A320 accident crew did not notice jammed AOA probes

 - September 29, 2010, 10:56 AM

The November 2008 fatal crash of an Airbus A320 into the Mediterranean Sea off Perpignan, France, was the result of the pilots’ improvisation of procedures during an “operational flight check,” raising the crew’s workload to the point that it failed to notice that two angle-of-attack sensors were jammed, according to France’s accident investigation bureau, the BEA. The final report reveals that the two probes ingested water during a rinsing operation conducted, without proper protection, by Perpignan-based EAS Industries maintenance technicians. The water froze at altitude, causing the XL Airways crew, in the presence of an Air New Zealand pilot, to lose control of the aircraft, killing all seven on board.

XL Airways was returning the aircraft to Air New Zealand at the end of a lease agreement and Air New Zealand, which owned the A320, had requested the flight. Such “acceptance” flights, however, are not defined in any official document. The procedures the crew eventually followed were improvised from Airbus demonstration flights. Regional air traffic control rejected the crew’s request for maneuvers because it was inconsistent with the flight plan. The pilots thought they had adequately informed local ATC but conducted the checks along the lines of the flight plan.

While conducting a low-speed check during approach, the pilots did not realize some inconsistency in speed indications. The blocked probes caused the fly-by-wire airliner’s flight envelope protection system to fail. When the aircraft stalled, the pilots did not perceive that the flight control laws had switched to direct mode, and therefore did not perform the appropriate actions needed to return the aircraft to normal flight.