Airliners without APU's

[steinycans]

How often do airliners fly without their APU fitted? What sort of consideration do ops/pilots have to give such an operation?

[BUSH BABY]

Airlines have to consider things like:-

. Are GPU's available dowroute
. Are airstarts available downroute

If the answer is yes to these then there is not really a problem with flying without the APU. the only real problem is that it can sometimes increase T/R times due to having to start up before pushback and conecting GPU's etc. for example easyjet allow and extra 10 min if the A/C requires an Airstart. Hope this answers your question.

brgds BB

[Techman]

How often do airliners fly without their APU fitted?

Very rarely. I suspect what BUSH BABY was refering to, was operation with APU inoperative, but not removed.

If the APU is removed the APU compartment have to prepped (various ducts, electrical connectors and fuel lines blanked off). The CG will of course also change - an APU can weigh approx. 350kg - and will have to be compensated for.

[canyonblue737]

Originally Posted by Techman

Very rarely. I suspect what BUSH BABY was refering to, was operation with APU inoperative, but not removed.

If the APU is removed the APU compartment have to prepped (various ducts, electrical connectors and fuel lines blanked off). The CG will of course also change - an APU can weigh approx. 350kg - and will have to be compensated for.

I don't think you will see an aircraft fly without the APU *in* the aircraft but you will see aircraft fly with them inoperative.

[BOAC]

Looks like there is an echo in here................... Glasses anyone?

[steinycans]

How big an effect on center of gravity would flight without APU be on say a 737? Would the aeroplane (generally speaking) have to carry fewer passengers or cargo because of the change in aircraft CG?

[notdavegorman]

APU removed altogether

On an aircraft such as a 737, the distribution of the pax and baggage/freight quite possibly would need to be non-standard, i.e. more of the load being placed towards the rear of the aircraft. Having said that, balance problems for airliners at least, tend to relate to the centre of gravity being too far to the rear. Assuming the balance problem can be overcome, the overall payload wouldn't be affected.

As has previously been mentioned, although aircraft regularly fly around with the APU inoperative, I would imagine it's very unusual for it fly around with it removed altogether. If the APU needs complete replacement, an aircraft would generally fly around with the duff one still in place until a replacement is fitted.

[Leezyjet]

When I worked at Bmi back in the late 90's, there was a 737 flying around with the APU removed for a couple of weeks. Just required a minor service weight adjustment (weight/ CofG adjustment) on the loadsheet to compensate. No big deal really.

[Dash-7 lover]

Brymon Airways (as it was) had apu's removed from the Dash-8-311's to save on weight. Rumour has it that they'll be installed again on refurbishment with BA Connect... Some aircraft like the RJ100 rely on the apu for cabin pressure and airconditioning rather that taking bleed air from the engines when extra puff is needed to get out of places like Innsbruck or Salzburg.

[In trim]

There are a few airports out there with no Air Start available, and therefore from an operational point of view this can mean a bit of juggling of aircraft allocations required if an APU is unserviceable.

Of course if an APU then fails on turnround at one of these airport, you can be up the creek!!

[Dash-7 lover]

or a GPU??

[ElNino]

Some aircraft like the RJ100 rely on the apu for cabin pressure and airconditioning rather that taking bleed air from the engines when extra puff is needed to get out of places like Innsbruck or Salzburg.

Not sure about the RJ, but the 146 can not take-off at all if using engine air for the packs. So if the APU is u/s (or not used, as our SOPs recommend), the cabin is not pressurised until the engine air and packs are switched on (only done after climb power selected). In this case, the packs and bleeds are switched off by 500' agl on landing. For both T/O and LDG, one engine air is left switched on, but only to drive the discharge valves.
Unpressurised operation, whether deliberate or not, sounds crazy. And it is, but that's the 146!

For non-APU starts, we use the GPU for all 4 engines, or else start one on GPU, then cross start the rest (usually use the GPU for all 4 unless in a hurry and want to start the rest during the push). The 146 doesn't use air start, each engine is fitted with an electric starter motor which turns the N2 shaft. It makes no difference timewise, whether we have an APU or not.

[Flap15Geardown]

When Air Malta had their 737's delivered in the mid 80's they came over without APU's fitted and flew around like that for a couple of months. The APU's were fitted latter and was supposedly done to save money - earn some cash from flying before spending it on a shiney new APU

[Swedish Steve]

Originally Posted by In trim

There are a few airports out there with no Air Start available, and therefore from an operational point of view this can mean a bit of juggling of aircraft allocations required if an APU is unserviceable.
Of course if an APU then fails on turnround at one of these airport, you can be up the creek!!

Happened to a BA B777 a couple of months ago. The APU failed on a West Indian island, and they had to SHIP an airstart in from Trinidad!( On a boat)

[CV880]

Some aircraft were certiificated for "APU Removed" flight and it was in the MMEL eg. 747. Boeing sold a blanking kit to plug the various fuel and pneumatic lines and a plug for the exhaust duct etc. A weight and balance correction had to be made when loading the aircraft, otherwise it was the same as operating with an unserviceable APU ie. a pain in the rear!