An aerodynamic stall at 35,000 feet may have caused the crash of Air France Flight 447 early Monday over the Atlantic, Britain’s Times Online and other news outlets are reporting.
The theory is that the pilots slowed the Airbus A330 down too much when they encountered a storm with severe turbulence on the flight from Rio de Janeiro. This caused an aerodynamic stall — a loss of lift, not a loss of engine power — and the aircraft broke up at high altitude.
The theory is based on a warning Airbus has just sent out about maintaining sufficient air speed when flying into a storm. The Times article suggests that the warning indicates investigators have a clear idea of what happened to the jet, based on data transmitted via satellite in the final minutes of the flight.
This comes after a great deal of speculation that the cause might never be known, especially if the flight data recorder is not recovered from the bottom of the sea.
Experts maintain that despite popular notions to the contrary, storms simply don’t take down aircraft. But they can present pilots with difficult situations. In the Colgan Air crash near Buffalo, a pilot faced with icing responded by doing pretty much the opposite of what he should have, a fatal mistake.
In this case, if the theory is correct, the pilots did the right thing but to the wrong degree. It’s appropriate to slow down flying into a storm; the warning suggeests they slowed down too much.
Or did they?
Before the warning came out, Patrick Smith, Salon’s Ask the Pilot columnist, wrote a convincing column that explains how a convergence of problems could have overwhelmed the pilots:
… we are forced now to acknowledge that every so often, however seldom, normally non-dangerous phenomena turn out to be dangerous — even catastrophically so. The odds become higher when one or more of such phenomena are encountered simultaneously.
Anyone who has driven a car in a New England winter storm is familiar with this principle. A maneuver that is perfectly safe on dry pavement on a sunny, summer day can be extremely dangerous in tough winter conditions and the risk factors can multiply suddenly and catastrophically.