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A320: APU BLEED with LP ground air unit?

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A320: APU BLEED with LP ground air unit?

Old 21st May 2019, 14:36
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A320: APU BLEED with LP ground air unit?

Hello everyone,

In the FCOM-PRO-NOR-SOP-04- AIR CON it says:
Do not use APU BLEED if the ground personnel confirms that a LP or HP ground air unit is connected to the aircraft
No doubt about the HP unit, but what about the LP unit connected with APU Bleed ON and packs OFF? Should not be an issue isn't it? Since the LP is connected downstream of the packs.
No bleed No coffee!

Thank you.

Last edited by pineteam; 21st May 2019 at 15:55. Reason: TYPO
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Old 21st May 2019, 16:04
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Are you sure Pineteam?
HP/LP air will pressurise the pneumatic system just the same as the APU bleed would so I think your coffee is safe with Gnd air connected.
Of course, I could be wrong!!
mcdhu
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Old 21st May 2019, 16:11
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Originally Posted by pineteam View Post
Hello everyone,

In the FCOM-PRO-NOR-SOP-04- AIR CON it says:

No doubt about the HP unit, but what about the LP unit connected with APU Bleed ON and packs OFF? Should not be an issue isn't it? Since the LP is connected downstream of the packs.
No bleed No coffee!

Thank you.
PRO NOR SOP assumes that after You will clear the white lights, ie turning the packs on. The actual limitation is from LIM-AIR : The flight crew must not use conditioned air from the packs and from the LP Air Conditioning Unit at the same time, to prevent any adverse effect on the Air Conditioning system.

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Old 21st May 2019, 16:11
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Originally Posted by mcdhu View Post
Are you sure Pineteam?
HP/LP air will pressurise the pneumatic system just the same as the APU bleed would so I think your coffee is safe with Gnd air connected.
Of course, I could be wrong!!
mcdhu
LP is direct to the mixer unit (COC, FWD, AFT), e.g. after the packs.

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Old 21st May 2019, 16:11
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Originally Posted by mcdhu View Post
Are you sure Pineteam?
HP/LP air will pressurise the pneumatic system just the same as the APU bleed would so I think your coffee is safe with Gnd air connected.
Of course, I could be wrong!!
mcdhu
Low pressure air will not get you coffee.
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Old 21st May 2019, 16:13
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Also be aware that by consuming free coffee on board You are jeopardising Your company financial results.
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Old 21st May 2019, 20:32
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I believe that is limitation is to prevent the packs from getting contamination from external sources, i.e. the air conditioning from the external unit might carry oil, dust, particles, etc... that might be absorbed by the packs if they are switched on.

And airplane coffee sucks big time.
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Old 21st May 2019, 22:39
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I was informed by an engineer that the HP air cart could run the packs in the absence of APU bleed air but it would soon over heat and there is the issue of contamination as external HP air is meant for engine starting not breathing.
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Old 22nd May 2019, 04:11
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Originally Posted by krismiler View Post
I was informed by an engineer that the HP air cart could run the packs in the absence of APU bleed air but it would soon over heat and there is the issue of contamination as external HP air is meant for engine starting not breathing.
I was informed by a pilot that it will indeed run the packs, but after inhaling that air, you won't run them for very long!
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Old 22nd May 2019, 06:59
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Originally Posted by krismiler View Post
I was informed by an engineer that the HP air cart could run the packs in the absence of APU bleed air but it would soon over heat and there is the issue of contamination as external HP air is meant for engine starting not breathing.
Depends on the unit, some are designed to run packs. I have done it many times in the Middle East.

interesting tidbit, some airports in the US had ground HP air that was reticulated like ground power.
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Old 22nd May 2019, 07:23
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This shouldn’t be an issue, as Long as the packs are selected OFF with the HP unit on, as the pack valves would be closed.

In fact, at where I work we would be in this configuration whilst performing the Engine Start with External Pneumatic Power procedure. The procedure calls for the Packs to be OFF, before powering up the HP unit. The LP unit would still be connected to the aircraft at this stage to provide Air Conditioning.
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Old 22nd May 2019, 14:50
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We were told that the non return valve in the external LP port will chatter, (i.e. vibrate rapidly), if external LP air and APU bleed are used together; which could reduce the life of the valve.

I can’t see a mention of this now in the FCOM.
.

Last edited by Uplinker; 22nd May 2019 at 15:04.
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Old 22nd May 2019, 15:01
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Originally Posted by Uplinker View Post
We were told that the non return valve in the external LP line will chatter (i.e. vibrate rapidly) if external LP air and APU bleed are used together; which could reduce the life of the valve.

I canít see a mention of this now in the FCOM but only did a quick search.
Can't remember exactly when it was changed, but it used to be :

‐ Do not use conditioned air simultaneously from packs and LP ground unit (to avoid chattering of
the non return valves).
‐ Airflow supplied by the ground cart shall not exceed 1.2 kg/s (2.60 lb/s).

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