Re: A-320 crash in Warsaw

From:         Robert Dorsett <rdd@rascal.ics.utexas.edu>
Date:         19 Oct 93 11:52:11 PDT
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In article <airliners.1993.650@ohare.Chicago.COM> adam@kurdel.harvard.edu (Adam Dobrzycki) writes:
>The plane happened to land during (or shortly after) a short, but very
>heavy rain. 

The initial DFDR analysis indicates they touched down at about 700 meters,
or 1/4 down the runway.  The normal touch-down zone is 300 meters.


>There were random gusts of wind. Some planes landed safely
>before the fatal A-320 though, and other landed later, after short
>(~30 min.) break caused by the crash.

Provided they were on the ground, I don't think the wind was particularly
relevant in this crash.  On the first day, an amateur organization in 
Germany ("Cockpit") was apparently defending the airplane against early 
suggestions that the plane had accelerated, taken off, and stalled out: in 
an unstallable airplane, windshear seems a likely culprit.  It seems they 
jumped the gun. :-)


>The plane was flown by the co-pilot (who was one of the two
>fatalities).

There were two pilots on board, a training captain and a captain who had
been returning to service after a long illness (kidney stones, apparently).
The training captain was in the right seat: the captain being re-qualified
was in the left.  He had passed his simulator tests fine.  To the best
of my knowledge, the captain has not yet made a public statement on the
crash.


>The plane touched down very far into the runway, for unknown reason
>(gust of wind? pilot error?). The plane ended up with ~700 meters of
>space to brake.

As stated, the initial touch-down area was around 700 meters.  Whether
they bounced after touch-down is open to speculation, but reports also
indicate that they were unable to deploy thrust reversers and spoilers
until 1400 meters.  This leaves just over 1400 meters to brake.  It is
an open question whether they had regular braking at this point.


>Now we're entering the most speculative part of the whole story.
>Apparently, under normal circumstances A-320 switches the reverse
>thrust on automatically by itself, when, among other things, the
>rotation rate of wheels reaches some value. 

No, reverse thrust must be manually selected.  Safety interlocks are
required: both engine control unit channels must be active, both air/
ground switches must be in the ground position, and the thrust lever
must be in the "reverse" mode.  Only when these conditions are satisfied
are the doors unlocked.  While the doors are in transit, the FADEC will
not command mode than idle thrust.

>plane too much and waited too long for the reverse thrust to switch
>on, instead of either immediately taking off or overriding the automat
>and switching the reverse thrust on manually.

There is no way to override the reverse thrust interlocks.  For a good
reason of why not, look at the Lauda 767 crash near Thailand.  In that
case, the automatic interlocks failed, and ripped the engine off the
airplane, *without* commanded reverse thrust, apparently causing 
catastrophic airframe damage in the process.  I imagine the situation
would be some- what worse on the A320, since Airbus doesn't believe in 
"break-away" engines.


>Now another speculation: apparently, the plane left Frankfurt carrying
>fuel for the whole FRA-WAW-FRA trip, which contributed badly to
>spreading of the fire.

This is not unusual.  Fuel can be very expensive in certain areas.  


>Conclusions:
>------------
>It appears that all the following may have contributed to the crash:
>- Airplane design error. NB, is there anybody more knowledgeable than
>  me who could verify whether this whole stuff with automatic
>  switching on of the reverse thrust is true?

I'll comment on this in a separate post.


>- Pilot error: landing too far into the runway; trusting the automat
>  too much; not aborting the landing procedure in bad weather.

That appears to be the most reasonable conclusion at present.  I am
concerned about the role of the braking computers, though, in control
of both the spoilers and wheel braking.


>- Very bad weather. People keep repeating that this rain was
>  incredibly heavy. A gust of wind may be responsible for pushing the
>  plane too far into the runway.

I don't think that's likely.  On the other hand, a tailwind of any magnitude
can significantly cut down on reaction times, and can very easily 
destory a good landing.  However, it's just a contributing factor: the
decision of the pilot to continue a landing in such a case is more 
significant.


>One bizarre thing is that the flight recorder was sent to France
>(hardly an impartial country!), supposedly because it has to be read
>with the use of a special equipment...

<groan>





--
Robert Dorsett
Internet: rdd@rascal.ics.utexas.edu
UUCP: ...cs.utexas.edu!rascal.ics.utexas.edu!rdd