PPRuNe Forums - B767300ER HDG question

Yes.

But if your APU is running the big black generator attached to it will be supplying full ships AC power no problem! That's pretty much the reason the APU is there. (i.e back-up elec source - not back up pnuematics - as APU pnuematics are only good up to approx 20,000ft) APU and gen are fully certified up to aircraft ceiling height.

From the Manual:-

The airborne auxiliary power system supplies electrical and
pneumatic power for the airplane. On the ground electrical and
pneumatic power are available to make the airplane independent of
ground support equipment. Pneumatic power is available in flight up
to approximately 18,000 feet. Electrical power is available in flight at
any altitude. The APU can be started up to the aircraft’s ceiling.

Spanner Turner
:ok:

Also from the Manual:-

The hydraulic motor generator system provides a non-time limited
5kva backup power source, both AC and DC after a loss of all
normal generator electrical power (both main AC power buses
de-powered).

System Description
The single hydraulic motor generator (HMG) is located in the left
wheel well. The generator is driven by a hydraulic motor supplied
from the center hydraulic system. The center hydraulic system is
pressurize by the air-driven hydraulic pump (ADP), supplied by left,
right engine bleed air or APU bleed air. A motor driven hydraulic
shutoff valve provides on/off control for the HMG.
Automatic activation of the hydraulic motor generator system occurs
with loss of power to both main ac buses and air mode sensed . A
flow limiter regulates hydraulic flow to the trailing edge flaps and
leading edge slats during HMG operation.
Control and protection functions are performed by the generator
control unit located in the P65 panel. The AC Bus Sensing Relays
and the Bus Transfer Relays are also located in the P65 panel.