BEA AF 44730/05/2011
The French BEA release an interim narration of newly discovered facts following the read out of the black boxes stating, that the captain had left his seat about 15 minutes prior to the last position report handing control of the aircraft to the first officer and the second officer, who were occupying the left and right hand seats and were flying at the time of the accident. The captain attended the briefing of the two officers about 11-9 minutes prior to the last position report (at 02:10Z), the pilot flying stated: "the little bit of turbulence that you just saw […] we should find the same ahead […] we’re in the cloud layer unfortunately we can’t climb much for the moment because the temperature is falling more slowly than forecast" continuing "the logon with Dakar failed". After the briefing the captain left the cockpit.
The airplane was flying at FL350 at Mach 0.82 at that time, weight was about 205 tons and the center of gravity was at 29%, well within limits
At 02:06Z the pilot flying called the cabin informing cabin crew: "in two minutes we should enter an area where it’ll move about a bit more than at the moment, you should watch out". At 02:08Z the pilot not flying suggested "you can maybe go a little to the left […]", the airplane entered a slight left turn turning off the course by about 12 degrees. Levels of turbulence increased and the crew slowed to 0.8 mach in response.
At 02:10:05Z the autopilot followed by autothrust disengaged (and remained disengaged until impact), the pilot flying said "I have controls", the airplane began to turn right and the pilot made a left nose up input. The stall warning sounded twice in a row. The recorded parameters show a sharp decrease of airspeed from about 275 knots to 60 knots indicated airspeed displayed in the left hand primary display followed by a similiar indication in the stand by instruments (the right hand speed indications are not recorded by the FDR).
At 02:10:16Z the pilot monitoring said "so, we’ve lost the speeds" followed by "alternate law […]".
The airplane's angle of attack progressively increased above 10 degrees nose up and the airplane started to climb reaching up to 7000 feet per minute of climb rate. The pilot flying made nose down inputs followed by left and right roll commands, the climb rate reduced to 700 feet per minute, the bank angles varied between 10 degrees left and 12 degrees right. The speed indication on the left primary instrument sharply increased to 215 KIAS (Mach 0.68), the airplane reached FL375, the angle of attack reduced to 4 degrees.
At 02:10:50Z the pilot monitoring repeatedly attempted to call the captain back into the cockpit.
At 02:10:51Z the stall warning sounded again. The thrust levers were placed into the TO/GA detent, and the pilot flying made nose up commands on his side stick. The angle of attack increased again through 6 degrees nose up and continued to increase, the trim went from 3 degrees to 13 degrees nose up in about one minute and remained there until impact.
About 15 seconds after the second stall warning the airspeed indicated on the standby instruments sharply increased to 185 KIAS and became consistent with the left hand speed. The pilot flying continued to make nose up inputs, the airplane reached FL380, pitch and angle of attack reached 16 degrees nose up.
At 02:11:40Z the captain entered the cockpit, at that time the indicated airspeeds became invalid (airspeeds are removed being considered invalid below 30 knots, AoA values are considered invalid below 60 KIAS) and the stall warning stopped.
The airplane at that point was at FL350, pitch did not exceed 15 degrees nose up, the angle of attack exceeded 40 degrees nose up and the descent rate had reached 10,000 feet per minute. The airplane encountered roll oscillations of up to 40 degrees of bank angles, the pilot flying made a control input to the full left and full nose up, that lasted for 30 seconds. Both co-pilots stated they had no (valid) indications.
At 02:12:02Z the thrust levers were placed into idle, the pilot flying made nose down inputs, the angle of attack reduced and the indicated airspeeds became valid again.
At 02:13:32Z the pilot flying remarked "we are going to arrive at flight level 100". About 15 seconds later inputs were recorded from both side sticks, the captain said "go ahead you have the controls".
The angle of attack remained above 35 degrees nose up.
The recordings stopped at 02:14:28Z, the last recorded values were: "10,912 feet/min descent rate, ground speed of 107 knots, pitch angle 16.2 degrees nose up, bank angle 5.3 degrees left and a magnetic heading of 270 degrees.
The BEA summarised the new findings:
- The composition of the crew was in accordance with the operator’s procedures.
- At the time of the event, the weight and balance of the airplane were within the operational limits.
- At the time of the event, the two co-pilots were seated in the cockpit and the Captain was resting. The latter returned to the cockpit about 1 min 30 after the disengagement of the autopilot.
- 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.
- After the autopilot disengagement:
* the airplane climbed to 38,000 ft,
* the stall warning was triggered and the airplane stalled,
* the inputs made by the PF were mainly nose-up,
* the descent lasted 3 min 30, during which the airplane remained stalled. The angle of attack increased and remained above 35 degrees,
* the engines were operating and always responded to crew commands.
- The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of 5.3 degrees left and a vertical speed of -10,912 ft/min.