force (torque) of boeing autothrottle servos

[strix]

Hi,

How much manual force would be required to override the autothrottle servos, and how does that compare with when autothrottle is inactive? (Boeing only of course, AFAIK Airbus treats the throttle position as a thrust limit and therefore doesn't have throttle actuators.)

I imagine that when inactive, the throttles are responsive (ie, not stiff) but not featherlight. Perhaps it varies by model, or even by unit. I'm just looking for something approximate subjective estimation - real effort required, notably stiffer than without A/T active, to not notably different at all.

I gather that the behaviour when manually overriding the commanded throttle position depends on which A/T mode is active. A/T will remain active, and the throttles will reposition them in all active modes except for THR HLD.

Any insight would be helpful. Thanks,

David.

[bcgallacher]

Boeing 747 classic autothrottle servos drive through the clutch pack which gives the normal throttle friction so there will be little difference in load if the levers are moved against the direction the A/T servos are driving the levers. Cnot comment on other types except to say that I would expect that all systems will give much the same result - not much if any incresa in load to move levers against a runaway servo.

[Jetdoc]

I dont have the AMM handy but I recall the force required to move the throttles is only about 5 pounds. We had to check it with a spring scale on the C Checks. Overriding the throttles took very little effort with the autothrottle engaged. The throttle would return to its original position when you let go of it.

[Port Strobe]

Not much difference from when the autothrottle is engaged on the 737 either, most probably a common part across most if not all types then (broken and fixing and all that eh?). Very useful to be able to do IMO, autothrottle can get a bit eager to stand the thrust levers up again when decelerating and running flap out, just lean on them to show 'em who's boss :ok: (I'd rather they err on safe side than get lazy though!)

[Henry VIII]

Overriding the throttles took very little effort with the autothrottle engaged. The throttle would return to its original position when you let go of it.Same same on 75/76.

[strix]

bcgallacher, jetdoc, port strobe, henry viii,

Many thanks for your insights (and apologies for the delay in saying so!)

@jetdoc - 5 pounds, an actual number - very useful, thanks. I tried to figure out what sort of radius that would be through. I imagine 10-12 inches.

Best,

David.

[an3_bolt]

The throttle would return to its original position when you let go of it.

.....unless of course the A/T mode has changed to HOLD whilst you have been manually hold the thrust levers - then they will stay where you left them. Example - using a FLCH descent and holding some thrust on.