Few technical questions
 

Today as we were boarding our SwissAir A330 bound for Zurich sat just behind the wings, this loud akin to a large dog 'barking' noise coming from below, sounded like a pump or actuator pulsing away, almost like the noise some flap pumps make, anyway we hadn't even pushed back. It stopped eventually before we pushed, i just wondered what it was, not heard it sitting there before.

Also in basic laymans terms! How do they differ to an A320 is it just capacity?

Like to say how impressed i am with Swiss Air, planes seem immaculate
well maintained and pilots always very good.



tia

I assume you mean a 320 not a 330? That 'barking noise' you heard was the PTU and is a question that gets asked on a regular basis. There is a fairly good explanation on its operation here.

...on a 330? don't think so

Thanks for the explanation, although out of the 8 or so flights ive boarded on the same airline over the past few months this is the first time ive heard it especially when the engines were off and people still boarding.

Why would it be pulsing then? It was going on for about 5mins or so... then switched off before we pushed back and before engines span up.

I didnt think Swiss flew A330's LHR/ZRH though I stand to be corrected. I am assuming you were on the LHR/ZRH route?

Normally they use A320 on that run. Power Transfer Unit - Wikipedia, the free encyclopedia

Regards,

G-BPED

Sounds to me that he's confusing the A321 for an A330. Swiss also use the A321 to LHR.

Yep well done sorry, looks like it was a 320series!

Ok sorry looks like this has been done to death, im just interested about why it was running before we pushed off whilst we were boarding: What's involved in taxi ops?

The ops is normally inhibited on ground when the parking brake is set for standard engine starting at departure. But for any single engine pushback or taxi ops the PTU will wake up


For the 50millionth passenger wanting detail on PTU:

the PTU is there to transfer hydraulic power from Green to Yellow or from Yellow to Green hydraulic system, but without exchange of hydraulic fluid.
It's a motor/pump power reversal configuration.
While normal system pressure is 3000 psi, the Power Transfer Unit cuts in when the receiving system pressure falls below 2500 psi. If there is high consumption of hydraulic power on the receiving system, then the PTU operation is continuous.
If there is only system leakage flow, then the PTU barks coming ON and OFF.

But is it getting worse?
 

Having been travelling Airbus for many years now I would suggest the PTU noise is getting more obtrusive and going on for longer periods - both at start up and shut down (the brief burst at gear-up often goes unnoticed).

Is this perhaps due to ageing hydraulic systems or is there some other reason?

Bigger, angrier dog.

With more airlines trying to save money I would expect that the use of single engine taxiing is more prevalent and thus a prolonged "barking dog"

Regards,

G-BPED