Re: 727 deep stall (Re: tip vortices *do* exist!)

From: (Dennis Chamberlin)
Organization: Tektronix, Inc., Beaverton,  OR.
Date:         25 Mar 93 00:08:46 PST
References:   1 2
Followups:    1
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In article <airliners.1993.267@ohare.Chicago.COM> (Gregory R. Travis) writes:
>In <airliners.1993.255@ohare.Chicago.COM> (Jonathan Thornburg) writes:
>>the Salt Lake City approach path is somewhat notorious for requiring
>>rapid altitude loss.  (Indeed, one of the early B-727 deep stall crashes
>>was on such an approach, I think.)
>Do you have a reference for this crash (how about Robert or Karl?)?
Years ago the 727 accident report was published in Aviation Week. As I 
remember, they hung this one on the pilot. He had set up a high rate of 
descent inside the Final Approach Fix, and I don't recall that terrain
was mentioned as a contributing factor. Might have been a failure to 
stabilize the approach.

Anyway, one of the measures he took to get back down to the glide slope
was to retard the thrust levers below a recommended minimum setting. 
This setting exists because turbine engines (particularly turbojets, as
those installed in that 727) get sleepy at low thrust settings---they 
become very slow to respond to throttle changes. One reason is that 
automatic fuel controls are acting to keep from cooking the turbine.

This in turn is one reason that landing jets have to hang out all sorts 
of drag-generating laundry to keep approach speeds reasonable while the
engines are still pushing.

The pilot finally caught the glide slope in close to the airport. When
he pushed the levers forward to check the descent rate, almost nothing
happened until too late. Result:

   "Failure to arrive at the airport prior to arrival at the ground." 

If a stall or deep stall was mentioned, it was only as a terminal effect
of the previous actions.