B737-800
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
General None Reported / Taken
Chart Or Publication; Aircraft; Procedure
Dispatched [with] MEL 49-XXX APU CONTINUOUS OPS ETOPS. 5+27 flight time. Fuel burn was 31.8 with 2.3 burn to alternate. MEL added 438 lbs for APU burn... That seem low to you? No extra fuel provided. Weather at destination 3/4 mile in rain and fog. Alternate weather good. Filed for FL350 and assigned FL330 for first 2.5hrs of flight. Got airborne with required fuel of 40.0. [Flight plan] estimated landing with 7.9. At altitude FMC totalizer estimated landing with 8.0. However; we all know that once center fuel pumps off; that estimate will drop 1000 lbs or more. That caused me concern. Called dispatch on SATCOM and discussed; specifically MEL fuel burn being way too low. She said the computer plugs that number in automatically. (Flight plan waypoint burns were initially +400 and eventually down to +200 and then even over CP.) Agreed that we'd keep an eye on it. (she agreed with estimated landing fuel of 7.9). Uncomfortable; I later called back to talk to ETOPS Maintenance control. Asked him what fuel burn for APU at altitude was. He had no idea...So center fuel finally gone and we watch FMC totalizer for landing march down to 6.7 as I had predicted. Weather now .5 mile. Called dispatch on SATCOM again and agreed to plan of one approach and immediate divert to alternate. Flew SA CAT I to mins and broke out at DA- landed with 6.7 fuel.Discussion: MEL fuel seems ridiculously low- about 1300 lbs low so; it would seem. Also; the known totalizer anomaly when center pumps on is a set up and should be corrected. Not an issue when you're +1200 on your flight plan waypoint burns until pumps turned off; but when you start out only +400; I knew something was amiss. Dispatch and pilot blindly following automated MEL fuel add of 438lbs for continuous APU ops for 5 hrs.
B737-800 Captain reported being dispatched on an ETOPS flight with an inoperative generator and the APU operated continuously for the five and a half hour flight. Four hundred thirty eight pounds of fuel are provided for the APU burn and the aircraft lands at destination with 1;200 pounds less fuel than planned.