Re: Unjamming Gear on 747 - how?

From:         Pete Mellor <pm@csr.city.ac.uk>
Date:         08 Aug 95 02:18:25 
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>>Airliners Question ... :
>> - Is poppin-jammed-gear-by-pullin-g's an acknowledged procedure for
>>   airliners, or at all a viable RL(tm), as opposed to TV, option?

To which Loco Hombre <tanksalot@megaweb.com> (is that his real name,
I wonder? :-) replied on 28 Jul 95 02:53:19:-

> Haven't heard of any incidents lately, and strangely, don't
> recall any McDonald or Airbus aircraft doing the g pull-ups...maybe they
> aren't strong enough? <G>

Well, regarding Airbus, there are some fairly heavy A320 manoevres on
record while landing, like one 6g landing (no damage, no injuries),
and the Bangalore crash, which involved a first impact at over 6g,
and a second at around 12g. In neither case did the wings come off.
(The fate of the Bangalore A320 was sealed when it went over an earth
bank and ripped out the belly.)

Of course, it is possible that the wings might snap off more easily in
response to an upward load, but intuitively I don't find that likely.

A problem with an A320 might be that the flight envelope protections
in the Electrical Flight Control System (EFCS) would prevent you
pulling a stunt like that. I think you could probably pull a few
extra g if you switched off the two main computers in the EFCS and
went into "direct mode", however.

In the A320 FCOM, there is a procedure for gravity extension of the
landing gear, which involves using a handcrank. (Whether a bit of extra
gravity would help is not clear.) If that fails, there is a procedure
for landing with abnormal landing gear. This seems to be fairly
straightforward (cigarettes out, dump fuel, strap the passengers in
and get them braced, etc.) but includes the following wise words:-

  It is considered preferable to use all available gears locked down
  rather than carry out a belly landing.
  Under these circumstances, a hard surface runway landing is to be
  recommended. Full advantage should be taken of any foam spread on
  the runway.

--
Peter Mellor, Centre for Software Reliability,
City University, Northampton Square, London EC1V 0HB
Tel: +44 (171) 477-8422, Fax.: +44 (171) 477-8585,
E-mail (JANET): p.mellor@csr.city.ac.uk