation.

The use of ADS-B in solution #110 is expected to reduce ground surveillance costs compared to installation of a radar infrastructure. The GAINS Surveillance Concept has the same aim.

ADS-B use for ground surveillance in both GAINS and solution #110 is more spectrum efficient than conventional radar. The GAINS Surveillance Concept offers further reduction of spectrum occupancy by transmitting at lower power than current certified ADS-B-OUT installations. However, this effect would be offset to some extent by the increase in number of ADS-B-OUT transmitters. Simulation studies to date indicate that more low power transmitters do not cause significant degradation of the 1090MHz environment.

A specific aim of the VLD is assessment of the usefulness of the GAINS Aerodrome Display Equipment for airborne traffic situation awareness by the ground operator. Conceivably this could lead subsequently to the aerodrome using more capable equipment than the GAINS display equipment that would conform more closely to solution #110. That consideration is outside the scope of the GAINS demonstration but is a possible future development.

Cockpit surveillance of aircraft in flight is the other important element of the GAINS Surveillance Concept, which is not part of solution #110, although the basic function to display ADS-B-OUT aircraft is the same.

7.1.1 Deviations with respect to the SESAR Solution(s) definition

The differences between solution #110 and the GAINS Surveillance Concept are as follows:

• SDPD as part of ground surveillance infrastructure. Solution #110 includes both the ground surveillance display and the SDPD. The SDPD is not relevant to a standalone ADS-B ground display device as in GAINS, because the GAINS surveillance data is received directly from the aircraft with no intervening network and minimal processing. However, initial experience from use of GAINS surveillance equipment could lead to an aerodrome requirement for a capability upgrade utilising networked surveillance and SDPD.


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• Operational functionality is different. The sole functionality to be demonstrated in GAINS is traffic situation awareness to augment some operational applications, a much less critical use than a separation service that can be supported by solution #110 infrastructure.

• The solution #110 operational improvements of capacity and flight efficiency are of much less importance for small GA airfields which are not usually capacity constrained, except in special circumstances such as “fly-ins” to events where a few hundred GA aircraft may arrive or depart in the course of a couple of days.

• Solution #110 does not include airborne cockpit traffic situation awareness.

In summary, therefore, the GAINS Surveillance Concept is the same in principle as ground ADS-B based surveillance described in solution #110 but the equipment specification is sufficiently different that solution #110 cannot be used directly in the GAINS demonstration. However, the operational experience from GAINS may lead to use of networked surveillance with SDPD at a later date.


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8 References

Reference Documents

[1] GAINS Demonstration Plan (D1.2).

[2] Surveillance Demonstration Conduct Plan (D4.2).

[3] Airspace 4 All, Mid-Air Collisions: An Evidence-Based Analysis of Risk – 1975 to 2018

[4] S.M. Moore “Comparison of Alerted and Visually Acquired Airborne Aircraft in a Complex Air Traffic Environment” SAE Technical Paper 981205 (1998).

[5] J W Andrews “Unalerted Air-to-Air Visual Acquisition” MIT Project Report ATC-152 (1991).

[6] https://www.gov.uk/aaib-reports/8-2010-g-eyes-and-g-bolz-17-august-2008

[7] “CAP1391. Electronic Conspicuity Devices.” Second Edition April 2018. Civil Aviation Authority, UK.

[8] “GA Airfields ATS ADS-B Traffic Display Trial: Trial Safety Plan v1.0” A4A Project.

https://www.gov.uk/aaib-reports/8-2010-g-eyes-and-g-bolz-17-august-2008


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