Definition
The calibrated airspeed at which the critical engine is assumed to fail during airplane certification testing. VEF is selected by the manufacturer but cannot be less than the minimum control speed on the ground (VMCG). It is used as the baseline reference point for determining takeoff performance data, including V1, in multi-engine transport-category aircraft.
Plain English
The speed the manufacturer picks for testing, where they pretend an engine quits, so they can measure how the airplane behaves and what speeds the pilot needs to know.
Context Anchor
Seen in V-speed and takeoff performance discussions for multiengine airplanes, especially when explaining how certified takeoff speeds are established.
Derivation
The 'V' comes from the French 'vitesse' meaning speed, used throughout aviation for standard reference speeds. 'EF' stands for Engine Failure. So VEF reads as 'speed at engine failure' — the speed assumed for the failure event during testing.
Why Pilots Care
It helps determine the aircraft's takeoff performance and safety margins if an engine fails at that speed.
Intuition Check
Do not read VEF as the speed where an engine is expected to fail. It is an assumed failure point used for certification calculations.
Example Sentence 1
During certification, the manufacturer selected a VEF that satisfied the regulatory requirement of being no less than VMCG.
Example Sentence 2
The published VEF value is used to calculate the accelerate-stop distance for the airplane.