767-300 Apu

[NSEU]

Hasn't happened to me yet, but....

What would happen if you tried to start a 767 APU without fuel in the main tanks?

From my training notes for our APU:

The APU starter motor is capable of motoring the APU to about 20% rpms (electrically).
Fuel and ignition should be automatically added at approx 7% and APU acceleration monitoring begins at about 16% (As I understand it, it would take about 30 seconds (after 16%) before the APU Controller realised that there was something wrong... However, I read that there are are also flame detection circuits which, I think, will activate after about 15 seconds after 16%)).

With no fuel in the tanks I assume a FAULT light will be generated after the flame detection circuits detect no flame and that fuel (not that there is any) would be cut off at this point, but would the APU continue motoring at 20% with starter power alone, until it burnt out? (or would the starter be automatically cut out at a certain point?).

Thanks.
Rgds.
NSEU

[B73567AMT]

On the 331-200 APU (B757/B767-2/300), a "NO FLAME" shutdown would occur if there were no fuel in the tank. A "NO FLAME" shutdown occurs if :
- APU Speed is greater than 7% or more for 14 seconds
- EGT is less than 204°F (400°F)

You are correct in that the "APU Starter motor is capable of accelerating the APU without the aid of combustion up to a speed of approx 20%".

Butafter the alloted time, the "No Flame" shutdown will occur. The APU ECU will remove power from all torque motors and the APU Starter Motor. So to answer your question,...NO, the Starter motor will not continue to run until it craps out.

[NSEU]

Many thanks, B73567AMT.

I'm sure this stuff is in my notes somewhere, but I haven't found it yet (I'll keep looking). :O

Rgds.
NSEU