Old 14th Jun 2010, 12:59
  #28 (permalink)  
Mansfield
 
Join Date: Jan 2007
Location: Vermont
Age: 63
Posts: 196
Perhaps a better way to come at this is to refer to Mad (Flt) Scientist's excellent explanation of the pusher concept back in 2007:

http://www.pprune.org/tech-log/27056...ml#post3213867

PBL, I believe the disagreement lies not with the point at which a stick pusher is triggered, but with the premise that it be interpreted as an approach to stall. The manufacturers and certification authorities intend for the pilot to interpret the stick pusher as an indication that a stall has occurred. Now, aerodynamically, the pusher may operate before the actual stall is reached, however it is defined, but this seems to me to be a technical point and not a practical one from the pilot's viewpoint.

s_bakmeijer and all: for a more representative look at these types of events in service, take a look at the following reports from the NASA Aviation Safety Reporting System:

ASRS - Aviation Safety Reporting System

376201
418260
441448
663390
665350
672119
749437

I believe you'll find three MD-80 series aircraft, and one additional that is unidentified but most likely also a DC-9 or MD-80. These provide some insight into how these types of events take place.

The major difficulty with in service stalls is that at the point of occurrence, the dynamics of the actual event and the flight crew's mental model of the situation are not aligned. Further, the behavior of the airplane in the fully stalled condition may well not be what the simulator has modeled, as PBL has said; this is particularly true of premature stalls resulting from ice accretion. The event is usually a terrifying surprise, developing very rapidly and possibly becoming somewhat violent. Pilot reactions can be surprising.

Although the response of the captain in the Buffalo accident was tragic, it was not as atypical as the Board seemed to think. In the icing accident database that I maintain, I currently have sixteen events in which I am able to document control column pull forces following a stall warning. These include AA 903 at West Palm Beach, ABX N827AX at Narrows, Virginia and a number of EMB-120 and ATR events. I am certain that none of these pilots would have done this in the simulator; but then, what they encountered in the airplane was like nothing they had ever seen in the sim.
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