View Full Version : A320 Ptu -- Stall Margin

24th Feb 2010, 12:43
1. Why Does the Power Transfer Unit PTU runs up for few seconds after ENG start and then goes off in A320??

2. Where can you get a better stall margin .. in higher or lower altitudes ??


24th Feb 2010, 13:40

I understand the PTU does a self test for a couple of seconds during the second engine start. I'm not aware of any stall margin on the PTU.

24th Feb 2010, 15:59
Hi Captain BH,
VS1G increases with increasing altitude, thus the margin will decrease. In normal law however, high AOA prot always keeps that margin at an acceptable level (alpha prot over alpha max).

Best Regard,

24th Feb 2010, 20:37
to 1: PTU is running when the difference between Yellow and Green HYD SYS is > 500 PSI, which happens when only one ENG is started, as soon the second EDP has enough pressure ,PTU is stopping.

25th Feb 2010, 08:45
I think it is a test.

By the way
In "conventional" airplanes does the PTU have to be tested in the first flight?

25th Feb 2010, 12:30

h3dxb, It's not quite so simple as that - and FCOM doesn't give much guidance.

During the first engine start - the PTU does not run even when there's a pressure difference of 3,000 psi between Green & Yellow systems. This allows quicker start up of the engine by removing unnecessary drag from extra hydraulics. During the second engine start, the PTU is allowed to run - but it stops once the hydraulic pressure on the second engine is within the figure you quoted. So the PTU has now been tested.

MB2002. Affirm. On a previous, very sophisticated aircraft (L1011), I seem to remember we tested the ATMs (air turbine motors with a hydraulic pump) and the PTUs after engine start - and it was all described perfectly in the OPS manuals.

I've noticed in the sim, on the ground and with an engine failed - the PTU does not run when the parking brake is set! Where is that mentioned in FCOM?

25th Feb 2010, 15:46
rudderrudderrat - have a look at the fiercely confusing PTU 'and/or' TIFF at 1.29.10 P1

25th Feb 2010, 19:14
Cheers mcdhu.

With the benefit of hindsight from the last sim detail - that tiff now makes more sense. (well almost).