A320 question

[ken]

Can anyone please enlighten me on the two-three second "saw" sound? It is easy to hear as a pax, sitting in the middle of the plane, before getting to the gate, and before the position and hold. It is a high tone like a dentist drill.
Thanks in advance.

 

[Cardinal]

Hydraulic Power Transfer Unit (PTU). Like a double-ended hydraulic pump; it uses one system to pressurize another. Activation after engine start as a self-test, then it's mostly a symptom of single-engine taxi. Ongoing activation can be avoided depending on how procedures are written. For us we leave an electric pump on during SE taxi, but kill the pump and thus ride the PTU during the second engine start.

Annoying as heck, but you can't hear it from the cockpit

 

[ken]

Thanks Cardinal.
The sound doesn't annoy me, I was just curious.
Inquiring minds need to know, lol.

 

[grog_sit_reserv]

I tell people its a dog in the cargo hold barking... then I tell the truth.

Can we please do something about the yellow pump. It's killing me when I'm in back and we're doing SE taxi.

 

[B6 Tech]

I tell people its a dog in the cargo hold barking... then I tell the truth.

Can we please do something about the yellow pump. It's killing me when I'm in back and we're doing SE taxi.

I've never heard the PTU sound described like the sound of a dentist drill..but whatever. Maybe the initial pack spool up? Those ACM's whines like crazy for just about two seconds... Especially the #2. Airbus should simply apply a placard at the L1 door explaining that the barking sound they hear is simply a hyd pump. Never fails that someone asks on every single flight. Shutdown at the gate always brings some amusing explainations from joe nobodys in the cabin.

Sure, all narrow body bus operators can do something about the yellow pump. Taxi on two engines and use the EDP rather than the elec pump.

 

[nosoupforyou!]

I tell people its a dog in the cargo hold barking... then I tell the truth.

Can we please do something about the yellow pump. It's killing me when I'm in back and we're doing SE taxi.

Well, I guess a steady high pitched whine is better than 30 minutes of the PTU sounding like the wing is being sawed off. That PTU is a great tool however, it's lousy for customers to listen to. We tried proceduralizing shutting it off on shutdown at the gate but it was more trouble than it was worth.

The barking dog is back.

 

[gutshotdraw]

Well, I guess a steady high pitched whine is better than 30 minutes of the PTU sounding like the wing is being sawed off. That PTU is a great tool however, it's lousy for customers to listen to. We tried proceduralizing shutting it off on shutdown at the gate but it was more trouble than it was worth.

The barking dog is back.

That high pitched whine is coming from the cockpit. It is a standard noise from every airline cockpit in America although it is a little louder in about 2/3rds of US Airways jets.......

 

[Blue Fish]

The "Barking Dog" is the PTO which will normally run for a few moments on startup and shutdown as well. The "Dentist Drill" is the back-up Electric Yellow Hyd Pump (normally Yellow runs off the #2 engine), which is run during single engine ops and when the cargo doors are opened (auto turned on and off). The interesting question is why doesn't the Blue Electric Hyd Pump, which is always running and is the exact same part #, make the same Dentist Drill sound?
Someone please translate into French and ask the right Pierre'.

 

[BiffF15]

And why does the damn jet call people "RETARDS"? I thought that wasn't PC anymore...

 

[TOGA]

Yeah, between that and having to ask for permission to go to the bathroom, I'm getting a complex!