bristolflyer
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Roaring Noise Inflight?

Fri Jul 06, 2012 2:24 am

I travelled DEN-LHR and return last week and noticed every so often a roaring noise (possible air disruption?) that would last for a minute or 2 during cruise. No other changes apparent. It was a 777 but I could swear I've head it on other planes before.

Any thoughts?
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Starlionblue
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 2:51 am

Could it have been some vibration?

Would it be all the time or periodically? If it was periodic it could have been the engines throttling up for an ascent.
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jetmech
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 5:06 am

Quoting bristolflyer (Thread starter):

I recently flew on a DL 772LR to and from the US, and I also noticed the phenomenon you talk about. Once or twice during the flight, for a period of 10-15 seconds or so, the slipstream noise seemed to rise noticably before returning to the prior levels. Perhaps it was either an increase in engine noise whilst climbing to a higher flight level, or spoiler noise to limit speed whilst descending to a lower flight level?

Regards, JetMech
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bristolflyer
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 10:47 am

Quoting jetmech (Reply 2):
Once or twice during the flight, for a period of 10-15 seconds or so, the slipstream noise seemed to rise noticably before returning to the prior levels.

Yes, that is exactly it. I didn't notice an altitude change but I guess that could be it. Or could it be something on teh body of the aircraft opening or closing and disrupting the air?
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ZSOFN
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 10:51 am

Were you sitting behind the wing? The increased thrust during a step climb makes that sort of noise, and I can't think of any other possible / plausible cause in routine ops. It's particularly noticeable of course flying on 777s and other large twins; more so after the BA38 incident where higher-power step climbs became SOP.
 
deaphen
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 11:27 am

Its possibly the outflow valve adjusting the pressure of the cabin?

Nitin

[Edited 2012-07-06 04:31:33]
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HAWK21M
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 11:35 am

Probably the Engine encountering a heavy head wind/tailwind.....similiar occurances noticed when an Aircraft taxies into a gate with a tailwind.
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CosmicCruiser
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 2:44 pm

pack surge is a possibility.
 
tdscanuck
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 3:45 pm

Quoting jetmech (Reply 2):
spoiler noise to limit speed whilst descending to a lower flight level?

This is very unlikely; a normal step down is pitch-control-on-speed so the spoilers shouldn't come up.

Another potential source is the lavatory flushing. At cruise, the vacuum source for the lavs is differential pressure to the outside. There will be a roaring wind noise any time the lavs cycle; the lav vent (one or two) is typically near the aft end.

Tom.
 
Viscount724
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RE: Roaring Noise Inflight?

Fri Jul 06, 2012 6:27 pm

Quoting HAWK21M (Reply 6):
Probably the Engine encountering a heavy head wind/tailwind

I've noticed the noise described by the OP on quite a few flights.

If an aircraft is flying in calm air and then suddenly enters an area (e.g. a jetstream) where there's a 100+ knot headwind (or tailwind) wouldn't that at least briefly mean the aircraft is moving faster or slower than it was in relation to the air it's flying through, and wouldn't that mean a brief change in sound in the cabin?
 
bristolflyer
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RE: Roaring Noise Inflight?

Sat Jul 07, 2012 12:44 pm

Quoting ZSOFN (Reply 4):
Were you sitting behind the wing?

Sure was. Thanks for everyone's replies.
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HAWK21M
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RE: Roaring Noise Inflight?

Sat Jul 07, 2012 6:54 pm

The sound is termed as the Blowtorch effect........
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jetmech
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RE: Roaring Noise Inflight?

Sun Jul 08, 2012 1:39 am

Quoting tdscanuck (Reply 8):

Fair enough. The only issue with lavatory noise, was that this particular roaring sound only happened once or twice during the flight. I don't think I really ever notice toilet flushing noise, but every time this roaring occurred, it got my attention straight away.

Quoting HAWK21M (Reply 6):

This could be it. I have also noticed a similar phenomenon when I have pushed out aircraft, especially as you say, when the engine is hit with a tailwind.

Regards, JetMech
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zeke
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RE: Roaring Noise Inflight?

Sun Jul 08, 2012 8:40 am

Quoting bristolflyer (Thread starter):
I travelled DEN-LHR and return last week and noticed every so often a roaring noise (possible air disruption?) that would last for a minute or 2 during cruise.

1-2 minutes would be a climb to a new level, that would be about 2000'. I normally in cruise start a climb with a gentle V/S as this will gradually increase the thrust and is not as a noticeable audible change over a period of time for the passengers. Asking the aircraft to do an immediate climb will increase the thrust more rapidly. That being said, I think on the 777 there was a requirement to do full thrust step climbs after the BA incident, not sure if that has been removed.

Quoting jetmech (Reply 2):
Once or twice during the flight, for a period of 10-15 seconds or so, the slipstream noise seemed to rise noticably before returning to the prior levels.

I have noticed shorter periods of cabin air conditioning noise to be associated with reducing speed, thus asking the engines to come back to idle. This changes the bleed available to the packs.
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jetmech
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RE: Roaring Noise Inflight?

Mon Jul 09, 2012 2:12 am

Quoting zeke (Reply 13):
I have noticed shorter periods of cabin air conditioning noise to be associated with reducing speed, thus asking the engines to come back to idle. This changes the bleed available to the packs.

Fair enough. So it could also be the noise associated with switching the bleed air from low stage to high stage. Interestingly, the air show on my return flight was displaying a head wind in excess of 250km/h a few hours out from SYD. Is this reasonably common? Have you ever had any head winds of such magnitude?

Regards, JetMech
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HAWK21M
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RE: Roaring Noise Inflight?

Mon Jul 09, 2012 10:15 am

Quoting jetmech (Reply 12):
This could be it. I have also noticed a similar phenomenon when I have pushed out aircraft, especially as you say, when the engine is hit with a tailwind.

Exactly......Sounds like a air blowing thru a hollow cone or a welding blowtorch......There is a distruption in the Air flowing Air thru the Engine due to the Tail wind or Shutting down engine.....
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zeke
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RE: Roaring Noise Inflight?

Mon Jul 09, 2012 10:44 am

Quoting jetmech (Reply 14):
Is this reasonably common? Have you ever had any head winds of such magnitude?

Very common, it is seasonal.
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wannabe
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RE: Roaring Noise Inflight?

Mon Jul 09, 2012 11:59 pm

I have also heard this noise, and it seems to be exclusively 777. I just came back from a round the world business trip, and flew 777 on 3 legs. The noise appeared on all 3 flights. It is definitely an engine spool up, and my thoughts were that it was an altitude change. At the same time, I could not perceive any acceleration nor pitch up to gain altitude. One other thought is that, if the air temp were to increase outside, and the aircraft was at the upper end of it's altitude rating, they may need to increase speed slightly to avoid stalling.

I also flew A330 and 747 on several of the legs, and noticed that there was no such sound when at cruise in either one of those types.
 
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ThrottleHold
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RE: Roaring Noise Inflight?

Tue Jul 10, 2012 5:07 am

Quoting zeke (Reply 13):
I think on the 777 there was a requirement to do full thrust step climbs after the BA incident, not sure if that has been removed.

The requirement for that is removed when an operators engines have been modified.

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