bristolflyer From United Kingdom, joined May 2004, 2135 posts, RR: 0 Posted (10 months 3 weeks 3 days 1 hour ago) and read 3494 times:
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.
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
JetMech split the back of his pants. He can feel the wind in his hair.
bristolflyer From United Kingdom, joined May 2004, 2135 posts, RR: 0 Reply 3, posted (10 months 3 weeks 2 days 17 hours ago) and read 3316 times:
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?
ZSOFN From United Kingdom, joined Jun 2005, 1393 posts, RR: 8 Reply 4, posted (10 months 3 weeks 2 days 17 hours ago) and read 3313 times:
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.
CosmicCruiser From United States of America, joined Feb 2005, 2214 posts, RR: 16 Reply 7, posted (10 months 3 weeks 2 days 13 hours ago) and read 3210 times:
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 8, posted (10 months 3 weeks 2 days 12 hours ago) and read 3175 times:
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.
Viscount724 From Switzerland, joined Oct 2006, 21498 posts, RR: 24 Reply 9, posted (10 months 3 weeks 2 days 9 hours ago) and read 3110 times:
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?
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.
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
JetMech split the back of his pants. He can feel the wind in his hair.
zeke From Hong Kong, joined Dec 2006, 7727 posts, RR: 73 Reply 13, posted (10 months 3 weeks 19 hours ago) and read 2637 times:
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 From Australia, joined Mar 2006, 2588 posts, RR: 53 Reply 14, posted (10 months 3 weeks 2 hours ago) and read 2471 times:
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
JetMech split the back of his pants. He can feel the wind in his hair.
HAWK21M From India, joined Jan 2001, 31201 posts, RR: 58 Reply 15, posted (10 months 2 weeks 6 days 18 hours ago) and read 2409 times:
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.....
wannabe From United States of America, joined Jun 1999, 675 posts, RR: 3 Reply 17, posted (10 months 2 weeks 6 days 4 hours ago) and read 2279 times:
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.
ThrottleHold From South Africa, joined Jul 2006, 622 posts, RR: 1 Reply 18, posted (10 months 2 weeks 5 days 23 hours ago) and read 2224 times:
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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