A 320 PTU question
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A 320 PTU question
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
a) 1000 psi
b) 500 psi
c)Will not operate under given conditions
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Hi MB2002,
Please explain. I don't understand why AB doesn't permit the hyds being pressurised via the PTU when the Park Brake is set.
The reason for the AUTO logic of the PTU, when on ground, is to allow power push.
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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
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
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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):
http://www.smartcockpit.com/data/pdf...Procedures.pdf
Here's a pdf presentation with pics showing how it works in practice (see pp 9-16):
http://www.smartcockpit.com/data/pdf...Procedures.pdf
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b) 500 psi 
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.
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.
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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
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
