Fmc stab trim changes when using atm on the 737max
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Joined: Jul 2020
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From: Around latitude 0
Fmc stab trim changes when using atm on the 737max
Hi guys! Since the introduction of the MAX on our fleet I’ve noticed that the FMC stab trim changes when entering an assumed temperature (we don’t use DERATE), whereas this doesn’t happen on the NG’s. Any thoughts why ?
Joined: Jan 2000
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From: FL410
Thread Starter
Joined: Jul 2020
Posts: 12
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From: Around latitude 0
Yep but later on and the change is only in the order of 0.01 unit , i guess had to do with APU fuel consumption which decreases a little bit the take off weight , on the MAX it happens instantly when you put an assumed temperature !
Joined: Nov 2010
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From: USA
Lower ANU moment with higher assumed temperature due to lower thrust? And calculations weren't as accurate back in the NG days, or NG has less thrust couple? Just taking a stab at it....
Joined: Oct 2019
Aviation Qualifications: Non-Aircrew
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From: USA
If there's an effect of engine I'd consider looking into if it's from the larger bypass ratio as more air will be passing through the fan and not having heat added to it making the thrust more sensitive to the density of the air. Also, in increased density conditions the CL required is lower so the trim should also change; if the density goes down then a higher CL is needed - also a trim change.
Perhaps the better question is why the delay on the NG? Maybe with the smaller bypass ratio the effects tended to cancel?
I know - more questions than answers.
Joined: Dec 2003
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From: Tring, UK
