777-300ER Fuel Efficiency

Happened to fly 777-300ER in Qatar Airways livery from OTHH to KFJK on the casual server. Fuel planning ensured we took off with tanks topped up ensuring us 22 hours worth of fuel (which is more than enough for this sector.) However over Montreal 2 hours away from New York alerts are recived that the aircraft has only fuel worth 2 hours 33 minutes which is dangerously less. Note that strong Headwinds were absent, cruising altitude was 32,000 feet. Could someone kindly explain to me what I did wrong or whether it was a technical error. Thanks in advance.


I think the likely culprit is cruising too fast - which resulted in very high fuel consumption.

For reference the B777 cruises at M0.84.


I would recommend in that situation to cruise at FL370-FL390, it increases range

If they had 22 hours worth of fuel they would have been too heavy for FL370-390 (at least initially).

It would have saved a bit of fuel to step climb however.


True, i forgot about step climbing

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Staying low in the 777 isn’t actually all that inefficient. You might burn like 2-3% more fuel but not enough to cause this. I agree with @BennyBoy_Alpha here, this is probably a speed problem.

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@LiamVas what speed did you cruise at?

@BennyBoy_Alpha @Hector_Wilson @AndrewWu I was cruising at Mach 0.88 to 0.89. I shall learn from my mistakes and do as you have said, thank you so much for all your help, I really appreciate it, we should do a flight sometime if it’s fine by yourselves. Thanks a ton!


Oh yes that is much too quick for the 77W… it should be around M. 84 or 85 as benny mentioned above


wait what? I’ve understood that for long range its better to do a step climb and start cruising low because engines cannot “breathe” as much at such high altitude

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You’re flying way too low for a flight like that mate. At least 35-38 thousand feet for maximum fuel efficiency.

I presume that he meant at that point in the flight you should be up there. It’s a 77W so that might be a tad high but that is the idea.

However, the overall speed for Mach 0.84 is lower, therefore there is less fuel consumption

That’s weird.

Currently flying the same route. Same fuel levels, i.e 22 hours worth, Loaded at 313,900kgs cruising over Iraqi airspace at 28,600ft, at Mach 0.84, as per the advice given by @BennyBoy_Alpha and the rest of the learned individuals who took time out to assist me. ETE Displays 11:18h with FR at 129,181Kg (17:25h) as opposed to ascent a few minutes ago i.e at 20,000ft crusing at 340Kts. Thanks for all the help and advice. Can’t put into words how grateful and appreciative I am. Thanks Guys!! I’ll keep ya’ll updated. Do chip in with more tips if any :))


Awesome! Have a safe flight!

Thanks very much.

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You’re either going to slow or to fast cruise Mach .84 at 36000ft stepclimb

It’s already been confirmed that OP was going too fast. This topic can be closed now.

You can also check out my topic Your Ultimate Guide to Infinite Flight Fuel Burn + Fuel Calculator [40 AIRCRAFT] for the best altitudes.