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Thread: APU Running post engine shutdown

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    Member Gunfighter's Avatar
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    APU Running post engine shutdown

    Is there any problems with running the APU for extended periods post sortie/engine shutdown? I've tried it today with attention getters going after a few minutes, but with no warnings?? Does it affect power in anyway running off the APU Gen? I also got a CDU warm start and loss of flight plan. Hmmm

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    476 vFG Founder Snoopy's Avatar
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    What "attention getters" are you talking about?

    The only factor with running the APU for extended periods is you need to have the APU generator on because it powers the hydraulic pump cooling fan. Without this fan running it could result in an overheating condiction. You won't get any warnings.

    Running power off the APU Generator is the same as running off external power or engine power. The CDU warm start is is an auto-download of system data which occurs after the airfract has landed and airspeed falls below 75 knots or when the LASTE EAC is automatically disengaged. It has nothing to do, directly, with the APU.

    Hope this helps...

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    Senior Member Jedi's Avatar
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    Correct me if i'm wrong: i think it's better to use ground power (ground crew comm) while on the ground for a long period.

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    Quote Originally Posted by Snoopy View Post
    What "attention getters" are you talking about?

    The only factor with running the APU for extended periods is you need to have the APU generator on because it powers the hydraulic pump cooling fan. Without this fan running it could result in an overheating condiction. You won't get any warnings.

    Running power off the APU Generator is the same as running off external power or engine power. The CDU warm start is is an auto-download of system data which occurs after the airfract has landed and airspeed falls below 75 knots or when the LASTE EAC is automatically disengaged. It has nothing to do, directly, with the APU.

    Hope this helps...
    It sure is nice to have a systemsmeister on staff. Thanks Snoopy.

    Markeebo

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    Member Coyote's Avatar
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    Quote Originally Posted by Jedi View Post
    Correct me if i'm wrong: i think it's better to use ground power (ground crew comm) while on the ground for a long period.
    It's because of the fuel save policy

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    476 vFG Founder Snoopy's Avatar
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    Quote Originally Posted by Jedi View Post
    Correct me if i'm wrong: i think it's better to use ground power (ground crew comm) while on the ground for a long period.
    For the sim APU is fine, real world we use the APU for many ops checks, for maintenance a lot of the time we'll use ground power. The thing about ground power, in the sim, is you don't have the noise of the APU. Real world, running a generator isn't as loud as the APU but still annoying and we have to wear hearing protection.

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    Member WildFire's Avatar
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    Wasnt there some kind of issue with starting the APU after flight? Like it could start a fire due to oil or fuel being around the APU after a flight? I know its not modeled in the sim but I thought I read something about it somewhere...

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    476 vFG Founder Snoopy's Avatar
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    Quote Originally Posted by WildFire View Post
    Wasnt there some kind of issue with starting the APU after flight? Like it could start a fire due to oil or fuel being around the APU after a flight? I know its not modeled in the sim but I thought I read something about it somewhere...
    Starting it is not a problem, the issue, real world, is having the APU running when you shut down the #1 engine.

    With the APU running the hot exhaust gas blows directly under the gang drain. When you shut down an engine we (crew chiefs) have to relay to the pilot they got a good drain otherwise there is potential for an internal engine fire.

    If you have the APU running the "potential" is there that the fuel could ignite.

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    Member WildFire's Avatar
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    Yeah that sounds like what I read.

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    476 vFG Founder Snoopy's Avatar
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    I actually had to yell at one of our lesser experienced crew chiefs a few weeks back. During his launch his left slat started leaking, hydaulic fluid running all over. At first, I didn't see the fluid and the way he was running I thought he had some type of fire. He took the train container (damn EPA, we have to catch the fuel that drains) and, with the APU running attached it to the jet. Not only is that a big no no per the TO you can burn the hell out of yourself doing that. he was lucky, the tailwind that day was very strong and blew most of the APU exhaust gas away from him.

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