Cause of crash in Buffalo (Colgan 3407) now evident

Posted on 19. Feb, 2009 by in Featured

In my last article I wrote:

“A possible explanation would be if the crew countered the pusher in accordance with the NASA procedures and caused an accelerated stall with subsequent departure and spin.”

I also said it would be some time before we really know; however I think the NTSB is making it very clear now. Initially, I went down the wrong path (tail ice/stall). However, as more information came out, it didn’t fit the tail stall scenario. First, they slowed to approach speed before putting out flaps and lowering the gear. This is not normal procedure; the flaps allow you to go slow so they are extended first and then you slow your speed. Second and the most significant to me, the initial pitch was positive, and it was at an excessive pitch rate reaching over 30 degrees nose up. Had the tail stalled the movement would have been a negative g pitch (nose down). Third the stall warnings and pusher activation. Both are for a wing stall, not a tail stall. Lastly, the aircraft impacted flat.

I think the likely sequence of events was:

-Crew distracted by icing (possibly fatigued) inadvertently got slow before extending flaps.
-The autopilot continued to trim into the pending stall, making the controls light in positive pitch.
-The crew extended gear and flaps significantly raising the drag count and further lowering the indicated airspeed.
-Rapid deceleration coupled with ice on the wing activated the stall warning and then the pusher.
-The crew having not been trained in the simulator to observe pusher characteristics (according to NTSB) misinterpreted it as a tail stall.
-Applying the NASA procedure for a tail stall they countered the pusher by pulling up. The light control resistance (trimmed in by autopilot) allowed an excessive pitch rate causing an accelerated stall and subsequent departure. Raising the flaps (in accordance with the procedure for tail stall) deepened the wing stall resulting in a flat spin.

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