B777 Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 245; Flight Crew Total 11151; Flight Crew Type 11151
Human-Machine Interface; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Weight And Balance
General None Reported / Taken
Procedure; Human Factors; Aircraft
This is the third of the last six aircraft that I've flown to exhibit this fault. If the FMC generated Gross Weight is deleted from the ACARS Takeoff Date Request Page during preflight; for example; fueling not complete; to receive Planned Takeoff Data Message; then the FMC generated Gross Weight (the actual aircraft weight after final zero fuel weight is uplinked) never repopulates to the ACARS Takeoff Data Request page. This causes the final Takeoff Data uplinked to be the sum of final ZFW (Zero Fuel Weight) and Planned Takeoff Fuel; a number which; in my experience; seldom if ever is the actual aircraft weight at takeoff. On this flight the FMC generated Gross Weight after final ZFW uplink was 629.4. The ACARS Takeoff Data Request page returned performance numbers for a weight of 627.7 (the sum of the final ZFW and OFP planned takeoff fuel. The actual aircraft weight at throttle advance was 628.4. Had we not caught this error; we would have departed using invalid performance data.When we manually entered the FMC generated Gross Weight on to the ACARS Takeoff Data Request page; proper performance data resulted but the weight entered was not dynamic. It never changed.Until whatever change was made to these aircraft's software the FMC generated Gross Weight; when available; always populated to the ACARS Takeoff Data Request page and was dynamic. If deleted; the FMC generated Gross Weight would have repopulated the next time you opened the Takeoff Data Request page and it would always reflect current aircraft weight.
B777 Captain reported under certain circumstances entering weight data for departure will give inaccurate aircraft weights.