A rejected takeoff is the decision to stop an aircraft during the takeoff roll instead of continuing into flight. The most important reference speed for this decision is V1, often called the takeoff decision speed. Before V1, the crew is expected to stop for serious problems because there is enough planned runway to brake safely.
After V1, continuing the takeoff is usually safer because there may not be enough runway left to stop.
Key Facts
- V1 is the maximum speed at which the pilot can begin a rejected takeoff and still stop within the available runway under certified assumptions.
- Before V1, serious failures such as engine failure, fire warning, or unsafe configuration can justify stopping.
- After V1, the aircraft is normally committed to takeoff because stopping distance increases rapidly with speed.
- Kinetic energy to remove during braking is KE = 1/2 mv^2, so doubling speed makes the brakes absorb four times as much energy.
- Stopping distance under constant deceleration can be estimated by d = v^2/(2a).
- Accelerate-stop distance must be less than or equal to accelerate-stop distance available, often written ASDR ≤ ASDA.
Vocabulary
- Rejected takeoff
- A rejected takeoff is the planned emergency procedure of stopping an aircraft during the takeoff roll before liftoff.
- V1
- V1 is the takeoff decision speed used to decide whether to stop or continue the takeoff after a serious problem.
- Accelerate-stop distance
- Accelerate-stop distance is the runway distance needed to accelerate to a decision speed, recognize a failure, and stop the aircraft.
- ASDA
- Accelerate-stop distance available is the runway length plus any approved stopway that can be used for stopping after a rejected takeoff.
- Balanced field
- A balanced field is a runway planning condition where the distance to continue takeoff after an engine failure equals the distance to reject and stop.
Common Mistakes to Avoid
- Treating V1 as the speed where the pilot decides what to do is wrong because the reject action must be started by V1, not considered after passing it.
- Assuming stopping after V1 is always safer is wrong because the remaining runway may be too short and the brakes may overheat from the high kinetic energy.
- Ignoring reaction time is wrong because the aircraft continues accelerating and moving while the crew recognizes the failure and begins braking.
- Using runway length alone without considering weight, wind, temperature, slope, and runway condition is wrong because each factor changes acceleration and stopping performance.
Practice Questions
- 1 A 70,000 kg jet reaches 70 m/s just before a rejected takeoff. How much kinetic energy must the brakes, spoilers, reverse thrust, and drag remove to stop it? Use KE = 1/2 mv^2.
- 2 An aircraft begins braking at 68 m/s with an average deceleration of 3.4 m/s^2. Estimate the stopping distance using d = v^2/(2a).
- 3 A crew detects an engine fire warning just after passing V1 on a dry runway. Explain why continuing the takeoff may be safer than trying to stop, using runway distance and kinetic energy in your answer.