VEF is defined as the calibrated airspeed at which the critical engine of a multiengine aircraft is assumed to fail.

• A. Vector
• B. VEF
• C. Vertical speed indicator
• D. Very-high frequency

Answer: (B)

In multiengine flight, engine-out performance is analyzed using a specific speed that represents the point where the most adverse engine failure is assumed to occur. This speed is defined as the calibrated airspeed at which the critical engine is assumed to fail. Using calibrated airspeed ensures the value accounts for instrument and installation errors so pilots can compare it reliably with performance charts. The critical engine is the one whose failure would cause the greatest loss of directional control and performance, so this speed provides a consistent reference for evaluating controllability and required margins after an engine failure. The other items listed aren’t speeds related to engine-out performance—one is a direction, another a climb-rate instrument, and the last a radio frequency—so they don’t describe this concept.