I do not think that "all" details have to move into the FCOM.
IMHO Pilots have to know the system not in that detailed form. You have to know that the funktion of the PTU will be tested during second engine start, but is it really relevant for you, how it is done in detail? I think not. If you do not get a PTU Fault during second engine start the PTU works fine.
OK, how does the "test" work? There is no PCU (PTU Control Computer), so someone else have to do the "test".
So how can i test the PTU in the normal operation? Airbus take a situation where the PTU have to work (albeit for a short time).
Best point is the start of the second engine.
In DSC-29-10-20 you find the inhibition logic for the PTU. The inhibition is off with both engine master lever in on.
Hydraulic situation before the second start:
- one engine running and EDP pressurize related system (B or Y system)
- other hydraulic system is depressurized
- PTU pb in auto
- PTU did not run due to inhibition
With second master lever to on, the inhibition is not longer valid and due to pressure difference between B and Y the PTU starts running.
The EDP of the starting engine needs some speed of the engine to provide sufficient pressure. Up to these speed the PTU hold up the pressure.
If the PTU is not OK, the pressure would not rise immediately after master sw in on.
Now we need a computer which have access to all inhibition parameter. The FWC have!
Simply said: As soon as both master levers are in on, the FWC gives a PTU FAULT if there is now a difference in the G and Y hydraulic system of more than 650 psi during at least 4 seconds. (the starting engine EDP needs more time to pressure up its related system during engine start.)
As soon as the engine speed is high enough the EDP pressurize the system and the PTU stop working.
Do you really want this all in the FCOM? I think that "The PTU is automatically tested during the second engine start" is enough info.