Airbus sound question

[great cornholio]

I was commuting in on an Airbus tonight and the pax next to me asked me what a sound was. I told them I had no idea what it was since I have no idea what it is. Anyways I hear it on the Airbus pretty often seems to happen right before or during push and then again pulling into or right after blocking into the gate. Best way to describe the sound is that it sounds like a midget with a hacksaw under the floor. Seems to be louder over the wings. Anyways have been asked a few times over the years and have even wondered myself, but tonight was the first night I was bored enough to ask about it here.

 

[kf4amu]

I was wondering the same thing. Sounds like a very loud pump turning on and off randomly.

 

[jetpig32]

Not an airbust flyer, but probably hydros or ptu.

 

[PeanuckleCRJ]

It's the hydraulic PTU.

 

[Guppiedriver]

Nope, it is a midget with a hacksaw.

 

[ImbracableCrunk]

I always think of a barking dog. RUH Ruh ruh. RUH Ruh ruh.

Where's Click & Clack when we need em?

 

[UALjan15]

Hydraulic power transfer unit (PTU) runs during single engine ops to keep dead side hydraulic pressure up. It can be turned off, but I don't know how many airlines do so in their procedures.

 

[AC560]

Nope, it is a midget with a hacksaw.

A French midget with a hacksaw to be more exact.

 

[Raskal]

A French midget with a hacksaw to be more exact.

Well? Is she hot?

 

[i fly boxes]

I always tell passengers they are sawing of the wing cause its due for replacement. Thats what it sounds like

 

[Volasl]

The PTU is a reversible motor-pump located between the Green and Yellow hydraulic systems. It enables the green system to pressurize the yellow system, and vice versa, without fluid transfer. The PTU is automatically activated when the differential pump pressure output between the green and yellow systems exceeds a predetermined value (500 PSI). On the ground, when the engines are not running, the PTU enables the yellow system electric pump to pressurize the green system. Operation of the PTU is displayed on the ECAM page and also indicated via an ECAM memo.

PTU operation is inhibited when the:

• <Nosewheel steering in the towing position
• First engine is being started (PTU operation is automatically tested during second engine start)
• Cargo doors are operated and for 40 seconds after the end of cargo door operation
• Parking brake is ON and only one ENG MASTER switch is ON
• PTU pb is OFF

 

[SpauldingSmails]

It's a fat lady in corduroy pants walking around.

 

[freeflyer14]

Funny this thread should come up, I was deadheading on a UA bus the other day, and this sound started. These passengers around me (obviously not the most well seasoned travelers) started to freak out. I then got to listen to a 15 minute dissertation about how this airplane was a piece of junk, was dangerous, old (this was actually a newer looking A319), too loud, unsafe, etc etc.

 

[MIAFO]

If you turn on the yellow electric pump you never have that noise..

 

[great cornholio]

The PTU is a reversible motor-pump located between the Green and Yellow hydraulic systems. It enables the green system to pressurize the yellow system, and vice versa, without fluid transfer. The PTU is automatically activated when the differential pump pressure output between the green and yellow systems exceeds a predetermined value (500 PSI). On the ground, when the engines are not running, the PTU enables the yellow system electric pump to pressurize the green system. Operation of the PTU is displayed on the ECAM page and also indicated via an ECAM memo.

PTU operation is inhibited when the:

• <Nosewheel steering in the towing position
• First engine is being started (PTU operation is automatically tested during second engine start)
• Cargo doors are operated and for 40 seconds after the end of cargo door operation
• Parking brake is ON and only one ENG MASTER switch is ON
• PTU pb is OFF

Thanks for the info. I always thought it was something related to the HYD sys.

 

[great cornholio]

It's a fat lady in corduroy pants walking around.

To me it sounds a bit fast for walking, but sounds more like runnin towards her next twinkie.

 

[NEDude]

If you turn on the yellow electric pump you never have that noise..

I am amazed at how few airlines seem to not turn it on during single engine taxi. I was riding in the back of a United A319 a few weeks ago during a long taxi in ORD and the PTU ran for 40 minutes before they started the other engine.

 

[flyn96]

Heard a pax say how it sounded like a barking dog down in cargo and how the airline was so bad that they couldn't even treat a dog with respect. Pretty funny stuff.

 

[Bringupthebird]

I am amazed at how few airlines seem to not turn it on during single engine taxi. I was riding in the back of a United A319 a few weeks ago during a long taxi in ORD and the PTU ran for 40 minutes before they started the other engine.

If you're taxiing on No. 2 then running the electric pump doesn't do any good (eng2 is driving the yellow pump anyhow). If you're taxiing on No.1, you have the yellow electric pump operating in the unlikely event you shuck the green pump. Moral of the story: SE taxi on eng 1 only (if you can ). Also the electric pump can overheat.


I had a passenger get off the airplane saying "I thought you'd never git that motor started with that dead batt'ry. She just cranked and cranked and cranked."

 

[critterair2]

wow a thread that made it through a whole page and no hijack...YET

 

[kf4amu]

If its a pump, why does it turn on and off so quickly? I'd expect those conditions for PTU operation to be pretty static and unchanging from second to second.

 

[Cardinal]

It's not so much a pump as two hydraulic motors bolted to each other. And like everything else is electronically controlled. When it senses a differential of 500 psi between systems it will "run" (allow one hydraulic motor to turn the other) in order to bring the low side up to 3000psi, then stop until the system bleeds down and the differential agains reaches the 500 psi threshold for activation.

The system will also run during periods of high demand when one system's pressure is pulled down, i.e., gear retraction. Why build each hydraulic system to be up to it's task? Better to do it the socialist way, a team effort, with each system helping out when times get tough. I am the green system, and I am my brother's keeper.

 

[CA1900]

The system will also run during periods of high demand when one system's pressure is pulled down, i.e., gear retraction. Why build each hydraulic system to be up to it's task? Better to do it the socialist way, a team effort, with each system helping out when times get tough. I am the green system, and I am my brother's keeper.

:laugh:

Well-done.

 

[Vingus]

Jetblue SOP is to turn on the yellow pump during single engine ops to keep it quiet. We used to have a SOP that shut the PTU off on engine shutdown which would keep it quiet at the gate. That SOP went away when too many guys forgot to turn it back on when the left the cockpit. It was a good idea, but as usual, a few dummies ruined it for everyone.

 

[lowtimedriver]

It's a fly-by-wire baggage handler.

 

[BLUE BAYOU]

I still turn the PTU off at shutdown until at least a cargo door is opened (which actuates the yellow hydraulic pump). This usually resolves the barking dog issue which is at its worst at engine shutdown at the gate.

 

[ACL65PILOT]

Most big jets have them. That is why on the 767/757 we start the left engine first. That way it will not go on.

 

[Ralph Cramden]

Fifi plays both ways. It's a French tradition! PTU can be powered by yellow or green (that's L & R to the non french speaking), and powers the lower pressure side. Blue (center to non french speaking) is lonely, only plays with itself (the rat is it's backup).

 

[PreContact]

Just say the words RED RUM, that's what it sounds like to me!~

 

[Guppiedriver]

If you turn on the yellow electric pump you never have that noise..

The high pitched whine of the yellow electric pump is just as annoying as the PTU.