When the airplane runs out of fuel, the engine stops. The drag then slows the airplane, which decreases the lift and, eventually, the airplane comes back to earth. The maximum flight time depends on how much fuel is carried by the aircraft and how fast the fuel is burned. A summary of information needed to determine the range is given on a separate page . In reality, calculating the range is a complex problem because of the number of variables.
Extra fuel is expended in climbing to altitude and in maneuvering the aircraft.
The weight constantly changes as fuel is burned.