Unusual sound from an overflying A320

[FullOppositeRudder]

Twice in recent times I’ve been startled by a short and loud burst of noise from an A-320 on descent over my home location – about 50nm from a major capital city airport. It’s a popular route for inbound traffic from the north when runway 23 is in use at the destination. Flight Radar 24 reports most aircraft as descending through FL 150 at a reported speed in the region of around 350 knots when overhead. I didn’t think to check the fine detail on the a/c at the time – only the type and airline. The sound lasted about 5 -8 seconds and was very loud – aerodynamic in origin was my reaction – and loud enough to have me come out of the shed in a serious hurry with the expectation of something very unusual. I was half expecting to see something at very low level in a tight turn – the airshow kind of sound.

Interestingly a friend who lives further down the street also heard the first event. He and his son were both alarmed by the event – the lad asked “Dad is there going to be a crash?” Dad replied that he hope not, but he feared the possibility.

Most days probably 10 or more jets use this track and are barely heard as they descend overhead. Most of them are B737 – more recently E190s and F100s as well as RJ45s – and the A320s.

What we heard was unique to these two occurrences. Any thoughts anyone? Speed brake extension perhaps?

[Uplinker]

Almost certainly speed brakes.

Difficult to put into words what a sound sounds like, but on Airbus; quite a loud howl of descending or increasing pitch, (i.e. frequency), that reverberates around the sky is what speed brakes can sound like. The frequency is high when the speed brakes are almost closed and lower when they are fully open. A typical deployment will start high pitch, reduce to low pitch for a few seconds then increase again to high pitch and fade in volume. The speed brake opening phase is faster than the closing phase.

You can go down, OR slow down with clean wings, but you cannot go down AND slow down without speed brakes, so those that you hear are having to do both.

We used to have to do this over London when ATC changed the plan and needed us to descend rapidly from FL190 and also keep below a certain speed by a certain point, and I would often think "sorry London" if I had to do it.

edit to add: BAe 146 aircraft have a loud howl caused when the flaps are extended, but that is unlikely up at FL150.

[Gargleblaster]

I also live under an approach path to a major airport, the right base leg to RWYs 22 at EKCH, and often hear when flaps and / or speed brakes are deployed.

What amazes me is that when sitting as pax on an aircraft, I've never heard the noise ! Good sound proofing ?

I flew gliders once, and, on the ground, the parachute on the wire, just under the belly of the plane makes an awful noise during a winch launch. Again, when up there myself, can't hear a thing ! Gliders certainly aren't sound-proofed...

[10 DME ARC]

About 20 years or so ago as ATC watch manager I was involved with what started out as noise complaint from a elderly gentleman living 7nm final main runway but only for Airbus A320's!! He said he had lived there for years and had no problems with any other aircraft but the A320 family! It got that bad that he threatened to shoot with his shotgun at the aircraft! This got the police involved who had words to start with and then after a frantic call from him telling us he had shoot at a landing A320 a armed response team were sent out and he was arrested! Not sure if a stay in a 'hospital facility' or he moved but he went quiet after that. :bored:

[pax britanica]

When i lived in Camberley the A320 howl was common with LHR on easterlies and aircraft coming from the Ockham Arrival. At less busy times they would keep speed up until they turned base leg which was often over Camberley .BA pilot friend -not on 320s at the time said that speedbrakes were the culprit Aircraft that had been held were already slowed down and so it was less common and why you dont hear it all the time.

Living in Somerset now I rather miss the varied streams of LHR departures and arrivals and honestly dont think that noise was a complaint issue with all the background ambient noise of modern life . What some people might regard as excessive noise was when a 747 inbound to Ockham was suddenly told to make a hard left turn to join the Heathrow downwind (easterlies again) to cut out the trip to Ockham and back . That did seem to involve a lot of flap extension and a lot of power and thus a lot of noise while in the turn . Good to watch the mighty beasts doing it though, sadly no more of course.

PB

[Leecj1]

None of the above. It's the fuel vent on the underside of the wing. Same process as when you blow air across a bottle. Aerodynamic fix developed quite a while back (like a little vane), some older A32X series still not retrofitted.
https://www.airportwatch.org.uk/2014/11/lufthansa-retrofitting-a320-family-with-simple-inexpensive-noise-reducing-device-to-stop-the-airbus-whine/#:~:text=A320%20series%20aircraft.-,Every%20A320%20series%20aircraft%20emits%20a,noise%20while% 20approaching%20to%20land.&text=Air%20is%20drawn%20in%20through,when%20the%20aircraft%2 0is%20refueled.

[Uplinker]

The fuel vents cause a constant drone, heard when the aircraft is on the glide slope etc. The OP asks about a noise that suddenly starts then stops after 5-8 secs, as the aircraft is descending around FL150. That's the speed brakes.

[STBYRUD]

Well, to a stationary observer that fuel tank vent causes exactly that, a six to maybe ten second long howl of descending pitch when the aircraft is right overhead.

[speedrestriction]

Interestingly, in the U.K. at least, landing fees for non-retrofitted A320 series aircraft are significantly higher than with the mod fitted.

[DaveReidUK]

Interestingly, in the U.K. at least, landing fees for non-retrofitted A320 series aircraft are significantly higher than with the mod fitted.

Do you have a source for that?

[FullOppositeRudder]

Thank you all for your most informative discussion - much appreciated. I think Uplinker's analysis of the sound itself is exactly what we experienced. Thanks again everyone.

FOR :)

[Load Toad]

Twice in recent times I’ve been startled by a short and loud burst of noise from an A-320 on descent over my home location – about 50nm from a major capital city airport. It’s a popular route for inbound traffic from the north when runway 23 is in use at the destination. Flight Radar 24 reports most aircraft as descending through FL 150 at a reported speed in the region of around 350 knots when overhead. I didn’t think to check the fine detail on the a/c at the time – only the type and airline. The sound lasted about 5 -8 seconds and was very loud – aerodynamic in origin was my reaction – and loud enough to have me come out of the shed in a serious hurry with the expectation of something very unusual. I was half expecting to see something at very low level in a tight turn – the airshow kind of sound.

Interestingly a friend who lives further down the street also heard the first event. He and his son were both alarmed by the event – the lad asked “Dad is there going to be a crash?” Dad replied that he hope not, but he feared the possibility.

Most days probably 10 or more jets use this track and are barely heard as they descend overhead. Most of them are B737 – more recently E190s and F100s as well as RJ45s – and the A320s.

What we heard was unique to these two occurrences. Any thoughts anyone? Speed brake extension perhaps?


Here is the explanation: Airbus Howling Sound

[FullOppositeRudder]

I flew gliders once, and, on the ground, the parachute on the wire, just under the belly of the plane makes an awful noise during a winch launch. Again, when up there myself, can't hear a thing ! Gliders certainly aren't sound-proofed...

Yes the winch launch using wire (which was SOP during the first 40 years of my gliding exposure) certainly was very noisy. Somewhere along the way we started using a short synthetic rope insert as part of the trace which helped greatly. These days we use Dyneema for the full length of the winching "cable". Very quiet, and easier both on the winch and the aircraft - and a surprisingly long life too. Modern gliders - with the emphasis on absolutely minimal drag - are very quiet in flight these days. I think I still preferred the character of the older aircraft - a certain amount of airflow noise was part of that.