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pacinolove
28th Feb 2017, 15:50
I am a A320 Pilot,One day in duty take off from an airport which take off performance require PACKs OFF for take off, but I can't turn off the two packs but I keep the apu bleed on for take off, after take off if if if I forgot to turn the apu bleed off, what will happen until the aircraft climb to the FL200??;)

Piltdown Man
28th Feb 2017, 20:20
I'm not trying to horrible but you should know the answer to this one. This should have been covered in your type qualification training. I feel your answer will lie in the limitations sections of your AOM. As to what happens when the APU can longer supply pressurisation will be answered in the air-conditioning/pressurisation section of your AOM. But it is really worrying such a simple question like this is placed on the internet by a "qualified" pilot.

I'll also pose you another question. Can you do a packs-off take-off with an inop APU?

gusting_45
28th Feb 2017, 20:36
Why bother with the APU for bleed air. Just do a Packs Off Takeoff. Simple

PENKO
28th Feb 2017, 20:37
Piltdown Man, FCOM only states the limitation of 15000 feet for running the packs with the APU. Nowhere is written what will actually happen in the situation described by topic starter, i.e. a continued climb to cruise level (say FL380) with the APU supplying both packs.

There was absolutely no need for those harsh words. Do you know what happens to the APU passing 15000 feet? You fly the type, you seem to know it all, so enlighten us.

learner001
28th Feb 2017, 21:30
Should "pacinolove" and others be too afraid to ask as a result of our answers ?

Very obviously, he is just looking unpretentiously for answers to some questions he has.

Wether he SHOULD have KNOWN, OR NOT, may have numerous reasons.

To assume the worst, as some 'aces' (also in respose to his other questions in other topics) do, is at least impolite.

If he puts these questions in his early days on the Airbus as a 'learner', there is no good reason to 'hammer him down'.

Know how some type qualification training is done nowadays...?

cinocav
28th Feb 2017, 23:03
I stand to be corrected but I believe you will get a "AIR - APU BLEED FAULT" ecam caution since the APU bleed valve will eventually close because it can't keep up with the demand while is commanded open

Piltdown Man
1st Mar 2017, 23:03
Penko - You are correct. My reply was probably a little harsh. Pacinolove I applogise. May I suggest the answer is that with a demand from two packs, somewhere above 15,000 the ECAM message as described by cinocav will be displayed. With a single pack the same message will be generated above 22,500'. Why? As the aircraft climbs the APU, like most other engines, suffers from a loss of power associated with reduced air density. Once the bleed air is lost, the next message to be expected will be EXCESS CABIN ALTITUDE. But exactly where and when this message will be displayed can not be precisely determined.

vilas
2nd Mar 2017, 05:44
APU bleed will close with APU bleed fault. Then you may get pack 1+2 fault may be bleed 1+2 fault and then excess cab altitude will come. So it is not something that is given anywhere or can be definitively answered.

Amadis of Gaul
2nd Mar 2017, 17:47
I am a A320 Pilot,One day in duty take off from an airport which take off performance require PACKs OFF for take off, but I can't turn off the two packs but I keep the apu bleed on for take off, after take off if if if I forgot to turn the apu bleed off, what will happen until the aircraft climb to the FL200??;)
I'd imagine that would be kind of hard to forget since:

1) You'll have two lights on the overhead that shouldn't be there;
2) You'll have an ECAM message (APU BLEED) that also shouldn't be there.

Then again, anything is possible.

safelife
3rd Mar 2017, 03:16
I was told this is the reason why Airbus doesn't recommend using APU bleed during takeoff (rather packs off instead), because it's not ensured crew wouldn't forget to turn it off in climb.
(Never understood why [APU...OFF] isn't part of the after takeoff / climb checklist)

Amadis of Gaul
3rd Mar 2017, 03:38
It's part of our after T/O checklist.

Daylight Robbery
3rd Mar 2017, 03:44
Considering you're probably doing 'packs off' because the temperature has limited the take off weight, it's a pretty good thing to have them on the apu and thus cool the cabin - especially with a decent load of pax

agg_karan
3rd Mar 2017, 12:04
Honestly no harm in asking simple questions. I m not Airbus 320 so don't know but previous Airbus I flew I was told if the APU bleed switch was left on beyond the limitation it would lead to pressurization problems (this is Airbus 310 I am referring to, and there were cases many many years ago in our line operations)

Compared to few Boeing a/c now I guess there's no harm as a pilot error wont lead to pressurization issues (for eg b777) the system design already switches to engine bleed above the limitation altitude.

while non standard practices are never encouraged but there is no harm in knowing the consequences of a pilot mistake with information that is validated correctly from simulator/books/other pilots/engineering etc.

Sorry have not answered your question.

FlightDetent
4th Mar 2017, 07:11
I was told this is the reason why Airbus doesn't recommend using APU bleed during takeoff (rather packs off instead), because it's not ensured crew wouldn't forget to turn it off in climb. The story from my Toulouse days was to think what happens should the APU fail and the engines' bleed start to supply the packs - effects on both performance and N1 / EGT.

Both have a merit.

That would follow a certain philosophy of SOP design, that they need to cater for the next failure. This is also a nice test to try when somebody starts to feel they are smarter than OEM FCOM. :)

vilas
4th Mar 2017, 10:09
Hey guys
All of us were assuming and all were wrong. What really happens is around FL290 APU bleed fault appears closing APU bleed and cross bleed which opens engine bleeds. Everything is fine after that.

Roger10-4
9th Mar 2017, 17:14
I was told this is the reason why Airbus doesn't recommend using APU bleed during takeoff (rather packs off instead), because it's not ensured crew wouldn't forget to turn it off in climb.
(Never understood why [APU...OFF] isn't part of the after takeoff / climb checklist)

Some airlines don't even have an after takeoff/climb checklist...