What are you bus drivers doing over my house ?

[tomahawk_pa38]

I live in West Swindon (I know - someone has to !) I often sit in the garden watching you guys tootal over but I've noticed with certain aircraft (and I think its limited to orange and white inbounds to Bristol so I'm guessing Airbus?) that you make a most peculiar engine noise approaching my house. It sounds like a hoover being switched on or like a bottle filling up with water (whooo - ooop sort of sound). From Casper it looks like you're in the descent at about FL15 - FL12 approaching POMAX. Just sort of wondered what you were doing to make that sound and why it's only certain aircraft.

As you can tell I'm not a commercial pilot so an idiot's guide would be appreciated and I'll enjoy a gin and tonic in the sun even more knowing what you're up to.

[A320baby]

It could be anything really, from deploying speeds brakes. As we descend through 10000ft we have a speed restriction of 250kts, So it could have something to do with that. I fly the Bus and off the top of my head I really cant put a pin on it :confused:

[eckhard]

The speed brakes do make a 'descending howl' when deployed. I've heard it several times from the flightdeck. Most noticable in the A319 but I can't recall hearing it on an A320 or 321, probably because the wing is further from the cockpit.

I've also noticed a similar noise when Flaps 1 is selected, this time when seated in the cabin near the leading edge of the wing.

If you lived in Slough instead of Swindon, you might be forgiven for worrying that it was the sound of the bomb-doors opening:

Come, friendly bombs, and fall on Slough!
It isn't fit for humans now....

(J Betjeman, 1937)

[A320baby]

Eckhard, I was also thinking about suggesting the flaps, but the gentleman suggested the Aircraft was flying overhead at FL150, Would be strange to start deploying flaps at that altitude on a regular basis.

[eckhard]

Yes that's right; probably the speedbrakes in that case.

[Capt Claret]

What! Can't you Poms slow down to 250 without speed brakes? Us colonials would never use the chicken stick on a routine basis like that! :p

[mustbeaboeing]

Just to back up the original poster.

Aircraft that fly into BHX pass near my house, at appprox 10,000 to 15,000 feet and you can always tell it is an Airbus aircraft, A320/A321, by the sound it makes. Definately an 'air' noise. Not engine.

Also curious.

[oopspff7]

I live on the Wirral under the flight path into Liverpool.Used mainly by Easy and Ryan.I can tell who is who without looking.The Airbus of Easy has a distinct whine to it,while the Boeing Ryan sounds like a normal plane....if there is such a thing.

[Jonty]

Usually around that point we are trying to empty the toilets

[misd-agin]

Could be an engine intake noice. USN S-3 Viking's nickname was the 'Hoover' because it makes a very distinct noise when power is applied at low/medium power.

Used to play golf at NAS North Island in KSAN and they'd overfly the golf course at very low alititude - whooot, whoooot, whoot. You immediately realize how it got it's nickname.

A-10 and CRJ's have similar engines but different cowlings and the sound is completely different.

Some aircraft wing/flaps make distinct airflow noises as the flaps are extended/retracted. DC-9/MD-80's leading edge extension/retraction is an example. It's probably not loud enough to hear from the ground, especially 10,000-15,000'.

[pattern_is_full]

I've also often heard a distinctive whooshing howl on a descending note - duration ~5 seconds - over my home ~20nm west of KDEN. Not associated with climb-thrust (or other) engine noise, so I've assumed it was related to inbound aircraft.

Definitely an "aerodynamic" sound, rather than engine thrust, and at an altitude (~8-10,000 ft. AGL) much too high/far away to be the sound of the mechanical movement/drive systems themselves. So I've always assumed it was flaps or speedbrakes being pushed into the airflow.

I've never been able to spot the specific aircraft type visually. I kinda thought it might be 757 flaps, since they are known to be uniquely "powerful" in affecting airflow, and United flies a lot of them in here. But I'll bow to Tomahawk if he's linked the sight and sound to 'Buses. United, and especially Frontier, fly a lot of those, too.

HOWWWWWOOOoOoOooooouuuuuu....

[MD83FO]

Pretty sure it's an acoustic effect from the engine,s and additionally as you know, doppler effect adds to the effect as the transmitter speeds past the receiver.

[Toryu]

Hello all, after a long time of read-only, this topic finally made me write something on this board.

I have been hearing those noises for quite some time, visiting my parents' house in the approach of TXL.

The airplanes pass overhead at approx. 2000-3000ft. The sound can be heard quite often - maybe 5-8 times on some days.

Most noticeable about the sound is that it's usually the first thing you hear of the airplane. It can be heard on both CFM and IAE birds - therefore, I'd say it's definately not engine-related.

At this alt. both landing-lights and spoilers are usually where they are for final, so they're propably not a candidate either.
Somethimes, the pitch does not just go down (WHOOooop) but down-up (-ooooOOOP), so there has to be a parameter-variation that can not just be explained by the Doppler-Effect.

Possible contenders (apart from Spoilers) are:

1) Flaps. (usually don't go out-in)
2) Aerodynamic noise of other components on the airframe.

There's a paper by DLR (German Aerospace Agency) about noise-sources on airplanes. http://www.fv-leiserverkehr.de/pdf-dokumenten/BMVBS/Bericht%20070123.pdf (in German)

Page 55 of the pdf / page 45 of the document will take you to the sound generated by the Tank Overpressure Relief Valves/ Openings.
The tones are in the region of 530Hz and 580Hz at over 110dB, which is quite consistant with the "blowing over a bottle" analogy.

This might be our patient here, with a change of AoA creating different noise-pitches. AoA-changes might be a result of flap-extension over here, so flap-travel might cause the noise on a secondary level.

The frequency of the noise-occurances (5-8 times a day at times) makes me discard the Spoilers as a source, as I have not that frequetly experienced the use of spoilers that low (though I have seen it happen once or twice).

[NOLAND3]

First thing, no I am not a spotter, enthusiast etc etc... However this phenomenon has had me confused for many years. I have always thought it would be pointless to bring it up since I could never explain it properly.

What I can say is it has nothing to do with configuration changes, thrust changes or IAE,CFM,PW,RR

What I have noticed is it only happens in certain areas (for me in a small radius near where I live in London) and it seems to be only with smaller aircraft like the A320

My conclusions is it must be an acoustic phenomenon, that is dependent on the buildings around you. It's definitely not the aircraft itself but a sound reflecting in a bizarre way.

As I said, very hard to explain but I understand what the op is saying.

[i_like_tea]

When you are a pax, and the aircraft descends through 3000 - 4000 (maybe 5?) thousand ish you can hear a tone change, which isn't linked to configuration, lights, flaps etc.
Something aerodynamic, and it is quite noticeable.

[misd-agin]

S-3 engine 'hoover' was both an increasing, or decreasing, noise depending upon power setting and amount of power increase or decrease and the rate of change.

Another interesting aerodynamic event is to listen to wingtip vortices. Different a/c have distinctly different vortices noises. Learned that playing golf at the golf course just south of KSEA. Got to the point that we'd try to guess the a/c type by the vortice noise in the trees.

[autobrake3]

It is definitely the deployment and retraction of the speedbrakes. 9 times out of 10 they are used totally unnecessarily by very inexperienced pilots (and some who should know better) unable to cope with energy management. Unfortunately easyjet does not covet experience, result : more noise and fuel wastage.

[A4]

If I recall, inbounds to BRS are always held high due to the London TMA (Terminal Manoeuvring Area) so if you're landing "straight in" to runway 27 you always end up "hot and high" i.e. you've got a lot of energy to loose and not enough distance to do it without some help. Hence the use of speedbrakes. I'd put money on it that the noise you're hearing is indeed the speed brakes being deployed - you'll only hear it very briefly as the noise footprint passes you (like the sonic boom of Concorde :ok: - it moved continuously across the surface but you only heard it very briefly).

[Halfbaked_Boy]

It is the engine thrust changing.

Think about it, it sounds like when an aircraft normally flies overhead, but sped up and with a 'whoosh' to it. If it's what I'm thinking of, the first second or so is VERY abrupt and breaks the silence nicely!

It is the changing engine thrust compounding the doppler effect which makes that cool sound and requires a specific change of power setting, altitude from the observer, and relative wind for it to be heard.

People here who are doubting this are probably thinking of the wrong sound. Or I am...

[Mr Optimistic]

Well I have been on dozens of 320's (pax), never heard anything out of the commonplace, and have seen speed brakes deployed in descent (sitting by the wing) and again don't recall anything (and I am curious about these things so would have noticed).

I do hope the following is true..

Usually around that point we are trying to empty the toilets

which is nicely symmetric as just about that point I am trying to fill them.

[A4]

But in descent, thrust is at idle (normally) - especially if the speedbrakes are out! (you don't put power against drag) - so I dont think it is engine noise.

I fly the A319 and have heard this from inside the aircraft - it is usually upon speedbrakes retraction - so I think it's purely an aerodynamic phenomenon. If the brake are out at hi-speed (>320 knots) the speedbrake retraction takes 30 seconds so it may prolong (or reduce?) the effect.

[1pudding1]

I'm an Easy pilot based in BRS, and can guarantee its the speedbrakes. Not engines or other random things people suggested. A4 was correct, landing on R27 we are held high due London TMA, so usually before we get to POMAX, we may have to use spoilers to help us get down and slow down. Sorry! :8

[MD83FO]

at around 2000 - 3000 feet is when you're extending the slats and thats when the engine fan blades accelerate about 7 percent to approach idle.
the engine could also be revving up to maintain slats speed usually close to 180 knots. i avoid this by selecting a lower speed. i wish i could be my own passenger some day and feel the difference.

the sound others are describing when the slats extend is the slat hydraulic servo which you can hear from inside, but impossible from the ground

[Toryu]

Just heard the sound again today: an EZY 319 passing at around 3000-6000ft over my place.

Speedbrake-retraction would give an explanation to the WHOOoop, but not to the WHOOoooooOOOOP - unless it's common to retract and re-deploy the brakes in short order.

[FlightPathOBN]

okay, couple of things here...the sound is from the flaps. You will hear it from different ac, depending on the flap location/size on the wing. The A320 has more of the outboard flaps, which run to almost the full length to the wing tips with a smaller inboard flap, while the B738, has large inboard flaps, and the flaps do not run as far out on the wing.

This has significant effect on the noise generated. (I have not observed any sound from speed brakes, unless its a FOQUA bust!)

In regards to wake vortex, the same principles apply. (while the vortex is generated near the wingtips, the wing tips do not generate the vortex)

AC that have outboard flaps, tend to generate a large core vortex. If you are standing under the flightpath, (best is about 1000m from threshold) this will sound like a deep, low roar...This is the larger volume, slower moving mass of air. For comparison, a 737-400 will make only a large core.

AC that have inboard flaps tend to generate a large core and small a core vortex. The small core is very high velocity, but dont last very long. These sound like tearing a piece of paper on breakup. In comparison, a 738 will make a large and small core vortex.

As misd-again pointed out, you can hear the differences between ac.

When you sit and study this, and observe 10 737-800's in a row, you can tell the difference in flap settings.

A380's are a kick to listen to...

[A4]

Whilst I'm sure the flaps will generate some noise I still think its speedbrake. I live directly under the approach at appoint where the aircraft are through approximately 4500' at, typically, 220 knots and "clean". It's usual at this point to be told to reduce to 180 knots and continue the descent to 3000'. Jets don't "go down AND slow down" ...... so speedbrake is usually deployed and "wooooooooooo". The flap isn't taken until the aircraft are past my house.

Next time I hear one I'll get my binoculars out :) and see what speed/altitude it's at with "Planefinder".

[FlightPathOBN]

I can see the flaps for the turbulence creating the noise, but speed brakes get thrown up all the time without the whoop...

I am usually set much closer to the threshold for the vortex measurements.

Good luck...

[Guernsey]

Engine thrust changes - I hear that over my house frequently which is under a STAR fix with an altitude contraint so aircraft are frequently spooling up as they level off at 5k. Airbus engines more noticeable than most as they spool up in flight at lower altitudes - like someone posted - a Hoover sound alike.

[i_like_tea]

Whilst I'm sure the flaps will generate some noise I still think its speedbrake. I live directly under the approach at appoint where the aircraft are through approximately 4500' at, typically, 220 knots and "clean". It's usual at this point to be told to reduce to 180 knots and continue the descent to 3000'. Jets don't "go down AND slow down" ...... so speedbrake is usually deployed and "wooooooooooo". The flap isn't taken until the aircraft are past my house.

Next time I hear one I'll get my binoculars out and see what speed/altitude it's at with "Planefinder".

A4

Don't really agree with that.
From my experience you don't often see people needing speed brakes to reduce at this stage unless you are hot & high or with a stonking tail wind.
From 220kts you can already deploy Flap 1 and from 200kts you can deploy Flap 2.. which gives you the drag to slow down to 180 easily.

It may be different with different Airlines or ATC units though.

[A4]

You said it. Tailwind. For this approach, 9 times out of 10 the decel+descent is also the turn to base leg which also usually has a tailwind. If you don't speedbrake it, you catch the fella in front fairly quickly. The decel with F1 (slats only) is not sufficient to meet ATC's requirement - they do expect us to do as asked promptly not in our own time. Of course if you can see you're going to get a extra couple of miles or there's no critical preceding traffic then you can give it your best shot "sans speedbrakes" - there's always the gear :}

I'm still nailing my colours to the speedbrake mast!

[hetfield]

zahnpasta hin, zahnpasta her..

It's not a matter of aircraft type im my opinion.

But, why not do a contest?

All kind of airline jets do a flyby with, let's say 320kts (737 can you do that?), airbreaks on/off:O

Must be fun and this very important thread can be closed thereafter.

[FlightPathOBN]

I dont think it is the speed brakes..on flight validations, when the Airbus goes to config 1, that whoop takes about 30 seconds..

so that appears to be a slat/flap issue!

[MD83FO]

beacuse the engines spool up when you select Conf1

[A4]

beacuse the engines spool up when you select Conf1

Why? When you configure your normally slowing down. Let's say you're at 220 knots selected speed, descending in OP DES (idle thrust) and ATC request 180 knots. "Manage" the speed to start reducing to GN DOT (clean spd approx 205 knots) and take F1 (slats only which takes about 8-10 seconds), target speed now "S" speed (approx 185 knots). You're still descending in OP DES and thrust will only start to spool as you approach level.

Your speed is controlled by pitch (not thrust which will be at idle) in OP DES. In "managed" DES the profile is FIXED and speed is controlled by thrust so if above or on profile even DES should result in idle thrust.

Of course if you held 220 knots and select F1 then yes the engines would spool - but why would you do that? You're then putting power against drag.

I still think it's speedbrakes ;) but I remember being a pax in a BAe 146 many moons ago and the aerodynamic noise on flap retraction after departure was UNBELIEVABLY LOUD! So may be there's a bit of slat stuff as well. (I know the 146 didn't have slats - or did it?)

[Craggenmore]

Could be the Delta P reaching 2.5 in the descent and the outflow valves and doors opening.

Next time in the flight deck after take off, have a listen to the hiss around you; it stops around 4-5000 feet. Have a glance at the Press page - Delta P should be very close to 2.4-2.5. The valves/doors close and the hiss stops.

The 320 does the same thing in reverse on the way down but at a higher altitude.

Might not be loud enough to hear it from the ground though :confused:

[John21UK]

I still miss the 146 flap sound every day, after flying it for 4 years. And yes, the 146 doen not have slats. The massive noise you are refering to is when selecting flaps 0 to 18. It certainly raised a few eyebrowse amongs first time 146 pax.

[Easy226]

The engines will spool up at some point on the approach, irrespective of THR IDLE annunciated. As MD83FO stated its to do with approach idle - from what I recall its either done from flap lever position not at 0 or upon flaps extension.

[Halfbaked_Boy]

I'm still convinced it's engine related for the following reason -

When the noise appears (very abruptly, as mentioned!), after 3-5 seconds it translates into normal engine noise until the aircraft is out of hearing range and fades away naturally.

It 'sounds' like the usual noise of an approaching aircraft (at circa 5,000 - 10,000 feet) has been massively delayed (just silence) due to conditions, wind or otherwise, then it hits you all at once for a few seconds before returning to normal.

[PENKO]

A4, the engines on the 319/320 always spool up on selection of flaps. But I do not think that's the cause of the howling noise.

It's either speedbrakes or the initial deployment of the slats. I think it is the slats. When you sit in row 2 or 3 there is a very distinct swoooooooooosh audible when the crew select F1 and I can easily imagine that this is very audible on the ground above and before the engine noise when and idle descent is flown.

But it could also be the speedbrakes since this howling sound on the ground sometimes changes pitch abruptly, which might coincide with selecting half speedbrakes.

[A4]

Yep - fair call. I forgot about Approach idle :O - but it's only about 5% on N1 I think not enough to generate the noise.

[FlightPathOBN]

sortof a sound like this.... AC sound (http://operationsbasednavigation.com/wordpress/wp-content/uploads/2012/08/ltsaberon01.wav) but deeper and longer..(without the blitz)

[MD83FO]

yeah thats the sound you hear sitting near the slats during extention. but i hvnt heard it from the ground.

[mustbeaboeing]

I believe there may be a multitude of 'sounds' here, causing possible confusion.

The original poster quoted, I think, FL15 to FL12 (think (s)he meant 15000 to 12000 feet).

I know the aircraft that pass over my house inbound to BHX (EGBB) Birmingham are above 10000 ft so this 'air' noise is not Flap/ Slat deployment.

I am of the opionion we are talking about Deployment, or Stowing of
Speed Brakes at this level, but am just curious as to its actual source.

[i_like_tea]

I still believe it is speed brakes as yes, we wouldn't be configured then in normal situations.

There is also a very pronounced aerodynamic noise (someone suggested its to do with Dp) around 4000 which is very clearly heard from within the aircraft but this would mean the aircraft is too low.

At / around FL100 the aircraft will be slowing down to 250kts (usually) and thus they may be going from idle back to a higher power setting once this speed is captured?

I would still bet on the speed brakes at that level.

[Tommy Tilt]

While on the subject, probably the best jet engine sounds you will ever hear. Particulary loved by Falkland Islanders.......superfuse :ok:
AVRO VULCAN XH558 TAKEOFF FARNBOROUGH AIR SHOW FRIDAY 13 JULY 2012 - YouTube

[1pudding1]

It definately is speed brakes. I fly the A320 over the OP's house anywhere from FL180-80 inbound to Bristol and its there where we often have to use speedbrakes to get down and slow down after being kept high on profile. Sure I said this a page ago ;)

[FlightPathOBN]

Its not the air rush noise, in the recording (which BTW is the lightsaber sound from star wars) its the low whoop...
Have an Airbus driver here from JetBlue, fortunately, there is a pub along the west approach to KSEA, the altitude on the flightpath is around 5500-6000 when the whoop sounds, he says it is when you go to config 1.

We had the ADSB running on the laptop. He pointed out by sound when it was an A320, vs the 737 which just makes an air rush noise...

(not sure about the original FL15-FL12 poster)

[tomahawk_pa38]

I am indebted to all you professionals who have taken the time to answer my query - I really didn't think it would generate that much interest !

Meant to say in my OP that I'm almost 'nose-on' to the aircraft concerned so maybe that makes a difference. In case Jonty isn't joking I'll sit under an umbrella ! and 1pudding1 - no need to apologise - I enjoy seeing you guys and sorely miss the Hercs, VC10s, C17s and other guests that no longer go over my house into Lyneham.

[i_like_tea]

That'll be €10 please.
Plus 150 taxes, 20 admin fee and a 10000 check in fee.

Thanks.

[FlightPathOBN]

Interestingly enough, there is a fix for this! No really...

It appears that they even had the folks at DLR looked at this. The study was only on the A320, so I am going to assume it is specific to that ac.
From the study and images provided, it appears the slat configuration causes the noise. As the slat extends, airflow is directed to the space behind the slat, rather than the bottom of the wing...creating what they call as 'cavitation resonance'.
I find it similar to blowing across the top of a bottle.

The fix is to place a small tab on the bottom of the slat, or slots, to reduce the cavitation pressure and direct airflow back to the bottom of the wing, rather than up through the space...

(just so you know, they even tried messing with the AoA to solve this...but to no avail)

So, there you go....

[peacekeeper]

1 pudding 1 is correct here, due to airspace restrictions there is always a last minute dive if landing on runway 27 at Bristol.

I would love to see the US guys do it without the 'Chicken lever' Maybe you prefer flying past the runway than landing on it?

[Landroger]

As the slat extends, airflow is directed to the space behind the slat, rather than the bottom of the wing...creating what they call as 'cavitation resonance'.
I find it similar to blowing across the top of a bottle.

That's the noise! I opened a thread about two years ago, asking almost the same question as the OP, although from a rather different viewpoint. I live in south London, where you guys are descending to intercept the ILS on 28L at Heathrow. I used to hear the 'blowing over a bottle neck' noise - I thought of it as a 'sharp groan', or 'dropping out of warp' - quite frequently, but not as often of late.

Of course, you will be at or a bit below 5000ft over my house, so aeroplanes would be in quite a different configuration to the OP's 18000, which is a bit of a mystery. My nephew is a Boeing driver and hadn't got a clue what I was talking about, so maybe it is only buses?

Roger.

[rudderrudderrat]

Hi Landroger,

Please see slide 24:
http://www.xnoise.eu/uploads/media/Almost-40years-Airframe-noise-Research.pdf

[pattern_is_full]

From Denver - yes, "dropping out of warp," "blowing across bottle neck," are also nice descriptions for what I'm hearing. Slat deployment also seems to make sense in terms of altitude/distance from airport.

Side question - in that report .pdf, where slat noise mitigation was attempted by "filling in" the slot between the slat and wing with brushes or extensions - wouldn't that to some extent reduce slat effectiveness? I though slats delayed onset of stall in part by the venturi effect of the slot (similar to slotted flaps).

[FlightPathOBN]

Concur, the 'fill' would seem to have overall effects throughout all phases of flight...perhaps that is why the issue is still around.

Interestingly, while observing, the Boeing ac still make a noise at the same point, but more of the air turbulence noise with no initial howl...

[PENKO]

Ok, after hearing aircraft flying over my house the whole afternoon and paying close attention to them for a change I am now convinced that it is the speedbrake. I even had a chap who deployed, retracted and deployed them again (as I have seen some colleagues do when selecting CONF1 with the speedbrakes out), with all the howling that comes with it.

Also in the flightdeck you can hear this howling at certain speeds when moving the speedbrakes.

[AKAAB]

That's when we're purging the chemtrail dispenser pump.

[NOLAND3]

We definitely must be talking about different sounds here. All the aircraft I have noticed making this brief groaning sound are flying the SID's and still below 6000ft.

It is definitely not the spoilers or a config change.. Not quite sure how some of you on the ground seem the know the flight crew are deploying the spoilers? X ray vision?

I'm still convinced it is some weird sound reflection of certain terrain, was hoping for a definitive answer from someone.

Btw, I think someone mentioned a lightsaber, a light saber turning off is exactly how it sounds to me, except the sound is much deeper.

Very strange and random, hense my curiosity.

[Landroger]

Thanks for that link RRR, although much of it went over my head. By mentioning folio 24, I take it you are thinking 'slat noise'? You may be right and I note that the noise propagation is to the rear of the aircraft, which might chime well with my, admitedly very unscientific, observations. I don't ever recall seeing the aeroplane I had just heard make the noise and surmise it had always just passed. With so many houses in close proximity round here, I don't get to see them very long.

We definitely must be talking about different sounds here. All the aircraft I have noticed making this brief groaning sound are flying the SID's and still below 6000ft.

It is definitely not the spoilers or a config change.. Not quite sure how some of you on the ground seem the know the flight crew are deploying the spoilers? X ray vision?

I'm still convinced it is some weird sound reflection of certain terrain, was hoping for a definitive answer from someone.


Brief groan is what I'm talking about Noland3 and only one. It is loud enough and sharp enough to be the only thing that calls my attention to that particular aeroplane. It is only unusual noises that make me look up much. Concorde always did, of course.

I always thought SIDs are 'Standard Instrument Departures', but I'm pretty certain the noise is only from aeroplanes descending and turning to intercept. I think my house is about 14 nautical miles from LHR and typically aircraft passing overhead come off the Biggin or Epsom stacks and are flying roughly north west. To give them 3000ft 10nm from touchdown, they need to be close to 4000ft overhead my house.

You guys will know exactly, but I can see from the ground that all sorts of config changes are going on above me, up to and including - rarely nowadays - wheels down or coming down. I can and have heard throttle up to arrest decent and throttle down to peg 240kts (is it 240 at that distance?)

My sense - as an engineer although not an aviation one - is the word resonance. Something about the noise says a resonant sound to me and since blowing across a bottle neck is exactly that, I can visualise slat or flap movements generating them. Just as they begin to move, new and temporary airsteams 'blow across' temporary cavities - bingo; a resonant oscillation that damps out almost immediately as the device reaches its normal or first operating position. It won't happen again because the cavity is no longer resonant.

I may be talking bo11ocks, but you have to admit it's good bo11ocks! :D

Roger.

[White Knight]

Bus Driver? What a twatty and patronising comment.

I'm an Airbus pilot matey. P I L O T. The B I G one too:ok::ok: I sincerely hope I wake you up in the middle of the night...................

[wheelie my boeing]

Hi Landroger,

When we leave the Biggin hold we are normally at / around 7000ft at 220kts (Airbus 320 that is). We are then turned northwest briefly before turning back on ourselves heading East. We reduce speed from 220kts to 180kts generally between after leaving Biggin and before turning onto final approach. We need to use Slats + Flaps to reduce our speed below 200kts (ish!) hence when we are asked to fly 180kts we need to use the slats + flaps which is most likely what you would hear. Generally people wouldn't need speedbrake on the A320 in that area, it's more needed once turning onto final approach if the aircraft is very light.

[dean4689]

Bleed air valves.

[Landroger]

There you go Wheelie, thank you. That puts some real numbers on my rather fast guesses, but my altitudes are about right! :ok: Which also highlights that some of the configuration changes to your aeroplane would be happening roughly overhead SW16. :)

As a field engineer, sounds are part of my stock in trade and for me there is rarely 'just a noise' - I can't help analysing them to figure out what makes them. I'm a Land Rover driver, so I'm very used to trying to work out what's going to break next! :ugh:

Roger.

[Landroger]

Bleed air valves.

And? You can't just leave it there Dean. :rolleyes: I can guess what bleed valves are, but what, where and roughly when? And, given how much - relative - noise the engines are making, would it be possible to hear one or more opening/closing/oscillating?

[aerobat77]

I'm an Airbus pilot matey. P I L O T. The B I G one too

sweet, so sweet ! :ok:

[dean4689]

Landroger,

The air for the air conditioning, pressurization, anti-ice etc is supplied from the compressor sections of the engine. On the type of engine that I am familiar with, the air during pressure normal power settings comes from the IP (intermediate pressure) section. However, during low power operations such as descent, there is not enough bleed air available so it is augmented with air from the HP (high pressure) section.

During operations in the terminal area where you may be carrying out step climbs or descents, as the thrust is varied, the HP bleed air valves will be opening and closing to make sure that sufficient air is available.

I think it is this that is making the strange noises.

Rgds,

Dean

[safelife]

It is certainly the sound of speed brakes being extended. The sound is very caracteristic and much louder than any other sound produced by the aircraft.
It can be heard on the ground while the aircraft is as high as 20000 ft.

The arrival routes for EDDH are coded -HAM-LBE-FAP but the actual distance flown is a direct to final, much shorter. So many pilots end up being much to high and have to use the speed brakes.

I flew the A320 for years, when my parents moved to a town 30 NM south of EDDH. When I sat in their garten for the first time I was nearly shocked what an extreme amount of noise those speedbrakes produce. Nearly 2/3 of all arriving Airbus end up deploying them more or less over our house, and while no aircraft noise is heard inside the house normally the sound of A320 speedbrakes being extended is clearly noticable.

[FlightPathOBN]

Check out this flex leading edge from DLR...put that on the howler (A320)...

http://www.dlr.de/dlr/en/portaldata/1/resources/documents/dlr_magazin_130/englisch/html/files/assets/seo/page29_images/0001.jpg

Page 29 - DLR_Magazin_130-GB (http://www.dlr.de/dlr/en/portaldata/1/resources/documents/dlr_magazin_130/englisch/html/files/assets/seo/page29.html)

[bille1319]

The more modern efficient jet engines do sound a bit like lawn mowers or fly-mos but usually at take off or at full thrust. This sounds quite different to the older noisier jets on take off but on the landing approach at low thrust would have a more pronounced whine than the more modern types.