Air France pilots lost control of their Airbus A330 over the South Atlantic and spent more than three minutes apparently struggling to figure out what was wrong before the aircraft smashed into the sea, killing all aboard on June 1, 2009.
A preliminary report by French accident investigators paints a grimly disturbing picture of an undamaged aircraft with engines working, falling vertically for nearly 12 kilometres as three Air France pilots held the airliner in a nose-high attitude. While speed and other instruments gave confusing readings, the aircraft controls were working.
The disaster began about 2½ hours into the Rio de Janerio-to-Paris flight, and about nine minutes after the captain, the senior of three pilots on board, left the cockpit for a routine rest period. He designated the junior of the two first officers as the "pilot flying."
First the Air France pilots flew straight into a towering series of massive thunderstorms - the only flight that night on a South America-to-Europe route that didn't divert around the dangerous weather.
Then the speed sensors apparently failed - possibly choked by ice crystals - and the autopilot clicked off. That's a problem but hardly creates an unrecoverable emergency. It does, however, require the pilots to take control and "hand fly" the big Airbus A330, something supposedly practised routinely to keep pilots from becoming overly reliant on automation.
Instead, nose-high, the aircraft zoomed upward, reaching nearly 38,000 feet, its speed decreasing in the sudden climb, and the first of repeated "stall warnings" sounded. In aerodynamics, a stall is when airflow over the wings slows to the point where lift is lost. Recovery requires an immediate lowering of the nose.
Instead, the pilots inexplicably kept pulling back on controls, kept the nose angled up, and then - for more than three long minutes - allowed the aircraft to free fall nearly straight down until it smashed, wings level, engines racing and nose still inclined up, into the sea at nearly 200 kilometres an hour. All 228 people on board were killed.
"The inputs made by the pilot flying were mainly nose-up," the investigation preliminary timeline said, offering no explanation why an experienced, well-trained crew would seemingly do the opposite of what even the most junior pilot is taught - that when an aircraft stalls, push the nose down to regain speed.
Air France's training manual says, in bold red letters: "APPLY NOSE DOWN PITCH CONTROL TO REDUCE AOA [ANGLE OF ATTACK]rdquo; in the event of a stall.
The preliminary findings issued Friday, after investigators had studied the cockpit voice recorder and flight data recorder recovered from the sea bottom by submersibles, was significant in that it included no warnings or advice concerning the aircraft. If the flight data recorder had shown evidence of a major airframe, engine or flight-control failure, such warnings could have been expected.
"These are so far just observations, not an understanding of the events," said Jean-Paul Troadec, director of France's Bureau d'Enquêtes et d'Analyses.
The investigation seems certain to focus on crew performance, although blame isn't laid.
The resting captain returned to the cockpit part way through the descent as the two first officers struggled to regain control. The most junior handed control over to the other first officer part way down. Until the full transcript of the cockpit voice recorder is released, the interaction among the three pilots won't be known.
The AF447 crash was Air France's third major disaster in a decade - a shocking rate for a major Western airline.
In 2000, an overweight Air France Concorde blew a tire on takeoff, rupturing a fuel tank and turning the needle-nosed jet into a massive flaming dart. Despite heroic pilot efforts, the supersonic jetliner crashed, killing everyone on board. In 2005, Air France pilots forced an unstable landing at Toronto's Pearson Airport, putting the Airbus A340 down half way along a rain-slicked runway rather than "going around" for another try. The airliner ran off the end of the runway, tipped into a ravine, burned and was destroyed although everyone managed to escape.
After the AF447 loss in mid-Atlantic, an outside safety study faulted the airline's top management and pilot arrogance. "In general, there is an absence of strong safety leadership at all levels," the study said, adding pilots were elitist and treated other Air France personnel "in an autocratic and arrogant manner."
After Friday's interim report, Air France said the pilots showed a "totally professional attitude" but said nothing about whether they did the right things to regain control.
"The crew, made up of three skilled pilots, demonstrated a totally professional attitude and were committed to carrying out their task to the very end, and Air France wishes to pay tribute to them," Air France said in a statement.