PlaneHunter
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Strange Noise On Singapore Airlines A380

Thu Mar 04, 2010 8:35 am

Some days ago I flew on the A380 (SIN-HKG on SQ) for the second time. What I found quite disturbing was a strange noise which could be heard in the back of the main deck during boarding (at least 20 minutes), on approach (ten minutes) and after landing (ten minutes). During boarding I thought it's flaps or cargo doors being moved/opened - but I dropped that thought after a few minutes. The sound, a constant up-and-down howling, was quite loud and somehow reminded me of a saw or an oversized vacuum cleaner...

I didn't notice that noise on my first A380 flight (Emirates) last year - probably it wasn't there or I overheard it, I don't know.

Any ideas?


PH
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curlyheadboy
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RE: Strange Noise On Singapore Airlines A380

Thu Mar 04, 2010 9:30 am

PlaneHunter,

That's gotta be the plane's PTU. I've never flown the 380 but all other Airbuses do make that noise a.k.a. "Barking Dog"
Cheers!
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PlaneHunter
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RE: Strange Noise On Singapore Airlines A380

Thu Mar 04, 2010 9:49 am

Quoting CURLYHEADBOY (Reply 1):
That's gotta be the plane's PTU. I've never flown the 380 but all other Airbuses do make that noise a.k.a. "Barking Dog"

Thanks. I was aware of different PTU noises on various Airbus types, but those had never been as loud and persistent as on the SQ A380.


PH
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Starlionblue
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RE: Strange Noise On Singapore Airlines A380

Thu Mar 04, 2010 10:24 am

Well, it MUST be bigger right?  
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KCmike
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RE: Strange Noise On Singapore Airlines A380

Thu Mar 04, 2010 1:21 pm

I havent heard of the PTU, is that along the lines of the APU?
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curlyheadboy
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RE: Strange Noise On Singapore Airlines A380

Thu Mar 04, 2010 2:56 pm

Quoting KCMike (Reply 5):
I havent heard of the PTU, is that along the lines of the APU?

KCMike,

The PTU (short for Power Transfer Unit), it's an evergreen topic on the forums due to the funny noise it makes, especially on the A320 family. If you do a search for it you'll get plenty of results with detailed informations on how it's built, and how it works.

From another thread:

Quote:
The Power Transfer Unit is used to transfer hydraulic power between the 2 main systems without transferring any fluid. This is accomplished by having a hydraulic motor in one circuit, connected to a hydraulic pump in the second circuit. I think Airbus calls them the red and green circuits. Say the pump is in the red, the motor in the geen. When red pressure drops, the motor on the green side starts to turn, thereby turning the pump on the red side, increasing the flow of hydraulic fluid on the red side. This raises the pressure back to normal, and the unit stops.

The reason for the noise is that the PTU accelerates up very fast, then stops just as suddenly. Each burst of speed takes a couple of seconds -- maybe as much as 5. The it stops for a while, and as pressure drops in red to a certain level, it picks back up.

The PTU is a safety measure, used when one engine is out and there is insufficient hydraulic power in that system to drive a selected function (say flap, or landing gear). The PTU is bi-directional, so it can supply either side when as needed.

(credits to member Delta-flyer)

Full topic can be found here: RE: A320 Sound (by DBOBA Aug 1 2001 in Tech Ops)
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musang
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RE: Strange Noise On Singapore Airlines A380

Fri Mar 05, 2010 5:41 pm

Where is the PTU in the 380?

thanks - musang
 
xero9
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RE: Strange Noise On Singapore Airlines A380

Tue Mar 09, 2010 12:58 am

Don't you only hear the PTU when not all engines are running? I know on the A320 for example when only 1 engine is running, I'm not sure how it works on the A380 (Having four engines). Seems kind of odd that the OP would hear it on approach.
 
curlyheadboy
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RE: Strange Noise On Singapore Airlines A380

Tue Mar 09, 2010 3:44 pm

Quoting xero9 (Reply 7):
Don't you only hear the PTU when not all engines are running? I know on the A320 for example when only 1 engine is running, I'm not sure how it works on the A380 (Having four engines). Seems kind of odd that the OP would hear it on approach.

I fly (as a passenger) on the 320 series airbuses once a week on average, and I can sometimes hear the barking noise also on approach. I remember hearing the PTU on the Airbuses normally works also when some extra hydraulic power is requested in any specific actuator, not only when single-engine. But here I stop because I lack the techinical insight which I'm sure can be found in the forum archieves... or maybe someone might be so kind and tell us again...?  
If God had wanted men to fly he would have given them more money...
 
PlaneHunter
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RE: Strange Noise On Singapore Airlines A380

Sat Apr 10, 2010 8:39 am

Quoting xero9 (Reply 7):
Seems kind of odd that the OP would hear it on approach.
Quoting CURLYHEADBOY (Reply 8):
I fly (as a passenger) on the 320 series airbuses once a week on average, and I can sometimes hear the barking noise also on approach.
Quoting CURLYHEADBOY (Reply 8):
or maybe someone might be so kind and tell us again...?

So the question is whether it really was the PTU. It's still a mystery.


PH
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tom355uk
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RE: Strange Noise On Singapore Airlines A380

Sat Apr 10, 2010 11:53 am

It would make sense for it to be the PTU at the given stages of flight - the time the noises are heard is when constant hydraulic demand is highest, especially on an aircraft the size of the A380. Think of all the systems....

Gear + Doors
Slats + Flaps
Trimmable Horizontal Stabiliser + Elevators
Ailerons + Spoilers
Rudder
Cargo Doors

There is some demand there, especially if conditions were not flat calm on the approach and constant control surface adjustments are required.
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zeke
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RE: Strange Noise On Singapore Airlines A380

Sat Apr 10, 2010 1:54 pm

Quoting PlaneHunter (Thread starter):
The sound, a constant up-and-down howling, was quite loud and somehow reminded me of a saw or an oversized vacuum cleaner...

Sounds like the ovens to me, they are convection ovens made by suppliers like B/E Aerospace. When the start up they sounds like a vacuum cleaner. On the 330/340 I can hear the ovens in the front galley start from inside the cockpit with the door closed.

Quoting CURLYHEADBOY (Reply 1):

That's gotta be the plane's PTU. I've never flown the 380 but all other Airbuses do make that noise a.k.a. "Barking Dog"
Cheers!

The PTU is only found on the A320 series and that is due to only one hydraulic pump per engine, and the blue hydraulic system being powered by an electric motor. The A330/A340/A380 series do not have a PTU, the A330 has two hydraulic pumps per engine, the A340 has one per engine (the green system is powered by two different engines), and the A380 only has two systems with electro-hydraulic backup.

We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
tom355uk
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RE: Strange Noise On Singapore Airlines A380

Sat Apr 10, 2010 2:20 pm

Quoting zeke (Reply 11):
The PTU is only found on the A320 series and that is due to only one hydraulic pump per engine

I'll shut up then   

Oh well, something new learned everyday!
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zeke
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RE: Strange Noise On Singapore Airlines A380

Sat Apr 10, 2010 2:44 pm

Quoting tom355uk (Reply 12):

Think nothing of it, I learn new things every day mainly from people like yourself !!! Apparently I have a good "nothing box", and normally only have the mental capacity for eating and breathing !!!! (Mark Gungor - Men's Brain Women's Brain)

Lucky you got an intelligent reply  
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
PlaneHunter
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RE: Strange Noise On Singapore Airlines A380

Sun Apr 11, 2010 7:13 am

Quoting zeke (Reply 11):
Sounds like the ovens to me, they are convection ovens made by suppliers like B/E Aerospace. When the start up they sounds like a vacuum cleaner. On the 330/340 I can hear the ovens in the front galley start from inside the cockpit with the door closed.

Thanks for pointing that out. But I'm wondering why those would make noise during approach and after landing, too.


PH
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zeke
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RE: Strange Noise On Singapore Airlines A380

Sun Apr 11, 2010 7:29 am

Quoting PlaneHunter (Reply 14):
But I'm wondering why those would make noise during approach and after landing, too.

I know on flights that arrive at destinations early in the morning local time, our crews normally do not start serving breakfast until 60-90 minutes before landing. In such cases, the only time our crews get to eat is after the passengers are off the aircraft, it takes 15-20 min to heat meals up. They could be heating up their own crew meals.

Prior to departure the ovens would be used to heat the towels up.
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baroque
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RE: Strange Noise On Singapore Airlines A380

Sun Apr 11, 2010 7:37 am

Quoting zeke (Reply 15):
Prior to departure the ovens would be used to heat the towels up.

What with vacuum cleaner and oven sounds, I am surprised Mrs Mop allows you up front Zeke. Or does she pop her head in and say "Can I do you now sir?"
 
wingscrubber
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RE: Strange Noise On Singapore Airlines A380

Thu Oct 14, 2010 8:15 pm

Folks, the A380 doesn't have a PTU according to AIR5005A. AIR5005 is the doc SAE produces for the aero engineering world covering many, but not all existing hydraulic systems of certified civilian western aircraft, rev A includes the A380 interestingly, you can buy yourself a copy for $100 or so, otherwise you need an IHS membership to read it...)

Some high points from the document:

System pressure: 5080psi (35,000kpa)

Hydraulic fluid:AS1241 (phosphate ester, skydrol/hyjet)

Number of hydraulic systems: only 2 Green & Yellow

Main engine driven pumps;
8 per aircraft, 4 in green system, 4 in yellow system (2 EDPs per engine)

AC auxiliary pumps;
4 per aircraft, 2 green, 2 yellow.

DC pumps;
3 per aircraft; 1 green & yellow system for braking, 1 in green system for steering

Accumulators;
17 altogether
1 main system accu. in green and yellow, 14 in braking systems of which 6 are bellow type, 8 are bladder type, and 1 in steering.

Reservoirs;
2 Air pressurized main sys reservoirs, 1 green & 1 yellow. 2 bellow type for braking, 1 bellow type for steering.

Pressure Filters;
13 per aircraft, 5 in green system, 5 in yellow system, 1 in each braking and steering sub-system
Case drain filters;
10 per aircraft, 1 for each EDP, 1 for each of the two main EMPs
Return filters;
2 main sys, 1 in each brake/steering sub-system.
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