Re: Recoverable flight attitudes?

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         08 Feb 95 01:21:19 
References:   1
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>Originally I assumed, without much thought, that airliners, given a
>reasonable altitude, were, like models, recoverable from any flight
>attitude they happened to get into.  Based on the sketchy technical
>details the public gets about airliner crashes, I am starting to see
>that this may not be the case.

Keep in mind that airliners are working with far greater speeds and
weights, and thus energy levels.  I suspect most people would be
surprised at the real abilities of a modern jetliner, but you need
a *LOT* of room in which to work.

>So my question is, if an airliner somehow gets into an unusual attitude,
>say straight nose down, at a reasonable altitude, say 15,000 feet, is it
>recoverable, or is crash at that point the only possible outcome?

THY 981 (the DC-10 which crashed near Paris on March 3, 1974) was at
about that altitude, give or take a couple thousand feet at most, when
its aft cargo door blew, severing all controls to the empenage.  The
pilots tried to use a fighter trick of firewalling the (remaining)
engines to pull out of the ensuing dive without benefit of elevators,
and the investigation showed that their efforts were met with some
success.  They would have needed many more thousands of feet of
altitude to work with to have pulled it off, though.

A more recent crash, the A330 test flight crash, illustrates what an
airliner is capable of with full control authority.  At about 19.5
seconds after takeoff, the autopilot had increased pitch to 31.6
degress, at about 1700 ft. altitude and only 100 kts. airspeed.  12
seconds later, pitch was nearly -45 degrees (note the sign -- the
nose was now aimed *down*) and the aircraft had rolled 110 degrees
to the left (i.e., wings had passed vertical) with an altitude of
about 1200 ft.  In the 7.5 seconds before impact, the pilots got
the pitch back to only -15 degrees, and roll to 18 degrees left.
Clearly they might have recovered and landed safely had they had a
bit more altitude to work with.

In the case of USAir 427 (Pittsburgh), they only had about 5000 ft.
of vertical to work with (they were at about 6000 ft. when the initial
upset occurred but the ground elevation was about 1000 ft.) and had a
lot of airspeed, 190 kts. accelerating to 260 kts. at impact.  Even if
they had full control, and it seems they didn't, that doesn't leave a
whole lot of margin for figuring out what's going on then doing some-
thing about it.

>I have similar questions about the Lauda 767 on which the thrust reverser
>deployed climbing at 24,000 feet.

I've never seen a model of the thrust reverser theory (officially, no
cause was identified for that crash) but it may again have been too
little recovery time.  I think, though, the aircraft broke up in
flight, which is difficult to recover from in any aircraft.  (!)

--
Karl Swartz	|INet	kls@ohare.chicago.com
1-415/854-3409	|UUCP	uunet!decwrl!ditka!kls
		|Snail	2144 Sand Hill Rd., Menlo Park CA 94025, USA
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