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tolosan
28th Jan 2014, 13:30
Hello to FMS specialist,

What are the assumptions used to compute fuel and time to Alternate from Destination ?

Yancey Slide
28th Jan 2014, 16:29
Nevermind, you're looking for what calculations the FMC is using to get it's fuel remaining on board rather than the pre-dispatch load aren't you....

EDA
28th Jan 2014, 19:22
From FCOM DSC 22-20-40-30 Other Computations:

Predictions on ALTERNATES page are based on:
-A default cruise FL equal to ​220, if the airway distance is less than ​200 nm. Otherwise, it is ​FL 310
-Simplified wind/temperature models, based on flight crew entries:


ALT CRZ wind, as entered on the FUEL PRED page
CRZ temperature interpolated from the temperature model for the primary flight plan.

-Airway distance, or direct distance, as provided by the database (manual entry, if not in the database)
-Cost index = 0 (minimum fuel)
-Initial aircraft weight equal to landing weight at primary destination.


Note:





No step can be inserted in an alternate flight plan
No predictions are displayed for the selected alternate on flight plan pages. However, the flight crew can read ALTN trip fuel and time on the INIT B page before engine start, and estimated time and estimated fuel on board at alternate on the FUEL PRED page after engine start.

tolosan
29th Jan 2014, 14:26
Thanks EDA, I had not been through this "Other computations" in this section...

EDA
29th Jan 2014, 19:28
I've been once but took some time to find it again. Airbus FCOM... :)