United737522 From , joined Dec 1969, posts, RR: Posted (7 years 7 months 3 days ago) and read 4733 times:
Hey everyone,
On one of my last AA 757 flights, after the first engine was shut down after landing, a sawing noise was very audible throughout the cabin. It went on for a good 5-7 minutes. I have a video of it and you can clearly hear it. If anyone know how I can post the video so you can hear, let me know.
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9 Reply 1, posted (7 years 7 months 2 days 23 hours ago) and read 4692 times:
Sounds like the Hydraulic Power Transfer Units. Because one engine is shut down, the hydraulic power from the hydraulic pump on the running engine has to be transferred to the other hydraulic systems.
Dl757md From United States of America, joined exactly 9 years ago today! , 1555 posts, RR: 18 Reply 3, posted (7 years 7 months 2 days 22 hours ago) and read 4589 times:
Quoting 474218 (Reply 1): Sounds like the Hydraulic Power Transfer Units
It is the Hydraulic PTU however there is only one on a 57. The PTU uses right system hydraulics to pressurize the left system hydraulics without fluid transfer when the left engine shuts down. For further info search 757 PTU in the Tech/Ops forum.
CdfMxTech From United States of America, joined Jul 2000, 1338 posts, RR: 29 Reply 6, posted (7 years 7 months 2 days 21 hours ago) and read 4516 times:
AA doesn't operate A320s...so its a sure bet it was a 57!
Dl757md From United States of America, joined exactly 9 years ago today! , 1555 posts, RR: 18 Reply 7, posted (7 years 7 months 2 days 21 hours ago) and read 4476 times:
Quoting RDUDDJI (Reply 5): I have never noticed said effect on a B757
Then you haven't been on one when the PTU is running. You can hear it in the cockpit it's so loud. It's very annoying and somewhat unnerving for pax who don't understand what it is or that it's normal. That would be most of them.
ETStar From Canada, joined Jan 2004, 2103 posts, RR: 9 Reply 8, posted (7 years 7 months 2 days 21 hours ago) and read 4465 times:
Ok I am assuming that this is the same noise as the ZZIIING ZIIIIIIIIIING ZIIIING noise that seems to come out from A320s right after pushback (and other times).
How about that other hissssssssssssssssssssss sound we hear when landing on a 757, right after the thrust reversers are activated and retracted (ok, might be wrong on actual terms, but it is after the thrust reversers). It can go on for many seconds.... hhsssssssssssssssssssss hshssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss
Can't be the breaks, can it? Only hear it on a 75.
Dl757md From United States of America, joined exactly 9 years ago today! , 1555 posts, RR: 18 Reply 9, posted (7 years 7 months 2 days 21 hours ago) and read 4459 times:
Quoting ETStar (Reply 8): How about that other hissssssssssssssssssssss sound we hear when landing on a 757, right after the thrust reversers are activated and retracted (ok, might be wrong on actual terms, but it is after the thrust reversers). It can go on for many seconds.... hhsssssssssssssssssssss hshssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss
Can't be the breaks, can it? Only hear it on a 75.
That's the 14th stage bleed valve relieving overpressure in the compressor section before it goes to the combustors due to the flywheel effect of the fan. N2 slows down quickly and N1 wants to keep going for a while. More info over in Tech/Ops.
ETStar From Canada, joined Jan 2004, 2103 posts, RR: 9 Reply 10, posted (7 years 7 months 2 days 21 hours ago) and read 4464 times:
Quoting Dl757md (Reply 9):
That's the 14th stage bleed valve relieving overpressure in the compressor section before it goes to the combustors due to the flywheel effect of the fan. N2 slows down quickly and N1 wants to keep going for a while. More info over in Tech/Ops.
Thanks for the quickie, although it was all jiberish to me. I recall seeing ET 752s arriving early in the morning at ADD, and after thundering down the runway, they seem to slow down and the hissss would go on and on. Anyhoo, will look at it in Tech-Ops.
F27XXX From , joined Dec 1969, posts, RR: Reply 11, posted (7 years 7 months 2 days 20 hours ago) and read 4403 times:
Quoting Dl757md (Reply 9): That's the 14th stage bleed valve relieving overpressure in the compressor section before it goes to the combustors due to the flywheel effect of the fan. N2 slows down quickly and N1 wants to keep going for a while.
Dl757md From United States of America, joined exactly 9 years ago today! , 1555 posts, RR: 18 Reply 12, posted (7 years 7 months 2 days 20 hours ago) and read 4394 times:
Dl757md From United States of America, joined exactly 9 years ago today! , 1555 posts, RR: 18 Reply 15, posted (7 years 7 months 2 days 20 hours ago) and read 4370 times:
Quoting F27XXX (Reply 11): Chr*st, Dorothy .. in ENGLISH this time .. Jeez!
Nice. Flame me for answering a question. I didn't have time to get into a long drawn out explanation breaking it down into layman's terms. That's why I pointed those interested to tech ops and the other thread I linked later. Stick to furniture if you don't want to get technical.
Dl757md From United States of America, joined exactly 9 years ago today! , 1555 posts, RR: 18 Reply 17, posted (7 years 7 months 2 days 20 hours ago) and read 4358 times:
Quoting F27XXX (Reply 16): Hey Hey ! Decaf! LOL .... Cmon i was just kidding with ya ... i wish it did make sense to me!
OK OK. You got me on the decaf thing. I'm doing chocolate covered espresso beans to stay awake right now. Sorry to jump all over you. When I have time I'll try and send you some info to explain how it all works.
Dfwagt From United States of America, joined Aug 2005, 75 posts, RR: 1 Reply 21, posted (7 years 7 months 2 days 15 hours ago) and read 4201 times:
Quoting Glareskin (Reply 19): American Airlines fleet:
Airbus narrowbody
A320: 278 aircraft
A319: 130 aircraft
A318: 46 aircraft in fleet and 40 on order
Well, this is new. I must have missed the memo where we replaced everything with Airbuses.
DrDeke From United States of America, joined Jun 2005, 830 posts, RR: 1 Reply 23, posted (7 years 7 months 2 days 14 hours ago) and read 4086 times:
Quoting F27XXX (Reply 11): That's the 14th stage bleed valve relieving overpressure in the compressor section before it goes to the combustors due to the flywheel effect of the fan. N2 slows down quickly and N1 wants to keep going for a while.
Alright, alright.
"14th stage bleed valve" = After 14 sets of 'blades' in the engine's compressor, there is a valve that can dump some of the compresed air overboard in case the pressure is too high at this point.
"flywheel effect of the fan" = The fan in the front of the engine is very heavy and was spinning very rapidly when the engine was being used to fly the plane. When they cut the throttle, the fan does not stop right away, and the fan blows air into the compressor, causing the pressure there to be too high after 14 stages.
"N2" = The compressor and turbine shaft.
"N1" = The fan shaft.
-DrDeke
If you don't want it known, don't say it on a phone.
MarBergi From Ireland, joined Aug 2004, 182 posts, RR: 0 Reply 24, posted (7 years 7 months 2 days 14 hours ago) and read 4058 times:
Quoting Glareskin (Reply 19): American Airlines fleet:
Airbus narrowbody
A320: 278 aircraft
A319: 130 aircraft
A318: 46 aircraft in fleet and 40 on order
25 Glareskin: I think you need to read more carefully!!!!
26 PiedmontINT: I think what he is trying to say is that the said "buzz saw" sound is very common on A320s.. hence the joke of saying are you sure it wasnt an A320.
27 Rdwelch: The PTU on the A320 Family sounds like Paul Bunyun on a bad date.
28 BWIA330: Thats like what I always hear on the Airbus A330. When on the ground, there is this loud clunk sound, im not sure if its the hydralics or brakes. Does
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