Case Study 2 A320 Accident at Warsaw At 15.30 pm on 14th September 1993, a fiully serviceable A320 belonging to Deutsche Lufthansa was clear to make an approach and landing at Warsaw. By 15.35 the aircraft was a blazing wreck and two people were dead. On the face of things, this was an avoidable accident. The pertinent facts, as deduced from the accident report supplemented by a few additional calculations are attached. As members of an airline safety team, you are asked to answer the following questions:- 1) Was there any operational contribution to this accident?. Do we need to take any actioneither in training or by modifying our procedures? If so, what? 2) Was there any design contribution to this accident?. If so, what should we ask the manufacturers to do about it?. 3) Was there any maintenance contribution to this accident?. If so, what should we do about it?. N.B.:- We are NOT seeking to apportion "blame", we are looking for ways to avoid repetition of such an event. page 1 DLH 2904 A320 Accident at Warsaw Pertinent Facts taken from accident report Chronology 15.30.45 [CVR - PNF] "Lufthansa is established." Tower calls " 2904 continue ILS approach, call me outer marker, wind 160 degrees 25 km/hr and before your landing it was reported wind shear on the final runway 11' 15.31.00 [CVR - PNF] "Tower, good afternoon, Lufhansa 2904, ILS runway 11' 15 31.18 [CVR - PF] I'Wind shear 15.31.21 [CVR - PNF] " Roger that's understood, I call you outer markerll [At this point the aircraft passed through 2800 ft, CAS was recorded as 163 kts, Ground speed (GS) 180 kts] 15.31.25 [CVR - PF] IIFlaps 3 15.31.26 [CVR -PNF] " Flaps 311 15.31.26JETAVIATION 101 whichhad justlandedcalled 11,.,..., 101 isvacatingrunway 11 on taxiway E0. For information we had severe windshears on final 15 31.29 [CVR - PF] "Flaps full 15.31.30 [CV:R - PNF] IFlaps fi 15.31.31 [CVR - PNF] "Itls got to be like that, we still have 240 with 30 kts 15.31.48 [CVR - PNF] 'IAha, showers" 15.31.51 {CVR - PF3 "Showers' 15.32.11 [CVR - PNF] "Cleared to land, 11, Lufthansa 2904' 15.32.12 Tower called "2904 you are cleared to land RIW 11. Wind 160 degrees, 25 kmJhr 15.32.14 [CVR - PF] I'Still turning a lot' 15.32.16 [CVR - PNF] 1l Its got to turnll 15.32.17 [CVR - PF] IIItls got to, it can't be anything else" 15.32.23 [CVR - PNF] I'Good" There follows a series of CVR records covering landing check list/ ~ear extension and acquisition of runway on visual 15.33.00 [CVR - PF31lStill from aft 15.33.02 [CVR - PF] IIRate of descent is out of limits 15.33.03 [CVR - PNF] "Yes, 1100 feet 15.33.08 [CVR - PF] "Rain repellent pleasell 15.33.10 [CVR] - Noise of windscreen wiper 15.33.15 [CVR - ACO] Four hundred 15 33.20 [CVR - ACO] Three hundred At this time DLH 2904 passed MM at 278 ft with 147 kts CAS and 168 kts GS. continued approach with landing gear down, full flaps (35ø) manual Gontrol of thrust and aircraft flight control surfaces (autoland off? until touchdown 15.33.26 [CVR- ACO] Two hundred 15.33.29 [CVR - PNF] "From the right coming up now" 15.33 31 [CVR -PF] "Wind shear is coming up" 15.33.33 [CVR - ACO] One hundred During DLH 2904 approach to R/W 11 (113ø magnetic) a front passed over from west to east, preceding the approaching aircraft. On final approach (in area of MM), DFDR and QAR recorded temporary (15 secs) decrease of CAS to 154 kts 15.33.36 [CVR - PNF] "Turning, turning" page 2 15.33.37 [CVR - ACO] "Fifty" The aircraft passed 50 ft with 159 kts CAS, i.e about 20? kts greater than VLS recommended according to it's weight. GS was 172 kts. 15.33.39 [CVR- ACO] "Thirty" The aircraft made first contact with the runway on the right landing gear at about 770 m from the threshold. As it was recorded, the left landing gear touched the runway 9 second laterl at a distance of 1525 m from the threshold, CAS 136 kts, GS 154 kts. 15.33.40 [CVR- ACO] Retard, retard 15.33.45 [CVR ] Reverser lever noise 15.33.49 [CVR - PF] "Help me braking" At the first point of impact the pilot attempted to apply brakes and when they failed to work asked the right-seat pilot to assist. 15.33.52 [CVR - PF] "Full braking" When the left gear touched the runway the automatic systems (which on the A320 require(d) both oleos to be compressed) unlocked the use of spoilers and reverse thrust. The systems began to operate, the spoilers deployed to full angle (50ø), thrust reverser system began to work and N1 ofthe engines came to 71%, but the wheel brakes, depending on wheel rotation being equivalent of circumferential speed of 72 kts began to operate after about 4 seconds. 15.33.56 [CVR PNF] "Reverse on?" 15.33.57 [CVR - PF] "Yes fully on" 15.34.01 [CVR - PNF] "One hundred" 15.34.02 [CVR - PF] "Go on with braking" 15.34.05 [CVR - PF] "Shit" 15.34.06 [CVR - PF] "What shall we do now?" 15.34.08 [CVR - PNF] "Well you can't do anything anymore" 15.34.10 [CVR - PF] "I don't want to crash into it" 15.34.11 ~CVR - PNF] "Turn it away" 15.34.12 [CVR - PF] "Hey?" 15.34.12 [CVR - PNF] "Turn it away" 15.34.16 [CVR - PF] "Shit" 15.34.17 [CVR] Noise of crash The aircraft rolled over the end of the runway with the GS = 72 ktS and having passed next 90 m collided its left wing with the embankment and stopped right behind the embankment. In this the landing gear and left engine were destroyed. Evacuation of passengers organised by 4 persons of cabin crew in conditions of commencing aircraflc fire, contributed to rescue of 63 passengers of 64 on board. As far as 2 person cockpit crew is concerned, the left seat pilot was injured but survived, the other in the right hand seat was killed outright. Post-crash analysis (taken from Polish accident report) Weather Landing of DLH 2904 was carried out while a cold front was passing over the aerodrome area7 on the head of Cb cloud with heavy showers. A shower began at 15.28 initially as light, but the heavy one occurred in the period 15.33 to 15.41. page 3 Amount of precipitation measured at the weather station was 2 mm. Taking into account the character of the shower and the accompanying strong wind, that could decrease the amount measured, it could be taken that the real precipitation on RWY 11 could amount to 3~4 mm According to the met. office interpretation of the record the wind at the time of landing was 220ø at 101m/sec (5 kts) and in gusts the velocity came to 15 m/sec (8 kts), variable with a tendency to come nearer to west. Runway 11 at Warsaw is given as 2800 m. Runway 15 (3690m) was assigned for departures Aircraft State The landing weight was estimated as 58 tonnes and FULL configuration, for which VLS = 130 kts. [Note the confusion with 159 kts and 20 kts above VLS given earlier - 20 kts is wrong - 30 kts is also quoted later] They quote 'considerable wear of three of the four tyres of the main landing gear' [all tyres survived the firel Crew actions (conclusions of Polish report) 1. Approach a) DLH 2904 crew three times heard the warning of windshear in RWY 11 approach area b) The crew complied with only one of the recommendations given in the OAM [see later], namely they increased speed by 20 kts c) The crew switched offthe weather radar; the radar could help to evaluate the situation d) The crew did not turn to account the wind display on EFIS and did not consider the discrepancy between these data and the information on wind given by air traffic services. Neither did they take into account that the tailwind component displayed by EFIS exceeded the value defined by the OAM as acceptable for this aircraft [see later] e) The crew did not analyse whether by the increased approach speed RWY 11 would provide enough distance to enable them to suppress the increased kinetic energy of the aircraft [see later] ~ The crew used FULL flaps configuration which on this aircraft disabled the braking system until recorded touchdown [see later] 2. Flare out Because of the windshear the pilot not only inc~eased speed but also increased thrust down to a relatively low altitude. Consequently the aircraft after passing the threshold was distinctly above the ILS glide path. Throttles were moved back at 6 ~, which caused a significant extension of the flare-out. Counteracting the crosswind, the aircraft contacted the ground at 3.2ø bank, which was enough to compress that oleo. Had this not been the case ~i.e. zero bank), the oleo switch~es) would come on at a considerably greater distance . This is important in that this first contact occurred at 770 m from the threshold and the bounce of the right landing gear gave the crew the false impression that both gears had contacted the runway. Further actions of the crew confirm this assumption The crew did not draw the right conclusions from the course of flare-out phase and did not appraise their own chances in the real situation - with that speed and point of touchdown page 4 3 Touchdown Based on the aircraft weight of 58 tonnes, touchdown speed near to the earlier calculated V = 130 kts should be expected. In fact the first recorded contact occurred with CAS = 151.5 kts and GS = 170 kts Fully recorded touchdown occurred at 136 kts CAS because only by this speed had the residual lift decreased to the point that the weight of the aircraft could cause the oleo struts to close (provided nearly identical compression of both main landing gear legs is achieved) Again in this phase of flight the crew did not appraise the situation properly and attempted to brake only instead of initiating go-around 4. Rollout The remaining runway length at the moment of the recorded contact of both main landing gears with the runway surface was 1275 m Airbus A320 automatic systems (dependent on compression of oleo struts) armed all three braking systems only when the left main gear assembly contacted the runway. The systems began to operate, the spoilers deployed to full angle (50ø), thrust reverser system began to work and N1 ofthe engines came to 71%, but the wheel brakes, depending on wheel rotation being equivalent of circumferential speed of 72 kts began to operate after about 4 seconds. Rollout of the aircraft progressed in conditions of heavy rain and with a layer of water on the runway. Aquaplaning that occurred during the rollout phase considerably degraded the braking effectivity. Aircraft was decelerated according to the possibilities in actual conditions, but on the last 180 m of runway deceleration decreased by about 30%. Residual length of the runway (left from the moment when the braking systems began to work) was too small to enable the aircraft to stop on the runway. Seeing the approaching end of the runway and the obstacle behind it, the pilot nlanaged only to deviate the aircraft to the right. Aircraft began to turn (yaw) right, but the path of its centre of gravity did not bend. The aircraft rolled over the end of the runway with the GS = 72 kts and having passed next 90 m collided its left wing with the embankment and stopped right behind the embankment. In this the landing gear and le~c engine were destroyed. Landing Distance Required The Polish accident report gives a rather confusing table. The values taken from the DLH AOM are as follows:- A320 Landing Distances - metres Landing Mode Weight tonnes Dry Dry Dry Wet Wet Wet 6mm 6mm 6mm water water water Wind -10 0 20 -10 0 20 -10 0 20 58 FAR 1,740 1,540 2,000 1,770 58 MAX 1,040 860 820 1,420 1,180 1,130 1,860 1,550 1,480 58 M:ED 1,420 1,180 1,130 1,520 1,260 1,200 1,860 1,550 1,480 58 LOW 2,210 1,840 1,750 2,300 1,910 1,820 2,320 1,930 1,540 page 5 Note that the AOM does not give data for more than 10 kts tailwind, and that distances have no credit for reverse thrust. The distances used during the accident are considerably greater than those given in the AOM. This is due to the long flare, the high touchdown speed and the condition of the runway surface. Causes of the accident (from Polish report) Cause(s) of the accident were the incorrect decisions and actions of the flight crew taken in a situation when the information about windshear at the approach to the runway was received. Windshear was produced by the front just passing the aerodrome; the front was accompanied by intensive variation of wind parameters as well as by heavy rain on the aerodrome itself. Actions of the flight crew were also affected by design features of the aircraflc which limited the feasibility of applying available braking systems as well as by insufficient information in the aircraft operations manual (AOM) relating to the increase ofthe landing distance [The accident report contains several recommendations which are not repeated here as they might influence your discussionsl Aircraft Systems Design At the time of the accident, the A320 braking system comprised the following: 1 Ground spoilers If selected "ON" the ground spoilers will extend if the following "on ground" conditions are met- either oleo struts (shock absorbers) are compressed at both main landing gears ~the minimumload to compress one shock absorber being 6300 kg). Qr (intended for take-offrun) wheel speed is above 72 kts at both main gears. 2 Engine reversers If selected "ON" the engine reversers will deploy if the following "on ground" condition is met Shock absorbers are compressed at both main gears (signal from at least one LGC~U) 3 Wheel brakes The above mentioned conditions (wheel speed above 72 kts and both shock absorbers compressed) are not llsed to activate the brakes. With the primary mode of the braking system, the brakes may be used as soon as wheel speed at both landing gears is above 0.8Vo where VO is a reference speed computed by the BSCU (Brake and Steering Control Unit).This is an antiskid system operation With the alternate mode of the braking system, the brakes may be used as soon as the A/SKID - NOSE WHEEL STEERING switch has been selected to the OFF position by the crew page 6 Autobrake system - can be armed by depressing LO, MED or MAX pushbutton. - is initiated by ground spoiler extension command. Consequently in the event of an accelerate-stop, if the deceleration is initiated with the speed below 72 kts, the automatic braking will not be operative because the ground spoilers will not be extended Flight Crew Manual data The data supplied regarding landing distance is given above. Note that the aircraft is certificated for operations up to 10 kts tailwind, and no distances for wind greater than this are given in the Flight Manual. The advice given for protection against windshear is very relevant, (italics are the authors): Minimise thrust reductions. Rather than immediately compensating for an airspeed increase, a brief pause to evaluate speed trends is prudent. If a tailwind shear occurs and recovery is initiated, the additional airspeed and earlier availability of thrust (due to the engines accelerating from a higher RPM) will be advantageous.. In the absence of a tailwind shear, this procedure may result in a higher than normal approach speed which may hfave to be accounfed for on landing Use the most suitable runway that avoids the area of suspected windshear and which is compatible with crosswind and tailwind limitations. A longer runway provides the greatest margin for increased ground roll due to unanticipated winds possibly resulting in high groundspeed at touchdown. Increased airspeed on approach improves climb performance capability and reduces the potential for flight at stick shaker during recovery from an inadvertent windshear encounter. If available landing field length permits, airspeed may be increased up to a maximum of 20 kts. This increased speed should be maintained to flare. Touchdown must occur within the normal touchdown zone. Do not allow the airplane to float down the runway. As many variables are involved, it is not practical to provide exact guidance on the effect of 20 kts extra speed on actual stopping distance. Wind can be a major factor since stopping distance is affected by ground speed rather than airspeed. yincreased airspeed is used and an increasing performance shear is encountered, a go-around may be necessary due to insufficient landingf eld length for the higher approach speed. Furthermore, if a pilot can be reasonably certain that wind changes (due to topography or unique local conditions) will not result in decreasing performance, it may be inappropriate to use increased approach speed. WARNrNG: Increased touchdown speeds increase stopping distance. An additional 20 kts at touchdown can increase stopping distance by as much as 25%. [not stated, but this is for a DRY runway] page 7 Supplementary Data The information given above is taken from published reports and operating manuals. This can be supplemented by additional data based on deeper analysis of the accident report and some estimation of the aerodynamic and performance characteristics of the aircraft. This estimation is necessarily based on some assumptions that come from engineering judgement, but comparison with the known facts appears to confirm that they are reasonable. Aerodynamic lift The aerodynamic lift with FULL flaps, but with the aircraft in ground attitude (all wheels on ground, including ground ef~ect on liflc) varies with airspeed Airpeed kts EAS 90 100 110 120 136 145 152 159 162 Lift on ground f 40 deg kg 18,145 22,401 27,105 32,257 41?432 47,098 51,755 56,631 58,789 [Let us recall that the landing weight was 58 tonnes, touchdown speed 151.5 kts CAS and that the breakout force on one oleo is 6.3 tonnes] Derived Speeds We can obtain graphical presentations of the speed variations during the accident page 8 Runway Braking We can also, with some filrther assumptions, calculate the various contributions to the deceleration and maybe see what went wrong. It certainly looks from this analysis that the aircraflc was never in filll contact with the runway, and that aquaplaning was present for virtually the whole ground run. Finally, we may produce a set of 'what if ?' calculations that help us to quantify the various effects and assess their relative importance. Sequential Individual Effects Distance Speed Distance Speed Datum 2,828 m 70 kts All conditionsas present at Warsaw Remove low friction at end 2.823 m 66 kts Assume no rubber contamination in touchdown zone Calculatetofullstop 3,160 m 0 kts 3,160 m 0 kts Hypotheticalcasefor reference Remove aquaplaning 2,910 m 0 kts 2,910 m 0 kts Use CAA Reference Wet runway friction Remove autobrake delay 2,510 m 0 kts 2,745 m 0 kts Assume trigger is as on sequence A340 - one MLG+NLG Removeautohrake 2,210 m 0 kts 3,145 m 0 kts Remove limitationto 0.25 g deceleration Remove long flare float 2,105 m 0 kts 3,035 m 0 kts FCOM value of 305m Removehigh on ILS 1,985 m 0 kts 3,055 m 0 kts Assume accurateflight path control to give 50 ft at ILS 50ft point Remove excess tailwind (to 10 1,825 m 0 kts 2,955 m 0 kts In two parts; Flight kts) Manual limit is 10 kts Removeexcessairspeed(to 20 1,660 m 0 kts 2,70(} m 0 kts Intwoparts; Initial kts) approach was at Vref + 15 Remove all tailwind 1,430 m 0 kts 2,650 m 0 kts Correction towards FM Datum condition Remove all excess airspeed 1,075 m 0 kts 2,200 m 0 kts Correctiontowards FM Datum condition Remove wetmnway 920 m 0 kts m 0 kts Correctiontowards FM Datum condition Remove reversethrust 957 m 0 kts m 0 kts Correctiontowards FM Daturn condition Celtification" flare correction 810 m 0 kts m 0 kts Correctiontowards FM Datum condition FARunfactored 810 m 0 kts m 0 kts FlightManualI)atum Condition FAR factored (110.6) 1,350 m 0 kts m 0 kts Flight Manual Landing Field Length Required (Dry) FARfactored(1.15/0.6) 1,553 m 0 kts m 0 kts FlightManual Landing Field Length Required (Wet) page 10