XL Airways Germany Flight 888T - Investigation

Investigation

On 30 November 2008, divers recovered the second "black box" flight recorder and a third body, unidentified at the time. Although the cockpit voice recorder was damaged, experts said that there was a good probability of recovering data from it.

In late December, French investigators attempted to retrieve data from both black boxes, but the data could not be read. Usable data from the flight recorders was later recovered at the manufacturer's facility.

The investigators' interest focused on the Air Data Inertial Reference Unit following recent similar Qantas incidents on A330s, exhibiting sudden uncommanded maneuvering (see: Qantas Flight 72). The investigation was led by the Bureau d'Enquêtes et d'Analyses pour la sécurité de l'Aviation Civile (BEA), with the participation of its counterparts from the German Federal Bureau of Aircraft Accidents Investigation (BFU), the New Zealand Transport Accident Investigation Commission (TAIC), and the United States National Transportation Safety Board (NTSB). Specialists from Airbus and from International Aero Engines (IAE), from XL Airways Germany, operator of the airplane and from Air New Zealand, the owner of the airplane, were associated with the work of the technical investigation.

Analysis of the data led to an interim finding that the crew lost control of the aircraft. While conducting a planned test of low-speed flight at low altitude, the aircraft was descending through 3000 feet on full autopilot for a go-around. Landing gear was just extended when at 15:44:30 UTC the speed dropped from 136 to 99 knots in 35 seconds. The stall warning sounded four times during violent maneuvering to regain control. By 15:46:00 the warning had silenced as the aircraft regained speed in a rapid descent, but six seconds later, at 263 knots, the aircraft had only 340 feet elevation and was 14 degrees nose down. A second later it was in the water.

In September 2010, the Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile published their final report into the accident. The primary cause was incorrect maintenance procedures which allowed water to enter the angle of attack (AOA) sensors. The water then froze in flight, rendering the sensors inoperative and thus removing the protection they provided from the aircraft's flight management system. When the crew attempted an improvised test of the AOA warning system (which was not functioning due to the blocked sensors) they reached loss of control. The crew was unaware that the AOA sensors were blocked, but they also disregarded the proper speed limits for the tests they were performing, thus reaching stall. Five safety recommendations were made.