Additional fuel x fuel burn

[CortaVento]

Gentlemen,

I have a question for B 777 pilots. If you choose to carry on extra fuel, is there any rule of thumb to calculate how much fuel you burn for this "additional weight"?

regards,

CortaVento

[BlueEagle]

On most heavy aircraft the calculation is 4% per hour of the extra fuel carried. 10 tons over 5 hours would be 20% of the extra fuel, i.e. 2 tons.

[CortaVento]

Thanks BlueEagle, I had these figures for DC10 and MD11... I thought it was different for each aircraft type.

Regards from Brazil,

CortaVento

[mabrodb]

4% is a good WAG. I've seen things range around 3-4% for a variety of Boeings & Airbus equip.

Really depends on how much fuel and how far. As the 2nd factor to compute, is a possible lower FL profile (2000' lower, etc).

Marc

[Old Smokey]

Assuming that you're already operating the B777, why not take a look at the "Fuel adjustment per 1000 Kg change in Zero Fuel Weight" print-out on the Computerised Flight Plan. Divide that by the number of hours flight time, and you have a pretty good adjustment per 1000 Kg per Hour.

Hope that that helps.

Old Smokey

[CortaVento]

Not yet, Old Smokey... I will start conversion training in a few days and this subject came after discussing with some fellow pilots. Thanks anyway,

CortaVento

[Old Smokey]

CortaVento,

Further to my previous suggestion, some actual figures for a 5:30 flight just completed -

Additional fuel per 1000 Kg ZFW increase = 227 Kg

That's 4.3% per 1000 Kg per hour, pretty close to the earlier 4% suggestions.

Bear in mind that that's for a B777-200 with RR Trent 892 engines, it will vary for the B777-300 and for other engines. Bear in mind too, that the flight I just operated was a positioning flight at just 206.3 Tonnes TOW, and will obviously be higher at more typical operating weights, or on shorter sectors where Climb fuel forms a much larger proportion of the overall burn. (The opposite for longer sectors).

Also, for info, the adjustment for a 1000 Kg DECREASE in ZFW was 199 Kg, i.e. -3.75% / Tonne / Hour. All of which approximates to 4% "Ball Park".

Regards,

Old Smokey