Balanced field length
Balanced field length is the runway needed for an aircraft, at a given weight and temperature, to either continue a take-off safely after an engine failure at the critical decision speed or stop on the remaining runway. It is the figure that decides which airports an aircraft can use with a full load: a Citation CJ3+ needs about 3,200 ft, a Challenger 350 about 4,800 ft and a Gulfstream G650 around 6,000 ft at sea level on a standard day. Heat, altitude and weight push the requirement up sharply, so a jet that works at London Biggin Hill in April may need a lighter load at Aspen or Kathmandu in July.