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B737 - APU BLEED - FCOM rev23

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B737 - APU BLEED - FCOM rev23

Old 22nd Feb 2020, 16:41
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Question B737 - APU BLEED - FCOM rev23

Hi Guys,

Im new around here and in air. I have an question on B737 FCOM rev 23, it suggest to give apu bleed air after 2 full min. But previous fcom revisions , it was 1 min. I wonder what is the reason that they increased the time to give bleed ( except the reason to extend the service life of the apu) ?

FCOM : Operate the APU for two full minutes before using it as a bleed air source. This two minutes stabilization is recommended to extend the service life of the APU.

Thank you so much guys for answers

Have safe flights
b.kahraman2011 is offline  
Old 23rd Feb 2020, 09:42
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Think you’ve pretty much answered your own question here.

Its to extend the service life of the APU.

Pretty much like letting your car warm up before you drive it hard.

The apu will of course, provide bleed air as soon as it’s available if the APU BLEED sw is selected on.
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Old 23rd Feb 2020, 10:14
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Thank you so much for answer, Dougie_diesel.
I check AMM , it is written there that you can give bleed as soon as possible when the apu available. But my wonder is that the reason why boeing increased from 1 min to 2 min waiting.

Thank you so much for your time.
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Old 6th Mar 2020, 07:15
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To allow for sufficient thermal stabilisation before the APU has a load applied to it which increases EGT, this increases the life of the turbine and compressor by reducing wear thus reducing overhaul costs.
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