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w6kd

Pneumatic system bug

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With the NGX on the ground, APU bleed on with both engine bleed valve switches off, switching both AC packs off causes the bleed duct pressure(s) to drop to ~9 PSI. Switching either pack to auto or high causes the bleed press to climb to ~38 PSI. With APU bleed, and both bleed valves and both packs shut down, I expect to see a fairly high press, which should then drop when either/both packs are turned on. Oddly, selecting either start switch to GND also causes the bleed press to climb from this configuration.

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This is actually correct, I believe. The APU supplies bleed air as needed. If theres no demand for air, it drops the pressure accordingly.

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Hi Bob, This is because the APU only provides what is demanded by the system. When you switch off the packs you don't need bleed air, so the APU reduces the bleed air output to save some fuel.The same when you start the engines, you need a lot of airflow, so the duct pressure is increased by the system. But there are some other threads about this fact.Try search them, if want more information. PS: First I thought it is a bug too. ;-) http://forum.avsim.net/topic/342066-duct-pressure-on-startup/page__hl__duct+pressure__fromsearch__1 Cheers

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