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Guest Bill Kingsford

Engine Start Prodecure clarification

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I don't mean to ask redundant questions (hopefully) but the manuals state the following regarding engine start sequence and associated pneumatics: APU running with bleed air valve open shut the packs off center isolation valve open engine 1 and 2 bleed air valves open start no 2 engine start no 1 engine center isolation valve auto apu bleed valve off shut down apuThis sequence has been truncated by myself for brevity in this post of course but I'm a little confused regarding the DUAL BLEED annuciator that comes on when either engine 1 or 2 bleed valves and the APU bleed valve is open at the same time. My orginal understanding of the start sequence was that only the no 1 engine bleed valve being open at the same time as the APU bleed would cause the DUAL BLEED annuciator to illuminate. With SU2 I get DUAL BLEED with either engine bleed valve and APU open.Could some nice person clarify the meaning/consequences of the DUAL BLEED light and proper pnuematics juggling for normal engine start sequence? Thanks very much!-Bill Kingsford"The Kingsford Edge"

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>Could some nice person clarify the meaning/consequences of the>DUAL BLEED light and proper pnuematics juggling for normal>engine start sequence? >>Thanks very much!>>-Bill Kingsford>"The Kingsford Edge"I'm only gonna cover the pneumatics only and not the electrics, but to start...The ISOLATION VALVE logic is now modelled correctly, so:All BLEED switches offStart APUAfter APU online:ISO valve in autoPACKS in auto (if you're going to cool the pax before starting)APU bleed on (you should see both ducts pressurize).For engine start:PACKS offStart either engine (whichever one you want to start first)Start the other enginePacks AutoIso valve AutoEngine bleeds onAPU bleed off (dual bleed light should go off)The Dual BLEEDS light is important because it indicates that you have the potential to overpressurize the bleed air manifold if the APU bleed checkvalve fails. Do NOT advance the throttles above idle in this configuration.

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Tim, thank you, that answers a lot of what I was confused about. In the procedure you described above though it appears that the engine bleed valves are not opened until AFTER engine start (I noticed this in the manuals too). I thought that the starter would have to access pnuematic pressure via the engine bleed air valve feeding the start valve from either the APU bleed or cross bleed from a running engine. Does the start valve in the 737 in fact recieve pnuematic pressure totally separate from the engine bleed air valve then? Thank you!-Bill Kingsford"The Kingsford Edge"

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