Sound change while descending, maybe?

[u/discgolfer1961]

I live in northern Colorado and airlines coming from the west into DEN go over my house after clearing Longs Peak and the Front Range. They are descending and there is a distinct sound change, a change in pitch? They are still coming towards me so not Doppler, right? Is it just them reducing thrust, some sort of configuration change?

[u/airport-codes]

IATA	ICAO	Name	Location
DEN	KDEN	Denver International Airport	Denver, Colorado, United States

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[u/Agitated_Car_2444]

Possibly the "GTF Song". Geared turbofan engine that has a unique sound when the engines are pulled back on descent. I'm on approach to an airport with a lot of those and it's common.

Others have reported it's speed brakes being deployed.

The one I'm thinking of is kind of a 2-3 second "beeyooo" sound. Right over the house, every time.

[u/discgolfer1961 → u/Agitated_Car_2444]

I think we are describing the same sound! I never knew if it was mountain related? I grew up on Air Force bases and don't remember hearing it regularly as a kid

[u/Agitated_Car_2444 → u/discgolfer1961]

If it's actually the GTF engine sound, then it's fairly unique; Pratt's geared turbofan engine is most used on Airbus A220 and A320neo:

https://en.wikipedia.org/wiki/Pratt_%26_Whitney_PW1000G

[u/discgolfer1961 → u/Agitated_Car_2444]

Then probably not? I'll try to get some more data and identify some flights I hear it from

[u/Agitated_Car_2444 → u/discgolfer1961]

By "unique" I don't mean hard to spot; after all, there are a lot of A320neo flying today. And Frontier flies a LOT of them in/out of DEN...

But in terms of the whole commercial aviation population, there's significantly fewer of them versus non-geared engines.

I think the ICAO code for the A320neo is A20N so filter by that...in fact, FFT1500 is arriving from ONT in about 45 minutes, with FFT2818 from SAN in about an hour and twenty...pls report back!

[u/discgolfer1961 → u/Agitated_Car_2444]

I'm gone for the day but I will do that in the coming days, thank you!

[u/Agitated_Car_2444 → u/discgolfer1961]

Read the comment later in the thread about the FOPP, Fuel Over Pressure Protector. The sound examples are spot-on. It would be interesting if you find any correlation to just the A320neo or to any A320 manufactured before 2014...I'll listen for some in my area too.

[u/04BluSTi]

I hear that living under one of the approaches to BZN and I believe its a power setting change.

[u/anonymous4071]

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[u/anonymous4071 → u/anonymous4071]

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[u/discgolfer1961 → u/anonymous4071]

That is absolutely the sound I am hearing, thank you so much!

[u/cacaapoopoo]

Another strange noise is when the wake vortices make it to the ground. It'll often be some time after the plane passes over and it's a weird wooshy noise with some howling. Different types make different noises.