A319 - Whistling noise in cloud ?!?!

[WaterMeths]

OK,

Either you will all think me mad, or there is a perfectly feasible reason for this - when passing through cloud in the 'bus there is a distinctive high pitched whistling noise / hissing noise. I can't remember hearing it on the Boeing, so its probably some sort of aerodynamic thing.

Its more pronounced in the descent, and I must say curiosity has got the better of me.

Any clues anyone ?

Or maybe I just need more rest periods......!!;)

[ARENDIII]

Hi, I may be able to shed some light on this.It could possibly be due to icing.What was your OAT? In the Hercules at temperatures from +5C to -10C with visible moisture present we can pick up icing and the first indication is on the windshield wipers, it can cause a whistling sound as the ice builds up and normally occurs just before the aircraft ice detection system picks it up.Hope this helps?

[WaterMeths]

Hi, thanks for the reply....

The sound actually starts the moment we enter cloud, other guys have heard it too. I will note the temp next time, and see if indeed there is a way of ascertaining the reason behind it. Your ice idea is a good one, maybe the sound is caused by ice crystals in the cloud hitting the fuselage before any ice accretion on the airframe. If the sound doesn't occur above +10C or so, then "wet" clouds as opposed to "ice" clouds may not produce the sound. Maybe the Airbus shape (rounded front end) is more prone.

The herc has quite a flattish front end too I suppose.

Cheers

WM

[Don Coyote]

I was told that it comes from the visual ice detector.

[WaterMeths]

FFR,

I don't fly into LHR, so we were not together.....(but that does at least confirm to me that the reason for this phenomenen is not the colour of the paint on the outside !!:)

And the temp was probably high enough to remove ice from the equation......perhaps water droplets themselves cause the hissing sound.

Thanks.

[WaterMeths]

Don C...

I must admit the ice detector does stick out at a perfect angle to cause some noise....so maybe you are onto something there. How did you come by this information? Have you also heard this hissing?

[Don Coyote]

I was told this by another pilot some time ago.

It does seem to only happen in the thicker cloud at around the temp range where engine icing could be a problem.

It is a helpful clue at night in that if I hear the noise I pop on the engine anti-ice even if it was difficult to tell that you were in cloud.

[Jump Complete]

It's not just airbus's, and not icing. I have noticed it in light aircraft in a high speed descents going through cloud, even with high OAT. I think its like when fog dampens the sound if you're walking though it, perhaps the aerodymanic noise of the aircraft is getting bounced back at you? Mind you it makes more sense to hear it in a light aircraft (especially one with the door off) than in the relatively sealed environment of a modern flight deck..

[speedrestriction]

Same phenomenon on the Q400 also - louder in clouds with a higher droplet density for some reason. Seems to come from wiper/visual ice accretion post.
sr

[ground_star]

Also quite noticable in the back rows of the pax cabin, does seem more obvious on descent mind...

[javelin]

It's simply the noise made by hitting a gazzillion water droplets.

We notice it all the time in the 320 and 330, espescially when fast.

If you think about the size of the drops and the probable frequency, it kind of makes sense.

[ChocksAwayUK]

Funnily enough I noticed it for the first time tonight (also A319) - my left hand seat colleague said it happened in cloud at high speed. We were doing 320 kts IAS in the descent. To me it sounded almost like some kind of angelic/operatic 'woohooohooh' (I'm not mad, really) which was pretty atmospheric considering we'd just hit the strongest turbulence I've ever encountered! Perhaps the environmental factors related to the turbulence also have an influence on the sound....?

[javelin]

No, that's the 5,6,7,8's I think :E