Performance Class A (CS-25): Take-off Theory

032-04-01Pablo Asensio Martínez2026-04-012 min

Key Speeds

Class A performance is defined by critical speeds:

  • $V_1$ (Decision Speed): The maximum speed at which the pilot must take the first action to stop the aircraft within the accelerate-stop distance. It is also the minimum speed at which the aircraft can continue the take-off following an engine failure.
  • $V_R$ (Rotation Speed): The speed at which rotation is initiated. $V_R \ge V_1$.
  • $V_2$ (Take-off Safety Speed): The target speed to be reached at the screen height (35 ft) with one engine inoperative. It ensures climb performance and controllability.
  • $V_{MCG}$ (Min Controllability Speed Ground): Minimum speed to maintain directional control on the ground using only aerodynamic controls (rudder) after an engine failure. $V_1 \ge V_{MCG}$.
  • $V_{MCA}$ (Min Controllability Speed Air): Minimum speed to maintain directional control in the air. $V_2 \ge 1.1 V_{MCA}$.

Distances Required

Declared Distances Diagram

Take-Off Distance Required (TODR)

The horizontal distance from brake release to the point where the aircraft reaches a screen height of 35 ft.

  • Condition: The longer of:
    1. OEI (One Engine Inoperative): Distance with critical engine failure at $V_{EF}$ (just before $V_1$).
    2. AEO (All Engines Operating): Distance with all engines operating $\times 1.15$.

Accelerate-Stop Distance Required (ASDR)

The distance to accelerate to $V_1$, experience an engine failure, recognize it (1 second), and bring the aircraft to a complete stop.

  • Condition: The longer of:
    1. OEI: Stop with one engine failed and reverse thrust (if credited, usually not on dry runway).
    2. AEO: Stop with all engines operating (Rejected Take-off for other reasons).

Take-Off Run Required (TORR)

The distance to accelerate to lift-off plus a portion of the airborne distance up to the screen height.

  • Relevant when the runway has a Clearway (area beyond the runway free of obstacles).
  • OEI: Run to midpoint between LOF (Lift Off) and 35 ft.
  • AEO: Run to midpoint between LOF and 35 ft $\times 1.15$.

Balanced Field Length

A condition where TODR = ASDR.

  • This occurs at a specific $V_1$ value.
  • If $V_1$ is lower, ASDR is shorter but TODR is longer.
  • If $V_1$ is higher, TODR is shorter but ASDR is longer.
  • Balanced Field Length is the minimum field length required for a given weight if $V_1$ is optimized.