Why do jet planes howl before they land?

September 5, 2023 7:34 PM

My neighborhood is, I think, under the landing path for planes approaching LaGuardia Airport, about 9 miles from the runway. There's pretty much always planes overhead. Sometimes, not always, a plane will emit a howling noise for about 2 or 3 seconds as it passes overhead. It's much, much louder than the engine sounds, and tends to rise or fall in pitch slightly over the duration. I'm not sure, but it seems like it's more likely to happen or to be particularly loud on hot humid nights like tonight. What am I hearing, and could there really be a correlation with the weather?
posted by moonmilk to Technology (16 answers total)

I don’t know the answer, but I’d like to add my anecdata as someone who lives under another approach to LGA (from the west). I seem to hear the planes more when it’s cloudy or overcast. My working hypothesis is that the cloud cover reflects the sound. I’d love to know if this is the case!
posted by computech_apolloniajames at 8:03 PM on September 5, 2023

When aircraft enter the airspace of a major airport, they slow down. This is mostly so air traffic control can keep everyone spaced out and in proper sequence for landing. Aircraft are usually below 10,000 feet at this point.

That transition from cruising speed to approach causes a few things to happen. Flaps extend from the wings, giving more lift at slow speeds but also create more drag. The engines also spin down to just above idle speed.

All of these things create a notable difference in sound coming from the aircraft. I live on the edge of O'Hare's class B airspace and I hear this all the time.
posted by JoeZydeco at 8:38 PM on September 5, 2023 [5 favorites]

As a frequent flyer, this sounds like a noise I often hear as planes are coming into land. I think it's the pilot throttling the engines up and down to maintain a precise speed/altitude as they make their final approach.
posted by dg at 9:14 PM on September 5, 2023 [2 favorites]

I also live about 6 miles from an airport and hear this often. There is some discussion about this on this stackExchange aviation channel on that page - a few theories there but I liked this explanation:

I think you will often hear the engines spooling up and down on final because they are adjusting altitude, and they might be coming in too low or high so they have to adjust accordingly.

Also flaps and gear are extended in the final because the glidepath is quite shallow which cause more drag, so to keep the airspeed where it should be and not higher (for safety) the engines need to put out more thrust, thereby causing the extra noise heard on final. In the initial descent, you probably are gliding with the engines at idle causing more drag than thrust. It is the most efficient way to descend in a jet.

So, I think the howl happens when a pilot extends the flaps for landing - finds that their airspeed is dropping too low and then needs to throttle up to compensate.
posted by rongorongo at 10:37 PM on September 5, 2023 [2 favorites]

Best answer: There are several different howls from different kinds of jet engine. Apparently one is called the Wookiee Howl.
posted by TheophileEscargot at 2:01 AM on September 6, 2023 [6 favorites]

I don't fly jets, but I agree with rongorongo. A landing pattern for a runway is typically a rectangle, with the runway one of the long sides. The first short side is about inserting yourself into the landing traffic patterns. The first long side is about dumping height and speed to get in the best glide path to land whatever type of plane most safely.

Then on final approach, the actual landing, things get more complicated. There's flaps lowered, heat and air rising from the runway (and also sounds bouncing off the ground) different wind patterns from trees and buildings and such. It's not at all uncommon to get gusts of air pushing a plane in the last few feet. And to counter that, sometimes you can use unpowered control surfaces (elevators/flaps/ ailerons) but for more speed or elevation, it's pretty much pure engine power.


So I'm going with a combination of the changing shape of the wings, closeness to ground, and hot and humid air is definitely more agitated and potentially more turbulent than cooler air at the same wind speeds/directions. Thus needing changing the engines from low power to somewhat higher for control and speed.
posted by Jacen at 3:53 AM on September 6, 2023 [2 favorites]

Response by poster: The Wookiee howl (or combuster howl or whale howl) from a certain model of jet engine is a good match for what I’m hearing! It’s ephemeral - only heard while the engines are speeding up or slowing down through a certain range. It’s only installed on certain models of aircraft. So it fits that I don’t hear it for every plane and it only lasts a few seconds as planes are adjusting their engines for landing.

Not sure about the weather connection. Maybe the ideal approach curve changes based on whether the air is hot and humid or cold and dry? Or maybe there’s no real connection at all.
posted by moonmilk at 4:53 AM on September 6, 2023 [1 favorite]

Humidity doesn't matter much but temperature does. Hotter air is less dense and the aircraft needs to fly a bit faster to maintain the same lift. But the howl/downshift of the engines should be fairly similar.

If you really want to conduct an experiment, visit ADS-B Exchange and see what type of aircraft is overhead when you hear the howl. Most likely it's a specific model and engine. Older jet engines are a LOT noisier than the high bypass turbofans you see on a 787, for example.
posted by JoeZydeco at 6:38 AM on September 6, 2023 [2 favorites]

Response by poster: I think TheophileEscargot's reddit link answers that question, JoeZydeco! Quoted:

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:

Airbus A220
Airbus A320-neo family
Embraer E-jets
Mitsubishi MRJ's
MC-21

The whale howl and wookie howl videos definitely match what I hear, and also mention the Pratt & Whitney engines.

Next time I hear the howl I'll try to match it up with a particular airplane - thanks for the link!
posted by moonmilk at 7:28 AM on September 6, 2023 [1 favorite]

Very occasionally we get a bOOOOOOOVoooop! passing overhead on the way to YYZ, not on the ground. Probably the same sort of thing though. We're not on any approach paths but when it happens I think the whole city can hear it.
posted by seanmpuckett at 7:32 AM on September 6, 2023 [1 favorite]

Also: Live Flight Tracker - Real-Time Flight Tracker Map | Flightradar24 is another source. WTF is that helicopter that's been circling for the last twenty minutes....
posted by zengargoyle at 8:09 AM on September 6, 2023 [1 favorite]

Thank you for this. I live under an approach path for YUL and hear a plane howl a couple of times a day, so this is interesting AF to me.
posted by zadcat at 8:46 AM on September 6, 2023

For anyone else who's also lived on a flight path, the FlightRadar24 app (from the site posted above) is awesome for figuring out what's above you right this second. What type of airplane, at what altitude, where they came from, their flightpath, etc. For basically a buck a month, I also found their Silver plan a worthwhile upgrade. I will admit to being basically addicted to the app when I was living under a very active flight path.
posted by cgg at 9:01 AM on September 6, 2023 [2 favorites]

If you have an iphone and are ok sending your location to the author's server, the siri shortcut "what's overhead" will read out this (ADS-B) information for whatever is, well, overhead.

https://twitter.com/lemonodor/status/1238149529469202433

It's pretty cool.
posted by zippy at 9:56 AM on September 6, 2023 [1 favorite]

Yeah, the whale howl happens on the newer Pratt engines that are common on Airbus 320 and Airbus 220 aircraft. It's on a newer geared engine, though the gearing is not the source of the issue.

Pratt is working on a fix for this, apparently.

There have been a couple explanation threads on Reddit but this sums it up pretty well:
Link
posted by Thistledown at 1:34 PM on September 6, 2023 [2 favorites]

So, this question made me a subscriber to Flightradar 24, so now I know the major noisy model flying over my house is the Airbus A220-300, although some planes from Embraer also howl.

But of course looking at plane approaches to town raise other questions I can't ask here...
posted by zadcat at 11:24 AM on July 15 [2 favorites]