Colgan Air 3407 crash update: auto pilot was on until upset

Posted on 15. Feb, 2009 by in Featured

According to the NTSB the Q-400 had its auto pilot on for the entire event. The stall warning and protect systems also activated. The stick shaker is the warning system; it has an aural warning and shakes the control yoke to warn of an impending stall. The stick pusher system is a protection system; it actually moves the yoke forward to reduce the angle of attack and prevent the stall.

This movement coupled with the tail ice phenomenon in the previous post no doubt caused a massive acceleration in negative g that the auto pilot would have then countered. It appears that the abrupt movement caused what is termed a departure as the angle of attack spiked. A departure is an abrupt separation of the boundary layer of airflow over the wing. The wing simply stops producing lift; it is normally violent with a rapid onset.

At that point it appears the aircraft entered a flat spin; impacting on its belly pointed the opposite direction it was headed at the start of the event (away from the runway).

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