Definition
VSSE is the minimum speed, established by the manufacturer, at which an engine may be intentionally rendered inoperative in flight for pilot training or testing in a multiengine airplane. It is selected to provide a margin above VMC (minimum control speed) so that loss of directional control is unlikely if the simulated engine failure is mishandled.
Plain English
It is the slowest speed at which an instructor or test pilot is allowed to deliberately shut down or simulate the failure of one engine during training. Below this speed, doing so is considered unsafe because the airplane could become hard to control.
Context Anchor
You encounter VSSE in multiengine training, especially before practicing engine-out procedures or simulated engine failures.
Derivation
The subscript 'SSE' stands for 'safe, single-engine.' The 'V' follows the standard aviation convention of labeling defined airspeeds with a 'V' followed by a subscript that identifies the speed's purpose.
Why Pilots Care
Provides a safety margin above minimum control speed so the airplane remains controllable during planned engine shutdowns for instruction.
Intuition Check
Do not read “safe” as “risk-free.” VSSE means the lowest approved speed for intentionally introducing the condition; the pilot still must use correct control inputs and follow the airplane’s procedures.
Example Sentence 1
The instructor waited until the airplane was above VSSE before pulling the right throttle to simulate an engine failure.
Example Sentence 2
During the training flight the pilot maintained VSSE while practicing single-engine climbs and turns.