Airplanes Making Strange Noise Over Home

So this is actually a very common occurrence but I'm wondering why they are making this specific noise. It sounds like a car when downshifting if that makes any sense. They'll be flying along, and at a certain point in the path the engines double in volume. A few people think that this is the landing gear coming down, but I think they re way too far away for that to be the case. I'm sure someone here knows what it is. These are jets, they are still relatively high up and I believe the ones that make the noise are approaching the airport to land.

Reply to post by Domo1

I've been hearing the exact same noises over here in Texas last night around 3 in the morning. Got no idea though.


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reply to post by Domo1


I know what you mean, I live just outside Manchester airport in the UK, right on the flight path, and I hear this on a daily basis, planes are typically 5-6 minutes from landing when they fly over my house, I always thought it was the engines going into "reverse" as they slow down approaching landing.......I may be wrong, but I'm sure someone in the aviation business will be along to set the record straight.

I get this all the time and i dont even live near an airport, at first it will seem fairly quiet for a plane and then all of a sudden the volume of it becomes craazy lol, thought it was a nuke the first time i heard it

reply to post by Argyll


Yeah it reminds me of the engines going into reverse or something. Weird part is that I've flown a lot and never remember hearing this, which I would have thought would be more pronounced in flight.

Poster above, I always think it's WW3 too. Even though it happens a few times a day. Another thing, not all the planes seem to do this, just some.

Actually it's the same phenomenon as when an ambulance changes pitch when it passes you.
Look up "Doppler Effect" -> en.wikipedia.org...

reply to post by Jubjub


Yeah I thought about that, but I don't think it's what I'm hearing. It doesn't happen with every plane, even the same size at what I estimate same altitude and same flight path.

reply to post by Domo1


Aaalrighty then
Check this video out -> www.youtube.com...
(It's "How to Measure Aircraft Speed Using the Acoustic Doppler Effect")

I am no aviation pro, i am sure someone will come up with a good explanation...but it could be simply that they compensate with increased thrust once the airbrakes/flaps are down or something.

reply to post by Domo1



It will depend on the height of the aircraft, type, weight and speed, it could be when coming in for approach, the pilots select flaps and slow the aircraft down changing the wing configuration, thus causing a change of flight characteristics. causing a change of pitch in the power plants due to the power change to compensate,this will be more noticeable depending on the wind speed and direction.

Other than this it could be a directional change causing the sound waves to be redirected causing a change in the sound, or a drop through a colder / warmer patch of air causing a change in power settings to compensate for the speed / altitude change.

Wee Mad

Hello all,

Yes, I know the exact noise you are describing and some of you may note that particular types like the 777 seem to do it whilst others dont appear to.

It is not as one poster here suggested, the engine Thrust Reverser's(T/R's) engaging. That is forbidden, highly dangerous and in fact virtually impossible due to multiple safeties designed to stop it from ever happening. If it did the end result would be something akin to the Lauda Air 767 accident that killed everyone onboard. These days it should be impossible for the T/R to cycle until you have weight on wheels and your throttle setting and air speed have reached there thresholds. The CF-6 for example (as used on the 767) has mechanical and electro-mechanical locks and brakes designed to compliment each other. In fact after the Lauda Air tragedy all CF-6 engines were mandated to be fitted with the second system to prevent such an accident from happening in the future.

Although I am in the business I must confess that I dont know the exact cause of the noise but I can make an educated guess. It is almost certainly the auto throttle system cycling to maintain a selected airspeed and altitude. The noise may be caused by the engine's Engine Electronic Control unit (EEC) changing the scheduling of say the Variable Stator Vanes (VSV's) in the compressor and therefore how it sounds. It is definitely not the doppler effect however.

As I said I dont know the exact cause but that is my educated guess. I have asked one or two other colleagues for an explanation but they were not sure either. It is something I do note that we dont hear around the immediate vicinity of the airport, or during takeoff, or engine runs we conduct on the ground whether idle, low or high power runs, so that is why I believe it may be the auto throttle maintaining a selected airspeed in flight. I have as one other poster eluded noticed it some 5-10 mins before they would touchdown at a height of 2-5,000ft. Anyone who can answer that here I would also appreciate it as well.

LEE.

I hear this noise sometimes as planes come over my place descending to land at ABIA. Yeah. some of them are revving their engines. In coming down from about 30,000 feet, they sometimes find that they are gliding down too fast to be at where points X and Y merge and so they must increase power to maintain the correct rate of descent.

I think the weird sound is more noticeable on certain aircraft more than others. The first time I heard it, I thought a plane was in serious trouble because we sometime hear in the details of a crash that witnesses heard the engines revving seconds earlier.

The first few times I heard it I thought it was some hot-rod pilot. I tend to believe that those a/c with the dark (blue?) undersides (United?) are the ones I typically notice producing that sound. So it could be the type of plane or their company's SOP procedure

Had to google a bit, but yes:

Approach and land. Again the flaps and landing gear have to be extended, so expect similar noises to that experienced after take-off. Sometimes pilots have to use their "speed brakes" to conform with Air Traffic instructions. Speed brakes are metal panels that are located on top of the wing and allow the pilot to create drag. Pilots use these when Air Traffic Controllers hold the plane high to meet some requirement.

The speed brakes will cause a slight turbulent feeling throughout the plane and can create a change in wind noise. This is totally normal. During the approach engine noise will increase because the pilot wants to fly a constant airspeed approach to the runway.

To any old timers or cool youngsters like myself... It sounds like forcing a truck into granny gear going too fast.

Thanks everyone who has answered. I never thought it was anything sinister, just always weirds me out. I'll be in bed (hopefully with a nice buxom young lady in my arms) and all of a sudden VVVVVAAAAAAAROOOOOOOOOOoooooooommmmmmmm!

Nice young lady: 'Baby come back to bed.'

Domo: 'Shutup woman we're all gonna die!'

Moment..... ruined.

The extra noise is wind-noise from flaps, gear and/or spoilers. Like wind blown through a whistle. If you've ever sat above the wing on a commercial flight you can see all the "holes" in the wing appear when the flaps come down. The wind is suddenly being blown through all those "holes" and crannies at several hundred knots and being redirected. If you've ever heard the wind through the trees or stuck your hand partway over the opening a vacuum cleaner or out the window of the car at free way speed, you may have noticed the roar produced by redirecting airflow.


With a high-bypass ratio turbofan engine spool-up (and -down) time takes longer than with smaller turbojets. This means a delay to add or subtract power. This is potentially dangerous. To eliminate some of this, the fans are kept at a higher RPM and the plane is made "dirty". The introduction of drag helps reduce airspeed without changing the engine setting. It can be much faster/safer to "clean up" the plane by retracting flaps, spoilers, gear, etc and thereby increase airspeed than might be possible by waiting for the engine to spool up and start producing thrust.

It's actually from the spoilers on top of the wings. Large aircraft such as airliners and such need the spoilers to aid in deceleration and the descent from cruising altitude all the way to when the aircraft is on it's landing rollout. When opened, the spoilers make a type of whistle with a very deep pitch.

As you can see from the pictures, the part sticking up on top of the wing is the spoiler, the part drooping down behind them are the flaps. the flaps allow for the aircraft to fly slower and still maintain sufficient lift to stay airborne. The purpose for the flaps is to allow landing at slower speeds, so we don't have runways that are 5 miles long. Flaps are also used on takeoff to gain extra lift so the aircraft can get airborne in a shorter distance.

en.wikipedia.org...(aeronautics)

reply to post by PKDragon


sorry, the link only directs you to the list page, just click on the top one

Traveling at high speed nose down for descent particular models will make a vvvvrrroooaamm lasting only a second then you will be able to hear the plane as normal afterwards. One key bit of evidence in solving this is the fact that (if you havent noticed before) until that noise is made you are unable to hear the plane in the first place. Dopler effect isnt fully to blame here as an ambulance is not loudest the first second you are actually able to hear it but rather (painfully) loudest as it is passing you by. If it was the engine and or flaps/mechanics of the plane i highly doubt the engines on before the vrooooam noise would be inaudible. What may be to blame here is the altitude drop. Air gets more and more dense as you approach landing, combine that with fact that at a certain distance you cant hear the plane and you get a weird incomplete form of the dopler effect that momentarily displaces the air pressure from a lower pressure area to a higher pressure area possibly causing a concentration of low pressure air on the front/belly of the plane which sound can travel faster and thus louder through. The end of the noise would signify the air infront of the plane now matching that off the surrounding air below.

If you live in the landing pattern, you're likely hearing them fly through a noise abatement zone. On approach, they have to crank in extra flaps, spool down, cruise over a bunch of nearby homes, then as they come into the airport area they throttle back up.

A spooled up engine is noisy, but safer for low level maneuvers because it takes way way too long to throttle up a jet to deal with an OMG right near the ground. So it's not kosher to limit the engine settings on final approach. But since people decided to build neighborhoods near the airport you have to limit the ruckus as much as possible.

Note that they're doing this on takeoff as well, but they're so high when they spool up on the way out that you don't hear the throttle up.

a reply to: Domo1 I live in the country about 70 maybe 80 miles from a major airport. I have lived here over 20 years and it was so quite you could hear a fly. Now you can hear planes in the distance. Can't see them but you can hear them. Reminds me of planes off to war? It's so many at one time. Live about 100 miles or so from a major military base.