Noises on start up from A320

[Viperzs]

Hi all!

I flew from MUC to MAN yesterday on an A320. As they were preparing everything there were a load of very loud mechanical whines coming from the belly of the plane. I assume this was them testing stuff but any idea what it would have been? Everyone looked concerned, I was merely intrigued!

[dazwalsh]

I know the noises you mean, i think itmay be the flaps being lowered for takeoff

[Viperzs]

It sounded a bit like someone was torturing a Dalek.

I doubt it was preparing the flaps though as we were still sat at the gate at the time.

[ninja-lewis]

Sounds like a barking dog?

Power Transfer Unit

The A320 has two separate hydraulic systems, each powered by a different engine. In the event one engine fails, or is not in use (as is common when on the ground these days to save fuel), the PTU transfers power (not fluid) from one system to the other whenever the pressure in one of the systems falls below a set level.

http://en.wikipedia.org/wiki/Power_transfer_unit

[Hooli]

Viperzs said:

It sounded a bit like someone was torturing a Dalek.

I've never been on any form of airliner, but I want to now just to hear this

[Viperzs]

ninja-lewis said:

Sounds like a barking dog?

Power Transfer Unit

The A320 has two separate hydraulic systems, each powered by a different engine. In the event one engine fails, or is not in use (as is common when on the ground these days to save fuel), the PTU transfers power (not fluid) from one system to the other whenever the pressure in one of the systems falls below a set level.

http://en.wikipedia.org/wiki/Power_transfer_unit

Thanks Mr Ninja, just checked Youtube for PTU noises and it sounded like that.

Is it only on the A320s? They are the last planes I have flown on so I don't remember if I have heard them on 777s.

[Spoof]

PTU or yellow electric hydraulic pump.

Our airline like us to single engine taxi where possible, this involves starting Eng 1 on pushback, disconnecting the tug and ground crew and while that is going on, switching on the yellow electric driven pump to take load off the PTU (the barking dog sound) you may hear it momentarily again a few minutes later when we start engine two.

A32x actually has 3 hydraulic systems, but the Blue system as its referred, is powered by an electric pump or RAT and has no PTU or fluid transfer to the other two systems.

Edited by Spoof on Sunday 1st September 11:24

[dvs_dave]

Thanks. Often wondered what that was. Now I know. Although why it's not quiter like on other aircraft is a bit odd though. It sounds as though the motor or whatever it is making the noise doesn't have enough power to turn over quite properly. Like when trying to start a car with a low battery.