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Within the last eighteen months, I'd say - commercial aircraft descending into Heathrow have started to emit a terrifying, short-lived but very loud whining howl when they pass over my house. They are about 1500-2000 feet on the final approach. it's a relatively recent phenomenon, so must be caused by a modification of some sort - I've only started to hear it lately. The worst examples are really scary, it sounds like a mechanical failure of some kind. The undercarriage are coming down around this time, so it may be that - but as I say, I've only started to hear it recently - and I've lived here for over forty years... what on earth might it be? It lasts for about 5 secs max, but frequently sets my pulse racing....

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    $\begingroup$ Is every single aircraft making this noise? I highly doubt so, as Heathrow sees just about every active aircraft design, and there are no global modifications across them all. It would be most helpful if you could identify which models are making the noise. There are several plane tracking apps, like FlightRadar24, which will tell you the aircraft type and it's altitude, which you can match to the sound. If you give us those we might be able to provide a proper answer. $\endgroup$
    – Ben
    Jun 16, 2022 at 23:04
  • $\begingroup$ Actually, it's not EVERY aircraft, but it's pretty common, and, as I say it's a relatively new phenomenon - I'd say post-pandemic... I've had Flight Radar for years - I haven't bothered to track the aircraft, because, as I say - it's too frequent. Maybe I'll try...It may be a change in procedure, rather than a change in hardware... or, perhaps a particular airliner - maybe it only happens when flights cut into the holding pattern and have to descend more rapidly? I'll see if I can pin it down $\endgroup$ Jul 25, 2022 at 5:39
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    $\begingroup$ This seems to be the most likely cause: aviation.stackexchange.com/a/96645/63967 $\endgroup$ Dec 31, 2022 at 9:27
  • $\begingroup$ @TimStaffell You can verify it - when you hear that howl, open Flightradar24 and check if it is one of the first three aircrafts mentioned on my list. If it is, you've got your answer. $\endgroup$ Jan 2, 2023 at 1:16
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    $\begingroup$ I did as you said... first time I've heard it for a while.... it was indeed an A-220... theory holds up! Thanks! $\endgroup$ Jan 5, 2023 at 8:41

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Some airplanes make strange sounds when the landing gear is deployed/stowed, or flaps are lowered/raised. The BA-146 is famous for making a loud descending boooo noise when the flaps are lowered, for example. I live under one of the approach paths for London City, and the first time I heard it I thought I was about to witness an accident, but it is perfectly normal.

So there's nothing wrong or broken, it is caused by changes in configuration.

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  • $\begingroup$ Yeah I was seated under the wing of a 146 when the flaps came out. Scared me silly. $\endgroup$
    – John K
    Jun 16, 2022 at 21:51
  • $\begingroup$ This plus maybe a route change that cause aircraft to perform this at a different spot (op house) $\endgroup$
    – Antzi
    Jun 17, 2022 at 15:35
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The possible sources

Multiple components on a turbine engine can produce a howl, and the three most common sources are the air inlet, the compressor, and the combustor. Please identify which one of these you are talking about.

Inlet Howl

The howl like the one on Vulcan is due to the shape of the inlet - at certain power settings, the air inrush through that uniquely shaped inlet produces the howl. But Vulcans don't operate at Heathrow, and neither do any other aircraft with such oddly shaped inlets.

Compressor Howl

This is a much higher frequency howl produced due to the leakage of air through the compressor blade tips. This is produced on all engines, but is drowned out by the fan and exhaust noise on modern turbofan engines used by the aircrafts operating from Heathrow. This howl is the predominant sound on Su-57.

Combustor Howl (Suspected)

To allow for expansion due to heating, the combustor is not directly connected to the nozzle box¹, it is connected through sealing rings² - this connection allows for the axial movement of the combustor. This along with the fact that the combustor is only supported on two points - one on the compressor side and the other on the turbine side, means that it is free to vibrate.

At certain fuel flow rates, the combustor vibration can produce a sound that can be heard from even 10-15 kilometres away, like during a GE90 startup.

On some engines, this sound can be heard at higher fuel-flow rates as well, producing a brief loud howl like on the Pratt & Whitney GTF series engines. Engines from this particular series are used on the following aircraft:

  1. Airbus A220
  2. Airbus A320-neo family³
  3. Embraer E-jets
  4. Mitsubishi MRJ's
  5. MC-21

The first three of these do operate from Heathrow, and are likely to produce that howl as power is adjusted during the approach, and it is probably this combustor howl that you are talking about.


¹ Gases exit the combustor into this nozzle box before entering the main turbine assembly.

² The sealing rings allow for the elongation of the combustor while ensuring an air-tight seal.

³ Not all A320-neo's have this engine - there are five engines in total that power the A320, two of which power the A320-neo. The models which are powered by the P&W GTF engines are: A320-171/-271/-272/-273.

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