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Fuel Planning

Are you always adding extra fuel to your flight just to be on the safe side, and afterwards you found out that you had three times as much fuel as you actually spent on the flight. Well then you might need a little lesson in fuel planning.

First some terminology:
Trip fuel - the amount of fuel used for the trip, calculated with the distance, including the longest departure and arrival route.
Contingency - this is a reserve, calculated with the help of the distance.
Alternate - the fuel necessary to have for reaching the alternate airport, the one that is the longest distance away if you have more than one.
Reserve - the amount needed to fly the aircraft for half an hour.
Taxi - the amount needed for all your taxi operations.
Extra - if the captains wants more, because of strong headwinds or so.

So how to do this? Let's take an example. Say we are flying a medium size jet like the DC-9. The first thing we do is calculate the distance. Let's say it's 600 nm in this case. A medium jet uses about 6 600 lbs per hour. The way we use this is by calculating our flight time, that is distance, divided by average speed in knots (true airspeed) times 6 600. In this case we use an average speed of 380 knots. For a turboprop we might use 2 700 lbs per hour and 220 kt, for a bigger aircraft like the B767 we might use as much as 12 200 lbs per hour and 390 kt. The calculations for our DC-9 will look like this:

(600 nm / 380 kt) x 6 600 lbs = 10 422 lbs

Ok, so next we need a contingency. This is usually 5 % of the fuel needed for the ground distance, I like to use 6 %:

10 422 x 0.06 = 626 lbs

So now we need to calculate how much fuel is needed to the alternate airport. This is done using the same formula as for the trip fuel. Let's say we have 40 nm to our alternate:

(40 nm / 380 kt) x 6 600 lbs = 695 lbs

The reserve is a fixed amount for each plane. I would use 3 300 lbs for a medium jet, 1 100 lbs for a turboprop and 6 200 lbs For a bigger plane like the Boeing 767. If you wish to calculate the exact amount you will need the fuel usage per hour. The reserve is a half an hour of flight time, i.e. fuel usage per hour times 0.5, anyway for the DC-9 it's 3 300 lbs.

Now we need some fuel for taxi operations, I like to use 440 lbs for a medium size jet, 150 lbs for a turboprop and 660 lbs for the B767.

If you think there will be heavy winds you might want to add some, this is called extra fuel, the captain adds as much as is deemed necessary.

So it's now time to add up the amount:

And so we have the amount of fuel we need, 15 483 lbs.

NOTE that since there are a lot of different flight models out there of different aircraft there might be significant difference between the different types on fuel consumtion. Also note that a bigger aircraft like the MD11 or the B747 will most likely use a bit more fuel per hour than the B767. If you have a look around the WWW you may find a good fuel planning software.

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Cyber Air Virtual Airlines. ©2006