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AA 757 Sawing Noise  
User currently offlineUnited737522 From , joined Dec 1969, posts, RR:
Posted (8 years 11 months 2 days 15 hours ago) and read 5335 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.

Thanks for your responses!

30 replies: All unread, showing first 25:
 
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 1, posted (8 years 11 months 2 days 15 hours ago) and read 5294 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.

User currently offlineJmc1975 From Israel, joined Sep 2000, 3279 posts, RR: 15
Reply 2, posted (8 years 11 months 2 days 14 hours ago) and read 5196 times:

Sounds like the typical sound of a Rolls-Royce engine.


.......
User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 3, posted (8 years 11 months 2 days 14 hours ago) and read 5191 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.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineGlareskin From Netherlands, joined Jun 2005, 1305 posts, RR: 1
Reply 4, posted (8 years 11 months 2 days 13 hours ago) and read 5138 times:

Are you sure it wasn't an A320?


There's still a long way to go before all the alliances deserve a star...
User currently offlineRDUDDJI From Lesotho, joined Jun 2004, 1483 posts, RR: 3
Reply 5, posted (8 years 11 months 2 days 13 hours ago) and read 5121 times:

Quoting Glareskin (Reply 4):
Are you sure it wasn't an A320?

Yeah, no joke the A320's are loud as heck! I have never noticed said effect on a B757.

Quoting United737522 (Thread starter):
I have a video of it

Tsk, tsk, shouldn't be using electronics during taxi... (ex. cellphones)  Smile



Sometimes we don't realize the good times when we're in them
User currently offlineCdfMxTech From United States of America, joined Jul 2000, 1341 posts, RR: 26
Reply 6, posted (8 years 11 months 2 days 13 hours ago) and read 5118 times:

AA doesn't operate A320s...so its a sure bet it was a 57!

User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 7, posted (8 years 11 months 2 days 12 hours ago) and read 5078 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.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineETStar From Canada, joined Jan 2004, 2103 posts, RR: 7
Reply 8, posted (8 years 11 months 2 days 12 hours ago) and read 5067 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.


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 9, posted (8 years 11 months 2 days 12 hours ago) and read 5061 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.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineETStar From Canada, joined Jan 2004, 2103 posts, RR: 7
Reply 10, posted (8 years 11 months 2 days 12 hours ago) and read 5066 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.


User currently offlineF27XXX From , joined Dec 1969, posts, RR:
Reply 11, posted (8 years 11 months 2 days 12 hours ago) and read 5005 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.


OH .. OK .. silly us for asking!

Chr*st, Dorothy .. in ENGLISH this time .. Jeez!


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 12, posted (8 years 11 months 2 days 12 hours ago) and read 4996 times:

Check out this thread in CivAv as well.
http://www.airliners.net/discussions...eral_aviation/read.main/1579396/4/

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineDLKAPA From , joined Dec 1969, posts, RR:
Reply 13, posted (8 years 11 months 2 days 11 hours ago) and read 4986 times:

Quoting Glareskin (Reply 4):
Are you sure it wasn't an A320?

Do a search on AA A320 and let us all know how it turns out.


User currently offlineF27XXX From , joined Dec 1969, posts, RR:
Reply 14, posted (8 years 11 months 2 days 11 hours ago) and read 4973 times:

Quoting ETStar (Reply 8):
hhsssssssssssssssssssss hshssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss

No, silly ... u heard Brendan, the F/A , making his arrival announcement... jeeeeezus!

tony   

[Edited 2005-10-25 09:32:56]

User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 15, posted (8 years 11 months 2 days 11 hours ago) and read 4972 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.  irked 

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineF27XXX From , joined Dec 1969, posts, RR:
Reply 16, posted (8 years 11 months 2 days 11 hours ago) and read 4966 times:

Quoting Dl757md (Reply 15):
Stick to furniture if you don't want to get technical.

Hey Hey ! Decaf! LOL .... Cmon i was just kidding with ya ... i wish it did make sense to me!

Tony

PS -- I am in total agreement with you -- the 757 is the most beautiful airliner in te sky!


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 17, posted (8 years 11 months 2 days 11 hours ago) and read 4960 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.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineF27XXX From , joined Dec 1969, posts, RR:
Reply 18, posted (8 years 11 months 2 days 11 hours ago) and read 4944 times:

Thanks man - sounds great -- and u can send a cpl of those choc covered espresso beans too, come to think of it! LOL

Tony  cheeky 


User currently offlineGlareskin From Netherlands, joined Jun 2005, 1305 posts, RR: 1
Reply 19, posted (8 years 11 months 2 days 10 hours ago) and read 4914 times:

Quoting CdfMxTech (Reply 6):
AA doesn't operate A320s...so its a sure bet it was a 57!



Quoting DLKAPA (Reply 13):
Do a search on AA A320 and let us all know how it turns out.

American Airlines fleet:
Airbus narrowbody
A320: 278 aircraft
A319: 130 aircraft
A318: 46 aircraft in fleet and 40 on order



There's still a long way to go before all the alliances deserve a star...
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 20, posted (8 years 11 months 2 days 10 hours ago) and read 4891 times:

Power Transfer Unit.
regds
MEL



Think of the brighter side!
User currently offlineDfwagt From United States of America, joined Aug 2005, 81 posts, RR: 1
Reply 21, posted (8 years 11 months 2 days 6 hours ago) and read 4803 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.


User currently offlineGlareskin From Netherlands, joined Jun 2005, 1305 posts, RR: 1
Reply 22, posted (8 years 11 months 2 days 6 hours ago) and read 4750 times:

Quoting Dfwagt (Reply 21):
I must have missed the memo where we replaced everything with Airbuses.

This fleet renewal happened at the same moment CdfMxTech and DLKAPA changed the subject of this thread from 757 noise to AA fleet.....  Wink



There's still a long way to go before all the alliances deserve a star...
User currently offlineDrDeke From United States of America, joined Jun 2005, 830 posts, RR: 0
Reply 23, posted (8 years 11 months 2 days 5 hours ago) and read 4688 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.
User currently offlineMarBergi From Ireland, joined Aug 2004, 182 posts, RR: 0
Reply 24, posted (8 years 11 months 2 days 5 hours ago) and read 4660 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

I think you need to check your sources!!!!!!

Try this one American Airlines.

The only Airbus I can see are the 300's


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 Post contains images 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
29 474218 : Sounds like a long drawn out grunt.
30 Glareskin : Thank you!
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