Re: Peruvian 757 crash

Date:         01 Dec 96 04:08:53 
From:         Pete Mellor <pm@csr.city.ac.uk>
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jfmezei <jfmezei@videotron.ca> wrote on 25 Nov 96 06:18:50 :-

> I was once on a A320 where the pilots explained to us the PAX that the
> "computer was not cooperating" and that they had to shut it down and
> restart it from scratch and that this would take 8 minutes and that we
> would thus be leaving a bit late. I assume a good part of the 8 minutes
> was running a checklist and recalibrating stuff, correct ?
>
> Just how long does it take to reboot the computers on a plane ?

Depends which computers they were rebooting (out the 150-odd on board
an A320!).

Since it happened before take-off, I would guess it might be the set
of computers in the flight control system ("Electrical Flight Control
System" or EFCS on the A320). There are five of these, and they can
each be cycled separately by five toggle push-buttons in the overhead
panel. This is a very simple matter, and takes about one second per
button. I've seen it done on a demonstration flight. This was during
the taxi out and it was explained that this was to do with the
Load Alleviation Function (LAF), which had a tendency to misbehave
otherwise. (I never quite got to the bottom of this, but I believe
it has now been cured by a software upgrade, so that this is no
longer necessary.) There was no check following this reboot.

The EFCS has to be operational during the pre-flight check, since
it is solely responsible for moving the control surfaces, and so
would be needed during the "full and free movement" check. It is
conceivable that the crew noticed something odd during this and
decided to reboot and rerun the check, but I would have thought
this would take nothing like eight minutes.

Another possibility is that it was the Flight Management and Guidance
System (FMGS) group of boxes. I am not sure how these are rebooted.
I believe a frequent problem is that the main Flight Management and
Guidance Computer (FGMC) on the captain's side does not communicate
properly with that on the FO's side.

If (for whatever reason) they had to reboot all or part of the FMGS,
they might have had to re-enter the flight plan via the Multi-function
Control and Display Units (MCDUs). If they were using a pre-programmed
company flight plan, this would have involved locating it on the
database and down-loading it. If it was not a "standard" flight plan,
they might have had to do quite a bit of typing. Either way, I would
expect this procedure to take considerably longer than the reboot
of the EFCS (on which everything is stored in ROM).

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