A320 family - what is the wierd noise?

[3141castro]

We live approx 65 kms north of BOD, France

We see A320 family a/c of AF overhead, on way into BOD.

Nearly every time they pass over, there is a very strange noise, a change of pitch and a whining noise - as if there is a sudden drop in thrust...

I know from the description it doesnt sound strange... but evry time it happens its as though they are dropping a bomb on us...

My theory would be that we are near a beacon or marker, and that the AF Op prec would to be to begin the descent, and cut down on engine power.. would anyone have an idea?

Having lived on flightpaths before, we have heard many noises, but this, i have never heard before.

[slingsby]

I've often wondered that myself, it would definately only eminate from an airbus, more likely the 320 or similar, boeings you can hear a few miles earlier. I was wondering if it was the sound footprint changing tone as the speed brakes may have been extended or just a general characteristic of airbus sounds. We live approx 8 miles from the centre line on 09L and approx 12 miles distance from the airport at LHR, so it's only on the base leg that they do it. As a big bus driver, there is nothing different we do on board that could attribute to any extra noise, I always thought we were nice and quiet, especially over my house when the wifes in bed!!.

[Carnage Matey!]

Could well be the speedbrakes. I live not too far from an airport and there's a definite difference in noise on a 320 when the speedbrakes are deployed. Can't hear a thing in the flight deck though.

[catchup]

guess it's that f.... vent blower.

[Flying_Sarah747]

I don't know about the noises you hear from outside, but why does it sound like the doors are about to crack off during take off, landing and turbulence?? I know why they call it the scare bus!! The first time I ever worked on one I was sitting right next to doors 1 and I thought the door was gonna fall off!!!

[747FOCAL]

What you are hearing is the bleeds opening on the engines. When the engines drop below a certain thrust the compressor make to much pressure so the engine ihas stability issues. So the engine is designed to let out this pressure. Not all engines have bleeds to maintain stability. :)

Unfortunately, the bleeds cause a lot of noise. The changing pitch also makes people notice the noise more. :(