The crew piloting a doomed Air France jet over the Atlantic did not realise the plane was in a stall, were insufficiently trained in flying manually and never informed the passengers that anything was wrong before they plunged into the sea, according to new findings.
Based on newly discovered cockpit recordings from the 2009 crash, the French air accident investigation agency is recommending mandatory training for all pilots to help them fly planes manually and handle a high-altitude stall.
The findings show that the two co-pilots were facing faulty speed readings from unreliable sensors and repeated alarm signals, but fail to explain why the pilots responded the way they did.
All 228 people, including five Britons, were killed when the Airbus 330, en route from Rio de Janeiro to Paris, crashed as thunderstorms hit over the Atlantic on June 1, 2009. It was the worst accident in Air France's history.
The French aviation investigation agency, known by its French acronym BEA, is forming a special group, including aviation experts and physiologists and psychologists, to study the pilots' possible responses to help determine why they did what they did.
The passengers were never told what was happening as Flight 447 went into an aerodynamic stall and then fell for three-and-a-half minutes into the ocean, according to the BEA.
The BEA released a 117-page report based on cockpit voice and data recordings retrieved from the ocean depths in May in an exceptionally long and costly search operation. A final report is expected in early 2012.
The report confirms that external speed sensors obstructed by ice crystals produced irregular speed readings on the plane. Since the accident, Air France has replaced the speed monitors on all its Airbus A330 and A340 aircraft.
The BEA says neither of the co-pilots at the controls had received recent training for manual aircraft handling, or had any high-altitude schooling in case of unreliable air speed readings. A stall warning sounded numerous times, and once for a full 54 seconds, but the crew made no reference to it in cockpit exchanges before the jet crashed, according to the BEA.
In a statement, Air France said there was currently no reason to question the crew's technical skills. The airline said the report showed a series of unlikely failures led up to the stall and crash. The airline also suggested the aircraft's systems and alarms may have "hindered the crew's understanding of the situation" during the stall, in comments possibly intended to shift some blame for the crash away from its pilots and on to the Airbus jet itself.