This is from the Charter thread, posted by Basil. Read senario 3.
Quote:
Originally Posted by
~~~^~~~ 
What I'm really wondering, is can you get the TR handle up and in use, while the TR are actually stowed because the squat switch is damaged resulting in a false aircraft in flight signal.
If I read your question correctly, the answer is yes and no depending on the
order of events. Keep in mind that the LR-60 requires that BOTH squat switches must be in the ground mode and both thrust levers must be at idle in order to ARM the T/Rs. When BOTH Thrust Reversers indicate that they are DEPLOYED, a solenoid actuated balk in the thrust lever quadrant is released and the piggybacks are free to move fullly aft beyond the idle position and command additional thrust from the FADEC.
Scenario #1 (all LR-60s)
-Aircraft on ground
-Squat Switch (either or both) damaged and now in air mode
-Thrust Levers to Idle
-No ARM for either T/R
-Piggybacks could be moved slightly aft to idle deploy position but no farther due to solenoid balk
-No movement of T/Rs and no thrust increase
Scenario #2 (pre s/n 276 and no SB 60-78-7)
-Aircraft on ground
-Thrust Levers to Idle
-Both T/Rs ARM
-Piggybacks to
Idle Deploy
-FADEC moves N1 Bugs to limit
available N1 based airspeed, etc
-T/Rs deploy
-Solenoid Balk released
-Squat Switch damaged=Air Mode
-T/Rs Autostow, FADEC commands Idle regardless of Thrust Lever or Piggyback position
-Solenoid Balk re-engaged
-after T/Rs stow, FADEC positions N1 bugs to Max Takeoff N1
-During the entire sequence, Thrust was at Idle because the piggybacks were never pulled aft of the idle deploy position
Scenario #3 (pre s/n 276 and no SB 60-78-7)
-Aircraft on ground
-Thrust Levers-Idle
-Both T/Rs ARM
-Piggybacks pulled to Idle Deploy
-FADEC repositions N1 bugs to Reverse schedule
-T/Rs Deploy
-Solenoid Balk Release
-Piggybacks pulled fully aft (beyond balk)
-Thrust increases to max reverse allowed by FADEC
-Squat Switch damaged=Air mode
-FADEC commands Idle and T/Rs autostow
-Engines reduce thrust to idle
-Solenoid Balk re-engages,
but piggybacks are already aft of balk
-After T/Rs stow, FADEC repositions N1 bugs to computed Takeoff N1.
-
Engines accelerate toward Takeoff N1, though may not actually achieve it. I suspect that you could expect around 90% N1. Note the the FADEC cannot distinguish between Thrust Lever versus Piggyback movement. The FADEC receives an input from a rotary switch in the thrust lever quadrant which is moved by both the thrust lever and piggybacks.
Scenario #4 (s/n 276-ish and up or aircraft with SB 60-78-7 [includes N999LJ based on s/n])
-Aircraft on ground
-Thrust Levers-Idle
-Both T/Rs ARM
-Piggybacks pulled to Idle Deploy
-FADEC repositions N1 bugs to Reverse schedule
-T/Rs Deploy
-Solenoid Balk Release
-Piggybacks pulled fully aft (beyond balk)
-Thrust increases to max reverse allowed by FADEC
-Squat Switch damaged=Air mode
-Thrust Reversers are receiving an input from wheel speed detect box (originally used for Autospoilers) and disregard the squat switch air mode input, thereby remaining deployed. This was a result of the N1DC accident in which the T/Rs stowed after the aircraft struck deer on rwy and damaged squat switch, creating a "scenario #3" event.
I think that what doomed N999LJ was that somehow the wheels locked up, thereby nullifying the protection that the wheel speed detect box provides to the T/Rs to prevent on-ground autostow when the wheels are spinning. This lockup could have been caused by the loss of antiskid associated with the failure of a squat switch or the loss of antiskid from use of emergency brakes. This would effectively make N999LJ a "Scenario #3" aircraft.
