Balanced Field Take Off – ASDR & TODR

Balance Field Take Off – A balanced field take off is a condition in which selection of field length is such that accelerated stop distance required (ASDR) is equal to take off distance required (TODR).

When V1 is selected such that accelerate-stop distance is equal to accelerate-go distance, the distance is known as the balanced field length.

Balanced field length is shortest field length required for a given WAT, aircraft configuration and runway conditions.

Performance charts are usually based on this balanced field concept as it allows for the highest takeoff weights to be achieved.

In the graph given above, light blue color AND blue color curve represents the TODR and ASDR respectively. With increase in V1 value TODR is decreasing and ASDR is increasing. There is certain value of V1 at which TODR = ASDR. At this V1, field length required in minimum and is called balanced field length.


Accelerate-Stop Distance – ASD

ASDR on dry runway is the greater of ASD(N-1 Dry) and ASD(N Dry)

ASD(N-1 Dry)

Sum of the distances necessary to:

  • Accelerate the airplane with all engines operating to Vef,
  • Accelerate from Vef to V1 assuming critical engine fails at Vef and pilot takes the first action to reject the takeoff at V1
  • Airplane comes to full stop
  • Plus a distance equivalent to 2 seconds at constant V1 speed

ASD(N Dry)

Sum of the distances necessary to:

  • Accelerate the airplane with all engines operating to V1, assuming the pilot takes the first action to reject the takeoff at V1
  • With all engines still operating come to a full stop
  • Plus a distance equivalent to 2 seconds at constant V1 speed

ASDR on wet runway is the greatest of ASD(Dry), ASD(N-1 Wet) and ASD(N Wet)

ASD(N-1 Wet) – same as ASD(N-1 Dry) except the runway is wet

ASD(N Wet) – same as ASD(N-1 Dry) except the runway is wet


Take off Distance – TOD

TODR on dry runway is greater of TOD(N-1 Dry) and 1.15 TOD(N Dry)

TOD(N-1 Dry)

It is the distance covered from the brake release to a point at which the aircraft is at 35 feet above the takeoff surface, assuming the failure of the critical engine at Vef and recognized at V1.

1.15 TOD(N Dry)

It is 115% of the distance covered from brake release to a point at which the aircraft is at 35 feet above the takeoff surface assuming all engines operating.

TODR on wet runway is greater of TOD(Dry) and TOD(N-1 Wet)

TOD(N-1 Wet)

It is the distance covered from brake release to a point at which the aircraft is at 15 feet above the takeoff surface, ensuring the V2 speed to be achieved before the airplane is 35 feet above the takeoff surface, assuming failure of the critical engine at Vef and recognized at V1.

Note: Delay between Vef and V1 is considered to be 1 second