238 J. , VOL. 33, NO. 1: ENGINEERING NOTES

Failure Detection Standards: Transport Category Airplanes, , Jan CF25 4 1 . R1994Pt , In spite of preflight test concerns, pilots readily detected all Paragraph 25.1309. 4Monagan, , d Smith"Head-U. E. J.S an ,. R , p Display Flight failures introduced durin flighe gth t tests wit sole hth e excep- Tests," Proceedings of the 24th Symposium, Society of Experimental failuresF tioAD f no , which resulte frozen di n indicators, both Test Pilots (Beverly Hills, CA), Societ f Experimentayo l Test Pilots, head-u head-downd pan design.F Thi criticisa AD s si e , th f mo Lancaster , 1980 . 75-87CA , ,pp . noHUDe th t . 5Haworth, L. A., and Newman, R. L., Test Techniques for Evalu- ating Flight Displays, NASA TM-103947, Feb. 1993. Unusual Attitude Recoveries 6Anon., Flight Test Guide for Certification of Normal, Utility, and Initial unusual attitude recoveries were performed with nav- Acrobatic Category Airplanes, Federal Aviation Administratio- nAC igation data remove dratingD fro HUDe HU m th se werTh . e 23-8, Oct. 1987. generally threes. During FA A flights, the pilots flew the un- usual attitudes with navigation data shown. The added clutter and conflicting rotational cues caused the ratings to deteriorate sevee modifies th eighr no o t wa tD leveldresulta HU s e A . th , to provide for automatic declutter during unusual attitudes. A Integrated Digital to yoke-mounted declutter button was also added. Improve Aircraft Environmental ILS Symbology Maintaining geographical orientation appear more b o est dif- Control Systems ficult with a HUD than with a head-down display. The ILS symbology used a small cross to show raw deviation and a single cue airplane to show flight director commands. Some Kenneth P. Katz* pilots reported difficult datyw ra wita e symbolhth , confusing University of Michigan, it with split cue flight director needles. Arbor,Ann Michigan 48109-2125 Choice of Pilots and combinatioe Th f tesno t pilot severad san l operational pilots Jame . OzimekL s t worked well. Generally, the two groups agreed on relative rat- Boeing Defense Spaceand Group, ings. However, operational pilots tende rato e displat d th e y Philadelphia, Pennsylvania 19142-0858 readabilit ratino handlind tw r gyan o point e gon s better than tese th t pilots. Introduction Lessons Learned NTEGRATED digital avionics technology has been an in- I novation of tremendous importance to aircraft design and f Surrogato e Us e Aircraft operations. The primary application of avionics traditionally single-engine Th e Grumman allowe inexpensivn da e screen- has been in the areas of missions systems, crew stations, and ing tool to develop HUD symbology. flight controls. More recently, aircraft utilities including envi- ronmental control, fuel, hydraulics electricad an , l power have Effec f Workloao t d also been interfaced with digital avionics. same Ath t e time, care mus takee tb n when usin gsurrogata e Ther severae ear l benefits that result from interfacing these aircraft recognizee W . d that initial Kin flightr gAi s would need utility systems with a digital avionics system. to check the dynamic response of the HUD to ensure satisfac- 1) Dedicated control displayd replacee san b n mulsca y db - tory handling using the HUD, but did not recognize that the tifunction control displaysd san eliminatioe Th . thesf no e ded- increased workload would be so dramatic for HUD functions icated components decreases weight and costs and increases such as using the checklist. reliability. The effect of workload caused by high-density air traffic was ) Automatin2 routine gth e operatio f utilitno y system- sim not anticipated. Future display evaluations should ensure that proves operational effectiveness and safety by lowering oper- representative ATC workload is present and not perform eval- ator workload. uations in a sterile environment. ) Built-i3 n test (BIT failurd )an e recording simplify main- tenance. Test Pilots vs Operational Pilots 4) Systems that are digitally interfaced can share data. The combination of two test pilots with two to four opera- Through the use of this shared data redundant measurements tional pilots seem givo t s suitabla e e combinatio f criticano l can be reduced with consequent decreases in weight and costs. evaluation and a variety of pilot background. 5) Mission reliability can be increased by dynamic reconfig- urations that retain mission capabilities, even with hardware Unusual Attitudes failures. e originaTh l flight tests taske e pilotth d s with recovering e V-2Th 2 Ospre tiltrotoa s yi r aircraft being developey db from unusual attitudes with decluttered HUDs. Whe tese nth t the team of Bell Textron and The Boeing Co. It was repeated with navigation data shown, the HUDs were sig- feature digitaa s l avionics architecture that integratee th f o l sal nificantly downrated. Futur flighD eHU t tests should conduct systeme vehicleth e f environmentao sTh . l control system unusual attitude recoveries with maximum symbol density (ECS) of the V-22 provides several examples of the benefits (i.e., minimum declutter). of integrating utility systems with digital avionics.

References Received Oct. 22, 1994; accepted for publication Aug. 11, 1995. n., "Transport Category Airplane Electronic Display Sys- Copyrigh Americae 199© tth y 5b n Institut f Aeronauticeo - As d san tems," Federal Aviation Administration AC-25-11, July 1987. tronautics, Inc l right.Al s reserved. 2Anon., "Equipment, Systems Installations,d an , " Airworthiness Technical Specialist, Mechanical Design; currently Graduate Stu- Standards: Normal, Utility, Acrobatic, Commuterand Category Air- dent, Program in Manufacturing. Senior Member AIAA. planes, 14 CFR Pt. 23, Jan. 1994, Paragraph 23.1309. tSenior Technical Specialist, Mechanical Design, Di- 3Anon., "Equipment, Systems Installations,d an , " Airworthiness vision, P.O. Box 16858, M/S P24-62. . AIRCRAFTJ : 1 ENGINEERIN . , VOLNO , 33 . G NOTES 239

Ambiant air s thei r n ai collecte e Th plenua n d i passe d man d througn ha NBC filter/coalescer before being passed through two avionics racks and the nose avionics bay. Two intake fans and two exhaust fan sr throug ai forc e avionice eth h th s bays. Pressure Surgadump and temperature switches sense AFACS failures. Eac h interfaceS subsysteEC e th sf mo wit integratee hth d avionics syste MILe bases mi th S (IASn -do IA e ) (FigTh . 2) . Oxygan-anrichad STD-1553B bus architecture. A mission computer (MC) is the flow to aircrew bus controlle d executean r s central processing with another Oxygan-daplatad actinC sparea M s ga . Remote terminal redundane th n so t MIL- flo fw uao t l systam STD-1553B buses includ vehiclthe e e management system (VMS) for flight control, cockpit management system (CMS) for contro displaysd an l , mission equipmen navigatior fo t d nan other tasks foud an ,r interface units (IU) e lUsTh . multiplex and demultiplex various analog, discrete ARIN- d se an , 9 C42 rial digital signals to interface them with the MIL-STD-1553B buses. The avionics bay interface unit (ABIU) is the IU that interfaces wit ECSe hth . Aircre maintainerd wan s operatd ean througS monitoEC CMSe e hth th r . Failures detecteT BI y db Outflowvalva are stored in the MC memory. After the completion of a flight maintainers downloa faule dth memorC t datM n ai y wite hth mission data loader (MDL). (AFACSS EC Fig 1 . , sensors ECSd an , C omitte clarity)r dfo . Features of ECS Avionics Interface Various features of the V-22 ECS and its IAS interface be- Maintain ers yond the basic control and monitoring functions illustrate the benefit f applyino s g digital avionic utilito st y systems. e utilitTh y hydraulic system pum e sams drivepi th ey b n gearbox that turn SDCe th s . During engine starts powee th , r demands of the hydraulic engine start motors require the SDC e removeloab o dt d fro gearboxe mth . Thi s automaticalli s y accomplished by the IAS. The VMS transmits to the MC that an engine start is in progress. By means of the IU, the MC commands the ECSC to de-energize the control solenoid that opens the guide vanes on the inlet of the SDC. When the solenoi s de-energizedi ceaseC dSD produco t s e compressed air. Since the V-22 wing must rotate 90 deg to its stowed po- sition to permit the aircraft to fit in the hangar deck of ships, SDC Emarg. venn tfa the compressed air from the SDC must pass through a swivel ECU AFACS fans join reaco t t remaindee hth ECSe th f , o r whic s locatehi n di NBC fitter sensors AFACS sensors Other sensors the . Rotating the wing while the swivel joint is pres- Other vah/es surized would shorte jointe th life f .nth eo Whe operatoe nth r Fig. 2 IAS with emphasis on ECS interfaces. execute a wins gs automaticalli sto C r unstowwo SD e th , y unloaded by IAS command to extend swivel joint life. e emergencTh y ventilatio providn ca n nfa efloa f freswo h System Description air to the cockpit and cabin when the SDC and ECU are not Three subsystems comprise the V-22 ECS (Fig. 1). operating. However, the emergency ventilation fan bypasses 1shaft-driveA ) n compressor (SDC poweres i ) mida y db - wern fa ee filter C useth contaminatea f n NB I di . e th d envi- wing gearbox and supplies compressed air to the ECS. The ronment, the cockpit and cabin then would be contaminated. environmental control unit (ECU) heats or cools, dehumidifles, The ECSC senses the presence or absence of the ECU NBC and filters the compressed air from the SDC. The ECU consists filter and transmits this data to the IAS. The I AS inhibits the of an air cycle machine, heat exchangers, and optional nuclear, operator from activating the emergency ventilation fan when biological, and chemical (NBC) filter. Distribution ducts, the NBC filter is installed, although this inhibition can be over- valves, and sensors control the flow of conditioned air to create ridden. This feature reduces the probability of an operator error a habitable cockpi cabid an t n environmen prese b t than - ca t that would imperi cree passengersd th lw an . surized to protect the crew and passengers against NBC agents. The diagnostic capabilities of BIT significantly reduce main- The SDC, ECU, and related components are controlled and tenance requirements by assisting troubleshooting and mini- monitored by an ECS controller (ECSC). An emergency ven- mizing maintenance-induced t onlfailuresno y T ensureBI . s tilation fan can be used to bypass the SDC and ECU. that full system operational capabilitie maintainede sar t alsi , o 2) Part of the output of the ECU is routed to an oxygen- provides informatioe th n require reconfiguro dt systee eth r mfo nitrogen concentrator (ONC), whic- h on form e core th th sf e o mission accomplishmen spitn i t f failureseo e ECSTh d . Can board inert gas generating system (OBIGGS) and on-board ONC have internal BIT capabilities, whereas AFACS uses the oxygen generating system (OBOGS)useC s ON molecu e Th . - MC to execute its BIT logic. Each subsystem has a nonintru- lar sieves to create an oxygen-enriched air supply for aircrew sive periodic BIT mode that senses failures during normal op- breathing through oxygen oxygen-depleten maska d an s r dai erations. The ECSC and ONC also have intrusive initiated BIT suppl o iner t ye ullage fue th th t l n i ecell r ballistifo s c pro- (IBIT) mode comprehensivelo st y determine their readinesr sfo tection. flight. While IBIT is in progress, it halts normal system op- 3) The avionics forced air cooling system (AFACS) intakes eration and exercises all of the components of the subsystem. ambient air and removes particulates with centrifugal filters. When conducting IBIT, the ECS ceases to supply conditioned 240 . AIRCRAFTJ : 1 ENGINEERIN . , VOLNO , 33 . G NOTES

air. This make t undesirablsi conduco et IBIS TEC t while air- envelope would result in excessively high stagnation temper- receiveS borneVM e s signalTh . s from switche landine th n so g atures in the flow. The VMS transmits the current airspeed to gear to determine if the vehicle is flying. This information is the IAS and the MC uses this data to automatically command used manr an d fo transmitte S y IA purposes e th o dt , including AFACe througf th . Wheof IU fan e d Se e n th an har fans th n so inhibitin IBIS gTEC while airborne. coolinoffe th , r passes\througgai h bypas wilC s ductsM l e Th . The means by which the CMS informs the pilots of ECS comman airspeey AFACe dan th t a f temperadi Sn fanru o t s - failures mus carefulle b t y designe conveo dt informatioe yth n ture switches in the avionics bays detect an overtemperature that they requir mako et e operational decisions without exces- condition absence th avionicn a n I .f eo s interface, eithee th r sive complication. This human interface design philosophs yi woulS EC d nee da separat e r airspeeo S EC d e sensoth r fo r known as the functional failure approach, in contrast to the else pilot workload would increase. hardware failure method that annunciates the failure of specific Two other examples als of avionic o illustrat e us se edatth a components and then forces the operator to evaluate the effects in lieu of dedicated sensors or wiring. The IAS transmits out- and operational implications of the failure. For example, the side air temperature data from the VMS to the ECSC via the woulS CM d annunciate outflow valve failure usin harde gth - IU and MC. This information is used to predict compressed ware failure metho e ECSth f di C determined thae valvth t e prevend an r temperature exposurai e U S th t EC EC e f eth o n si t responsivno s commandss it wa o et contrastn I . woulS CM ,d component excessivo t s e temperatures s availabilitIt . e th n yo failurC NB e S messag evene senEC piloe th n f th da n o ti t o et MIL-STD-1553B obviate dedicatea neee r sth d fo out S -dEC outflon a w valve failure, since this valv s requireei e th r dfo sid r temperatureai e sensor. Similarly transmitS IA e - th , am s compartment overpressurization that is part of the NBC pro- bient stati pressurr cai ECSCe th o ecombinatiot n I . n with data tection scheme. from the SDC discharge pressure sensor, the ECSC uses the r faulFo t isolation purposesmusC informee b tON e th , d that stati r pressurcai e dat monitoo at performanceC SD r . it is getting an adequate supply of compressed air from the monitorS IA e Th s temperature switche AFACe th n si n Sfa ECS to detect and isolate internal failures with BIT. The ECSC motor automaticalld an s y shutf thei fane f yth s of soverheat . dischargC SD use n a s e pressure senso determino t r e th f i e alsS oIA e monitorTh s temperature switche avionice th n i s s compressed air supply from the ECU is adequate and then bays that sense bay overheating. Since the value of the avi- transmits this informatio theS nIA I o nASt e supplie Th . s this onics greatly exceeds that of the fans, in the event of avionics informatio ONCe th o nt , eliminatin dedicateneea e r gth dfo d bay overheating wilC M l e turAFACe th , nth S fan, eveon s n ONC inlet pressure sensor. if their motors are overheated. e Ogroundforwarw nth lo t hovern a i d, d speedsan , e th , avionics cooling airflow is provided by the four AFACS fans. Summary t higA h forward speeds dynamie th , c pressur inlete th f t so ea The V-22 ECS illustrates the variety of improvements to the AFACS particle separators alone is sufficient to cool the operational effectivenes d maintainabilitan s y that result from avionics. Continuin operato gt fane ethith n si flighse parth f tto integrating utility system digitad san l avionics.