Report: blocked AOA sensors caused loss of control during A320 check flight

September 17, 2010

The French Bureau d’Enquêtes et d’Analyses (BEA) issued their final report of the investigation into the cause of a fatal accident involving an Airbus A320 in November 2008, citing amongst others blocked AOA sensors.

Airbus A320 D-AXLA had been leased by XL Airways Germany since May 2006. The airplane was due to be returned to its owner, Air New Zealand, on December 1, 2008. The Airbus was ferried to Perpignan (PGF), France where it underwent maintenance at EAS Industries. It was also repainted in full Air New Zealand livery. The leasing agreement specified a programme of in-flight checks to ensure the airplane was fit for purpose.

The programme of planned checks could not be performed in general air traffic, so the flight was shortened. In level flight at FL320, angle of attack sensors 1 and 2 stopped moving and their positions did not change until the end of the flight. After about an hour of flight, the aeroplane returned to the departure aerodrome airspace and the crew was cleared to carry out an ILS procedure to runway 33, followed by a go around and a departure towards Frankfurt/Main (Germany). Shortly before overflying the initial approach fix, the crew carried out the check on the angle of attack protections in normal law. They lost control of the aeroplane, which crashed into the sea killing all seven on board.

BEA concluded that the accident was caused by the loss of control of the aeroplane by the crew following the improvised demonstration of the functioning of the angle of attack protections, while the blockage of the angle of attack sensors made it impossible for these protections to trigger.
The crew was not aware of the blockage of the angle of attack sensors. They did not take into account the speeds mentioned in the programme of checks available to them and consequently did not stop the demonstration before the stall.

ˆˆThe following factors contributed to the accident:

  • The decision to carry out the demonstration at a low height;
  • The crew’s management, during the thrust increase, of the strong increase in the longitudinal pitch, the crew not having identified the pitch-up stop position of the horizontal stabiliser nor acted on the trim wheel to correct it, nor reduced engine thrust;
  • The crew having to manage the conduct of the flight, follow the programme of in-flight checks, adapted during the flight, and the preparation of the following stage, which greatly increased the work load and led the crew to improvise according to the constraints encountered;
  • The decision to use a flight programme developed for crews trained for test flights, which led the crew to undertake checks without knowing their aim;
  • The absence of a regulatory framework in relation to non-revenue flights in the areas of air traffic management, of operations and of operational aspects;
  • The absence of consistency in the rinsing task in the aeroplane cleaning procedure, and in particular the absence of protection of the AOA sensors, during rinsing with water of the aeroplane three days before the flight. This led to the blockage of the AOA sensors through freezing of the water that was able to penetrate inside the sensor bodies.

The following factors also probably contributed to the accident

  • Inadequate coordination between an atypical team composed of three airline pilots in the cockpit;
  • The fatigue that may have reduced the crew’s awareness of the various items of information relating to the state of the systems.

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