Re: DC-9 Flight Control/ hydraulic systems

From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
Date:         01 Jun 96 16:27:13 
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>There are some places all four systems have to go, or else it makes no
>sense to have four.  That makes for some vulnerable places in any
>plane.  The JAL 747 lost all four when the tail blew out.
>The L-1011 lost three and the fourth was damaged on two occasions,
>where all four systems crossed the aft pressure bulkhead.

My impression had been that no more than 3 of the 4 are present in any
one portion of the aircraft.  For example, one system in the L-1011 is
located only in the aft section and does not venture forward to the
wings, while another is present only in and ahead of the wings, never
venturing back to the tail.

Obviosuly, this appears to conflict with the 747 and L-1011 incidents
you cite.  Can anyone who works on these planes clarify this matter?

>>I do not believe there has ever been a crash of a 727 due to a failure
>>of the flight controls.  The DC-10, on the other hand, has had three

>There was the Turkish Airways DC-10 out of Paris, and the UAL at Sioux
>City.  What was the third crash?

I believe he's referring to AA 191 (Chicago; 1979), though I would
disagree with that reference.  The engine separation damaged one of
the hydraulic systems, which in turn caused the leading edge slats on
the left wing, which unlike other designs lacked any sort of mechnical
lock, to retract.  The non-redundant stall warning and slat disagree-
ment systems were powered only by the engine which separated from the
airframe, and thus the pilots were not aware of the asymmetric lift,
nor of the left-wing stall, once they reduced airspeed in compliance
with AA operational procedures.  With these warning systems intact,
simulations showed that the plane was still flyable -- there was no
total hydraulic failure and the flight controls were largely intact.

He may instead be referring to AA 96 (Windsor, Ontario; 1972) which
did suffer a substantial, though not total, failure of flight controls.
However, there was no crash and there were no fatalities.

Karl Swartz	|Home
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