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ASN Wikibase Occurrence # 171411
Last updated: 22 July 2017
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Type:Silhouette image of generic A321 model; specific model in this crash may look slightly different
Airbus A321-231
Registration: D-AIDP
C/n / msn: 5049
Fatalities:Fatalities: 0 / Occupants: 109
Other fatalities:0
Airplane damage: None
Location:12 NM NE of Pamplona -   Spain
Phase: En route
Nature:International Scheduled Passenger
Departure airport:Bilbao Airport (BIO/LEBB)
Destination airport:München-Franz Josef Strauss Airport (MUC/EDDM)
The incident occurred on November 5, 2014. Lufthansa flight LH1829 departed Bilbao Airport at 07:48 hours local time with 109 passengers on board. The first officer was Pilot Flying. It was raining at the time of departure. Information from the Flight Data Recorder indicates that at 07:56 the Angle of Attack (AOA) sensor nr. 1 remained at a constant value of 4.2°. One minute later the value of AOA sensor nr.2 remained at 4.6°.
At 08:03 the flight was cleared to head directly to the LATEK waypoint and the airplane changed course. At this time the captain noticed that the Alpha Protection Bands on the Primary Flight Display increased abnormally. The first officer then reduced the climb rate with the Vertical Speed selector of the autopilot from about 800 ft/min to 500 ft/min to give the aircraft the ability to accelerate.
Shortly thereafter, the first officer switched off the autopilot and gave a brief sidestick control input to reduce the pitch of the aircraft. The nose of the aircraft lowered further, and the co-pilot pulled on the sidestick in order to raise the nose again. However, the aircraft did not seem to respond. Approximately 45 seconds after turning off the autopilot the first officer mentioned the limited response of the aircraft to the control inputs, and then the captain took over control of the aircraft.
At this time the airplane was in a descent at a rate of about 4000 ft/min and a pitch of -3.5°. The commander made a maximum rearward sidestick input, whereupon the aircraft nose raised again, the descent rate was reduced and the aircraft went back to level flight. The aircraft had lost about 4000 feet during the event.
The flight was then continued at FL270. The captain had to make a continuous rearward side stick input of more than 50% of the maximum possible in order to maintain altitude. The autopilot failed to engage and it was no longer possible to manually trim nose-up. The crew was convinced that the indicated airspeed was correct after checking the Quick Reference Handbook (QRH). Subsequently they decided to restart Flight Augmentation Computers (FAC) 1 and 2. This had no effect on their situation.
At 08:11 the crew contacted the maintenance department of the airline. After exchanging information, the technician suggested to switch off the nr.3 Air Data Reference unit (ADR). This did not help either. At 08:52 the technician sent a message, stating the possibility that both AOA sensors 1 and 2 could have been frozen, thus remaining stuck at an incorrect (too high) angle of attack. It was decided to switch off the nr.2 Air Data Reference unit (ADR). This changed the flight control system to 'Alternate Law' but sidestick inputs were no longer necessary to maintain altitude. Also, the autopilot and autotrim were working again.
The crew decided to continue flight to Munich were a safe landing was made at 09:49 hours.

The incident occurred over Spain, however the Spanish investigation committee CIAIAC handed over the investigation to Germany. The BFU reported that AOA sensor 1 and 2 were frozen while the aircraft was climbing to FL195 with an outside air temperature of -35°C. Both sensors remained stuck until the descent into Munich was started.

When the crew disengaged the autopilot at 08:03, AlphaProt became active. AlphaProt protects the aircraft from an excessive angle of attack. Depending on the Mach number and angle of attack (as reported by the AOA sensors), the AlphaProt can activate. In this case the aircraft was flying at Mach 0.675 and the AlphaProt limit was 4.2°. Since the AOA sensors incorrectly reported a value of 4.5°, AlphaProt activated. AlphaProt disabled the (manual) trim and lowered the airplane's pitch. The third AOA sensor, operating correctly, now started showing conflicting values, and the flight computer disregarded this value as incorrect since it was programmed to consider two similar values as the correct values.

Following this occurrence EASA issued Emergency Airwothiness Direcive AD 2014-0266-E_1 to introduce a new flight crew procedure.



Selection of FDR parameters (BFU)

Revision history:

18-Nov-2014 20:14 harro Added
29-Dec-2014 13:11 Aerossurance Updated [Time, Source, Narrative]
25-Mar-2015 10:04 harro Updated [Source, Narrative]
25-Mar-2015 10:26 harro Updated [Location]
25-Mar-2015 12:29 harro Updated [Narrative, Photo, ]

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