Easy A319 noises after pushing back
 

Hi,

I commute regularly BRS-EDI on Easyjet's A319s. I've noticed there's always a really weird noise that happens after pushing back, and as we start to taxi for takeoff.

It's hard to describe, but from inside the cabin, it sounds a bit like my printer does when the mechanism jams, some kind of electic motor, but a bid "grindy" as well. It's repeated over a few seconds, in gradually shorter bursts, kind of a whaaaaaaaaaa, whaaaa, whaa, whaa, whaa. It seems to come from somewhere beneath the cabin, around the area of the wings, but doesn't seem to be connected with the flaps going down.

Obviously it's nothing to be worried about, since it happens every flight and I'm still here, I'm just curious as to what it is.

Thanks,

Steve.

We at easyJet tend to describe the noise as the 'dogs barking in the hold', as it sounds more like dogs barking than a printer. The sound is very common on A319 aircraft.

The sound comes from the hydraulics and I believe that it happens either due to the way the hydraulics were shut down/started up (someone will no doubt correct me on that point!).

Some of the aircraft are noisier than others, but the noise does stop once you get into the air :)

I'm only a PPL, did I did ask my former neighbour (an A32x pilot) about this and IIRC it is a hydraulic transfer pump (PTU?), theat senses less pressure on one side of the circuits during engine start up and works hard to equalise it.

If I've got this wrong, please correct me!

He described it as a "clapped out mini starting on a frosty morning" sound, but dogs barking in the hold works for me too :}

This has come up so many times on other forums and i always find it quite amusing reading.
The A319 hydraulic pump/pressure noise prior to departure.
Most people describe it as a barking dog in the hold, I always liken it to the noise you hear in the dentists.. Great stuff

Indeed, the first time that I heard it (after shutdown at the end of my first 319 flight), the cabin crew made an announcement to say please not to worry, it is not dogs barking in the hold. :)

Transfer pump?
 

I always thought it was a loadie sawing his way out of the cargo hold :}

Its nopt just the 319 it happens on. All the smaller buses have the same thing.

It is indeed the Hydraulic Pressure Transfer Unit (PTU) and mainly happens just as you go to start the second engine on push back. Although it does also happen sometimes on shutdown.

The noise after shutdown can also sometimes be the Yellow Hydraulic Electric pump kicking in to open the Cargo doors if the pressure left in the system after shutdown had dropped quickly.

Thanks for the responses. I like the "dogs barking" and "clapped out mini" descriptions!

Steve.

The A343 makes a noise like someone is chucking scaffold poles around in the hold when it is taxiing out. Apparently this is hydraulics too,unless they use that to explain all odd noises!

I heard the scaffolding poles being chucked around as we were taxying out on an EK A330 the other day too! - Airbus must either have some funny musicians or deaf engineers working in their Hydraulic Pumps department.

Thanks to all who posted the answer....earlier this year a group of fairly experienced ATCOs was somewhat taken aback on board an A320, after parking on stand, to hear a loud sawing from the hold! Now we know (and are mighty relieved.....)