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DUCT PRESSURE on the ENGINE START

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Gentlmen,AOM 5-12 describes:Verify that sufficient duct pressure exist for a normal engine start. Duct pressure should exceed 30 psi immediately after ENGINE START SELECTOR is pulled.However, I have couldn't on either 400 PAX or 400F CARGO. What is wrong?Sincerely,Kan-ichiro Fushihara

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Secondary EICAS push ECS, just under packs 1,2 and you see Duct PSI 35regardsTon

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Hi, Ton,On my ECS, duct PSI has been not displayed 35 but 27 under packs 1,2.Sincerely,Kan-ichiro Fushiharap.s.After all engines was running, it has been displayed 39.

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You need at least 2 packs off for engine start. I normally turn all three off personally.

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It is strange in my case that packs off lower the duct pressure,All packs on: 281 packs off: 272 packs off: 193 packs off: 22Sincerely,Kan-ichiro Fushihara

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This system is quite complex, Kan-ichiro.... The APU is designed to output more air as the load (demand) increases, but the system doesn't always operate as designed (in real life).Main engine start signals the APU to put out maximum bleed pressure.But, if the APU is getting a bit old or the outside air temperature is hot, you may not get the pressure you expect.If the aircraft is new and everything is running perfectly, you would expect the pressure to rise in steps as each pack is turned on, but even on new aircraft, I've seen it step down(at some point). However, I can't recall at what point this happens.When you start an engine, the system logic looks at Start Switch position, Autostart switch position.... and the fuel cutoff lever (if the autostart switch is ON). If the Autostart Switch is on and you pull the Start Switch, nothing should happen to the bleed system (I've confirmed this this in real life)27psi is low-ish pressure, but you shouldn't have too much trouble starting an engine with this pressure. Just make sure the engine continues to accelerate.Running all packs and starting 1 or 2 engines at the same time will put a huge demand on the APU and it may not be able to handle it. Rapid increases in pressure can also be a problem. If you go from no packs mode to main engine start mode, you can get a huge change in pressure. Sometimes it's best to run a single pack whilst starting and engine. It all depends on what modifications have been carried out on the aircraft.In summary... If the PMDG bleed system is erratic... it's probably closer to reality than a sim designed to Boeing specifications :(Hope this helps.Cheers.Q>

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Dear Qavion,Thank you very much for your kindest instructions again.Oh, Complex!!! Realistic???As you say, practically, I have had no trouble to start engines.Anyway, I have relieved to hear your words.Thanks again,Kan-ichiro Fushihara

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amazing! you sure did your homework!thanks for the explanations.Cheers,Pedro Venda.

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