Most people look at the cost of fuel at their departure point and if it's cheaper than the cost at their destination they load up. But it's not always that simple. It takes more fuel to carry more fuel which negates much of the savings.
I developed the following charts for the Boeing 737-300. Your mileage may vary. I had our flight planning service (Air Routing) show how much extra fuel (in pounds) we burned for each 1000 pounds of extra weight we carried for each trip. Over the course of a few weeks I was able to come up with Chart 1. This shows that there is a direct correlation between distance flown and extra fuel used. This is expected. There were more data points than shown here which were scattered along the trend line. This was due to different winds on different days but I think the results are close enough to be useful in making fueling decisions.
I then calculated the break even point for a given amount of fuel at arbitrary prices for origin and destination. I kept getting inconsistent results as I varied the fuel prices. After much number crunching I discovered that the break even point varies with the extra fuel burn andthe departure point fuel price. Chart 2. Not quite so intuitive but it does make sense. If you want to carry a lot of extra fuel you need a greater savings per gallon to pay for it.
Enter Chart 1 with the mileage for the next leg. Go up to the line and to the left to find the extra fuel burned per thousand pounds of extra weight.
Enter Chart 2 with the fuel cost at the departure point. Go up to the line for extra fuel burn for the next leg. Note that the legend on the right is in inverse order from the chart. This is the way my spreadsheet wanted to do it and I did not feel like arguing. Interpolate if necessary. Go to the left to find the fuel savings required to break even. Any savings above this justifies tankering. Naturally, if the destination fuel is cheaper then you do not want to tanker fuel.
By using these charts we are tankering less fuel than we used to which makes our home base FBO happy.
If anyone sees a flaw in my reasoning or calculations please let me know. Meanwhile maybe you can save your company money by not tankering.
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