During a rejected takeoff, autobrake engagement requires the wheels to reach a minimum speed of at least how many knots?

• A. 60 knots
• B. 40 knots
• C. 50 knots
• D. 70 knots

Answer: (A)

Autobrake is designed to provide a controlled, automatic deceleration during a rejected takeoff, but it only engages when the airplane is actually moving forward fast enough for the braking system to work reliably. The wheels must be turning at a minimum speed before the system will apply the autobrake. This gate prevents false activations from just engine idle or very slow taxi/windmilling and ensures there’s enough kinetic energy for the braking action to be effective.

The required minimum is 60 knots, which strikes a balance: below this speed, engagement could be unreliable or unnecessary, and above it, you’d still want the autobrake to respond promptly when a rejection occurs. Once the speed threshold is reached and the autobrake is selected, the system applies the chosen deceleration rate with anti-skid control to modulate brake pressure and help prevent tire skid, aiming to stop within the available runway.

So, the minimum wheel speed for autobrake engagement during a rejected takeoff is 60 knots.