Vmc is defined as:

Vmc is defined as:

• A. Maximum controllable airspeed with all engines operating
• B. Minimum controllable airspeed with the critical engine inoperative
• C. Airspeed at which directional control is regained after engine failure
• D. Airspeed for minimum stall with one engine operating

Answer: (B)

Vmc is the minimum speed at which you can maintain directional control when the most critical engine has failed, with the remaining engine(s) producing takeoff power and the airplane in takeoff configuration. The idea is that, when one engine isn’t producing thrust, the remaining engine’s power creates a yaw moment. At low speeds, the rudder and other controls may not be able to counter that yaw, so you could lose directional control. As speed increases, control effectiveness improves, and you can keep the aircraft under control. That’s why Vmc is defined as the lowest controllable speed under the critical-engine-out condition. This differs from the other descriptions: it’s not the maximum speed with all engines operating, not the speed at which directional control is regained after an engine failure, and not the stall speed with one engine operating. The term specifically targets the minimum controllable airspeed with the critical engine inoperative.

Vmc is the minimum speed at which you can maintain directional control when the most critical engine has failed, with the remaining engine(s) producing takeoff power and the airplane in takeoff configuration. The idea is that, when one engine isn’t producing thrust, the remaining engine’s power creates a yaw moment. At low speeds, the rudder and other controls may not be able to counter that yaw, so you could lose directional control. As speed increases, control effectiveness improves, and you can keep the aircraft under control. That’s why Vmc is defined as the lowest controllable speed under the critical-engine-out condition.

This differs from the other descriptions: it’s not the maximum speed with all engines operating, not the speed at which directional control is regained after an engine failure, and not the stall speed with one engine operating. The term specifically targets the minimum controllable airspeed with the critical engine inoperative.