Re: 737 musings

From:         Pete Mellor <>
Date:         19 Sep 94 12:36:23 
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Jonathan N. Deitch <> asks (19 Sep 94 01:28:39):- 

> Considering that anything can happen in a crash, can anyone explain just
> how a thrust reverser works ?

Gary L Waldman <> answered this question, but asked 
(19 Sep 94 01:28:38):- 

> Another confusing thing is the simulated reenactments of the accident
> being showed on the networks.  The graphics show a target reverser
> similar to that found on the CFM56 on an A340.  It seems possible that
> activation of some of the actuators could cause a partial thrust
> reverser deployment.  However, this is not the thrust reversing system
> on the 737 to my knowledge.

As I understand the earlier mailings on this subject, on the older 737s 
with P&W engines, the top rear part of the cowling moves back and down 
over the nozzle. This can be fun if you are sitting just behind the wing 
on your first flight in one of these. It nearly cured my constipation 
when I saw it for the first time and thought the engine was falling off! :-) 

The CFM56 engines which are fitted to the A320 have a different arrangement 
in which 4 separate doors move out of the sides of the engine. The doors 
*can* move independently, so partial reversal is theoretically possible, 
however the FADEC is programmed not to take the engine out of reverse idle 
until all 4 doors are fully extended. (Seen from the front, it would look 
like 4 petals opening up on a tulip.) 

The 737 that crashed at Pittsburgh was apparently fitted with CFM engines 
which presumably have a blocker door arrangement similar to the CFM56. 
Perhaps someone with a more thorough knowledge of airframe and engine 
types could fill in some more technical details. (Hi, Karl! :-) 

Peter Mellor, Centre for Software Reliability, 
City University, Northampton Square, London EC1V 0HB 
Tel: +44 (71) 477-8422, Fax.: +44 (71) 477-8585, 
E-mail (JANET):