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Old 30th Aug 2008, 15:53
  #1311 (permalink)  
lomapaseo
 
Join Date: Mar 2002
Location: Florida
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Regarding inadvertent thrust reverser deployment.

Lots of considerations have been taken in both the design phase and the certification phase.

For aircraft where the reverser efflux can wash over the wing and destroy pilot commanded roll recovery capability, it is essential that the effulx be diminished ASAP, since it is likely that the aircraft will roll in-flight into the dragging engine. The upset sequence in some flight regimes (high speed climb) is faster than most pilots can interrupt thus the available FADEC instant electronic response steps in. Unfortunately the engine spool down rate and thrust loss can not be instant enough due to inertia and aero issues in the engine itself so only fast thinking and correct interpretation by the crew can easily recover.

An extra layer of safety was then added ,after Lauda by informing the pilots of this behavior and training them to anticipate an inadvertent deployment when one barrier to deployment is activated (reverser light unlock). Even then we have had at least one instance following Lauda where a crew only took temporary action to pull back the engine where upon they readvanced the throttle and the reverser deployed flipping the aircraft on its back (they continued the roll 360 deg.and recovered the flight)

However in the case of aft mounted engines this threat does not exist and much more time is available to recover the aircraft from an inadvertent deployment through normal stick-n-rudder skills.

Now considering warning lights inhibition on any aircraft after V1 and below 400-1000ft. This is done based on human factor learning where it was learned that even precautionary light activation, including electrical malfunctions, were likey to lead to quick but unnecessary actions by the crew to abort flights, overrun the airfield, and by themselves create the circumstances for an accident. Taking into account that most failures of engine symptoms at this flight regime are accomodated by normally skilled crews it was decided that we could save more lives by inhibiting warnings in this flight regime.

I realize that many SLF reading this thread will wring their hands and damm the engineers but I can assure you that this has passed the test of time and been validated by the certification authorities.

Now if you want to more closely examine the "what-ifs" of this specific accident in this regard have at it but don't try to redesign the certification in this thread (take it to another thread)
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