A320 "whirring"

[Lump Jockey]

Hi, and I hope I've posted this in the right section!
Here goes then,
Been on a few A320s and while the baggage is being loaded etc. I've heard a slight whirring sound from underneath, around the middle of the a/c! Sounds like a screw jack turning or the like, but really I haven't a clue what it is!
Any help would be appreciated here! Cheers!

[Wubble U]

Probably the electric pump on the hydraulic system which is used to power the cargo doors.

[Jetset320]

Hardly likely that the cargo door electric pump is audible from the cabin.

Most likely the noise is of the PTU (Power Transfer unit), which self tests during engine start, and is also activated if the yellow hydraulic system is put on from the cockpit to test something.

Cheers

[Fil]

'Hardly likely that the cargo door electric pump is audible from the cabin.'

Afraid it is audible from the cabin, even the FD on some occasions. As baggage was still being loaded in the example then I doubt that the noise would be the PTU.

UNLESS, the example is on shutdown, where it could be that after a single engine taxi the yellow hyd pump has ben left one hence energising the PTU.

[744rules]

As bag loading was in progress, it might be the in-plane loading system you heard (the post does not mention the fact that containers were used or not)

[m&v]

AS FIL says,
It's probably the yellow hydralic pump ,left on after shut down,used as part of the single engine Taxi procedure.
Pax often remark of it whilst deplaning..

[ABusDriver]

Sometimes the cargo door operating handle can get stuck on, this results in the Yellow Hyd pump operating.

The whirring noise can be heard while walking around and can be heard from the flight deck.

Solution, waggle the door operating switch outside, or pull the cargo door CB on the FD, remembering to reset it before the handlers try to close the door.

We used to have to do this to avoid Yellow Hyd Overheats while on the ground.

[Young Paul]

First answer was almost certainly correct.

The PTU specifically does not operate on the ground when Y system hyds power the doors - which is why it is tested during engine start. In hundreds of sectors on the airbus, I have only manually selected pumps (and hence PTU) on the ground about twice, so that's a pretty unlikely explanation.

I believe that Airbus don't recommend single engine taxying.

[Lump Jockey]

It was a long time ago, but I remember the distinct sound, and yeah, it did sound a LITTLE like a barking dog!! (LITTLE, right!) It has happened on a couple of different flights after too, so it's probably something you guys know about! And why is it called the "yellow" systems hyd? (I'm not a pilot, ok!)

[woderick]

Coloured Hyd systems is British and goes back at least to the Comet in my experience, and probably before. Comet was Green, Blue, Yellow, Red and I expect that has rubbed off in the European Conglomerate that has brought us the wonders of the 'bus. They have all had coloured systems too, unlike the colonies which can't seem to decide between numerical systems and Left, Right & Center !

[m&v]

Airbus 320 single engine taxi procedure ,in their SOP's,both for taxi out or in..
Cheers

[Fil]

...we also taxi our 319's on one engine, but only taxi in.

In the SOP's it is permissible to shutdown engine 2 cos the APU and Yellow pump can supply the Yellow hyd system.

On the 319 only we can shutdown eng 1 (obviously not after shutting down 2 first) if we need to park at fixed pier stands as eng1 can get within 6ft of the pier in some cases.

At BA at LHR we have 50 or so 319/320's and very often taxi on one engine so if flying BA to Europe it is likely that you could here the PTU.