Consumption of fuel is one of the largest costs of operating a large commercial airliner, making it a major concern to the airline industry. The weight of the fuel at the beginning of a flight adds to the consumption since the airliner will have to burn more fuel to take off, climb to cruising altitude and reach cruising speed. Fuel consumption also varies by altitude. By design, jet engines are most efficient at higher altitudes and thus burn more fuel at lower altitudes to perform the same amount of work.
- Jet fuel for commercial and private aircraft is a kerosene based fuel. In the United State, the standard fuel is Jet A. It is lighter than water and has a clear or straw colored appearance. Outside the United States, Jet A-1 is the standard jet fuel and has slightly different characteristics than Jet A. Jet A freezes at -40 F and Jet A-1 freezes at -52.6 F. Jet A and Jet A-1 are interchangeable for most purposes. Military aircraft use a JP designation and there are various types for use depending on the aircraft.
- The amount of fuel loaded onto an aircraft is carefully calculated. Fuel must be allotted for the taxiing to the runway, take off and climb to altitude, the flight, descent and taxiing to the gate. A reserve that would allow the aircraft to change airports is added to the total fuel load. The airliner cannot be simply "filled up" as the higher weight of the aircraft would increase fuel consumption.
- The Boeing 747 is available in four basic models, the 747-100, 747-200, 747-300 and 747-400. Each of the four basic designs uses four engines which consume Jet A or Jet A-1 fuel. The 747-100 carries a maximum of 48,445 US Gallons of fuel, the 200 and 300 each carry 52,410 and the 400 carries 57,285 US Gallons. Boeing lists maximum ranges as 6,100, 7,900, 7,700, and 7,260 statute miles respectively for each 747 model. Fuel capacity is calculated in gallons, but fuel consumption and planning are calculated in pounds. Jet A and Jet A-1 weigh 6.84 pounds per gallon.
- Typical fueling considerations in a 747-200 or 300 allow for 2,200 pounds of fuel to be used for taxi to take off. A fully loaded aircraft will use 33,000 pounds during take off and climb to cruising altitude. During the first half of the flight, the aircraft will consume an average of 28,000 pounds of fuel per hour. The aircraft lightens as it burns fuel and at the end of the trip, the fuel consumption drops to about 21,000 pounds per hour. Descending and landing consume the least fuel, around 6000 pounds. Unburdened of its fuel load, the aircraft will consume only 1000 pounds of fuel, less than half what it needed to taxi before take off. A reserve of 25,000 to 40,000 pounds is loaded to allow changing airports should it become necessary.
- Fuel burn is affected by a number of factors. At sea level, the dense air negatively impacts the efficiency of the jet engines and at any given engine speed, they use more fuel compared to what they would use at a high altitude. Waiting in line on the taxiway to take off burns fuel that just goes to waste. At take off the engines are working the hardest, carrying the greatest load and consume the most fuel. Once cruising altitude is reached, the engines are throttled back a little and less fuel is consumed. The plane lightens as it burns fuel and therefore uses less and less as the flight progresses. Descent and approach use very little fuel. The engines are cut back to nearly idle with the aircraft in a glide.