Start APU with EXT PWR A320

[qwsa]

Hi to all!
Just wondering... Can we start the APU on A320 with both BAT in OFF position,but EXT PWR in ON?
Any thougts are appreciated.

[deptrai]

http://www.pprune.org/engineers-technicians/487467-a320-apu.html :)

to summarize the old thread, maybe it will work, but probably it won't, and it shouldn't work. If you look at the status page with BAT OFF it says ""APU BATT START NOT AVAIL". But yes, it will have DC power via GPU, and it will spool up, but the ECB is supposed to initiate an auto shutdown, anecdotically this will happen at about 20%, ie before the APU is self-sustaining (if the BAT OFF condition is met); shutdown report in status page "no accel acft batteries not selected".

...and for the following reasons you shouldn't try this:

- IF THERE IS AN APU FIRE, THE APU FIRE-BOTTLES WILL NOT OPERATE
- THERE WILL BE NO DE-OILING OF THE APU DURING SHUT-DOWN. THIS WILL CAUSE
SMOKE IN THE CABIN
- THERE WILL BE NO COOL-DOWN SEQUENCE OF THE APU
- THE IGV WILL NOT CLOSE FULLY. THIS CAN CAUSE PROBLEMS WHEN YOU START THE
APU AGAIN.

(source: AMM)

[munster]

I have to type ten characters to post a reply, I hope this is enough!

NO!

[Cough]

Why would you want to?

Many a person has been bitten by not using SOP's where appropriate...

[tubby linton]

Deptrai can you post a page reference to your post please?

[deptrai]

49-00-00-860-003-A (APU Start by external power), subtask 49-00-00-860-060-A for the BAT caution

or 49-00-00-860-005-A / 49-00-00-860-065-B

[deptrai]

out of morbid curiosity, since this question already came up, I wondered why exactly will the APU fire extinguisher bottle not work when BAT is OFF.

According to FCOM both APU fire detection loops as well as the single APU bottle squib is powered by DC BAT; NOT DC2, HOT1, HOT2 as the engine extinguisher squibs (or DC ESS for 1 of each engine detection loops).

So, I'm thinking out loud here....BAT OFF will close the contactor from TR1 which supplies DC BAT (?), therefore no fire protection is available (you should see "INOP SYS : APU FIRE DET") and that's why the logic will initiate an auto shutdown if you try to start the APU (?), not a "normal" shutdown, but quick and dirty, in the interest of safety, hence no de-oiling, cooldown etc.

I assume Mr Airbus has put some thought into this, it makes some sense that not everything can be connected to DC ESS etc.

[Willie Nelson]

I have tried it inadvertently and , No....it does not work.
From memory it comes up with AUR EMERG SHUTDOWN, it was some time ago though.

[vilas]

Different APUs are fitted depending upon MSN of the aircraft. I am giving below from FCOM. However my experience is APU auto shuts down with batteries off,


Applicable to: MSN 0185-0249, 0264, 0384-0400, 0724
The APU may obtain power for starting from the aircraft's batteries or normal electrical system, or from ground service.

Applicable to: MSN 0138-0148, 0255, 0497-0557, 0932-0943
The APU may obtain power for starting from the aircraft's batteries alone or in combination with the external power, or from ground service.

Applicable to: MSN 0250, 0301-0335, 0440, 0758, 0976-1818
The APU may obtain power for starting from the aircraft's batteries or normal electrical system, or from ground service.