APU inoperative

[colsie]

Hey all. Me here with some more bad pilot complaints.

On my outbound from Edinburgh in a 757 the APU on the aircraft was not fucntiong. This is happened once before to me on a different airline, and during the previous case we were off loaded and had a replacement aircraft brought to us. Now we where kept on the craft and flown, it of course posed no problems in flight but on the ground before engine start it was horrid.

Anyway I wished to ask if it was legal to fly an aircraft if you had a non operative APU. And if it is an essential piece of equipment should an engine fail (which I think it is. I am probably wrong however)

[extreme P]

Inop APU is legal. ETOPS considerations will change the status.

[DBate]

wished to ask if it was legal to fly an aircraft if you had a non operative APUIt is perfectly legal - no problem with that.

And if it is an essential piece of equipment should an engine failNo, it's not. In any case you still have at least the other engine with its generator supplying electrical power.
On some types it is not even possible to start the APU in flight (I think B744 is one of those).

And there are even other types, which don't even have an APU (DC8 comes to mind).

So all in all, it is legal and SAFE to fly without APU. In extreme weather conditions on ground it might just be a matter of passenger comfort.

[No_Speed_Restriction]

Other possible backups could be an HMG or a RAT

[411A]

Type, L1011.

APU is allowed to be unserviceable, however, the flight can not be operated more than 400 nm overwater and, the maximum allowed calendar time the APU can remain unserviceable is ten consecutive days.

An MEL stipulation.

[mini-jumbo]

An MEL stipulation.

Type specific I should imagine regarding time allowed before rectification.

[411A]

Type specific I should imagine regarding time allowed before rectification.

Yup, certainly is.

[SU-GCM]

HZ-APU is a Saudi Arabian Airlines MD90 with an always non operative APU Since it entered service
been flying as PAX on it a couple of times and APU wasn't working on both flights :)

[SNS3Guppy]

The APU is an essential tool, but hardly necessary. APU's on different airplanes accomplish different roles. All provide bleed air for air conditioning and other purposes, most generally drive at least one electrical generator, and some also run hydraulics, too. However, each of those functions can also be accomplished by outside sources and equipment, until the aircraft's engines are running and supplying bleed air, electrical power, and other aircraft system's needs.

I've flown airplanes around the world with an inoperative APU. It's an inconvenience at times, requiring keeping an engine running on arrival until ground power is attached, or cross-bleed starts and slow starts from ground carts...but it's do-able.

From a passenger perspective, not having air in the cabin can be uncomfortable, especially in a full cabin on a hot day. An airline may not simply have another one hundred million dollar airplane on hand to substitute for you...after all, how many spare cars do you keep handy in case yours breaks, or how many spare homes do you own in the event you might lose one in a fire or flood? A spare isn't always available or convenient...or may be in use for a similiar situation affecting another airplane.

Each airplane has a minimum equipment list which specifies what can be inoperative, for how long it may be that way, and under what conditions the aircraft can be operated, as well as specific maintenance or pilot operational requirements to make the flight safe and legal. The APU will be included in this list.

We can't start our APU in flight anyway; it's a ground function item only...so not having one really has no impact on our ability to go fly. It might have an impact on whether we can start the engines, keep the airplane warm or cool, or do certain things on the ground, but it's perfectly legal and those are operational convenience issues, rather than things which affect the safety of flight or the legality thereof.

[GlueBall]

"colsie" . . . you write as if you're a B757 pilot, . . . but you can't be, because if you were, you wouldn't be asking this question.

[SNS3Guppy]

Coulsie sounds to me like a passenger who was uncomfortable, and is simply asking the question.

[DenizD]

I think alot of pax would be suprised about the amount of stuff that is inop on their jets prior to takeoff. Hey colsie, did you know there was a 744 BA flight from LA to LHR that lost an engine and continued on three?

[grumpyoldgeek]

Coulsie sounds to me like a passenger who was uncomfortable, and is simply asking the question.

Even the most green private pilot knows about MEL.

[dream747]

How does the APU aid in ETOPS operations though?

[vortsa]

It can supply electrical power and pneumatics, many other systems can be run from the electrics in flight, and of course aircon on the ground, so it is critical for ETOPS. When on the ground with engines shut down the aircraft can be supported with ground equipment GTSU ( air start to engines), AIRCON ( speaks for itself), GPU ( electrical power)

[G-STAW]

hello,

on the subjects on APU operation,

what is the exhaust sound heard from the APU when the aircraft is about to commence push?

i know that the a/c would be out of power if the APU was to be shut down at this time as ex pwr has already been disconnected plus none of the EDG's have not come online yet (the a/c hasnt started its engines)

hope you guys can help,

G-STAW

[FlyingSpanner]

Not really sure what your getting at here G-STAW.

Of course when the aircraft is starting engines packs are switched off (either manually Boeing or Automatically Airbus) At that point the aircraft EEC commands the APU controller to up the bleed pressure for engine start.

Consequently, there is more fuel going into APU and as such there will be an increase in volume which MAY be the sound which you hear.

Regards to if you lose the APU on push back there is no way to start as you have lost bleed preessure to start the engines. However if you were on stand there is a procedure to do a battery start if you have pneumatics but not electrics. Not the preferred method but it can be done.

Hope that this helps.

Spanner :ok:

[dream747]

If everything is shut including the APU and the engines, how long can the batteries supply the power to the necessary DC and AC equipments for? Are these the same batteries that power the electric starter motor for the APU too?

Thanks!

[vapilot2004]

If everything is shut including the APU and the engines, how long can the batteries supply the power to the necessary DC and AC equipments for? Are these the same batteries that power the electric starter motor for the APU too?


Target requirement is usually 1/2 hour and the equipment supplied is very minimal but enough for safe flight. The APU battery is usually dedicated. The EEC computers have their own PM generators and critical flight control modules have their own powerpacks on some aircraft.

Re:Limitations etc...
A 727 APU can only be operated on the ground. Many 707s had no APU so a huffer truck was needed to start the engines. Buick V8s were commonly used as the motive source if I recall correctly.

[G-STAW]

Not really sure what your getting at here G-STAW.

Of course when the aircraft is starting engines packs are switched off (either manually Boeing or Automatically Airbus) At that point the aircraft EEC commands the APU controller to up the bleed pressure for engine start.

Consequently, there is more fuel going into APU and as such there will be an increase in volume which MAY be the sound which you hear.





ahh this helps alot, thanks