Noises?

[Tracy]

I tried to do a search for this but didn't come up with anything.

My question is why do I sometimes hear the engine noise of the plane change?
Sometimes it sounds like the plane is slowing down.
It really freaks me out to hear any change although nothing ever happens of course :)
It's just that it momentarily makes me feel something IS about to happen....like the engines are going to conk out, lol!

BTW, I'm only aware of this once we are up in the air...not on take off or landing (I'm too busy then talking to God.)

[maroonwings]

I'd love to know the answer to this one too. I've assumed that it was the plane slowing down, but it always scares me. It makes me think that the engines stopped and we're going to fall out of the sky (of course that doesn't happen). I think that on my upcoming flight I'm going to take my iPod--if I can't hear the weird noises, I can't be afraid of them, right?

[Tracy]

You know, nine years ago I flew to the US from Australia and the whole "weird noises" thing got to me SO much that I resorted to listening to the inflight advertising message for a number of hours after the movie had finished.
lol!
Listening with headphones to ANYTHING is much better than being so acutely aware of the plane noises. :)

[LeslieDEN]

I think this is one thing that United's channel 9 really helps with. (Channel 9 is their "From the Flight Deck" channel -- lets you listen to communication between Air Traffic Control and your plane, as well as other planes in the area.) You hear ATC tell your plane, "Slow speed to <whatever>," you hear your pilot repeat the command back, and you hear the engines slow. So instead of being a why-are-the-engines-slowing moment, it's a wow-cool-I-got-to-hear-the-instruction moment.

I don't hear it very often during cruise, but once in a while it happens. After a few minutes, ATC tells the plane to "resume normal speed" and thanks the pilots for accommodating the controllers, and the engines rev back up.

I'll be interested to hear Capt. Hutch's response, but that's my take as a little layperson in the back listening in to channel 9.

[scottr0829]

The following may not be completely true, but I hope it is all true.

The only time the engines really need to be at full power is when the plane needs to gain altitude. When you are at cruise, the engines fall back because you are level and cruising along - not as much power is needed to keep the plane steady. When you descend, the engines are basically idle (or near it?? - they don't want any power because they don't need it). You are actually gaining speed when you descend even if the engines are idle - think of your car going down hill in neutral. Gravity is pulling and speeding it up. When my buddy brought me up in his Cessna, he told me a rule that you must learn to start being a pilot - pitch is for speed and power is for altitude. I am not sure if this applies for all planes, but from my experience flying the big birds in X-Plane, I think it does.

Captain Hutch or the others that are more knowledgeable will certainly correct the things that are wrong above. :)

[Captain Hutch]

Hi Tracy,

That is a great question. The changes in the sound of the engine that you hear are due to changes in the engine thrust caused by either the pilot moving the throttles manually or being moved automatically by the autopilot. As Scott mentioned, during takeoff the thrust is usually maintained at a constant setting. During cruise a constant power setting will be used to maintain constant speed. Often times however, and most of the time the reason is due to other aircraft traffic in the vicinity, air traffic control will direct the pilot to slow down or speed up while in cruise, or level off at an intermediate altitude lower than the cruise altitude. In order to maintain spacing between aircraft at the same cruise altitude, air traffic controllers will use speed or delaying vectors (turns) between aircraft.

I believe you will find the engine sounds changing more and more often as the skies become more and more crowded because the controllers are constantly having to adjust the aircrafts' speed to maintain the sequencing of the aircraft.

I also listen to the sound of the engines changing as I move the throttles. It is sweet music to my ears because I know that the engines are responding to even the slightest adjustment. In fact, I find it quite interesting that even a tiny change in thrust will be audibly noticeable, both in amplitude (loudness) and pitch. When I am flying the final approach I try to make it a little game with myself to have the thrust set so exactly that don't have to move the throttles until I am in the flare just prior to touchdown, and then I want to bring them slowly back to idle. I don't always succeed, and so when I do have to make even the smallest adjustment the passengers will hear that in the cabin, even if is only a 1 percent change. The sound is important, too, because when I am flying the approach most of the time I am looking out ahead at the runway, with only occasional glances into the cockpit at the instruments--when I move the throttle slightly, one of my clues that the thrust has changed is the change in sound of the engine.

I imagine that if you really knew a lot about jet engines, you might be able to tell what type and manufacturer as you taxied off the gate just be listening to the sound. Well, maybe!

Thanks again for an interesting question, and I hope that helps.

Hutch :tiphat:

[Tracy]

Thanks!
I'm due to board my flight in four hours.
I'll be listening to the engines with more understanding and less concern now. :)

[bellevueace]

This might be a stupid question but if aircaft can be glided down in the case of a total power loss and engines are throttled right back when coming in to land as the power isnt needed why does stalling the plane cause it to crash? Wouldnt stalling the engine just mean you havent got power, and whats the difference in this to a mechanical loss of power? Or have i got it all wrong as usual? Lol.

[MathFox]

This might be a stupid question but if aircaft can be glided down in the case of a total power loss and engines are throttled right back when coming in to land as the power isnt needed why does stalling the plane cause it to crash? Wouldnt stalling the engine just mean you havent got power, and whats the difference in this to a mechanical loss of power? Or have i got it all wrong as usual? Lol.

When pilots talk about "a stall" they talk about a change in airflow over the wings that causes a (partial) loss of lift on one (or both) of the wings. Pilots are trained to avoid stalls and recover from them. As stalls are caused by flying at too low a speed for the "attitude" (too much nose up) of the plane, pointing the nose down (which also helps to gain speed) brings the plane back in normal flying conditions.

Just set a safe speed in the autopilot and the plane won't stall during cruise. ;)

[Passenger Mark]

Good explanation Fox!

And Welcome Aboard Taking Flight!!!

:welcome2:

[Captain Hutch]

Hi Bellevueace,

That is a good question. As long as the air flows smoothly over the surface of the wing, the plane can glide or fly in a controlled maneuver. As soon as the airflow is disrupted, either when the airplane is gliding, flying under power, climbing, or turning, then the aerodynamics of flight are lost and the object is ruled by gravity--i.e., it will fall. The disruption of air over the wing is called a stall as I discussed in one of the other threads. You might even have one wing essentially flying and the other wing stalling, still an out-of-control and disastrous situation.

As a side note, though I think you didn't exactly intend to mention the stalling of an engine, this can actually happen if the airflow over the blades of the jet engine as the turbine is turning is disrupted. You may hear a loud noise if this occurs in flight and is called a "compressor stall".

Hutch :tiphat:

[bellevueace]

Many thanks for the explanations, its finding out information like this that goes some way to making me feel safer and less anxious when i have to fly.

[Jumbo]

I wondered this too! It scared the hell out me when it happened in pitch black flying over the atlantic.:eek:

[Falcon]

The 737s we fly react to wind changes while in the cruise. If the wind speed changes, ie entering or leaving a jetstream, the autopilot will adjust the thrust levers.

[CAflyer]

I just always try to think of a plane as my car. I think of take off as going up an on ramp onto the freeway, when I am on the free way that is the plane cruising, sometimes you need to speed up sometimes slow down due to traffic, going down an off ramp is landing. When you hit dips and pot holes that is turbulence. I know it's hard to think of when I am in the plane but I try.