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737 takeoff performance calculations

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I have troubles understanding t/o performance calculations when it comes to derates and assumed temperatures. I use PMDG 737 and their manuals which are pretty much copy-paste Boeing's FCOMs.

TODA = 2000m
Wind: calm
Slope =0%
Airport elevation = 0ft
Runway: DRY
Temp = 12C
Flaps: 5
Let Assumed temp be 42C
and 22K derate

This is how I do it:
In FCOM vol 1 I go to page PD.30.1
because of the wind strength and 0% slope TODA = corrected field length
on PD.30.2 I can see Field Limit Weight of 64.4t (no derates and assumed temp included into calculations? correct me if I'm wrong)
on PI.30.38 I get N1 = 91,7%
From here I can calculate V1/VR/V2 based on first two tables on PI.30.28.
How can I get Field Limit Weight for that derate and assumed temp setting?

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Posted (edited)

For assumed temp, you just look the SAME table and find the temperature that has limited weight closest but lager to your actual weight, makesure check all field\climb\obstacle\Tire....weight, and use the lowist one.

N1 is not the direct N1 form your Assumed temp, go to the 3-table corrction in PI. BUT, the FMC-calculated N1 is ready to use.

Check V1/VR/V2 with that temp, BUT VMCG with actual temp

De-rate is not in FCOM.PD. as I know, it uses an different table.

Edited by C2615

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Derates may be available in FPPM(Flight Planning and Performance Manual) if your company choose to purchase that option. (Yes, a table in manual is DLC)

BTW the PD in FCOM is just "good enough" to get you get off ground, in FPPM you can find more option like Flaps1~25, improved climb etc....

But now a days it's all software, after 787, no FPPM and PEM, or even the 1st generation Boeing Performance Software(BPS), it's all PET and OPT....

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