Re: Lufthansa crash in Warsaw - Preliminary findings

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: New Large Airplane, Boeing Commercial Airplane Group
Date:         22 Oct 93 01:05:03 PDT
References:   1 2
Followups:    1
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In article <airliners.1993.655@ohare.chicago.com>,
Stefano Pagiola <spagiola@leland.Stanford.EDU> wrote:
>I'm not sure about thrust-reversing, but I remember Piedmont lost a  
>737 at Charlotte some time ago when some combination of aquaplaning  
>and floating in ground effect meant spoilers could not be deployed  
>because releasing them requires the mainwheels to be firmly on the  
>ground and to have begun turning.  Just as it makes sense (most of  
>the time) to prevent spoiler deployment in flight, it probably would  
>make sense to have similar safeguards to prevent thrust reverser  
>deployment in flight.  Can anyone confirm whether/how its actually  
>done?

[Quoting from the Airplane Systems Familiarization book - an in-house
Boeing publication]

Thrust reversers require the following to deploy:
1)  28VDC power available
2)  Engine fire switch in the normal position
3)  Airplane on ground (squat switches activated)
4)  Thrust lever in idle position
5)  Reverse thrust in the reverse idle detent position

Autospoilers require the following to deploy:
1)  Hydraulic pressure to the truck tilt indicators
2)  Both thrust levers at idle
3)  Both truck tilt sensors detect a no-tilt condition (a/p on ground)
4)  Speedbrake lever in the armed position

[End of quotes]

I can't imagine anyone using tire spin-up as an activation criterion for
autospoiler or thrust reverser operation.  Too much attention is paid to
the icy runway scenario (which is one reason that thrust reversers are
included even on the 737 where there is some concern about their
cost/benefit ratio).  Safety is of primary importance to Boeing, and I'm
quite sure, to Airbus as well.  No one benefits from an unsafe airplane.

My suggestion is to wait for more information before coming to any
conclusions about the contributing causes of the accident.  Pilot error
seems to be the primary cause given the weather.  This bears some
similarity to the Mokpo accident of a couple of months ago where the pilots
attempted three times to land in really bad weather.

Questions for Robert Dorsett:  Could the pilots high levels of experience
and presumed competence have contributed to a false sense of security
which led to an error in judgement?  If so, how can this be avoided in the
future?  Did the 'cocoon' effect of the A320 cockpit contribute to the
possible overconfidence?  

Another idle thought:  The descriptions of the weather at Warsaw seem to
match the profile for microburst activity.  Did the pilots and controllers
not recognize this, or did I miss something?

-- 
Terry
drinkard@bcstec.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."