Airbus A320 - wierd noise - help!

[3141castro]

We live approx 65 kms north of BOD, France

We see A320 family a/c of AF overhead, on way into BOD.

Nearly every time they pass over, there is a very strange noise, a change of pitch and a whining noise - as if there is a sudden drop in thrust...

I know from the description it doesnt sound strange... but evry time it happens its as though they are dropping a bomb on us...

My theory would be that we are near a beacon or marker, and that the AF Op prec would to be to begin the descent, and cut down on engine power.. would anyone have an idea?

Having lived on flightpaths before, we have heard many noises, but this, i have never heard before.

[AVIACO]

Not specifically sure but the A320's that AF operate are powered by CFM engines, I believe, as opposed to IAE engines.

I regularly fly european on BA, and they have two different types of A320 in their fleet - some are powered by CFM engines, the same as the AF Airbuses, whilst ther majority of the BA fleet is powered by IAE engines.

I am a novice in the industry, but there is definitely a very distinct difference in sound generated by the CFM engine. I would say, to use your words, it is more whining (almost like a hover-mower short of lubrication) whereas the IAE engine is more placid in its tonal changes.

As I say, I am a novice (and the above answer probably shows it), but I am sure one of the real flying experts will be along in a moment with a proper answer.

By the way, any BA A320 pilots out there - was I dreaming the above, or am i correct? I just flew LHR-ABZ on G-EUUK (?), and back again on G-BUSB. Seated in row one both times. Very different engines noises, partic in climb and descent.

AVIACO

[TURIN]

AVIACO

You are not mistaken.

The early fleet of A320s (-100 & -200s) were a legacy from the BCal 'merger', they are fitted with CFM56 engines.
The later aircraft, A319/20/21s all have IAE V2500 series motors. :ok:

They make very different and distinct sounds, especially when throttling back from TOD etc.

AF are, naturally flying with CFM56s fitted as the company (CFM International) is half French.;)

[AVIACO]

Thanks Turin. I thought perhaps that i'd had too much of the excellent BA Chardonnay on my flights, and it was the old ears playing up!

So, am I also right in saying that the legacy aircraft that you are referring to (from BCAL) are also the ones that do not have wing fences? I am now starting to piece the jigsaw together.

What about the original question about the aircraft approaching landing into BOD? Is it the same phenomenon that I find on ascent that Castro is hearing on descent?

Also, one final question on the CFM engines, (sorry to be an inquisitive fellow), but are the CFM engines on the A320 that you mention above, also the same CFM engines that can be found on the Boeing 737-300?

I have very vague memories of flying with Monarch in 1987 on a B737-300, G-MONG, from LTN to PMI and back. (In the days when Monarch had the designator OM before MON) I had always flown on Boeing 737-200's of Britannia up until that point, and then found meself on a MON 733, which appeared to have an engine with the bottom squashed flat. (I now know why, by the way). But, are the engines the same, because I do not recall the same terrible din on the B733 as I did on more recent A320's, although my MON 733 was very possibly newer than your earlier BCAL A320????

I have childhood memories of looking out of the much coveted window seat on my MON733 (had to fight my brother for it) and seeing the big words CFM in a red circle on the engine housing.

I know there may be hundreds of different types of CFM engines, but just curious to know. (I am using the sole logic of the aircraft being of approx the same size in the thrust of my query!)

Thanks.

AO

[flybywire]

I am not a pilot, so I cannot be technical, but changes in "noise" are very frequent on take off and approach.

On take off usually pilots soon after take off, when the plane is safely airborne, reduce the thrust to minimise noise. The plane is safely in the air and doesn't need as much thrust as when lifting off the ground. This is done purely to save a bit of the engines' life and to reduce noise.

On approach I can always tell when the pilots disconnect the autopilot and start flying the plane manually by the noise. Changes in speed at low altitude determine the change in noise as well as when the flaps are extended or the spoilers used to decelerate/descent. It's far more obvious when you're onboard, but you can notice it also when on the ground, especially if you live near an airport and on the flight path.
I know my city's airport (LIMJ) so well that everytime I fly there I can foresee what noise I'm going to hear and when :D

I wouldn't worry too much :ok: and it's true, IAE V2522 and CFM56 engines do make different noises, with a bit of practice you can recognise them without even looking up in the sky!!! :cool:

Ciao!!

FBW:)


To answer to your last question, 737 CFM engines are very similar to the A320 CFMs, they differ in a few things, starting from the shape. 737 engines are "flat" at the bottom since the plane is not so tall after all!

BA 737-300/500/400 are equipped with CFM56-31C (speed of Mach 0.74)
A320 with CFM56-5A1, slightly more powerful (Mach 0.78)

As for the winglets on the A320, I am not sure, I know that AF A320-100 don't have them, while A320-200 do.
But, again, I could be wrong......I am more of a Boeing girl!! :)

[TURIN]

AVIACO

The first few of the 'legacy' A320s are -100 series, they do not have the winglets fitted, (wing fences are an entirely different subject and I will not go into that now). The rest are -200 series. Ten a/c were inherited from BCal.

The noise on ascent is probably the so called 'buzzsaw' sound which is created (mainly) from the fan blades being supersonic at the tips.

The throttle back on descent is an entirely different sound and can sound very disconcerting as if the a/c is plummeting.

As f by w states the 737- 3/4/500 series are cfm56s as are the A320, just slightly different models/ thrust ratings.

As far as I know CFM International have only produced the CFM 56 so far. I could be wrong but it has been used on many a/c types including.....DC8, A320, A340, 737-3/4/5/6/7/8/900.

Hope this helps. :ok:

[AVIACO]

Thanks Turin and others for another very informative reply.

So what is the difference between winglets and wing fences?

AO

[BahrainLad]

Thanks Turin. I thought perhaps that i'd had too much of the excellent BA Chardonnay on my flights, and it was the old ears playing up!

I think with a comment like that it's more likely for your tastebuds to be playing up!

Wing Fences/Lets:

Winglet: 747-400/MD-11/A330/A340
Wing Fence: A300/A310/A320Family/A380

Basically, in appearance terms, the wing fence extends to an equal distance below the wing as well as above.

Don't know jack about the aerodynamics, but it's something to do with vortices.....

[747FOCAL]

The noise you are refering to is the bleeds opening. The Pratt powered 757 is one of the better examples. Sounds like a tuba.

[Atlanta-Driver]

I used to live under an approach path and very close to where most pilots elected to lower the landing gear. I noticed a strange sound on Airbuses as well as on the B737NG's. And guess what, sounded just like on demand hydraulic pumps, quite loud though.

AD

[AVIACO]

Thanks BahrainLad. I can see your point about the taste buds. Now fully understand difference too between winglets and wing fences.

[TURIN]

BahrainLad...

Wing Fences.

These are the scimitar (blade not car) shaped devices fitted to the upper surface and leading edge of wings on aircraft such as the BAC 1-11, DH 125.
Usually situated about half way between the wing root and tip, they reduce the spanwise flow of air from root to tip and increase the efficiency of a swept wing.
Boeing do a similar job with little bits of metal stuck to the top of the wing, these are known as vortex generators and do the same job as a wing fence but in a different way.

The devices you describe with a "an equal distance below the wing as well as above", I think are referred to as 'end plates'.

[Sliding member]

So is it the sound of engine bleeds? I often hear this sound from A/C on awy A25, it's quite a sudden and loud sound that takes one by suprise, just as a/c is in the overhead. It's always intrigued me