Balanced Field Length

Balanced field length is the runway length at which the accelerate-stop distance equals the take-off distance. At the balanced field condition, the decision speed (V₁) is the critical engine failure speed at which the pilot can either stop the aircraft on the remaining runway or continue the take-off and clear all obstacles, using the same runway length for both options.

Why It Matters

For multi-engine transport aircraft, performance planning requires confirming that the runway available meets or exceeds the balanced field length for the prevailing conditions of weight, temperature, pressure altitude, and wind. Operations at runways shorter than the balanced field length for the conditions are not permitted under CARs Part VII.

Components

• Accelerate-stop distance (ASD): Distance required to accelerate to V₁, experience an engine failure, decide to abort, apply brakes, and bring the aircraft to a stop
• Take-off distance (TOD): Distance required to accelerate, lose an engine at V₁, rotate, and clear the 35 ft screen height

Related Terms

See also: Critical Field Length, Critical Engine.