Engine Noise on Flight

not1but4

I was on this flight on Saturday.

Just after take off and when we started to bank left it (while still climbing) it sounded like the right engine rolled back. I know the sound after we level off at our cruising attitude but this was less than a minute after take off. I was sitting just behind the wing so I could see the flaps etc of the wing.

Does anyone know what happened here or what I was actually hearing? As even though I'm not a nervous flyer (don't enjoy flying either) it did give me very sweaty hands for a minute

Locker10a

not1but4 wrote: »

I was on this flight on Saturday.

Just after take off and when we started to bank left it (while still climbing) it sounded like the right engine rolled back. I know the sound after we level off at our cursing attitude but this was less than a minute after take off. I was sitting just behind the wing so I could see the flaps etc of the wing.

Does anyone know what happened here or what I was actually hearing? As even though I'm not a nervous flyer (don't enjoy flying either) it did give me very sweaty hands for a minute

Probably just the engines decreasing thrust as the climb rate was adjusted, departures out of Gatwick are generally into very congested areas and there are often many adjustments to the climb rate between take off and cruise.

billy few mates

Probably just the change in engine tone due to the transition from flex or toga (take off power) to climb thrust, perfectly normal.

bkehoe

Gatwick departures have a low altitude level off (4000ft) and often continuous climb isn't given so the reduction in thrust would be quite noticeable at this stage in flight.

EchoIndia

not1but4 wrote: »

I was on this flight on Saturday.

I know the sound after we level off at our cursing attitude

Is this a technical term?!

Cianmcliam

While we're discussing strange noises, on two Ryanair flights after take off there was this very loud constant noise that I haven't heard on any other flights, hard to describe but just a constant, loud 'nehhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh' all through the flight. What's up with that?

IngazZagni

Thats just how the CFM 56 engines sound on a 737 but only in front of the engines. In the back half of the cabin you wont really hear that.

But that should only be during the climb so if you heard it during descent as well then its something else.

Cianmcliam

IngazZagni wrote: »

Thats just how the CFM 56 engines sound on a 737 but only in front of the engines. In the back half of the cabin you wont really hear that.

But that should only be during the climb so if you heard it during descent as well then its something else.

Thanks! Now that you mention it, I usually sit as far back as I can but probably was a lot more forward on those two flights. Definitely persisted well after reaching cruising height, might have stopped before descent.

That must be what it was, sounded a lot like this video I just found: https://youtu.be/5Ej_ITwTIrQ

Chris_5339762

bkehoe wrote: »

Gatwick departures have a low altitude level off (4000ft) and often continuous climb isn't given so the reduction in thrust would be quite noticeable at this stage in flight.

This.

I've had the same on the LGW - DUB flight on the easterly runway. Takeoff, low altitude level off and then a 180º left turn. Its to stay away from the Heathrow approaches from the SE as far as I know.

Nothing to worry about but it is quite a noticable drop in engine noise if you're in certain parts of the cabin.

billy few mates

Cianmcliam wrote: »

While we're discussing strange noises, on two Ryanair flights after take off there was this very loud constant noise that I haven't heard on any other flights, hard to describe but just a constant, loud 'nehhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh' all through the flight. What's up with that?

Are you sure it wasn't more of a 'mehhhhhhh' than a 'nehhhhhhh'...?

Cianmcliam

billy few mates wrote: »

Are you sure it wasn't more of a 'mehhhhhhh' than a 'nehhhhhhh'...?

Definitely no 'm', but saying that there were two guys from a remote Amazonian tribe behind me saying 'what's that gazzzzzzzzzziiiiiiiiiiiii noise?'.

PukkaStukka

billy few mates wrote: »

Are you sure it wasn't more of a 'mehhhhhhh' than a 'nehhhhhhh'...?

I've heard nehhhhh coming from certain individuals around O'Connell street lately. Obviously whatever variant of Jet-A1 they're using isn't getting them to their desired altitude....

Mebuntu

not1but4 wrote: »

I was on this flight on Saturday.

Just after take off and when we started to bank left it (while still climbing) it sounded like the right engine rolled back. I know the sound after we level off at our cursing attitude but this was less than a minute after take off. I was sitting just behind the wing so I could see the flaps etc of the wing.

Does anyone know what happened here or what I was actually hearing? As even though I'm not a nervous flyer (don't enjoy flying either) it did give me very sweaty hands for a minute

Have experienced this many times and believe it is noise abatement procedures off 08. I would agree with you that it is a bit daunting in that it happens so soon after lift off when you expect the engines to continue at full blast. Hope you didn't curse too much when you got up there

1012594711

I first noticed this on Airbus engines generally after plane reaches cruising height. There is no roaring sound audible in the cabin, presumably due to sound proofing but also because the plane is moving so fast away from the gases that provide thrust, so the engine roar would only be heard on the ground. I never worked out what caused the metallic 'nehhhhhh' sound like a metallic zipping or ratchet heard in the cabin. It could be the effect of a number of different factors, or it could be the gears connecting the different shafts in the engines meshing together with an extra gear engaged at cruising height. Many jet engines have different gear settings When a car reverses, its gearbox makes a different sound from when the car goes forwards due to the extra reversing gear engaging the 'gear train'. Perhaps a jet engine's gears make different sounds and a different gear is selected once cruise height is reached

Stovepipe

there's no way you'd hear the gearbox as it's under the engine, at least three yards from your seat and completely drowned out by the noise of the fan. Also, the gear ratios do not change; it's a fixed ratio box unlike a car gearbox and it's function is to drive pumps and generators. The ratcheting noise is the sound of the PTU (power transfer unit) in the hydraulic system which is under the rear of the cabin.

1012594711

Appreciate message. It's good to know about what generates the jet engine ratchetting noise. I had at first thought it was to do with hydraulics or pumping, then hit upon gearing, and was convinced more and more that it was gear meshing as I typed message, but the gears are indeed too far away from the seat in a plane to hear, outside fuselage and under the wing, whereas in a car they are very near the gear lever, not comparing like things at all. It was a mystery until now

billy few mates

Nothing to do with 'gearing' I'm afraid, and the PTU (in the main wheel well) is normally only heard on the ground during opening and closing of the cargo doors but that sounds more like a dog barking (woof, woof, woof) than 'nehhhhh' or 'mehhhh'....

1012594711

Saw some youtube clips of the 'buzzsaw' jet engine sound, eg 'Scandinavian buzzsaw' video with more theories of the cause posted as comments. Amazing how the sound seems so commonplace, and how I didn't notice any such sound in any flights I was on before year 2000

Captain_Crash

1012594711 wrote: »

Saw some youtube clips of the 'buzzsaw' jet engine sound, eg 'Scandinavian buzzsaw' video with more theories of the cause

I wouldn't call the cause a theory. It's caused by the tips of the fan blades breaking the sound barrier, and the resulting "sonic booms" echoing in the cowling.

In relation to the OP asking about the sudden change in engine noise,as explained earlier, it's just a transition to climb thrust. In the below video it's quite clear just after take of, the eagle eyed will also notice the pitch angle change so while power reduces, the aircrafts speed increases

https://youtu.be/im32AHm0qq8

H3llR4iser

Mebuntu wrote: »

Have experienced this many times and believe it is noise abatement procedures off 08. I would agree with you that it is a bit daunting in that it happens so soon after lift off when you expect the engines to continue at full blast. Hope you didn't curse too much when you got up there

That has probably to do with it as well - If you ever fly out of Naples airport in Italy, this situation extremely apparent since being it in the middle of the city, climbs have restrictions in terms of airspeed (180kts) and ascent rate; It makes for an interesting situation where the power decrease is quite marked - imagine storming away from a traffic light at full song in a relatively quick car, being pushed in the seat et all, only to lift off when hitting the speed limit in order not to go over it. I can understand how non frequent flyers and non-aviation enthusiasts can get a bit surprised and even worried by that, it does feel and sound like the engines "stopped pushing" all of a sudden.

The oddest takeoff I experienced was in Gatwick as well, not sure which runway, on a BA 737-436: instead of the classic lineup, 50% power or so, forward roll then take off power, the pilot seemed to hold the aircraft on the brakes for quite some time with some serious power flowing (not sure how much can the 737's brake/tires take before the plane starts skidding forward), everything shaking like crazy, then he/she released the brakes and we were out of Gatwick like the proverbial bat out of hell. I frankly loved it and am disappointed it doesn't happen more often , but still have no idea why it was done...

Mebuntu

H3llR4iser wrote: »

The oddest takeoff I experienced was in Gatwick as well, not sure which runway, on a BA 737-436: instead of the classic lineup, 50% power or so, forward roll then take off power, the pilot seemed to hold the aircraft on the brakes for quite some time with some serious power flowing (not sure how much can the 737's brake/tires take before the plane starts skidding forward), everything shaking like crazy, then he/she released the brakes and we were out of Gatwick like the proverbial bat out of hell. I frankly loved it and am disappointed it doesn't happen more often , but still have no idea why it was done...

A possible explanation. Some years ago I used to travel out from LGW a lot and I recall similar experiences at a time when maintenance was being done on the main runway and the shorter standby runway was being used for the late evening departures. I agree with you...a great experience

Locker10a

H3llR4iser wrote: »

Mebuntu wrote: »

Have experienced this many times and believe it is noise abatement procedures off 08. I would agree with you that it is a bit daunting in that it happens so soon after lift off when you expect the engines to continue at full blast. Hope you didn't curse too much when you got up there

That has probably to do with it as well - If you ever fly out of Naples airport in Italy, this situation extremely apparent since being it in the middle of the city, climbs have restrictions in terms of airspeed (180kts) and ascent rate; It makes for an interesting situation where the power decrease is quite marked - imagine storming away from a traffic light at full song in a relatively quick car, being pushed in the seat et all, only to lift off when hitting the speed limit in order not to go over it. I can understand how non frequent flyers and non-aviation enthusiasts can get a bit surprised and even worried by that, it does feel and sound like the engines "stopped pushing" all of a sudden.

The oddest takeoff I experienced was in Gatwick as well, not sure which runway, on a BA 737-436: instead of the classic lineup, 50% power or so, forward roll then take off power, the pilot seemed to hold the aircraft on the brakes for quite some time with some serious power flowing (not sure how much can the 737's brake/tires take before the plane starts skidding forward), everything shaking like crazy, then he/she released the brakes and we were out of Gatwick like the proverbial bat out of hell. I frankly loved it and am disappointed it doesn't happen more often , but still have no idea why it was done...

This is done in cold conditions, ice/snow/freezing fog

Dardania

It could also be more noticeable due to position in the cabin. From a book I read years ago, apparently the noise is loudest at 45 degrees (when viewed in plan) from the engine - be that front or back.

Locker10a

Dardania wrote: »

It could also be more noticeable due to position in the cabin. From a book I read years ago, apparently the noise is loudest at 45 degrees (when viewed in plan) from the engine - be that front or back.

This particular noice can only be heard infront of the engines. The only glimpse of it you may here is if a crew member is making an after takeoff PA from a forward crew station. You can hear the engine noise over the PA

billie1b

H3llR4iser wrote: »

The oddest takeoff I experienced was in Gatwick as well, not sure which runway, on a BA 737-436: instead of the classic lineup, 50% power or so, forward roll then take off power, the pilot seemed to hold the aircraft on the brakes for quite some time with some serious power flowing (not sure how much can the 737's brake/tires take before the plane starts skidding forward), everything shaking like crazy, then he/she released the brakes and we were out of Gatwick like the proverbial bat out of hell. I frankly loved it and am disappointed it doesn't happen more often , but still have no idea why it was done...

The brakes on the aircraft are pretty amazing, I can remember being out doing engine runs on the Ryanair -200's and -800's at full thrust and 80% power and the aircraft would be bouning and shaking like a mad thing but wouldn't budge an inch.
I've also experienced a few of the same take-off's, used to request them in the jump seat years ago, there's actually no better feeling on an aircraft.

irishgeo

billie1b wrote: »

The brakes on the aircraft are pretty amazing, I can remember being out doing engine runs on the Ryanair -200's and -800's at full thrust and 80% power and the aircraft would be bouning and shaking like a mad thing but wouldn't budge an inch.
I've also experienced a few of the same take-off's, used to request them in the jump seat years ago, there's actually no better feeling on an aircraft.

whats the reason for them?

billie1b

irishgeo wrote: »

whats the reason for them?

Which them?

Pat Dunne

irishgeo wrote: »

whats the reason for them?

If you mean brakes, it the same reason for anyother vehicle with wheels.

bkehoe

irishgeo wrote: »

whats the reason for them?

To ensure there are no leaks or any abnormal indications after an engine replacement or maintenance action usually but occasionally to help troubleshoot engine faults reported by crew. Most are idle ground runs for a period of time defined by the maintenance manual but some would occasionally require higher power settings for brief periods of time.

irishgeo

i should have clarified myself a bit better. Why would you do a takeoff mentioned above with the plane at take off power been held by brakes?

Simon Gruber Says

Shorter take off distance. The engines are at TO thrust before moving, rather them spooling up whilst already rolling.

bkehoe

irishgeo wrote: »

i should have clarified myself a bit better. Why would you do a takeoff mentioned above with the plane at take off power been held by brakes?

Its a fan blade ice shedding procedure thats required during certain winter operations. Boeing SOP is 70% thrust for up to 30 seconds. So if its below 3 degrees C and snowing/fog/rain then you can expect this.

jimbis

I was on a flight from Faro-Dub in summer of '99 that done an engine spool up on the brakes, I guess the reason for it was runway length + weight (full holiday charter).
Some experience being shot back into your seat when the brakes were released.

1012594711

I first noticed this sound on an Airbus in 2000. I have found videos of this sound on YouTube, described as 'Buzzsaw' sound. I searched the Web for explanations of 'Buzzsaw' and found a few long explanations, which I downloaded. I have kept copies. Hopefully if you search using that word you'll find the explanations too