The Air France 447 flight that crashed into the Atlantic Ocean three years ago was caused by technical failures in the cockpit and mistakes made by inadequately trained pilots.
French air accident investigator, the BEA revealed its findings into the June 1, 2009 crash in its final report, released on Thursday.
All 228 passengers on board the A330 flight from Rio de Janeiro to Paris Charles de Gaulle were killed after a chain of events triggered by ice crystals blocking the plane’s pitot tubes, which provide airspeed readings to the pilots.
The plane’s manufacturer, Airbus was aware of a problem with pitot tubes icing up on previous Airbus flights but had not taken action.
The blocked pitot tubes disconnected the autopilot – as designed to do on a fly-by-wire plane – and put the two co-pilots in control, catching them by surprise.
The captain at this point was taking a routine rest break outside the cockpit.
Unable to interpret what was happening to the aircraft, and facing inconsistent airspeed data readings, the co-pilot, Pierre-Cédric Bonin reacted by pulling back sharply on the controls.
The ‘nose up’ input from Bonin put the plane into a climb from 35,000ft to 38,000ft and rapidly slowed it down, triggering a stall warning.
It was the first of a continuous set of stall warnings that sounded for 54 seconds until the crash.
The BEA’s final report said that the crew – unsure of what flight data to trust – failed to respond to repeated stall warnings: “The crew never understood they were in a stall situation and therefore never undertook any recovery procedures.”
The standard recovery procedure for pilots is to lower the jet’s nose to gain airspeed and fly out of the stall. But Bonin, for reasons only known to him, continued to raise the nose when the plane stalled, causing it to lose more airspeed until the plane couldn’t recover.
Confusion in the cockpit
The report said that the lack of cooperation and discussion of the situation between the two co-pilots made the problem worse and added to the confusion in the cockpit.
The report said: “The investigation brought to light weaknesses in the two copilots – the inappropriate inputs by the PF (pilot flying) on the flight controls at high altitude were not noted by the PNF (pilot not flying) through an absence of effective monitoring of the flight path.
“The stall warning and the buffeting [of the aircraft] were not identified either. This was probably due to a lack of specific training.
“The copilots had not undertaken any in-flight training, at high altitude, for manual aeroplane handling.”
The crew were experienced and their training was in line with regulatory requirements, the report added.
It took 3 and a half minutes for the plane to descend 38,000 feet – hitting the Atlantic Ocean belly up and with its nose still raised.
It took almost two years for accident investigators to find and recover the flight recorders from the Atlantic.
Calls for better flight training
The BEA’s report made a series of recommendations to try and prevent this type of accident from happening again.
Among them, the report is calling for pilot training for manual flying to be improved at high altitudes, including stall recovery procedures.
The findings thrust into the spotlight concerns that modern airline pilots are too dependent on fly-by-wire technology.
An analysis after the crash led Airbus and Air France to replace its problematic pitot tubes, and the first plane was modified in May 2009, the report noted.