Which term defines the calibrated airspeed at which the critical engine failure is assumed in a multiengine aircraft?

• A. Vertical stability
• B. VEF
• C. VHF
• D. Velocity

Answer: (B)

The speed is V_EF. In a multiengine airplane, the most critical engine is the one whose failure would cause the greatest loss of directional control or power. For certification and performance calculations, the engine-out scenario is assumed to occur at a specific calibrated airspeed called the engine failure speed (V_EF). This is the airspeed used to evaluate how the airplane behaves with one engine inoperative, guiding takeoff and climb performance and ensuring the airplane remains controllable in that worst-case condition.

VMC, by contrast, is the minimum control speed with an inoperative engine and is a different, more specific limit related to controllability at a given configuration. The other terms listed aren’t related to engine-out performance speeds, and VHF is a radio frequency, not an airspeed.