Balanced Field Length

Balanced Field Length (BFL) is the runway length at which the accelerate-stop distance equals the accelerate-go distance when an engine failure occurs at V1. In other words, it is the point where the distance required to abort the takeoff and stop on the remaining runway is exactly equal to the distance required to continue the takeoff on the remaining engine(s) and clear the screen height (typically 35 feet).

BFL is a critical parameter in takeoff performance calculations. If the available runway length equals the BFL, the pilot has no advantage in choosing to stop versus continuing — both options use exactly the same amount of runway. If the runway is shorter than BFL, V1 must be reduced (favoring the stop decision). If the runway is longer, V1 can be increased (favoring continuation).

Factors affecting BFL include aircraft weight, air temperature, pressure altitude, wind, runway slope, and runway surface condition.