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JammedStab
31st Mar 2017, 01:55
I have noticed this quite a few times on descent at an altitude that seemed to be at around 10000 feet. I figured that it was landing lights being extended(I suppose that comes from older aircraft types).

But a recent article I read about Gatwick noise charges may have answered the question. Unfortunately, no link available.

The article says that Gatwick is charging A320 operators extra if they have not installed a mod to cut down on the noise(by up to 11 db). I suppose, it is audible on the ground as well.

Apparently, the noise comes from the fuel over-pressure protector cavity with the noise typically being emitted at 27-6.5 nm from landing. Is this the noise I hear in the cabin on descent?

EGPFlyer
31st Mar 2017, 07:26
I agree that it's probably the lights being extended or the speed brakes, both of which will be heard in the cabin due to the extra drag. The deflectors for the fuel vents reduce a noise that you would only hear on the ground.

Uplinker
31st Mar 2017, 09:38
I don't fly Boeing, but A320 family speed brakes sometimes emit a breath-like tone, similar to blowing across the top of a bottle, starting with a high frequency and reducing in pitch the further out the brakes are set.

When the brakes are stowed, the tone goes from low to high pitch.

A bit like the flaps on the BAe146 and for similar reasons; resonance of air in the gap between the moving surface and the wing - the size of the gap determining the frequency.

The A320 family landing lights add a bit of rumble and vibration to the noise inside the aircraft when they are deployed.

EmDeer
31st Mar 2017, 11:15
A quick Google search showed me this:


An even quieter approach: Airbus introduces air flow deflectors on the A320 Family | Airbus Press release (http://www.airbus.com/newsevents/news-events-single/detail/an-even-quieter-approach-airbus-introduces-air-flow-deflectors-on-the-a320-family/)

Major European Airbus operators take steps to avoid A320 whistle noise nuisance on GreenAir Online (http://www.greenaironline.com/news.php?viewStory=2116)

a320 Whine (http://a320whine.com/)

B2N2
31st Mar 2017, 22:25
Does the pressurization logic have anything to do with it?

JammedStab
1st Apr 2017, 05:12
It is definitely not speed brake deployment that I have been hearing but just to confirm then...there are lights that extend from the aircraft.

Denti
1st Apr 2017, 06:36
Yes, right out of the underside of the fuselage. And in our outfit they have to be on below FL100, therefore around that altitude during descend they get extended and turned on.

Lookleft
2nd Apr 2017, 09:03
And can anyone explain why Airbus decided to put the landing lights there and not in the wing body fairing?

applecrumble
2nd Apr 2017, 13:07
Because that would be too similar to a Boeing :}

Fursty Ferret
2nd Apr 2017, 18:12
And can anyone explain why Airbus decided to put the landing lights there and not in the wing body fairing?


Miniature speedbrakes. Landing light extension is part of my descent planning on a CDA... ;-)

Amadis of Gaul
2nd Apr 2017, 19:35
Polish speedbrakes. Or Italian speedbrakes.

TURIN
3rd Apr 2017, 00:17
A320 landing lights are in the wing root. Not the fuselage.

EEngr
3rd Apr 2017, 00:33
Polish speedbrakes. Or Italian speedbrakes.

Are you certain the Germans didn't have some input into this design?

https://petrollovers.files.wordpress.com/2013/03/porsche928lightsup1327116809.jpg

Intruder
3rd Apr 2017, 05:54
Cessna 310. Theirs were under the wing, too.

EEngr
3rd Apr 2017, 17:00
Cessna 310. Theirs were under the wing, too.

That's understandable, given the dimensions of a classic incandescent landing light and the limited height of a wing root fairing where a fixed light could be mounted.

What with the increasing performance of LED lighting and the flexibility of design of LED arrays, future aircraft designs may incorporate fixed lighting in locations that won't accommodate big, round lamps.

Intruder
3rd Apr 2017, 22:48
...but they may have to give way to the distributed radar arrays. ;)

RVF750
3rd Apr 2017, 23:00
Like the 737 you mean? Current ones lose not only the extending landing lights but the taxi light on the nose is gone too. Those LEDs are VERY good indeed.....

FlightDetent
4th Apr 2017, 08:51
A320 landing lights are in the wing root. Not the fuselage. Underside of the wing.