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Apu Limitation On A320

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Apu Limitation On A320

Old 8th Oct 2010, 03:28
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Apu Limitation On A320

Hi, prunners:

well I have a question and I'm sure someone will help me , why if we have one generator inop and deffered by MEL the flight altitude is limited to 33500ft and the operating limitation of the apu could be up to 39000ft?

thank you

toby320.
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Old 8th Oct 2010, 04:06
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Thats a new one on me.

It might be a Co-imposed limitation. As far as I know the Airbus MMEL states no such lim.

Check with your chief pilot. If so ask him the reason - Id be interested myself.
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Old 8th Oct 2010, 04:32
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Something to do with the recommended APU start altitude being 25,000 feet and the amount of time descent to this altitude would take?
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Old 8th Oct 2010, 06:07
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As far as I know the Airbus MMEL states no such lim
It's certainly in the FAA MMEL
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Old 8th Oct 2010, 09:58
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If you look at the APU envelope in the 'Limitations', there is no limit on starting the APU unless in the Emerg Elect Config but the 90Kva limit starts at 35000'. Perhaps there's a clue there!

There are, of course, other limits concerning bleed air from the APU.

Cheers
mcdhu
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Old 8th Oct 2010, 10:12
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Hi Toby320,

Edit.

All our aircraft have that limitation. FL335 ISA + 30 is just about where the maximum APU 100% available generator output starts to fall off.

I can only guess that the regulations specify that, at dispatch, we must plan a FL where 100% APU generator is available (in case the remaining main engine geny failed).

Last edited by rudderrudderrat; 8th Oct 2010 at 12:51. Reason: re-read MEL
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Old 8th Oct 2010, 14:09
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thks for your replies I'm still looking for an answer may be the clue is like rudderruderrat said, sounds logic but let wait for some more reference as soon as I have some answer I will waiting for some more clues
tks
toby320
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Old 8th Oct 2010, 15:27
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It's in my companies MEL .. (UK airline)

One may be inoperative provided :

6. Flight altitude is limited to 33500 ft, and
I agree with rudderruderrat,

From APU Envelope info:
30000 @ ISA 100 % (90 KVA)
35000 @ ISA 93 % (84 KVA)

Last edited by SupaMach; 8th Oct 2010 at 15:41.
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Old 8th Oct 2010, 19:26
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It is on the Airbus MMEL and has to do with load capability. It is assumed that the only operating engine GEN would fail and the APU GEN would be carrying 100% of the aircraft load.

G
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Old 9th Oct 2010, 14:58
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ok on limitations of apu operation those limitations are correct so I asume that's why we can go up to 33500fts so many tks guys

toby320
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