Additional fuel x fuel burn
 

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

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.

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

Regards from Brazil,

CortaVento

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

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

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

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