Sawing up an A319 just after it's parked?

[Jumbo Jockey]

Been doing a bit of positioning up and down twixt LHR and MAN lately on BMI A319s, and I can't help noticing that shortly after they've parked it, a sound comes from underneath the floor which sounds for all the world like somebody's sawing the thing up. Wossat?

[palmdeira]

it's the hydraulic power transfer unit - PTU. Shouldn't really be operating unless the yellow system electric pump has been turned on, perhaps due to single engine taxiing.

[TopBunk]

It will also operate when the loaders activate the opening of the cargo doors to get out your luggage, irrespective of taxi practices.

[IFixPlanes]

Originally Posted by TopBunk

It will also operate when the loaders activate the opening of the cargo doors to get out your luggage...

Sorry, but not true. PTU-Funktion is inhibited when the Yellow electric pump is in operation to open/close the cargo doors.

[TopBunk]

IFix

Sorry, you are of course correct, the Yellow system Electrical pump powers the hydraulics to open the cargo doors. No longer fly the 'bus - how quickly one forgets detail....

[Jumbo Jockey]

Thanks to all!

[mcdhu]

Yup, usually due to the SE taxi procedure. On stand the procedure is Ylo Elec Pump OFF, Eng 1 Shutdown which finds the Ylo(Eng2) hyd system now powered via the Ptu from the running down Eng1 (Green) hyd system and is so until 5% or so N2 whereupon it all dies.

Cheers,
mcdhu

[Swedish Steve]

I reckon that about 50% of A320 that arrive on gate after a single engine taxi have the PTU running. Our crew have a drill to turn on the Hyd pump before shutting down Nbr 1 engine, but turning the pump off is not in the shutdown drill.

[mcdhu]

But it is in the SE Taxi Procedure at 3.4.90 which says:

"At parking :

-Y ELEC PUMP OFF

-ENG 1 SHUT DOWN"

Cheers,
mcdhu