Funky Fuel Consumption

[Guest RyHoffman113]

Looking for help here, I'm not sure exactly why, but on every flight, before departing, the FMC says I will have X amount of fuel at destination, however during flight the amount always increases, usually by thousands of pounds. I like to cruise a bit fast, at .81 or .82, but youd think the amount would go down since I was going faster. Anyone know why this happens and if its possible to stop it from happening? Ryan HoffmanZDC/VUAL

[Guest]

This is one of very few quirks that PIC has. It is partially due to the fact that the FMC does not calculate wind data, so if you have tailwinds, the destination fuel prediction will increase at an even higher rate. I myself have not been able to find a fix for the problem altogether, but there a lot of topics on this board about this subject. Try doing a search for "fuel consumption" or "fuel".Good luck---and let me know if you figure anything else out!-twilky

[michal]

I have seen it too but in my opinion it is a very minor thing. It may actually reflect the reality - FMC not being able to calculate actual fuel left precisely specially far in advance due to many uncertainties. However one thing should be happening - the closer you are to the destination the better the accuracy and so the FMC number should "converge" to the final, correct value. And I believe I satisfied myself that this part works well therefore I don't even consider it a bug anymore. Michael J.

[Guest RyHoffman113]

While its not a critical thing, I still wonder why I gain upwards of 10000 pounds on the way from JFK to LAX, AGAINST the wind. I have been subtracting a great deal of fuel from the amount the quick fuel planner calculates, and on departure the FMC will say i will have 0 fuel upon arrival and when i touchdown its typically around 10000 pounds. That's quite a bit of change, don't you think?Ryan

[michal]

10,000 lbs ? I agree that is excessive.I haven't seen anything like that but I usually fly short trips.Michael J.

[Guest]

On a recent trip from KATL to EDDF (Frankfurt), I was halfway across the Atlantic and the FMC still predicted 0 fuel on arrival, but i actually wound up arriving with about 13000 pounds.

[michal]

What was the prediction when you were much closer to destination, say 1 or 2 hours out ?Michael J.

[Guest RyHoffman113]

For me, the amount steadily increases throughout the entire cruise and into the descent, if I use a reduced climb power it will usually increase during climb as well. Ryan.

[michal]

Then maybe there is intentional bias from the start to err on the side of being very conservative. The further from the destination - the bigger the error. Whether it is realistic - I am afraid we have to wait for some of the resident 767 pilots to chip in.Michael J.