767 systems quesion

[corky]

Regarding a left pitch trim motor runaway. The Left and Center Autopilots use the left pitch trim motor. If you disable the Left Pitch trim motor with the cutout switch can L/C autopilots use the center stab trim motor or do you have to engage right ap to enable autopilot pitch trimming?

Thanks

 

[Archie Bunker]

Regarding a left pitch trim motor runaway. The Left and Center Autopilots use the left pitch trim motor. If you disable the Left Pitch trim motor with the cutout switch can L/C autopilots use the center stab trim motor or do you have to engage right ap to enable autopilot pitch trimming?

Thanks

Minor point here.....it's called stab trim, not pitch trim.

First off, when you position a stab trim cutout switch to the "cutout" position, you're not shutting off a pitch trim motor, you're shutting off hydraulic power to the respective stab trim control module.

With a single autopilot engaged, the autopilot trim will only use one stab trim motor to trim the aircraft. Under normal operations with the "Center Command" autopilot engaged, it will use the left stab trim motor. If hydraulic power were cut off to the left system, the center autopilot would automatically switch over to the center stab trim motor....this is why we normally fly around in "Center Command."

The 767 also has a system called the "Pitch Enhancement System." It automatically activates with the loss of of both left and center hydraulics. It uses a PTU powered by the right hydraulics to pressurize trapped left trim system fluid to power the stab. It trims only with electric trim, and only at 1/4 the rate.