It’s obvious that aircraft need fuel or else they wouldn’t be able to fly. But when an airline captain is calculating how much fuel will be required for a flight, he or she will never say, “Just fill it up.” Why? Surely the sensible thing is to take as much fuel as necessary? Well, no. Fuel is heavy and extra weight means you need more fuel. And that means higher costs.
To illustrate this, short-haul flights to perhaps destinations around Europe, the fuel load may account for 75% of the cost of the flight. And for long-haul flights, this rises to as much as 90% of flight costs. So getting the correct fuel load is very important. You need enough fuel for your flight and extra in case of unforeseen factors arising which might extend your flight time.
So how does a pilot work out how much fuel to upload for a particular flight? The answer is to break-down the fuel needed into sections of a flight. And it looks something like this.
Taxi Fuel – this amount takes into account the distance and time it is likely to take before being able to take-off. Some major airports are so large and busy that it can take a considerable time to be able to take-off and you could be taxiing for a couple of miles before reaching the runway in use. This amount will also include the taxiing at the destination airport.
Burn-Off Fuel – this is the overall amount of fuel used when the aircraft is in the air. It includes the take-off, climb, the cruise to destination, the descent and landing.
Contingency Fuel – this is the amount needed to cover any unforeseen circumstances arising such as headwinds and having to divert around thunderstorms. It also includes having to divert to an alternate airport if the destination one becomes unavailable for any reason. This alternative will already be known so the amount of fuel will be part of the calculation. By law, contingency fuel usually accounts for about 5% of burn-off fuel.
Reserve Fuel – this is the additional fuel in case the aircraft is put into a holding pattern before being able to make its final approach and land at its destination airport. At busy times, aircraft are stacked over a radio beacon at different heights and they fly a set pattern around the beacon, called a holding pattern. Each circuit takes about 4 minutes and at the end of each, the aircraft is directed onto a lower level. Eventually it is their turn to make the approach to land.
Once all these factors have been taken into account, the captain will sign off the fuel request and the refueller will upload the correct amount.