Placekicker
Topic Author
Posts: 9
Joined: Thu Apr 10, 2008 10:43 am

### Method Of Calculating Fuel Expenditure

Is there any roughly accurate way at determining the fuel expenditure in gallons for an aircraft based either on minutes flown or flight miles for a given aircraft?

Example of what I am asking:

Assume the following:

1) A flight between DTW and DFW
2) Aircraft Type: A320, B757, or Embraer 170
3) Flight Miles: 995
4) Flight Time (actual time flying): 135 minutes

Are the four parameters listed above sufficient to gauge a rough estimate of how much fuel would be burned? Is there a formula given by any of the aircraft manufacturers which help estimate fuel consumption?

Also, a secondary question: I assume that airlines don't fill the tanks to maximum capacity when a flight is known to only need, say 30 or 35% of a full tank. I assume the airlines save the cost of hauling the extra fuel, and would just re-fuel the needed amount at the destination. Question is, and this is purely speculative, if a flight from Detroit to Dallas is known to consume 35% of a full tank, then how much extra fuel do airlines normally allow as a buffer, for instances like circling over a storm, circiling for some miscellaneous airport delays, or unforseen extra flying which may be required? Do they allot a given percentage of fuel to buffer the occasions I just mentioned? And how much?

Thanks in advance, and I appreciate any help any of you could be.

tb727
Posts: 1902
Joined: Thu Jun 30, 2005 1:40 pm

### RE: Method Of Calculating Fuel Expenditure

I can't give you all your answers but I ran numbers for the A320 and 757 for you on this route from a flight planning perspective. I don't have the E170 profile. These numbers are from fltplan.com so I am not sure exactly how accurate they are for these 2 planes since I don't fly them, but it should give you an idea.

I used the same routing for both, 894NM for the preferred routing of FWA3.FWA RBS STL RZC FSM.BYP5.

A320, planned at 459 KTAS at FL360 with forecast winds for a 6pm departure:
2:20 13,908 pounds of fuel used, 2075 gal.

B757, planned at 459 KTAS at FL360 with forecast winds for a 6pm departure:
2:20 18,544 pounds of fuel used, 2767 gal.

I couldn't tell you the fuel prices at either airport since I don't know what the airline would pay. Generally speaking, an airplane doesn't go full fuel all the time for many reasons. A big reason is it burns fuel to carry fuel if that makes any sense. Someone that is a 121 dispatcher would have to help you with contingency fuel questions and everything else. I do all my own planning when I fly and I take a lot of things into account but I am usually doing legs at the max range of my airplane so I am usually topped off.
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futurecaptain
Posts: 1918
Joined: Sat Sep 09, 2006 1:54 am

### RE: Method Of Calculating Fuel Expenditure

 Quoting Placekicker (Thread starter):if a flight from Detroit to Dallas is known to consume 35% of a full tank, then how much extra fuel do airlines normally allow as a buffer,

The bare minimum fuel requirement for this type of flight would be.

Fuel to fly to the destination +
Fuel to fly to the furthest alternate airport +
Fuel for any known delays enroute +
Fuel to fly for 45 minutes
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FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

### RE: Method Of Calculating Fuel Expenditure

Aircraft manufacturers will put everything you need for fuel planning in the AFM (Airplane Flight Manual). Not just enough for a rough estimate either, it will be pretty exact.

You'll have
A) Taxi fuel
B) Trip Fuel
C) Contingency fuel, an extra 5% on the trip fuel to cover for deviations etc
D) Alternate fuel, enough for an approach at the destination, climb back to altitude and the trip to the alternate
E) Final reserve, 30 min holding IIRC
F) Extra fuel at the discretion of the PIC to cover for shite weather, expected delays/holds and so on.

Not really my area of expertise, so I'll refrain from putting more detail in. You should have enough to do a proper googling now anyway.

As for your secondary question, airlines will at times haul the fuel for the next leg. Quicker turnarounds and/or fuel cost differences would probably be the main reasons. This is referred to as tankering fuel.

Rgds,
/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.

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