MD-11 slat extension

From:         rdd@cactus.org (Robert Dorsett)
Date:         06 Aug 93 02:53:40 PDT
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The August 1993 Airline Pilot (p. 19) warns pilots to watch the flap/slat 
handle on MD-11's.  This was in reference to the much-publicised incident
involving a China Eastern Airlines MD-11 on April 6, which experienced
uncommanded slat extension and a series of violent oscillations.  The plane
lost 5000', and spooked the crew enough that they made a diversion to an air
base in Alaska to inspect the airplane.

Subsequent commentary in RISKS and elsewhere speculated that the digital
cockpit in the airplane might have been responsible for the deployment.
Comments on sci.aeronautics.airliners tended to indicate that this aspect
of the flight control system was conventional in nature, however.

The article notes:

"NTSB cautioned, in its safety recommendation issued June 29, that 'The
cause of the slat deployment has not been determined  However, preliminary
evidence strongly suggests that the flap/slat handle became dislodged from the
slat-retract position... because of inadvertent contact with the handle
by a flightcrew member.'

"At least 10 other cases of inadvertent or uncommanded inflight slat 
deployments have occurred on MD-11's since April 1991 (!!!).  NTSB said
Douglas Aircraft Company has advised operators of those incidents, "is
aware of the continuing nature of the problem, and is... working with FAA
and MD-11 operators to redesign the [MD-11] flap/slat actuating system."

[ Snide personal note: cargo doors, anyone? ]

The article notes that the NTSB urges:

1.  That the FAA establsih an interim measure to prevent inadvertent slat 
extension.

2.  MD-11 operators to inform crews of the danger.

3.  That the revamped system be installed ASAP.

"The Safety Board said the incidents continued to occur 'despite several
attempted fixes' by Douglas.  The China Eastern Airlines airplane had been
modified to meet all Douglas service bulletins and applicable slat system
[airworthiness directives].

"The day after the first incident, [Douglas told operators about the problem]

"[...] 'Sharply striking the aft side of the handle [it is normally at the
furthest-forward position when flaps are retracted] will allow the handle
to move upward if a very light vertical force is applied,' Douglas
said.  'Normal spring and cable tensions will move the handle aft once
disengaged from the FLAP UP/SLAT RET detent and allow the slats to extend.'

"In August 1992, Douglas designed a protective cover for the zero-degree
detent gate.  FAA later mandated that air carriers use the cover."

"[...] Douglas will replace the current flap/slat handle and its cable
system with an electrically operated system designed to eliminate the cable
tension forces that bias the slat system to the extend position. [...]
The electrically operated flap/slat handle system should be available in mid-
1994; the interim system, within several months.

"Meanwhile, don't bump that flap/slat handle."

[And stay away from DC-10's and MD-11's, as a guiding philosophy in life :-). 
--rdd]





---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd