B737 - APU BLEED - FCOM rev23

[b.kahraman2011]

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

[Dougie_diesel]

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.

[b.kahraman2011]

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.

[YOUNGBUCK]

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.