A319 Engine Cooldown Noise

[lcarus]

First off - what a fantastic forum! Huge fan of aviation but alas on the wrong side of the apron :)

Anyway, I'm a regular flyer (twice a week UK>Holland) and more often than not I fly on the Airbus A319. Great aircraft but when even we disembark in the UK the engines make a very disconcerting metal on metal noise as the fan slowly winds down.

Can any of the experts out there tell me what this noise is? I notice this in pretty much 50% of my flights.

Many thanks!

[Hand Solo]

It's not the engine that makes the noise, it's the hydraulic power transfer unit operating. It is activated when an engine is shut down (normally during taxy in) and people usually describe it as sounding like a dog barking. It doesn't occur every flight as you don't always shut an engine down during the taxy phase.

[easy1]

The metal on metal sound you can hear is perfectly normal!! It's just the blades going round as the engine stops, you can't hear the sound when the engines are on.

[Hand Solo]

You won't get a metal on metal noise from a V2500 engine, which all the AMS-LHR 319 operators use. You sometimes get the fan blades clanking on CFM engines due to the different way in which the blades are fixed to the spools.

[lcarus]

Thanks for the reply - however its definitely not the PTU I'm talking about (which funnily enough I always thought sounded like someone sawing a piece of wood :O))

It's a proper metallic clang which slows as the same frequency as the fan. Only audible when you're outside looking into the engine nacelle

[lcarus]

"You won't get a metal on metal noise from a V2500 engine, which all the AMS-LHR 319 operators use."

AMS-LPL actually - there is more to the UK than London :)

[lcarus]

Think I may have found the answer - it was this thread that got me onto a different lateral thinking plane (pun intended :))...

Someone has actually posted a movie of the sound on the web?...

http://www.youtube.com/watch?v=y0vxor8xT-o

Is it some form of rotational braking system for the fan?

[Notso Fantastic]

The fan blades rock slightly sideways in their mounts. At speed, they are obviously tightly supported by centrifugal force (don't start that argument please!), bit slowly rotating they produce an awful racket. The 747 can be deafening. They rock from side to side during the rotation. It's amazing to see the tip clearance from the inner surface of the cowling- as long as they keep clear of that, that's all that matters!

[lcarus]

AH! That would explain it - thanks for that. I can only hear it on an A319 and it's pretty loud - on a 747 it must be defeaning!

I did post a link to a popular video website ;) which actually plays out this noise but the post is in the hands of the mods. I did a search on that video website of 'windmilling'

Thanks again! Looking forward to checking in here with more stuff soon, have my Monday morning flight tomorrow :)

[Chris Scott]

Yes, the fan blades do rock gently from side to side in their mountings as they lazily windmill round (so not under any load to keep them still). The loudest contact may be between the mid-span shrouds - sometimes called the clappers - of adjacent blades, as they hit one another. This makes a loud tinkling sound.

Re the A320 family, if memory serves, the CFM-56 engines have mid-span shrouds on their fan blades, but the IAE V2500 engines do not.

[Hand Solo]

Doh! Must read the original post properly, although I wasn't aware that Easy operated A319s. Must get out of the south more often! Looks like Easy have the CFM engines on their 319s.

[spekesoftly]

Yes, easyJet have operated CFM powered A319s for over five years, and now have well over a hundred of them, with more deliveries pending. No scarcity of them down south either - Gatwick and Stansted for example.

[Hand Solo]

For some reason I thought easy operated A320s, not 319s. Must pay more attention.

[Chris Scott]

Hand Solo,

The reason EasyJet's A319s can easily be mistaken for A320s is that they have 2 overwing exits per side, whereas most A319s only have one. Something to do with the way they cram extra seats in. [No offence intended, I am a fan.]

Chris