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B737NG Packs & Apu bleed

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B737NG Packs & Apu bleed

Old 9th Jun 2019, 06:36
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Join Date: Nov 2018
Location: Turkey
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B737NG Packs & Apu bleed

Dear all,

I am new on aircraft. I checked documents and saw the real procedures in the cockpit. But I haven't decided on one thing yet which is very simple.

Is there a flow to follow when both packs off, iso valve open and apu bleed off and we want to operate the packs with bleed air. In which order we should configure the switches and what's the logic behind that ?

Do you operate firstly the packs auto then apu bleed on or vice versa or mixed order ?

Y37 is offline  
Old 9th Jun 2019, 15:38
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Join Date: Apr 2010
Location: IRS NAV ONLY
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Makes no difference anyway. In absence of any bleed air pressure (i.e. engines OFF and APU bleed air switches in OFF position), the pack valves will not open anyway when the PACK switches are moved to AUTO, since they are pneumatically operated.

In the preflight procedure, Boeing recommends a “top down approach”: packs first, then isolation valve, then engine bleeds, then the APU.

Air conditioning PACK switches – AUTO or HIGH


Engine BLEED air switches – ON

APU BLEED air switch – ON

Verify that the DUAL BLEED light is illuminated.
FlyingStone is offline  

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