Airbus A320 sound and photos on approach

An Airbus A320-232 on approach producing its unique noise. On three photos it can be seen that no slat or flap is extended. Since no boing ever makes this noise, it can neither be an effect of the engines nor the speed brakes (on the upper side of the wing).
They are only recognizable with difficulty but have a look on the four holes of the FOPP cavities under the wings. FOPP stands for Fuel Over Pressure Protector. This is an Airbus peculiarity and these little holes producing a very distinct howling or whine noise while the airspeed of the plane reduces on approach.
The effect is the same as blowing over a bottle with the mouth. At a specific airspeed (TAS) there is a very high pitched howling noise due to this effect (can be heard at 00:15). Befor and after it is just like a nearly constant and significantly more silent whine.

[@bananana2624]

Finally explained. I hear all the time when planes descend over my house at around 1200 ft

[@solarianick1495]

At night, when I'm in bed, and I hear this sound, it freaks me out because it sounds like some UFO, but I remind myself it's just an Airbus descending. Beautiful sound indeed.

[@BlackRedsPlaneSpottingChannel]

At around 0:26, sounds either like a mid altitude Airbus A400M at like between 10,000ft to 20,000ft higher, or a cruising Antonov AN-70 at 30,000ft high!!

[@philocohen]

The FOPP system also causes the a320s to create a musical humming sound.

[@helispotter.main_taunus8584]

I love that howl Sound

[@cannedham8630]

I've lived under the flightpath of Stansted airport in the UK for 30 years and this noise from an airbus used to spook me as a kid 😂

[@flightplanaviation.]

I’m the same I used to hear them from easyJet’s coming into Newcastle 😂

[@peacearbiter]

what a beutiful sound record more please!

[@pilotflyingvirtual]

Thank you very much!

[@peacearbiter]

@@pilotflyingvirtual so I live in North Carolina and I used to live far out from Charlotte Douglas International Airport which I was in the range 30 miles from the airport basically the outskirts and I always hear them A320s at 7000 ft they fly over my house and it be such a loud noise and it scare me because I thought some was wrong with the engine and the plane was drastically losing altitude or some but I finally learned what it was years later and it’s a really nice noise so please record more if you can I’m a aviation enthusiast and love everything that has to do with it and no problem!

[@Danny_Jarquin]

i hear this every day here in miami

[@joshfoley8862]

This is a recent sound from planes near the Ottawa Internaltional airport.

[@mxpspotter2387]

I always hear this sound when an a320 is about 9000/6000 ft, which altitude was the plane you recorded?

[@pilotflyingvirtual]

Thank you for your comment. The altitude was about 9000 ft here too. It is mostly just under 10000 ft because the planes have to fly below 250 kt and further reduce the speed on the way to the airport. Typically the distance to the airport is 40 to 50 km at this point.

[@Mert-gs4ki]

I hear this sound coming in from about 13000ft / 10000ft somewhere there i hear it

[@fernandovergara3119]

Policía donde va droga

[@blue4splash]

What is the sound that happens between 00:13-00:17 sound like it's braking... Is it still the FOPP cavities? I have been trying for ages to determine where does it come froms, I always thinks of air brakes or slats/flaps

[@Major_Tom98]

I’m pretty certain it’s the flaps. I’ve heard this from several Airbuses plus a C-17. If you search “Avro jet flaps sound” you’ll hear something very similar.

[@DavidSmith-yi8ou]

I fly these for a living and I’m not sure what is meant by ‘FOPP’ mentioned in this comments section. I can say though that the howling sound heard in this clip definitely occurs when deploying speed brakes at higher speeds with a clean wing.

[@LeTo-971]

🍎🍎🍎