Originally Posted by Lyman (post#610)
At what point did 447 Stall?
In certification stall tests, an airplane is considered stalled when the buffet reaches “a magnitude and severity that is a strong and effective ‘deterrent’ to further speed reduction” (ref. FAR 25.201(d)(2)). Post-AF447 tests conducted by Airbus established “that the level of buffet was considered to be a deterrent by the test pilots when the angle of attack was about 10°, corresponding to normal acceleration amplitude of 1 g at the pilot’s seat. This angle of attack was reached at about 2 h 10 min 57 s during the accident flight.” (ref. Final report, 1.16.4.2). At the same time, the normal acceleration and lift coefficient started to decrease while the AoA continued to increase.
What is the relationship of the power ceiling, and the lift ceiling exceedances to the "climbing only due to her momentum"?
The power ceiling is the maximum altitude where the available thrust permits the airplane to maintain speed and altitude. The airplane can only exceed it by trading speed (kinetic energy) for altitude (potential energy). The lift ceiling is the maximum altitude where the airplane has a lift equal to its weight (1g) without exceeding alpha-max. At cruise altitude alpha-max is defined by buffet onset.
I have been trying to establish the cues available to the crew around the STALL.
The cues available to the crew were:
2:10:51 Begin of stall warning
2:10:53 Buffet onset
2:10:57 Deterrent buffet level reached
2:10:58 Airplane begins uncommanded rolling motions
2:11:02 Steadily increasing rate of descent while pitch attitude fluctuated around 15 degrees
2:11:32 Airplane rolls against full opposite sidestick, PF announces “no control”
2:11:45 Airplane pitches down from +15
° to –10
°, against full NU sidestick
She more or less just started to 'fall', rather than break? This suggests there was no immediate and drastic increase in drag.
The drag increased progressively with increasing AoA. Above about 9
° the drag increase was ten times steeper than below 7
°:
Time ...... AoA ..... CD
2:10:05 ... 2.3 ...... 0.020
2:10:49 ... 5.0 ...... 0.032
2:10:53 ... 7.1 ...... 0.046
2:10:57 .. 10.5 ..... 0.16
2:11:28 ... 25 ....... 0.54
2:11:37 ... 30 ....... 0.71