A320 Family/ Evolution Of Ground Spoiler Logic

Stéphane BOISSENINElisabeth SALAVYEngineer, Handling QualitiesEngineeringEngineer, Flight Control SystemsEngineeringA320 Family/Evolution of groundspoiler logic2. Current groundspoiler extensionconditions1. IntroductionGround spoilers reduce the liftproduced by the wings and hencetransfer the weight of the aircraftto the landing gear, allowinga more effective wheel brakingaction.Their non or untimely extensionhas been a factor in the followingtypes of A320 Family events:q The absence of spoiler exten-sion contributed to increase thestopping distance during landing.q The untimely spoiler extension2.1. Full extensionDepending on whether the groundspoilers have been armed or not, thefollowing conditions must be metfor their full automatic extension(as outlined in FCOM 1.27.10 p12):q Ground spoilers armed (fig. 1) Both main landing gears seenon ground. Both thrust levers at or belowIdle notch (fig. 2).This modification applies to thecomplete as well as to the partialground spoiler extension.It was achieved by creating anew standard of Spoiler Elevator Computer (SEC), which isin charge of spoiler control, theSEC standard 120.This article will describe:q The current ground spoilerextension conditions.contributed to a number of hardlandings.q The identified causes of run-In both cases, the cause couldbe traced back to non arming ofthe ground spoilers and/or inappropriate thrust levers positionsduring the flare.q How the new SEC standardway excursion and hard landings.will reduce the number of theseoccurrences.Figure 1Figure 2ArmedTo reduce the frequency of theseevents, Airbus has modified thespoiler extension logic.The new logic is now tolerant toinappropriate speed brake and/orthrust levers positions.Safety first #09 February 2010 - 1/5

Safetyq Ground spoilers not armed (fig. 3) Both main landing gears seenon ground. Reverse is selected on at least oneengine (the other thrust lever mustbe at or below Idle notch, fig. 4).2.2 Partial extensionThe Phased Lift Dumping functionallows the ground spoilers to deploywith a reduced deflection and servesto accelerate the full spoiler extension when landing in crosswind conditions or on contaminated runways.The necessary conditions to triggerthe partial ground spoiler extension, independently of the positionof the ground spoiler lever are:q One main landing gear seen onground.q Reverse is selected on at leastone engine (the other thrust levermust be at or below Idle notch).3. In-serviceevents3.2. Hard landingsAmong hard landings, one specificcategory has been identified whereby the hard landing occurred aftera bounce. They fit to the followingscenario (fig. 7):q e No engine throttle reduction (retard) during the flare p Noground spoiler extension.q r Bounce induced by a too highenergy level and by the lack of liftdestruction.q t Enginethrottlereductionperformed during the bouncep Ground spoiler extension ifthe retard is performed within3 seconds following the firsttouchdown.q u Severe hard landing due tosudden loss of lift leading to a fallfrom a height of about 5ft to 15 ft.It has been established that most ofthe hard landings occurring after abounce are severe.Not ArmedFigure 3Figure 4Full ground spoilerextentionThe genesis of this flight controlcomputer modification is comingfrom two types of events:Figure 5The ground spoilerswere not armedFigure 6The spoilers could notextend3.1. Longitudinal runwayexcursionRunway excursions resulted fromthe spoilers not extending duringthe landing.This was traced to the followingtwo causes:q The speed brake lever was in anon retracted position (fig. 5).q One engine throttle was not inthe area that authorized groundspoiler extension (fig. 6).2Figure 7314Safety first #09 February 2010 - 2/5

4. Expandedground spoilerextensionconditions4.1. General philosophyThe Airbus philosophy regardingthe ground spoiler activation logicis still based on the achievement ofthe following three conditions:q  Armingq  Ground detectionq  Thrust lever positionThe arming and thrust leverposition conditions have been expanded to be more tolerant to inappropriate speed brake and thrustlever positions.The ground detection condition hasbeen expanded as well, albeit onlyfor the partial ground spoiler extension, to address failures of grounddetection sensors.Figure 8Expanded groundspoiler armingcondition based onmore tolerant speedbrake lever position.Figure 9Figure 10Expanded groundspoiler extensioncondition based onmore tolerant thrustlever position4.2. Changes introduced to limitrunway excursionsThe changes introduced by the newSEC 120 standard are highlightedin bold.Complete ground spoiler extensionconditionsq Ground spoilers armed or speedbrake lever in non retracted position(fig. 8). Both main landing gears seenon ground. Both thrust levers at or belowIdle notch or Reverse is selected on at least one engine (theother thrust lever must be below the Maximum Continuous- MCT- notch).1Figure 112q  Ground spoilers not armed (fig. 9) Both main landing gears seenon ground. Reverse is selected on atleast one engine (the otherthrust lever must be below theMaximum Continuous - MCT notch, fig. 10).Partial ground spoiler extensionconditionsThe partial ground spoiler extension conditions have been expanded to mirror the full spoiler extension conditions.q Ground spoilers armed or speedbrake lever in non retracted position One main landing gear seenon ground. Both thrust levers at or belowIdle notch.q Ground spoilers not armed One main landing gear seenon ground. Reverse is selected on atleast one engine (the otherthrust lever must be below theMaximum Continuous - MCT notch).noteAll combinations that would triggerthe full ground spoiler extensionhide the partial ground spoilerextension.4.3. Changes introduced to limitbounces at landingA new spoiler extension logic isproposed on the SEC 120 to minimize the magnitude of the bouncein the event of an inappropriatethrust lever position during the flare.34Safety first #09 February 2010 - 3/5

SafetyThis logic provides some lift destruction through the partial extension of ground spoilers as soon asground conditions are detected onboth landing gears, as long as boththrust levers are at or below theClimb notch (ATHR).5. ConclusionNew ground spoiler partial extension conditions:Expansion of the ground spoilerextension conditions means thatthe spoilers will extend evenwhen the speed brake and/orthrust levers are in inappropriatepositions, thereby improving theaircraft’sdecelerationonground.q  Ground spoilers armed.q  Both main landing gears seenon ground.q  Both thrust levers at or belowthe Climb notch (ATHR).Landing scenario with SEC 120(fig. 11):q e No engine throttle reduc-tion (retard) during the flare p Noground spoiler extension.q r With the SEC 120 modifi cation, the ground spoilers willextend partially at touchdown, aslong as both engines levers are ator below the Climb notch (ATHR).Lift is decreased and the bounce isreduced or cancelled.q t As soon as the thrust leverconditions are fulfilled (for instance engine throttle reductionto Idle), the ground spoilers extend fully (if achieved within 3seconds of the initial touchdown).AnnexeHard landing effect followingbounce is reduced by 50%.Runway excursion and hardlanding events have promptedAirbus to develop a new standard of Spoiler Elevator Computer, the SEC 120.The modification proposed to reducebounce occurrences at landing has beenvalidated using a back to back approach.A dozen of major hard landingoccurrences following a bounce havebeen simulated with Airbus flightdynamics simulations tools with andwithout the partial ground spoilerextension at touchdown.Without the partial spoiler extension atthe first touchdown, the average verticalload factor at the second touchdown isabout 3.2g.With the SEC 120 modification allowingpartial ground spoiler extension onground even with thrust levers on Climb(ATHR) notch, the average load factor atthe second touchdown is reducedto about 1.7g.In addition, a new ground spoilerpartial extension logic has beendeveloped to limit bounces thatmay lead to hard landings.To summarize, the SEC standard120 provides means to reduce:q Runway excursions by enabling: Arming of the ground spoilers even when the speed brakelever is not retracted. Extension of the ground spoilers even with a thrustlever above the Idle position.q Hard landings by minimizing: The number and amplitude of bounces by triggeringpartial spoiler extension attouchdown even with boththrust levers in the ATHRposition.Example of typicalhard landing eventNZ F(TIME) - Vertical load factor[g]4.03.53.02.52.01.51.00.51st touch2nd touch3.57gbounce1.78g4041424344Before SEC 120454647484950SEC 120Hard landings statisticalbreakdownq u As the height of the bounceis significantly reduced, the vertical speed at the second touchdown is largely reduced as well.Computer hardwareModification numberService Bulletin numberB15047127-1198B’15085727-1201The SEC 120 will become production standard on A320 Family fromMSN 4472 on.A statistical analysis has revealed thata significant bounce (Nz 1.6g) occursin about 50% of the hard landing events.In about half of those cases (i.e. 25% ofall hard landings), the second impact isharder than the first one.More globally, the ground spoilerextension during a bounce has beenidentified as the root cause of the hardlanding in 15% to 20% of the cases.Moreover, those events also represent40% of the cases with costly issues(aircraft grounded, structural damages,landing gear changes ).Safety first #09 February 2010 - 4/5