Initial findings from black box recorder reveal flight 447 fell 10,000ft per minute after Airbus jet hit heavy Atlantic storm
An Air France jet that crashed into the Atlantic claiming 228 lives dropped 38,000 feet (11,600 metres) in three-and-a-half minutes before slamming belly first into the ocean, according to investigators.
French air accident experts published a chilling chronology of events that showed the three Air France pilots battling to regain control on flight 447 from Rio de Janeiro to Paris in a heavy thunderstorm on the morning of 1 June 2009.
Air France acknowledged that the disaster was triggered by faulty speed sensors, with one of the pilots exclaiming "we have no valid indications" as the Airbus A330 fell at 10,000ft a minute. Moments before the crash, one of the pilots, again unnamed, reportedly shouted "Je ne comprends rien" ("I don't understand a thing").
Air safety specialists have been baffled by the loss of AF447, but the causes have become clearer since its black boxes were discovered two-and-a-half miles underwater this month.
According to the BEA, the French air accident investigation agency, one of the pilots called the cabin crew two hours and six minutes into the flight to tell them: "In two minutes we should enter an area where it'll move about a bit more than at the moment, you should watch out." Just over eight minutes later everyone on board was dead following a descent that, according to experts, none of the passengers would have noticed.
"The aeroplane probably felt more or less under control. The passengers probably would have felt their ears popping as it descended but the aircraft was held in a consistent pattern until it hit the sea," said Guy Gratton of Brunel University and a member of the Royal Aeronautical Society.
The report states that the experienced captain, Marc Dubois, 58, was resting when the Airbus began encountering difficulties, but had been present at a briefing with co-pilots David Robert, 37, and Pierre-Cedric Bonin, 32, shortly beforehand, when they discussed the turbulence ahead. The plane was flying towards a large storm system, a common obstacle on that route.
The pilot flying the plane at the time, who was not identified by the BEA, said: "The little bit of turbulence that you just saw [?] we should find the same ahead."
Two hours and 10 minutes into the flight, the computers controlling the flight switched off the autopilot after becoming confused by conflicting speed readings, caused by the icing up of pitot tubes monitoring the plane's velocity.
"There was an inconsistency between the speeds displayed on the left side and the integrated standby instrument system (ISIS). This lasted for less than one minute," the BEA document said.
Unable to calculate speed because monitors were showing an impossible drop from 275 knots to 60 knots, one of the pilots appeared to make a fatal assumption that the plane was flying too fast and was in danger of breaching "coffin corner": the narrow aerodynamic envelope that keeps a plane flying at cruise altitude.
The 37-year-old co-pilot, Robert, then suggested the plane perform a slight turn to the left, which resulted in an increase in turbulence. Two minutes later the plane's serious difficulties became clear as the report describes a flight deck that would have sounded with scores of warning signals as AF447, buffeted by stormclouds and confused by contradictory speed readings, went out of control.
The autopilot disengaged and the pilot took over the controls, uIn the middle of the night over the Atlantic and Buffeted by turbulence, he tried to lift up the plane's nose, in an apparent attempt to slow it down. The A330's stall warning sounded twice, signalling the aerodynamics were not generating enough lift and that AF447 was in danger of losing control, although its twin engines were working normally.
Experts said the pilot was receiving erroneous speed readings although one aviation source said he appeared to contravene standard procedure for a stall which is to pitch the nose down and increase engine thrust.
"You cannot call it pilot error because it may have been caused by reactions to data that was wrong," said Chris Yates, an aviation industry consultant.
At this point the co-pilot was heard saying "we've lost the speeds" and "alternate law", which signals the autopilot has been disengaged.
Seconds later the co-pilot decided to seek the help of Dubois and "tried several times to call the captain back" as another stall warning was issued. To add to the confusion, the speed readings returned to normal but the pilot kept the plane in a nose-up position, slowing it down and keeping the plane in a position where it was not generating enough lift.
By the time the Dubois appeared, just over a minute later, and as the plane began its fatal descent, another stall warning had been issued.
With the plane now rocking and falling at 10,000ft a minute, the pilot acknowledged the terrifying speed of the descent, saying "we're going to arrive at level 100", meaning 10,000ft.
At that point, just over a minute before the recordings stopped, the control sticks were used simultaneously, indicating the battle to control the plane had reached a frantic pitch. The pilot handed control to an unnamed colleague, presumed to be Dubois.
By now the "angle of attack", a critical indication of airflow over the wings, was at more than 35 degrees ? nearly triple the outer limits for safe flight.
The BEA said the plane remained stalled throughout its three-and-a-half-minute descent, with the last recorded measurement showing the plane plummeting at 10,912ft per minute. Only 51 bodies were found in the immediate aftermath. Among the dead were five Britons and three young Irish doctors.
Air France said on Fridaythe investigators should be allowed to get on with their inquiry and said its thoughts were with the families of the victims.
In a statement the airline said: "It appears that the crew followed the evolving weather conditions and had changed their route, that the failure of the speed sensors is the initial event that caused the automatic pilot to fail and a loss of the associated flying tools, that the aircraft stalled at high altitude.
"It also appears that the commander on board quickly interrupted his rest to return to the cockpit. The crew fought right to the end to control the plane which is proof of their professionalism and Air France would like to pay its respects to them."
A pilot's analysis
You look at this as an A330 pilot and it's a case of there but for the grace of God. The first sign of trouble was the expectation of turbulence voiced by the first officer. He reduced the speed in anticipation to Mach 0.82, which is normal, and warned the crew. Shortly after entering the turbulence and associated ice, the autopilot disengaged and the first officer commented that the flight control computers had disconnected. This happened because the computers were no longer receiving speed information and neither were the pilots.
I cannot speculate why the pilot climbed the aircraft but it could have been due to confusion caused by the turbulence and sudden instrument failure. The controls at very high altitude are very sensitive and there is only a very small speed envelope, often called "coffin corner", where only a few knots of speed up or down can cause a stall.
So you are flying in this little window of a flight envelope which is perfectly normal and, indeed, you do it every day. But if you are suddenly handed control of an aircraft you can breathe on that little stick and the aircraft can go down one degree. In a very short space of time lost speed and stalled, causing it to fall from the sky. Despite what the pilots must have been going through in the cockpit, the pitch attitude remained fairly constant throughout so the passengers would not have sensed something was seriously wrong. They would have felt mild buffeting of the stalled airflow over the wings and the initial sinking feeling. That's all.
I feel a lot of empathy for the pilots. One could imagine suddenly suffering a total loss of airspeed indication in turbulence in the middle of the night and with all the autopilot systems suddenly failing. The indications, both visual and aural, would have been very confusing. The question for me is why did the instruments that are triple redundant, which means that there are three back-ups, all fail together?
Anonymous A330 pilot
Source: http://www.guardian.co.uk/world/2011/may/27/air-france-crash-inquiry
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