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

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

  1. Peter Corran says:

    It always amazes me why, in this century especially, any commercial aircraft can be allowed to take off with defective sensors, pitot tubes, fuel quantities, C of G discrepancies etc etc. There are checks and balances for every situation, either electronic or manual/visual, and yet the most common cause of an accident is human error, one way or the other. Lack of proper maintenance supervision is probably the most frequent error, but the pre-flight checks are so critical.

    I still maintain that commercial aircraft should be fitted with a multi-chute pod on top of the fuselage so that, in the case of non-fire in-flight emergencies, the chutes can be deployed to allow a survivable descent.
    One day, perhaps.

  2. F/E Koblan Alsakarneh says:

    I follow up on the 2 man crew air planes accidents with regret and deep sorrow . an airplane with flight engineer would never depart with the pitot/static tubes or the AOA or any other sensors still masked , or may be having the landing gear locking pins still installed. From experience it always has been common to be found by flight crew those items and many others like having the fuel not distributed in the proper tanks or having some sytems placed on test mode . specially when the airplane is released by the hangar rather than the line maintenance staff.
    Its to be mentioned here that few fatal accidents involving 2 man crew airplanes specially when electrical smoke or fire was the cause of the emergency , with a third crew member on board the accident would have been avoidable.
    Wishing every body all the best and happy flying

  3. firouzi says:

    The world of temporary economic minded ,several years ago concluded with one extra person in the cockpit called flight engineer and omitted this seat to increase the version of ACFT.
    I have the experience of flying with B-737,707,747,tu-154.i used to feel more safe with flts of 3 man crew rather than B-737 (2 man crew).if you compare the expenses of loss of lives ,material,property
    during past several years of 2 man crew ,regarding causes of accidents with respect to 3 man crew,hopefully you will become aware that engineering job has been sacrificed and victimized.pilots normally do not think of elec,hyd ,pressurization etc.just app&dep is at the back of their minds.systems are forgotten as flying hours increase.thanks for your full consideration.

  4. As I understand it, the aircraft took off with AOA sensors that had water in them which subsequently froze. The water became lodged in the sensors following a wash which did not protect the sensors from the water (although protecting them may not have been part of the process)

    I seriously doubt a flight engineer would have spotted anything like this on a walk-around as the water was inside the sensors.

    As to 3 crew being better than 2 – yes, a good case can be made for this. However, 3 person crews (and more) have certainly caused their own fair share of accidents (eg: the L1011 crash in the Everglades when everyone on the flight deck became fixated on a faulty bulb and forgot to fly the aircraft). More analysis of the stats is required (flights & flight hours vs accidents by number of crew) to determine whether having an FE on board would reduce the number of accidents.

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