N612UA
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Question About APU's

Sat Jan 08, 2005 5:59 am


Question about APU's. What all do they power while the plane is on the ground?

Thanks
 
smcmac32msn
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RE: Question About APU's

Sat Jan 08, 2005 6:01 am

Just a guess...... lights, ovens, coolers, all instruments in the cockpit, toilet flusher. Anything that needs power in the cabin is run off of the APU.
Hey Obama, keep the change! I want my dollar back.
 
Goldenshield
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RE: Question About APU's

Sat Jan 08, 2005 6:08 am

The APU can provide enough power to run the aircraft on the ground, as well as act as a second generator in flight. On top of that, it also provide pnuematic bleed air for air conditioning and engine starts.
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mtnmanmakalu
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RE: Question About APU's

Sat Jan 08, 2005 6:20 am

And the most important thing the APU powers is the Air pressure for the water on a DC-9 so I can have my coffee at 0-dark:30 on my originator out of some wonderful, wicked tundra city such as Fargo, Duluth, Minot, etc.,etc.......  Smile

I do, I don't, whatever.......
 
N612UA
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RE: Question About APU's

Sat Jan 08, 2005 6:55 am


Ok thanks a lot Does the GPU do the same thing as the APU expect using ground power?

Thanks again
 
mtnmanmakalu
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RE: Question About APU's

Sat Jan 08, 2005 7:00 am

If I remember correctly from my Aviation class years ago, the GPU provides electricity only- It can't provide bleed air, A/C air, or air for my precious morning Java!!!!

mtnman  Smile
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wbmech
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RE: Question About APU's

Sat Jan 08, 2005 7:00 am

Electrically, yes. A GPU does not supply any pneumatics like an APU.
 
N243NW
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RE: Question About APU's

Sat Jan 08, 2005 8:02 am

As mentioned above, the GPU only provides elecrical power for the aircraft. If you need air, you use an air start cart, often referred to as a "huffer." Most airports provide air conditioning ducts that lead from the gate to the plane, not to mention electrical connections as well, so usually a GPU isn't needed.
-N243NW Big thumbs up
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N612UA
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RE: Question About APU's

Sat Jan 08, 2005 9:40 am

ok thanks alot was not sure what all each of them were for.

Thanks mike
 
avioniker
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RE: Question About APU's

Sat Jan 08, 2005 10:12 am

Let's not forget the venerable old "-60" GPU. There's still a bunch of them in use.
It was, among other types, a GTCP 85 on wheels. That's air as well as electricity.
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533
 
PhilSquares
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RE: Question About APU's

Sat Jan 08, 2005 10:15 am

Just a point of clarification, all APUs are not certified for inflight operation. Some are certified for inflight operation, but can't be started in flight.
Fly fast, live slow
 
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HAWK21M
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RE: Question About APU's

Sun Jan 09, 2005 3:32 am

What all do they power while the plane is on the ground
APUs supply Pneumatics used for Engine Starting,AirConditioning.
Electricals via Generators for Lights,Galley Equipment etc & anything operated Electrically on the Aircraft.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
LimaFoxTango
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RE: Question About APU's

Sun Jan 09, 2005 7:23 am

Philsquares - Just a point of clarification, all APUs are not certified for inflight operation. Some are certified for inflight operation, but can't be started in flight.

That sentence makes no sense. First you say "all APU's are not certified for inflight operation." Then you say "Some are certified for inflight operation, but can't be started in flight". So if it can't be started or used in flight, how could it be used in flight in come cases?
You are said to be a good pilot when your take-off's equal your landings.
 
PhilSquares
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RE: Question About APU's

Sun Jan 09, 2005 8:32 am

Makes sense to me.

For example on the 747 some APUs can not be used in flight. Simple enough, the 727 is also like that.

On some later 747s and the 747-400, the APU can be used in flight, but not started in flight. That makes sense to me. It would be used in high temp/pressure altitude takeoffs at high gross weight where you need all the engine performance you can get. You would take off with the APU on and it would provide bleed air to the air conditioning. After takeoff, the engine bleeds would be turned on and the APU would be turned off.

Please go back and read what I wrote again. You will find it makes a lot of sense.
Fly fast, live slow
 
Santhosh
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RE: Question About APU's

Sun Jan 09, 2005 12:49 pm

When the engine produces enough power and also runs the Generator producing electrical energy why do they need to use the APU in flight? In what all conditions does pilots use APU in flight? Also which all aircraft are certified to use APU’s in-flight.

Thanx
George
Happy Landings :)
 
PhilSquares
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RE: Question About APU's

Sun Jan 09, 2005 1:06 pm

The engines are also used to produce bleed air which powers the air conditioning system which in turn pressurizes the aircraft, in addition to other uses.

ON extremely critical takeoffs the there are performance charts for a "packs off" take off, which in the 400 has the APU providing bleed air for the a/c. The use of the APU for takeoff provides about 1500lbs/thrust/engine.

As far as individual a/c that can use their APUs in flight, are you talking about starting in flight or just use? All the new generation twins can start and operate the APUs inflight. Don't know about the 340, the 400 can operate in flight, but not start. Some of the 747s can depending if the operator has modified the APU inlet door.
Fly fast, live slow
 
Goldenshield
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RE: Question About APU's

Sun Jan 09, 2005 1:20 pm

If a generator on an engine is deferred, the APU must be on and running in flight. There are restrictions as well, like the plane can not go above X altitude (which is usually in the 20-30,000 foot range.)
Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
 
PhilSquares
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RE: Question About APU's

Sun Jan 09, 2005 1:26 pm

Goldenshield,

Not on the 744....you can be dispatched with both the APU inop and a generator inop....
Fly fast, live slow
 
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HAWK21M
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RE: Question About APU's

Sun Jan 09, 2005 1:32 pm

When the engine produces enough power and also runs the Generator producing electrical energy why do they need to use the APU in flight? In what all conditions does pilots use APU in flight? Also which all aircraft are certified to use APU’s in-flight.

In case of Malfunctioning Engine Gen on one Engine,The APU Gen can provide the Electrical supply to the required bus.
APU in flight is used for providing alternate Electrical source as explained above.
On B737,APU can supply Electricals.
APU Can supply only Pneumatics [Alt limited]
APU can supply Pneumatics & Electricals [Alt limited]

BTW...George,Procured a DVD Writer & I tried both DVDs & they are working fine,Thanks.

regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
747NUT
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RE: Question About APU's

Sun Jan 09, 2005 6:09 pm

In what all conditions does pilots use APU in flight? Also which all aircraft are certified to use APU’s in-flight.

For ETOPS aircraft the APU needs to be operational for dispatch, this refers to twin aircraft. If one generator fails, the APU will be started and the APU generator used for powering the failed bus.
If it's not broken, don't fix it !
 
Santhosh
Posts: 543
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RE: Question About APU's

Sun Jan 09, 2005 11:07 pm

Thanx for the information on APU usage.

BTW...George,Procured a DVD Writer & I tried both DVDs & they are working fine,Thanks.

Mel I am more than happy to hear that from you.Have a gr8 time and enjoy

Regards,
George
Happy Landings :)

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