Narrative:

I was first officer and pilot monitoring. The aircraft had two deferrals; one of which was the weight and balance (west&B) computer system. The MEL was consulted and no pilot actions were required. This was also verified by the mechanic. The aircraft was empty and the takeoff was going to require the low weight/aft center of gravity (cg) procedure. At the appropriate time; I read the cg from the west&B to the captain who was loading the FMS. He repeated the cg station to me and said the resulting trim setting; which correlated reasonably with the printed performance data. When it came time to set the trim; it was forward of the central green band. The forward green band was not illuminated; which I believed to be due to the deferred west&B system. When the takeoff was initiated the takeoff configuration warning was activated and the takeoff discontinued. We exited the runway and explored the situation; discovering that the displayed cg data was one digit/one percent in error. The correct data was reentered and the forward green band illuminated; encompassing the trim as previously set. After double checking all the other performance data entries and rerunning the checklists; we departed.upon reflection; I suspect that there was either a rounding error or a mistyping of the cg location into the FMC. I will need to be more vigilant for this type of error. Also; I should have suggested getting the mechanic's input and verification with regard to the absence of the forward green band. I will have a more thorough discussion with mechanics on the ramifications of any deferrals going forward.

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Original NASA ASRS Text

Title: B747 flight crew reported rejecting takeoff due to a takeoff configuration warning. An FMC data entry error was identified.

Narrative: I was FO and pilot monitoring. The aircraft had two deferrals; one of which was the Weight and Balance (W&B) computer system. The MEL was consulted and no pilot actions were required. This was also verified by the Mechanic. The aircraft was empty and the takeoff was going to require the low weight/aft center of gravity (CG) procedure. At the appropriate time; I read the CG from the W&B to the captain who was loading the FMS. He repeated the CG station to me and said the resulting trim setting; which correlated reasonably with the printed performance data. When it came time to set the trim; it was forward of the central green band. The forward green band was not illuminated; which I believed to be due to the deferred W&B system. When the takeoff was initiated the takeoff configuration warning was activated and the takeoff discontinued. We exited the runway and explored the situation; discovering that the displayed CG data was one digit/one percent in error. The correct data was reentered and the forward green band illuminated; encompassing the trim as previously set. After double checking all the other performance data entries and rerunning the checklists; we departed.Upon reflection; I suspect that there was either a rounding error or a mistyping of the CG location into the FMC. I will need to be more vigilant for this type of error. Also; I should have suggested getting the Mechanic's input and verification with regard to the absence of the forward green band. I will have a more thorough discussion with mechanics on the ramifications of any deferrals going forward.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.