[American Institute of Aeronautics and Astronautics 44th AIAA Aerospace Sciences Meeting and Exhibit...

American Institute of Aeronautics and Astronautics1

The Embraer-170 and -190 Natural Icing Flight Campaigns:Keys to Success

Ben C. Bernstein*

Leading Edge Atmospherics, LLC, Longmont, CO 80503

William Campo, Luiz Algodoal and Fabio Bottino†

Embraer – Empresa Brasileira de Aeronáutica S.A., São Jose dos Campos, SP, Brazil

and

Lyle Lilie‡ and Agostinho Henriques§

Science Engineering Associates, Inc., Mansfield Center, CT 06250

During the spring of 2003 and winter of 2005, the EMBRAER-170 and -190 aircraftcompleted the natural icing flight campaigns portion of their in-flight icing certificationprocess. All flights were completed in approximately two weeks for the 170 campaign and inonly four days for the 190 campaign. A robust set of icing encounters was collected andthoroughly documented. The success of these programs hinged on extensive planning, pre-flight testing of the aircraft, application of ice accretion models, flow analyses, icing windtunnel data, proper placement of high-quality instrumentation, reliable data collection, idealbase location, real time information regarding aircraft positioning into icing cloud andoptimized sampling of Appendix C icing conditions. In this paper, each of these aspects ofthe flight program, and their importance will be described.

NomenclatureAMS = Air Management SystemAPU = Auxiliary Power UnitDAS = Data Acquisition SystemERJ = Embraer regional jetFSSP = Forward Scattering Spectrometer ProbeLWC = Liquid water contentMAU = Modular Avionics UnitMVD = Median Volumetric DiameterNASA = National Aeronautics and Space AdministrationSAIV = Slat Anti-Ice ValveSATCOM = Satellite telephone communications systemSEA = Science Engineering AssociatesSLD = Supercooled large dropsSPS = Stall Protection SystemOAP-2DG= Two dimensional Optical Array “grey” Probe

* Manager, Leading Edge Atmospherics, LLC, 3711 Yale Way, Longmont CO 80503, AIAA Member.† Engineers, Embraer – Empresa Brasileira de Aeronáutica S.A., São Jose dos Campos, SP, Brazil.‡ President, Science Engineering Associates, Inc., Mansfield Center, CT 06250, AIAA Member.§ Senior Software Engineer, Science Engineering Associates, Inc., Mansfield Center, CT 06250.

44th AIAA Aerospace Sciences Meeting and Exhibit9 - 12 January 2006, Reno, Nevada

AIAA 2006-264

Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


I. IntroductionHE certification of a new aircraft for in-flight icing has often proven to be a difficult and expensive endeavor.In particular, flight campaigns into natural icing conditions may require several months or even years to

complete, depending on the circumstances. Today’s very competitive market makes an efficient natural icingcampaign an important part of the certification process. For example, the Embraer-145 regional jet natural ice flightcampaign lasted 6 weeks, and the aircraft had to be flown over two continents. This required a significant movementof the aircraft and crew, plus extensive time in the field and in flight. Much of the program was spent chasing icingclouds that provided little, if any, quality data that could be used for certification. The inefficiencies of that programresulted in unnecessarily high costs and delayed the certification of the aircraft.

In stark contrast to this, the Embraer-170 (Fig. 1) and -190 regional jets (ERJ-170 and ERJ-190) completedtheir natural icing flight campaigns in less than two weeks during the spring of 2003 and in less than one weekduring the winter of 2005, respectively. A robust set of icing encounters was collected and thoroughly documented.The success and efficiency of these programs hinged on extensive planning, application of ice accretion models,flow analyses, icing wind tunnel tests, proper placement of high-quality instrumentation, reliable data collection,pre-flight testing of the aircraft, an ideal base location, real time information regarding aircraft positioning into icingclouds and optimized sampling of FAR-25 Appendix C icing conditions. In this paper, each of these aspects of theflight program and their importance will be described.

Figure 1. The Embraer-170 Regional Jet.

II. Embraer E-Series Regional Jet Ice Protection SystemsThe ERJ-170 and -190 series regional jets were designed to carry 70-86 and 98-118 passengers, with ranges of

1,800-2,000 and 2,100-2,300 nautical miles, respectively. Both use bleed air systems to heat their wing slats andengine inlets that are triggered automatically by ice detectors on either side of the aircraft’s nose, while otherportions of the aircraft (windshields, Air Data Smart Probes, drain mast and pressurization static port) are protectedat all times using electro-thermal energy, independent of ice detectors signals. Detailed specifications of each seriesof aircraft are provided in Appendix A, and an in-depth description of their ice protection systems is given inAppendix B. Certifications of the ERJ-170 and ERJ-190 systems were completed in 2004 and 2005, respectively.

An overview of the in-flight icing certification process is shown in Fig. 2. The main objectives of each naturalice campaign was to demonstrate that the airplane can operate safely in icing conditions and to confirm the validityof the other means of substantiation. The substantiation of airframe ice protection systems operation andperformance was achieved primarily by analysis, by component testing in artificial icing facilities, and by groundand flight-testing in dry air conditions. Nevertheless, confirmation of performance and assessment of the aircraft as awhole must be completed in natural icing conditions.

Overall, the natural icing assessments included the following:• Airframe icing assessment.

T


• Systems thermal performance demonstration (wing and engine inlet).• Confirmatory assessment of thermal analysis.• Confirmation of ice detection performance in installed position.• Confirmation of normal operation of air data system, radios, antennas, APU, air-conditioning packs,

landing gears, flaps, etc.

III. Preparation for Natural Icing TestsIn advance of the natural icing campaign, Embraer engineers used the Onera, Lewice 2D and Lewice 3D codes1

to predict the location and shapes of ice that would form on the aircraft during flight through FAR-25 Appendix Cicing conditions. In order to predict the performance of thermal systems, Embraer developed its own code, whichwas validated using icing tunnel tests performed at the NASA Glenn Research Center icing tunnel and at AerospaceComposite Technology in Luton, England as well as dry air flight tests, conducted over Brazil and the United States.Some wind tunnel and dry air tests were flown with artificial ice shapes that were developed from accretion modelsand icing tunnel tests.

For the flight campaign, itself, two prototypes of each aircraft were developed with the required provisions forthe installation of the equipment and instrumentation that were necessary, but only one ERJ-170 and one ERJ-190prototype were flight-tested in natural icing conditions.

IV. InstrumentationTo accurately document the weather conditions that the aircraft sampled, the ice that built upon them and its

effects upon performance, a complex suite of instruments was employed. A brief summary of the main airframesystems and meteorological instrumentation is given below.

Figure 2. Diagram of the in-flight icing certification process.

Wing Anti-Ice Engine Inlet Anti-Ice

Aerodynamic Wind Tunnel Tests

Impingement Analysis

Icing Tunnel Tests

Dry Air Flight Tests

Correlated Thermal Model

Flight Tests With Artificial Ice Shapes


Engine Ice Ingestion Limits



Natural Ice Campaign

SYSTEM CERTIFICATION

Wing Anti-Ice Engine Inlet Anti-Ice

Aerodynamic Wind Tunnel Tests


Icing Tunnel Tests



Flight Tests With Artificial Ice Shapes


Engine Ice Ingestion Limits



Natural Ice Campaign

SYSTEM CERTIFICATION


A. Wing Ice Protection SystemTo assess the performance of the wing ice protection system (Fig. 3), temperature and pressure were measured

within the bleed air supply ducting and piccolo tubes, as well as inside the heated leading edges. The airflow withinthe bleed air supply lines to the wing root was monitored in addition to the valve status. Measurements of thetemperature of all heated surfaces were also made, while video and still photography of the wing surfaces wasrecorded.

B. Engine Inlet Anti-IcingInstrumentation for assessment of the engine cowl anti-ice system is shown in Fig. 4. The left hand cowl and

inlet were recorded on video during all tests with an external camera. In addition, both inlets were monitored frominside the cabin and recorded using hand held video as required.

C. Auxiliary Power Unit (APU)Specific instrumentation beyond that required for normal performance assessment was not required for the APU

assessments. However, APU performances parameters (notably exhaust gas temperature), temperature and electricalload were monitored. Video recordings of the APU inlet and oil cooler inlet were monitored to ensure properoperation following APU shut down after start up and operation in icing conditions.

D. Probes, Antennae And Ice Detection SystemSpecific instrumentation was not required for the air data probes, unheated antennae or ice detectors. Ice detector

discrete outputs were available after the flight test campaign in order to assess precise trigger points for icedetection. Normal performance of the air data system and electrical equipment was monitored and any anomaliesnoted in the pilot reports and flight logs.

E. Video Monitoring And Still PhotographyExternal video cameras were mounted around the fuselage to obtain a visual record of airframe and protected

surface characteristics in icing conditions. Portions of the aircraft were painted to allow for easier assessment of theice accretions, and ice thickness measuring probes were installed. The general arrangement of cameras on theaircraft is shown in Figure 5. In some cases, hand held digital video and still cameras were used to record specificobservations of the wings from inside the aircraft, as well as from the ground after flights were completed. Videorecords were made of the engine spinner and cowl ducts.

F. Meteorological Instrumentation

1. Description Of Probes And Interfaces With AircraftInstrumentation for measurement of icing cloud characteristics was supplied by Scientific Engineering

Associates (SEA) and was mounted on dedicated flight test instrumentation pylons on either side of the aircraftforward fuselage. The installation is shown in Figure 6. The in-situ package to document the meteorologicalconditions present consisted of several instruments. These included those needed to document Appendix Cconditions, as well as additional instrumentation that extended the measurable drop size range and enableddifferentiation of pure water, mixed phase and glaciated conditions. The following probes were included in thepackage: an SEA Liquid Water Content Meter (formerly Johnson-Williams/Cloud Technology) hot wire probe, aCSIRO King Probe Liquid Water Content Meter, a Particle Metrics Inc. (formerly Particle Measurement Systems)Forward Scattering Spectrometer Probe (FSSP), and a Particle Metrics Inc. 2-D Optical Array Probe (OAP-2DG).

The data recorded from the icing equipment was processed on the aircraft in real time using a dedicated system.Processed icing data, primarily MVD and LWC, was passed directly to the aircraft and recorded on the flight testdata acquisition system (DAS). The data were viewable on the aircraft in real time, allowing the crew to relate thecurrent conditions to the Appendix C envelope and consider it in the context of points collected in previous flights.Raw data files and probe output were downloaded from the icing instrumentation system discs after each flight forstorage, post processing and expert verification as required. Instrument time was synchronized with the aircraft DASthrough the use of IRIG-B time code.


Figure 3. Wing slat probe locations.


Figure 4. Engine inlet probe locations.


Figure 5. Video camera layout used for the ERJ-190.


Figure 6. Locations and photos of meteorological probes.

2. Liquid Water Content MeasurementWithin the droplet size range of FAR/JAR Appendix C encounters, the SEA probe provides the primary

measurement of LWC, however, its response diminishes for drop sizes above about 45 µm2. Larger drops tend to besplit and break up on impact with the hot wire such that the total water mass is not evaporated. The King provides asomewhat better response for larger drops2 but also tends to provide a measure of LWC that includes some crystalsin mixed phase conditions.

The SEA LWC was used as the only quantitative measure of LWC during exposure to icing. When exposure tomixed-phase conditions was indicated, the SEA LWC was assessed against the King probe to ensure the measure ofliquid water content remained reasonable and consistent.

Secondary measurement of liquid water content can be inferred from the FSSP and OAP instruments bycalculation of the water mass contained in the measured drop counts in each size bin. In Appendix C conditions,these measurements are of little value since their absolute accuracy is not determined. Conversely, in large dropconditions, they provide the most reliable measurement of liquid water content. No SLD conditions wereencountered and the FSSP derived LWC was not used except to provide a qualitative check on the SEA LWCbehavior. The uniformity of the cloud could also be judged visually by assessment of asymmetry on unprotectedwing surfaces (winglets) as well as from the SEA and laser probes.

3. Drop Size MeasurementMeasurement of drop size is obtained from the FSSP and OAP instruments. The FSSP counts droplets in the 0 to

45 µm range over 15 size channels thus providing a 3 µm resolution. The OAP measures droplets up to ~1000 µmranges with a 15 µm or 25 µm resolution per channel. The FSSP MVD (median volumetric diameter) was used


directly as the only measure of MVD in Appendix C conditions and was also inspected qualitatively to assessstability of the icing condition.

Figure 7 shows an example ~17-minute time series of temperature, LWC and FSSP MVD measurements takenwithin an all-liquid cloud encounter during which the ERJ-170 built a 3-inch ice accretion. The consistent, AppendixC values seen in this time series were fairly ideal for a certification data point. It is important to note that whileseveral such clouds were sampled during the two flight programs, such consistency is not found in many icingclouds, especially those with such relatively high liquid water contents (0.6, +/-0.1 gm-3).

Figure 7. Time series of temperature (oC), SEA (JW) LWC (gm-3) and FSSP MVD (µm).

4. Glaciated and Mixed Phase EnvironmentsThe addition of the OAP-2DG to the meteorological instrument package permitted a more rigorous assessment

of the presence of ice crystals, indicating whether the conditions being sampled were all water, mixed phase (amixture of supercooled liquid water and ice crystals) or completely glaciated (only ice crystals) via inspection of the2-D images. Inspection of the OAP image data during and after flights confirmed the presence (or absence) ofsignificant solid particulates (crystals). For those instances where there were mixed-phase or glaciated conditions,the data segment was disregarded for the purposes of thermal model correlation. Nevertheless, since the aircraft wasexposed to such conditions and accumulated ice on the airframe, the data was presented to the authorities in itsentirety for completeness.

5. Probe CalibrationThe FSSP and OAP probes were calibrated prior to delivery by an independent agency. After installation and

prior to testing, the calibration was confirmed using calibrated glass beads of known size. Calibration was re-checked during the middle and at the end of the tests prior to removal of the probes from the aircraft.

The SEA hot wire probe was calibrated prior to testing and was automatically re-zeroed during each flight, priorto entry into icing conditions. Following a test, the data from the SEA probe could be assessed (and re-processed ifnecessary) to correct for any zeroing error that may have existed. The data from the King probe could also beprocessed after the test in a similar manner.

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FSSP MVD (microns) Static Temperature (C) JW LWC (g/m3)


Due to the location of the probes on the aircraft there was a possibility that the fuselage could affect the flowlines and droplet trajectories nearby with the result that the LWC and MVD measured at the probes could have beendifferent from those of the free stream. An analysis exercise was conducted to determine the extent of the deviationsof LWC and MVD concentrations at the position of the probe locations due to fuselage effects. They indicated thatthe effect of the concentrating effect of the fuselage is negligible for both probes within the droplet size range ofAppendix C.

V. Choosing an Ideal Base Location for Aircraft OperationsOnce a fully instrumented aircraft was ready for flight, it was important to choose a good base from which to

conduct the natural icing flight campaign. Over North America, icing is most common over the Pacific Northwest,Alaska and in a swath from the Midwest and Great Lakes to the Canadian Maritimes3. The Midwest and GreatLakes regions were of particular interest because of a good combination of relatively high winter and spring icingfrequencies, gentle terrain and a large number of airports that could serve as landing sites for the ERJ-170 and -190.Given the range and speed of these aircraft, these areas were within reach of two Embraer maintenance facilities,located at Nashville, Tennessee and West Palm Beach, Florida, helping to mitigate the cost to base the aircraft.Nashville’s closer proximity to the icing maximum made it the prime candidate. However, while close proximity toareas with high icing frequency is ideal in terms of being in position to sample the icing quickly and with little ferrytime, snow commonly reaches the ground in icing prone areas. This is a concern for certification programs, becauseground de-icing fluids can play havoc with the instrumentation and cameras described earlier. Icing clouds are alsooften associated with low ceiling and visibility, which can sometimes limit the use of airports for landing andalternates, as well as cause delays. Because many icing events are short lived and/or small in scale, such problemscan result in missed opportunities to acquire valuable samples. For aircraft with limited range and/or on-station time,it is essential to choose a base that it very close to the icing prone areas, at the expense of having to deal with grounddeicing, ceiling and visibility issues. Increased speed and range allow for the ability to base nearby, but not withinthe icing and snow prone areas. While snow almost never falls at West Palm Beach, snow frequencies were stillrelatively minimal at Nashville, making it the ideal choice.

It is important to note that base location choice depends greatly upon the time of year for which the program isplanned. The location of icing conditions changes dramatically with time of year, moving from the central UnitedStates during the winter to Alaska and northern Canada during the summer3. Similar latitudinal changes in icingfrequency are evident over other parts of the globe4. If an icing program is slated to take place during the lessfavorable May to September time frame, manufacturers may face additional difficulties in finding base locationswhere icing is both available and flyable, especially if their range is limited. Fortunately, the 170 and 190 programswere conducted between January and April, when icing conditions were relatively common in the central andeastern portions of North America.

VI. Daily Flight Operations

A. Pre-flightAt the start of each day, the aircraft and system readiness had to be assessed. This process included the

following:• Determine the optimum test points and ordering to be performed for each flight based on

importance/criticality and icing forecasts.• Ensure paint scheme and external thermocouples are in a state of good repair.• Operational check of meteorological instrumentation.• Calibration of icing instrumentation (prior to first flight, after completion of approximately half of the flights,

and at the end of the campaign).

After all aircraft and instrumentation systems were found to be ready, the next question was whether or not therewere icing conditions available and whether they were worthy of sampling. Given the range of the ERJ-170 and-190, a large domain for flight was available, from the east slope of the Rocky Mountains to the east coasts of theUnited States and Canada. This usually provided the opportunity for several potential icing flight locations on anygiven day. To determine which provided the best flying opportunity, many aspects of each cloud had to beconsidered. As described above, proximity is somewhat of an issue, even for a regional jet, but the primary factorslaid in the “quality” of a given cloud for sampling. For each cloud, the meteorologist would assess its temperature,liquid water content, drop size, potential for mixed phase conditions, cloud consistency and size (both horizontally


and vertically), its projected movement and location relative to dense air traffic regions and terrain. Thetemperature, liquid water content and drop size determine where the icing conditions fit within the Appendix C icingenvelope. They must be considered within the context of the clouds that the aircraft may have already sampled, forit may be desirable to sample a different portion of the envelope, especially in the latter stages of a flight campaign.Clouds that maintained relative consistency for those parameters were ideal, especially if they were persistent,widespread and reasonably deep (e.g. 0.3 km [1,000 ft] or more). Attempts were made to avoid mixed-phase cloudsbecause the coincident presence of ice crystals with the liquid water confounded the measurements of the watercontent and assessment of the drop size spectrum.

Air traffic was an important consideration because effective sampling often required the establishment of blockaltitudes and long transects within the clouds. “Quiet” flight areas away from heavy air traffic were most conduciveto such flying, because air traffic control is more likely to provide the pilots with adequate 3-D space in which towork. Following the sampling period, the aircraft typically climbed above cloud top to document the ice withphotographs and to complete performance maneuvers. Sun angle was sometimes important for the photography,requiring the aircraft to fly in one particular direction before any ice would shed, sublimate or melt. Again, quietairspace allowed the pilots more room in which to complete these tests. Areas with significant terrain often makefor difficult sampling because minimum vectoring altitudes tend to eliminate much if not all icing altitudes fromavailability for sampling. They also tend to eliminate the ideal escape route for safety – descending to altitudesbelow the freezing level or beneath cloud base. The identification of reliable escape routes was a crucial aspect ofenhancing the safety of the missions. If the aircraft had needed to depart the icing conditions quickly, immediateknowledge of the locations of icing-free altitudes and/or horizontal locations was imperative.

Regardless of the location of the target clouds, the meteorologist needed to examine the surface observations,terminal area forecasts and relevant weather features to determine if the landing location may have ceiling, visibilityor precipitation issues. If any were evident, alternate landing locations had to be provided and the conditions andexpected changes at these locations were monitored closely. The relevant information was presented to the flightcrew in the morning flight briefing, where decisions about the day’s operations were made.

B. In-flightFollowing takeoff, the aircraft would climb to a cruise altitude and ferry to the target location. An altitude with

clear air was chosen, allowing for the meteorological instruments to be “zeroed” and for dry air points to becompleted along the way, as needed. Using a satellite telephone communications system (SATCOM), themeteorologist provided updates to the crew regarding any changes in the target clouds (e.g. movement, temperature,liquid water content, drop size, cloud top height), allowing for minor adjustments to the sampling plan. As theaircraft approached the target clouds, it descended toward the appropriate altitudes. Prior to entering the icingconditions, the aircraft was prepared and the systems were configured per the procedure for the tests that wereplanned. The aircraft then entered the icing condition and the crew recorded the time interval from entry into cloud(as indicated by the icing instrumentation and/or by pilot recognition of entry into visible moisture from passivemeans) until indication of icing conditions by ice detection system. Using the SATCOM and the real-time SEA datasystem, the crew reported the observed meteorological conditions (temperature, water content, drop size, phase,cloud top height and consistency of these parameters) to the meteorologist on the ground. They jointly determined ifthe clouds were as forecast and were appropriate for sampling. If they were not appropriate, then the plan and thelocation were adjusted to get the aircraft into a more favorable environment. If they were appropriate, then thesampling of those clouds was continued and the aircraft would accrete the desired ice.

The aircraft was kept within the cloud until the test point was completed, which typically required an iceaccretion of at least 2 inches (5 cm), preferably 3 inches (7.5 cm) or more on unprotected surfaces (Fig. 8). An “icestick” with depth markings was used to determine when this criterion was met. Depending on the liquid watercontent of the cloud, it would typically take 15 to 45 minutes to accumulate that much ice.

While flying in the icing clouds the crew would observe altitudes, temperatures and airspeed for any indicationsof abnormal operation. The crew would also 1) observe any CAS message related to the SPS (Stall ProtectionSystem), 2) operate radios and monitor and record any abnormal operation, 3) conduct checks on windshields, 4)observe and note ice accumulation on central glazing bar and wiper blade arms, 5) observe and record any icing onside windows, and 6) observe and record the behavior of wing and engine air inlet heated surfaces for visual signs ofrunback icing particularly during low power operation or when operating with slats deployed. If run back icing wasobserved on the slat or wing upper surfaces, then the test duration was extended to properly assess run back icegrowth characteristics. System performance tests were conducted for sufficient durations to achieve stabilization ofstructural temperatures a) for at least one complete Appendix C encounter (equivalent to a 17.4 nautical mile cloudper Appendix C definitions or greater extent with the appropriate reduction factor applied to the LWC) accounting


for the static air temperature and MVD and b) for specific exposure times as defined by individual test procedures.Following the encounter, the aircraft left the icing conditions, usually by climbing above cloud top. The wing

anti-ice was turned off immediately upon exit from cloud (and prior to shedding maneuvers) in order to photographice accumulations and/or residual icing that may have been present. Outside of the icing cloud, a series of testsand/or maneuvers were performed, as directed by the pre-defined procedures for each flight configuration: holding,simulated approach and landing, descent, and engine air inlet 2-minute delayed turn on. The number of testscompleted depended upon the life span of the ice accretion. An accretion that remained on the unprotected surfacesfor a long period of time would allow the crew to complete several test points. If adequate fuel remained when thetest points were completed, the crew and meteorologist would again confer about the status of the clouds. Ifappropriate clouds were still present within reasonable range, the aircraft would sometimes re-enter the clouds andbuild additional ice accretions, to be followed by further above-cloud tests. These were commonly performedduring the return flight to the base at Nashville.

Throughout the flight, the meteorologist monitored the evolution of the clouds being sampled, updating the crewif changes in location were needed to maximize the icing encounter. Any changes in the escape route locations(cloud top or base height, locations of cloud edges and above-freezing layers) were immediately relayed to thepilots. Weather conditions at the planned destination airport and alternate landing sites were constantly monitoredas well, including ceiling, visibility, precipitation and winds. Changes to these conditions, as well as those en routeto that destination, were relayed to the pilots, as needed. Flight following software was used to watch the progressof the flight. As the aircraft approached the home base, the ground crew was alerted so that they would be fullyprepared for post flight duties, including photography of any residual ice present upon landing. If the crew desiredto make a second flight, the entire procedure was repeated.

C. Post-flightImmediately after every flight, the crew had to complete the following procedures:• Check for signs of fuel venting from under-wing NACA scoops and/or other drainage.• Check and photograph residual icing on nose radome, forward drain mast, and airframe components.• Record progression of any fan blade damage.• Check for signs of airframe Foreign Object Damage especially around intakes and air inlets.• Download icing data for transmission to icing specialists for confirmation of the conditions encountered.• Download parameter data from DAS for transmission to engineers for analysis.• Check slats for ingestion of water or drainage from slat drainage holes.

Once these procedures were completed, and if no second flight was planned on that day, the team wasreassembled to debrief the flight and plan for the next day’s operations. The engineers, pilots and the meteorologistdiscussed the meteorological conditions that were encountered, including their location, temperature, liquid watercontent, drop size, presence or absence of ice crystals, consistency and evolution. This information was put into thecontext of all icing events flown to date, to assess the portions of the FAR-25 Appendix C envelope that had beencovered and what was still needed. The ice accretions were described, including their character (rime, glaze, mixed,roughness, feathers, runback, etc.), amount of time that was needed to build an adequately large ice shape (e.g. 3inches in 30 minutes) and the ability of that shape to be maintained after departing the icing clouds (partial orcomplete shedding, sublimation, melting). Pilots assessed the severity of the icing encounter (light, moderate,heavy), as well as the ability to stay within the cloud using directions from the meteorologist in combination withinteracting with air traffic control. The meteorological instruments team gave an initial indication of the quality ofthe meteorological probe data (signal, consistency, presence of ice crystals), which was refined later that day via in-depth, post-flight analysis. The engineers and pilots discussed the performance of the ice protection system andwhether there were any issues with the day’s flight operations, during data collection both within the cloud andwhile completing test points after the ice was accreted.

After the day’s flight operations were debriefed, planning for the next day’s operations began. The weather andassociated icing conditions expected for the next day were described in terms of location, timing, temperature rangeand a rough estimate of the liquid water content (low, medium, high). Expectations for the following 2-3 days werealso described to provide context. Such information allowed Embraer engineers and pilots to determine the relativeimportance of the expected events, based on the remaining desired weather conditions, and to plan for upcomingoperations, including crew scheduling and the next day’s briefing times. After such plans were settled, somemembers of the team set to work reducing the data collected on that day and preparing the aircraft and data systemsfor the next planned flight.


Figure 8. Ice stick instrumentation and ice accretions.

VII. Summary and Assessment of ImpactsBoth the ERJ-170 and –190 natural icing flight campaigns proved to be quite successful, thanks to quality

system design, thorough preparation and teamwork between several companies. In a relatively short amount oftime, robust datasets covering a significant portion of the Appendix C envelope were collected in an efficientmanner, with enhanced safety. The icing environments were thoroughly documented in terms of the cloudcomposition, the ice that built upon the aircraft and its effects on flight. Following the program, a detailed report ofthe meteorological environments in which the aircraft flew (location of icing conditions relative to fronts, features


on satellite, radar, etc.) was provided to the manufacturer. This information, in combination with detailed reports onthe in-flight observations described above, the theoretical results from ice accretion codes and results from icingtunnel and dry air tests, was submitted to the authorities for the in-flight icing certification of the two aircraft. Thisevidence was accepted and this portion of the certification process went rather smoothly.

The downstream impacts of the natural icing tests on a civil aircraft certification program have two relevant anddistinct aspects: The first and more intuitive one is the time and cost to perform the necessary tests in order to get thecertification authorities’ approval. The second and less intuitive one is related to the impacts of the natural icing testsin all the other correlated test campaigns, such as the artificial ice shapes performance and handling tests (whichusually depends on the shapes validation from the natural ice observations), and the anti-ice system operationcertification in natural conditions (which may have a very significant impact on the test program due to a possiblenecessity of repositioning ice detectors, temperature sensors, etc.). This latter aspect could result in a particularlylarge impact on the complete airworthiness certification cycle, depending on the obtained results. It also had a muchmore restrictive time constraint to the complete airworthiness certification program planning due the great numberof system certifications that were dependent on it, thus it needed to be conducted after the completion of the naturalicing tests. Considering all the different aspects affecting the cost and duration of the natural icing tests, accurateforecasting of the ice encounters forecast has shown to be the primary factor in having an optimized (less expensiveand time consuming) test program.

A typical FAR 25 natural icing test certification program requires an average of ~10 flight hours to have allflight-test points successfully executed. Comparing the three most recent Embraer projects, which have performedthe same natural icing flight test program (10 flight hours dedicated only to the execution of the flight testsmaneuvers) the following figures are revealed:

ERJ-145 ERJ-170 ERJ-190

Natural Icing Flight TestCampaign Duration

28 days (USA)10 days (Chile)

9 days (USA) 4 days (USA)

Natural Icing Flight TestCampaign Flight Hours

100 35 17

From these numbers, the following conclusions can be drawn:1. Considering all the flight test programs required about the same number of flight hours in icing (~10) the

expended ice hunting and ferry flight time can be calculated:

ERJ-145 ERJ-170 ERJ-190Ice Hunting Flight Time (hours) 90 25 7Percentage of Natural Icing TestCampaign spent searching for andferrying to the icing conditions

90% 71% 41%

During the ERJ-145 flight tests, inadequate forecasts were provided, resulting in a very long test campaign (38days and 100 flight hours) with 90% of the flight hours spent searching for the necessary ice conditions and only10% of the flight hours spent within the icing needed for the execution of test points. For the ERJ-170 program,different real time icing forecasts were employed, resulting in a drastic overall reduction in the flight test campaignduration, which took less than half of time spent with the ERJ-145. Although the percentage of the ERJ-170 testcampaign flight hours spent searching for and ferrying to/from the icing conditions did not present the same drasticreduction compared with the ERJ-145 campaign, this cannot be directly related to the forecast accuracy. Additionalconsideration should be given to the season in which the campaigns took place (late March, early April for the ERJ-170 and winter for the ERJ-145). Because of the nature and location of springtime icing, some of the icing cloudswere a considerable distance from Nashville and a significant amount of ferry time was required to reach them. Thesame real time forecast techniques used for the ERJ-170 were also employed for the ERJ-190 program and a muchmore dramatic reduction in the overall time and in the percentage of the flight test campaign spent searching for andferrying to/from the icing clouds was evident. Considering that the ERJ-190 and the ERJ-145 were both testedduring the winter, comparing those two campaigns provides a more coherent comparison possible, showing the realrelevance of an adequate forecasting in the campaign optimization.

2. Cost wise, a simple conclusion can be drawn assuming a fixed flight hour cost for the three considered


campaigns (which is roughly true). Overall, a reduction of 65-83% in the necessary flight hour as a result of theadequate forecasting would roughly result in a proportional 65-83% cost reduction.

3. Considering the overall time spent in the tests, reductions of 29 and 34 days were found comparing the 38days test campaign of the ERJ-145 against the 9 and 4 days test campaigns of the ERJ-170 and –190, respectively.The value of the reduced time that it took to complete the required natural icing tests is easily evidenced when acomplete certification flight test campaign is scheduled to take place in 10 months nowadays, due to the marketaggressiveness, compared to the 18 months taken at the time of the ERJ-145 certification. The more streamlined,efficient natural icing campaigns completed for the ERJ-170 and –190 programs played an important role in gettingthese aircraft through the certification process in a timely manner.


Appendix A – Aircraft Specifications

ERJ 170 ERJ 175 ERJ 190 ERJ 195Passenger seats 70-78 78-86 98-106 108-118

Range 2,000 nm 1,800 nm 2,300 nm 2,100 nm

Certification Date February 2004 December 2004 3rd Q/2005 2nd Q/2006

WEIGHTS

Maximum Takeoff Weight- STD 79,344lb 82,673lb 105,358lb 107,563lb

Maximum Takeoff Weight-LR 82,011lb 85,517lb 110,892lb 111,972lb

Maximum Landing Weight 72,310lb 74,957lb 94,798lb 99,208lb

Maximum Zero Fuel Weight 66,447lb 69,886lb 89,948lb 93,696lb

Basic Operating Weight 46,606lb 48,083lb 61,906lb 63,868lb

Maximum Payload 19,842lb 21,804lb 28,043lb 29,829lb

Maximum Fuel 20,576lb 20,526lb 28,377lb 28,377lb

EXTERNAL DIMENSIONS

Wingspan 85ft 4in 85ft 4in 94ft 3in 94ft 3in

Length Overall 98ft 1in 103ft 11in 118ft 11in 126ft 10in

Height Overall 32ft 4in 31ft 11in 34ft 8in 34ft 7in

Horizontal Stabilizer Span 32ft 10in 32ft 10in 39ft 8in 39ft 8in

Fuselage Width 9ft 11in 9ft 11in 9ft 11in 9ft 11in

Fuselage Height 11ft 0in 11ft 0in 11ft 0in 11ft 0in

INTERNAL DIMENSIONS

Cabin Length (except cockpit) 63ft 9in 69ft 7in 84ft 6in 92ft 5in

Cabin Width (at armrest height) 9ft 0in 9ft 0in 9ft 0in 9ft 0in

Cabin Height 6ft 7in 6ft 7in 6ft 7in 6ft 7in

Aisle Width 19.75in 19.75in 19.75in 19.75in

Seat Width 18.25in 18.25in 18.25in 18.25in

ENGINE CHARACTERISTICS GE CF34-8E GE CF34-10E

Sea Level Flat Rating 86°F/30°C 86°F/30°C

APR Thrust - Installed 14,200lb 20,000lb

NTO Thrust - Installed 13,800lb 18,500lb

Length 121.2in/307.8cm 145.5in/369.6cm

Weight - Dry Engine 2,627lb/1,192kg 3,700lb/1,678kg

Maximum Diameter 53.4in/136cm 57in/145cm

Thrust-to-Weight Ratio 5.41 5.41

Fan Bypass Ratio 05:01 5.4:1

Noise Stage III and IV Compliant Stage III and IV Compliant


ERJ-170:


ERJ-175:


ERJ-190:


ERJ-195:


Appendix B - Ice Protection Systems

Slat Anti-Ice and Ice Detection Systems (ERJ-170 AND ERJ-190)

The slat anti-ice system is a thermal system that utilizes hot bleed air from each engine to provide thethermal energy for anti-ice purposes. Bleed air flows through the Slat Anti-Ice Valve (SAIV) and into the slatpiccolo tube via a telescoping duct. Holes in the piccolo tube cause the hot air to impinge on the inner surface of theslat, providing protection against ice accumulation. The Air Management System (AMS) controller receives signalsfrom the pressure transducers and slat skin temperature sensors, which, in turn, control the SAIV.

The slat anti-ice duct intersects the bleed line aft of the firewall connected to the SAIV located in the wingleading edge. The duct proceeds through the fixed wing to the telescopic duct. The telescopic duct connects to thepiccolo tube at Slat 2. The piccolo tube proceeds through slats 2, 3 and 4. Slat skin sensors are mounted along theslat wall in slats 2 and 4.

The anti-ice system includes a primary automatic in-flight ice detection system comprising two icedetectors located near the nose on either side of the aircraft. The location is chosen to ensure that they respond tothe icing condition in a timely manner before aircraft critical surfaces are affected. Each ice detector is directlyconnected to the Modular Avionics Unit (MAU) and to the AMS controller, in order to segregate system monitoring(MAU) and control (AMS controller).

Engine Anti-Ice System (ERJ-170 and ERJ-190)

The ice protection system is a thermal anti-ice system that utilizes hot bleed air from each engine to providethe thermal energy for the anti-ice purposes. The function of the ice protection system is to supply bleed air to heatthe inlet lip during icing conditions to prevent the hazardous formation of ice on the inlet lip. The air flow into theEAI system is controlled by an EAI valve. This valve is activated by an aircraft mounted AMS controlled automaticice detection system with a command override that is available to the flight crew. The valve is spring loaded to theopen position assuring that the EAI system defaults to the open position in the absence of a control signal (electricalsystems failure). Pressure sensors, pressure and position switches are used for system monitoring, which isperformed by MAU.

References1Wright, W., 2005. Validation Results for LEWICE 3.0. AIAA-2005-12432Strapp, J.W., Oldenburg, J., Ide, R., Lilie, L., Bacic, S., Vukovic, Z., Oleskiw, M., Miller, D., Emery, E., Leone, G., 2003:

Wind Tunnel Measurements of the Response of Hot-Wire Liquid Water Content Instruments to Large Droplets. J. Atmos. andOceanic Tech., 20, 791-806

3Bernstein, B.C. and F. McDonough. An Inferred Icing Climatology - Part II: Applying a Version of IIDA to 14-years ofCoincident Soundings and Surface Observations. Preprints, 10th Conference on Aviation, Range and Aerospace Meteorology,Portland OR, 13-17 May, Amer. Meteor. Soc., Boston, 2002, pp. J21-J24.

4Bernstein, B.C., 2005: An inferred European climatology of icing conditions, including supercooled large droplets.FAA/DOT AR-05/24. Federal Aviation Administration Technical Report. Available from the National Technical InformationService (NTIS), Springfield, Virginia.

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