Originally Posted by
eaglespar
What is the difference between autothrottle being armed and off?
Reading all the entries in this topic my guess is armed means
its ready to intercept the ILS to activate the autothrottle?
Auto Throttle really has nothing to do with the ILS. A/T controls engine thrust to maintains speed, or rate of climb and descent in all phases of flight. Sometimes it will command idle thrust during a descent other times it will command thrust to satisfy the speed or vertical profile needed by the A/P or Flight Director.
The A/T Arm Switches are checked in the on position during the preliminary cockpit scan before engine start. (you never really dis-arm them except for unusual circumstances). A/T comes on during the Takeoff roll and generally stays on until after landing.
You can "click off" the A/T by pressing a button on the Thrust Lever but it remains armed and will come back on when you select a "vertical" mode on the autopilot. (Speed, or Vertical Nav, etc)
In flight, if you turn off the A/T arm switch on the glareshield, A/T will be turned off and will not come on again until you turn the A/T arm switch back on, and then select a vertical mode.
EDITED to correct some errors.