Noise on A319
 

I don't think I'm going to be able to describe this accurately enough to give anyone a chance of answering, but here goes....

Flew twice on an Easy A319 last weekend, and both times, during pushback and while the engines were being started, there were a series of quite loud noises. I can only really describe these as a whirring, one longer one of perhaps 1-2 seconds and several shorter ones of less than a second. They sounded like a large electric motor spinning.

I was sitting over the wings, and the noise seemed to come from directly below. They weren't related to the flight surfaces as I was looking out of the window and neither the flaps/slats or ailerons moved.

Can anyone offer a suggestion of what it could have been from my very poor description?

AC electric pump to pressurise the Hydraulics (for the brakes), or possibly a PTU (power transfer unit) which is a way of transferring energy from one hydraulic system to another without fluid crossover (basically a turbine in the pressurised system drives a pump in the unpressurised system).

These can be quite noisy with one system depowered.

This is quite normal on pushback.

I'm not completly familiar with the Airbus family (Boeing driver myself), but either of the above would be a lightly explanation until someone who is A320/319 qualified can elaborate further...

It’s the hydraulic power transfer unit (PTU) that allows one of the two main systems to pressurise the other in the event of a failure of the engine driven pump. It is a vital system so its function is tested automatically during engine start. People describe it as a bit like a dog barking and it runs for about 3-5 seconds.

I've heard this on 319's/320's - it reminded me of sitting down the back end of Herc's, when the hydraulics for the ramp/door are started and stopped - very similar noise.

this has been discussed on forums here before. I liken it to the sound of the dentists.

As Max Angle said it's the Power Transfer Unit (PTU). Normal ops on pushback is to start the No. 2 engine on the right hand side first. This powers up the hydraulics on that engine and the system sees that the other hydraulic system has low pressure. It therefore powers up the PTU to pressurise the No. 1 engines system hydraulics. This runs up until the No. 1 Engine has been started and then cuts out. Common across all the A320 fleet.

Woof, Arf, Arf, Bl:mad: dy loud if it's on during the walkround! (not to mention brake fans, APU and packs!! What??? Eh???? wheres me ear duffs!)

Thanks for the replies guys. I'm very impressed you knew what I was talking about from my not very good description!

ALLDAYDELI - you're right, is it like the dentists.

But guess what... can hardly hear any of those 'barking sounds'/'dentist noises' on new 319/320s.

Guess they improved the system on recent MSNs, coz despite the PTU doing it's thing, I'm still to notice the sound on any of our new 319/320s.

I still cringe about when I travelled on a 320 not so long ago. I was very aggravated that the dog in the hold was in distress and nearly insisted that someone go see to it as I know my dog barking sounds, and that was an unhappy dog!

When I was a stew on the A320 I got my (admittedly) cheap kicks from telling the yanks it was a dog in the hold that we couldn't catch before boarding... I used to reassure them that it would have frozen to death before landing so it wouldn't casue too many problems.... Got 'em every time... :E

this has been discussed on forums here before. I liken it to the sound of the dentists.

Nah, clapped out Mini trying to start on a winter morning :}