Here's another scenario, considering the possibility that the PF caused the 31 degree pitch up. I still think this scenario unlikely but I'm considering it anyway. I've read every post in this thread over a number of days, so apologies if someone else mentioned this.
Again from Chealander's briefings, aircraft is on approach level at 2300ft, flaps at 5 degrees, anti-ice on, +20kt switch on, speed somewhere around 134kts, vref 119kts. Then one minute prior to impact, landing gear is selected, and speed either falls somewhat or pilot adjusts speed for the gear (I don't think we know this detail). Then flap 15 is selected 26 seconds after gear is selected. Then as the flaps transition to 10 degrees, the stick shaker begins, followed almost immediately by the stick pusher. For all we know, the shaker and pusher may have been triggered by a reduced speed within the additional +20kt margin, as the flaps moved towards 15 degrees.
As we know, the pilot recently transitioned from the Saab 340 to the Q400. The 340 had a tail plane stall problem, but I recall someone posted this had been corrected on the 340. Anyway, if the pilot had a ready vigilance about tail plane stall from his time on the 340, then this might explain what happened next.
If somehow, the stick shaker and pusher triggered thoughts of an icing induced tail plane stall in the pilot's mind, he may have responded to what he thought was a tail plane stall. We know the flaps were raised immediately, as they never got to 15 degrees. We know a flap deployment can cause a tail plane stall in aircraft susceptible to it, so raising the flaps would be a normal response for a tail plane stall.
When the stick pusher activated, the yoke pressures may have mimicked a tail plane stall as well. We know the low pressure area on the bottom of a stalling tail plane pulls the elevator down, resulting in a pitch down moment. This also creates light yoke forces pushing forward, and heavy stick forces pulling aft. With the stick pusher activated, this is exactly how the yoke may have felt to a pilot thinking about tail plane stall. During a tail plane stall, recovery includes pulling back against the heavy yoke force (in this case against the stick pusher) to recover the tail plane stall.
I still think the great mystery of this accident is what caused the initial 31 degree pitch up, and this scenario might explain it, if it was caused by the pilot.
Last edited by Flight Safety; 24th Feb 2009 at 12:51.
Reason: To make the language more clear.