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Does A320 APU start only by battery?

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Does A320 APU start only by battery?

Old 7th Dec 2021, 00:32
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If you don't start the APU then you don't get a cup of tea.

Priorities.
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Old 7th Dec 2021, 11:16
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Good idea. thanks
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Old 7th Dec 2021, 11:22
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Thanks . it is ambiguous when Fcom or TM doesn't say what to do exactly . .
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Old 7th Dec 2021, 11:27
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Originally Posted by Locked door View Post
IIRC there are a couple of MSN’s where APU start is not recommended after loss of AC power (inc emer elec config). They are few and far between, I think we have one of them. That might be part of his confusion, or it might not.

All from memory, please be gentle.

LD
Not recommended doesn’t mean not allowed.

For this particular serial number, you have one additional reason to start the APU as soon as possible, in order to avoid the “not recommended” situation in case of further degradation.

Usually companies train for the majority of the fleet and they point out the differences/exceptions.

With the same logic, the company should train and take advantage of the “weakest” MSN of the entire fleet.

As an other member previously noticed :

Will the TRE, in a real aircraft, disregard the “APU(if available)… Start” part of the ELEC emer configuration, because the procedure of an other MSN doesn’t recommend the action ?
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Old 7th Dec 2021, 11:43
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Originally Posted by elonmussk View Post
meanwhile there was one instructor who says that we might want to reserve the battery power by not starting the apu,
because he said the Starting APU uses battery power..
If the APU fails to start, once the sequence is completed, the remaining GEN, will start changing again the batteries.

In addition in case of failure of one generator (FCOM):
The system automatically replaces the failed generator, with the :
‐APU GEN, if available, or
‐Other engine generator.
So according to the airbus logic, APU if available automatically takes priority to relieve the remaining generators (no action required to connect the APU to the failed side).

Originally Posted by elonmussk View Post

He was insisting that if the apu didnt start for some reason then it would end up using battery power.
The APU will use the battery power anyway as long as the start motor is activated (successful start or not).

Originally Posted by elonmussk View Post

Which means, if we get to lose remaining generator for some reason (I dont think so,. but...)
it would lead to electric emergency configuration,
if we had have used battery power with starting apu, saying that it would shorten the time with electricity .
The condition to be in Elec Emer configuration is :
Both AC BUS 1 and AC BUS 2 are lost.

Even with batteries fully charged you will be in the same condition.

The instructor is confusing/concerned of the situation “flight with batteries only” which is time limited to 30mins minimum(case of Elec emer configuration + RAT failure).
The batteries provide power to Hot BUS1,HOT BUS 2, DC ESS BUS and AC ESS bus through AC STAT INV.

In case of Elec Emer configuration, you are time limited as well as the batteries are not charging, being segregated from the part of the electrical system which is powered by the RAT.

But in this case the available time is much longer than 30 minutes as they only provide power the Hot Bus 1 and Hot bus 2

In that case you are mostly concerned by the lack of redundancy. (LAND ASAP Red)

So yes the instructor could be right If the APU fails to start, you immediately loose the second generator and the RAT fails to deploy.

He either misunderstood the redundancy of the system, or he is not trusting the certification of the A320 and he does not feel comfortable flying this Aircraft.

Last edited by pilot-737; 7th Dec 2021 at 12:46.
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Old 8th Dec 2021, 02:57
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Huge amount of overthinking on this thread.
If you are down to one generator start the APU. That’s what’s its there for. If it fails to start the remaining generator will replace any loss from the battery.
What are you going to do ? Wait for the remaining generator to fail before you start the APU. I don’t think so.
Then start the APU when you KNOW you are discharging the battery ? That would be dumb.

Last edited by Alt Flieger; 8th Dec 2021 at 03:21.
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Old 8th Dec 2021, 03:17
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It can be used to start the engines. The APU may obtain power for startingfrom the aircraft's batteries or normal electrical system, or from ground
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