Originally Posted by
paradoxbox
But.. When you are in the air, and the reverser has deployed, for example by aerodynamic forces, or mechanical failure (parts falling off etc) - will the indicators still appear in your aircraft? Is there some kind of mechanical or electrical sensor that physically or electronically detects that the reverser door or doors are not stowed completely? Does it detect when the door is only open slightly or do the doors need to open to the stops before the sensor detects it? If the cause of the deployment is due to faulty maintenance, will the sensor (i.e. in the Airbus) still be able to detect that the door is open?
I'm only speaking for Boeing here (although I'd be surprised if they other guys are meaningfully different). The T/R translating sleeve position is monitored electronically - prox switches, L(R)VDT, or a combination there of, and works exactly the same for an uncommanded deployment in-flight as it does on the ground (one of the last words on the Lauda flight recorder was "it's deployed" - not that the knowledge helped them much).
Sounds like some aircraft have a physical link to the throttles which slams the throttle lever down. That sounds like a nasty hospital bill but certainly better than crashing. What about in the Boeings and others i.e. CRJ?
Again, speaking strictly Boeing here but would be surprised if the others are meaningfully different. There is a mechanical linkage to something called the 'strut drum box' - the position feedback to this box serves a dual purpose by preventing advancement of the throttle above idle while the T/R is in transit and moving the throttle to idle if the T/R isn't in the commanded position. FADEC eliminated the need by doing everything electronically.
IIRC, the F100 crash occurred when the T/R deployed, the crew didn't realize why the throttle retarded and were able to force it back forward (basically they managed to override the safety device). In the aftermath we were tasked to determine if was physically possible for the crew to override the strut drum box on the Boeing aircraft that used that feedback (we determined they couldn't).
EMIT, again going by memory here, but I recall for Lauda is that there was a recurring T/R feedback fault to the FADEC, unrelated to actual cause of the deployment (although the troubleshooting of that fault
might have contributed - one of the things we discovered during the investigation was the maintenance manual was junk). On the event flight, what we believed happened was the 'reverser stowed' prox sensor was slightly miss-rigged and would occasionally indicated the T/R wasn't stowed - this caused the auto-restow system to open the hydraulic isolation valve which would pull the T/R up tight, the prox sensor would indicated stowed, auto-restow would close the isolation valve. Normal vibration would then allow the T/R to move slightly, the prox sensor would indicate not-stowed and the cycle would repeat. On one of those cycles, when auto-restow opened the isolation valve - for reasons that were never firmly established - the directional control valve changed state to deploy... Whoops
The FDR was destroyed in Lauda and there was no usable data - so most of what we know is from the Voice Recorder and the non-volatile fault memory of the event engine FADEC. The FADEC was recording a T/R position feedback fault every time the T/R deployed - so there was a list of 'normal' deploy conditions - 500 ft., Mach .23, 800 ft. Mach .25, etc., then 24,000 ft. Mach .78.
The first time I looked at that fault dump was one of the darkest days of my life...