Balanced field takeoff
A balanced field takeoff is a condition where the accelerate-stop distance required (ASDR) is equal to the takeoff distance required (TODR) for the aircraft weight, engine thrust, aircraft configuration and runway condition. For a given aircraft weight, engine thrust, aircraft configuration and runway condition the shortest runway length that complies with safety regulations is the balanced field length.
The rejected takeoff initial actions speed V1, or critical engine-failure recognition speed (Vcef), is the fastest speed at which the pilot must take the first actions to reject the takeoff. At speeds below V1 the aircraft may be brought to a halt before the end of the runway. Above V1 the pilot must continue the takeoff even if an emergency is recognized.

To achieve a balanced field takeoff, engine power is selected to provide enough acceleration so that at the lowest possible speed to continue the takeoff the remaining necessary takeoff distance with one engine not working is equal to the remaining & necessary accelerate-stop distance.

The balanced field length is the shortest field length at which a balanced field takeoff can be performed.

Factors affecting the balanced field length include:
  • the mass of the aircraft - higher mass results in slower acceleration and higher takeoff speed
  • engine thrust - affected by temperature and air pressure but reduced thrust can also be deliberately selected by the pilot
  • density altitude
    Density altitude
    Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground...

     - reduced air pressure or increased temperature increases minimum take off speed
  • aircraft configuration such as wing flap
    Flap (aircraft)
    Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...

  • runway slope and runway wind component
  • runway conditions - a rough or soft field slows acceleration, a wet or icy field reduces braking

Regulatory Background

Aviation regulations, especially FAR 25
Federal Aviation Regulations
The Federal Aviation Regulations, or FARs, are rules prescribed by the Federal Aviation Administration governing all aviation activities in the United States. The FARs are part of Title 14 of the Code of Federal Regulations...

 and CS-25 (for large passenger aircraft) require the takeoff distance and the accelerate-stop distance to be less than or equal to the available runway length, both with and without an engine failure assumed. The speed below which takeoff must be aborted upon engine failure is called V1. On longer runways a pilot can nominate a V1 within a range, but where the runway length is no longer than the balanced field length only one value for V1 will exist.

Landing and Takeoff Performance Monitoring Systems
are devices aimed at providing to the pilot information on the validity of the performance computation, and averting runway overruns that occur in situations not adequately addressed by the takeoff V-speeds concept.

Using the balanced field takeoff concept, V1 is the maximum speed in the takeoff at which the pilot must take the first action (e.g. reduce thrust, apply brakes, deploy speed brakes) to stop the airplane within the accelerate-stop distance and the minimum speed at which the takeoff can be continued and achieve the required height above the takeoff surface within the takeoff distance.
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