744 Auto Speedbrake Curiosity
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744 Auto Speedbrake Curiosity
The 744 has a speedbrake auto restow function (like most aircraft)... That is, if the speedbrakes are extended on the ground, and the throttles are advanced for takeoff, the speedbrake will stow, c/o the speedbrake electric actuator.
Now the what-if/idiot factor...
The throttles are advanced for takeoff.. and for some reason, the pilot decides to arm or completely deploy the speedbrake after he has advanced the throttles. I tried this at the gate a few days ago (engines off, but EEC test switches on and all hydraulics on). I expected the speedbrake lever to auto-restow in this situation also... but it doesn't. The spoilers reamained in whatever position I left them in.... On the takeoff run, I would imagine the aircraft would remain well and truly on the ground.
Can't figure out why it doesn't restow (wiring schematics are not so easy to understand).
Does the 767 operate this way also or does the fly-by-wire spoiler control keep the spoilers down?
Thanks for any insight.
Rgds.
NSEU.
P.S. (Edit) Sorry, just noticed this thread....http://www.pprune.org/forums/showthread.php?t=106016 I see that the auto-restow requires the spoilers to have been automatically extended.
Now the what-if/idiot factor...
The throttles are advanced for takeoff.. and for some reason, the pilot decides to arm or completely deploy the speedbrake after he has advanced the throttles. I tried this at the gate a few days ago (engines off, but EEC test switches on and all hydraulics on). I expected the speedbrake lever to auto-restow in this situation also... but it doesn't. The spoilers reamained in whatever position I left them in.... On the takeoff run, I would imagine the aircraft would remain well and truly on the ground.
Can't figure out why it doesn't restow (wiring schematics are not so easy to understand).
Does the 767 operate this way also or does the fly-by-wire spoiler control keep the spoilers down?
Thanks for any insight.
Rgds.
NSEU.
P.S. (Edit) Sorry, just noticed this thread....http://www.pprune.org/forums/showthread.php?t=106016 I see that the auto-restow requires the spoilers to have been automatically extended.
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The answers you found on that thread, i.e. spoilers have to be automatically deployed, are correct but incomplete.
Actually, what moves the spoilers is either a motor, or your hand.
The motor will be active in the "up" direction when the main gear is on the ground, airpeed above 80 knots, spoilers' handle in "arm" position or reversers levers up. For that motor to be activated in the "down" direction, it obviously needs to have been turned in the "up" direction first....duh!
That would happen by either advancing thrust lever 1 or 3 (which are linked to the "down" channel of the motor, or after mannually placing the spoilers handle in the down detent; in fact, when you replace the handle manually after landing, even passengers in the first calss compartment can hear that motor turn.
As in the air the motor cannot be activated in the "up" direction (see reasons above), it can't obviously be activated the other way, which is why, in the air, there will me an EICAS caution message with music to tell you when spoilers are deployed with engine thrust levers out of idle, that is on 744, I dunno for the other types.
Cheers.
Actually, what moves the spoilers is either a motor, or your hand.
The motor will be active in the "up" direction when the main gear is on the ground, airpeed above 80 knots, spoilers' handle in "arm" position or reversers levers up. For that motor to be activated in the "down" direction, it obviously needs to have been turned in the "up" direction first....duh!
That would happen by either advancing thrust lever 1 or 3 (which are linked to the "down" channel of the motor, or after mannually placing the spoilers handle in the down detent; in fact, when you replace the handle manually after landing, even passengers in the first calss compartment can hear that motor turn.
As in the air the motor cannot be activated in the "up" direction (see reasons above), it can't obviously be activated the other way, which is why, in the air, there will me an EICAS caution message with music to tell you when spoilers are deployed with engine thrust levers out of idle, that is on 744, I dunno for the other types.
Cheers.
