View Full Version : A 320 PTU question

6th Aug 2011, 10:13
What differential pressure will trigger power transfer between the yellow and green system, when A/C is on ground with parking brake set, bypass steering pin inserted and both ENG switches in same pos ?

a) 1000 psi

b) 500 psi

c)Will not operate under given conditions

John Citizen
6th Aug 2011, 10:35

FCOM 1.29.10 p1

14th Aug 2011, 09:58
FCOM 1.29.10 p1

fcom 1 no longer exist.....if my manuals are up-to-date. ( i hope ):O

Dream Land
14th Aug 2011, 10:17
Correct, it is inhibited with the parking brake set.

14th Aug 2011, 17:33
and the NWS by passed with the pin.

The reason for the AUTO logic of the PTU, when on ground, is to allow power push.

15th Aug 2011, 08:44
Hi MB2002,
The reason for the AUTO logic of the PTU, when on ground, is to allow power push.
Please explain. I don't understand why AB doesn't permit the hyds being pressurised via the PTU when the Park Brake is set.

15th Aug 2011, 09:58
For power push you need NWS to steer the airplane, so in old models you need green hydraulic power. You could get green pressure by means of the PTU with the yellow elec, if both engine master switches are in off or on, according to the logic. But as soon as you started one engine, the NWS would be lost and power push impossible, wasn't it for the fact that PARK BRK OFF and NWS NOT IN TOWING POSITION is a condition where PTU works, as well.

On ground, engines off, with parking brake released and without the pin bypassing the NWS (no NW STRG DISC memo), PTU will operate as soon as the yellow system is pressurized (when number 2 is running). Then you can initiate power push. I think the elec pump is not used for the procedure, you just start number 2 before starting the push.

I've never done this powerpush myself

16th Aug 2011, 07:01
The procedure is set out in FCOM 3.04.80 "Pushback with Power Push Unit via the Main Landing Gear".

Here's a pdf presentation with pics showing how it works in practice (see pp 9-16):

16th Aug 2011, 09:25
FCOM 3?? what's that? ;)


17th Aug 2011, 06:06
I'd go with b) - 500 psi. .... 'cause I don't believe the ptu is inhibited in that situation. :cool:

17th Aug 2011, 06:56
b) 500 psi :ok:

The key is "both ENG switches in same pos". Same position means that you only get power to the inhibition solenoid via the PTU switch or cargo door operation.
http://img691.imageshack.us/img691/8783/a320ptuinhibition.th.jpg (http://imageshack.us/photo/my-images/691/a320ptuinhibition.jpg/)

17th Aug 2011, 08:46
500 psi.

PTU will work. I've used it myself many times to move the flaps in the parking with engines not running.

The NWS pin and brakes set means it will not work if eng master switches are in different positions. With both on or off, PTU will activate

Dream Land
17th Aug 2011, 10:46
Oops, I must learn to RTFQ, yes, this is when the self test is being performed. :ugh: