Definition
The airspeed at which a multi-engine airplane gains the most altitude per unit of time after one engine has failed, with the failed engine secured and the operating engine producing maximum available power. Commonly designated VYSE and marked by a blue radial line on the airspeed indicator.
Plain English
On a twin, if one engine quits, this is the speed that gets you the most height for each minute that passes. It is the speed you reach for when you need to climb on the one engine you have left.
Context Anchor
Seen on multiengine airplane airspeed indicators, especially as the blue line used during engine-out training and procedures.
Derivation
The 'V' in VYSE comes from the French 'vitesse,' meaning speed. 'Y' marks it as a best rate-of-climb speed, and 'SE' stands for single-engine. Knowing the label is built from these pieces makes the marking on the airspeed indicator easier to recall under pressure.
Why Pilots Care
Used to decide whether an aircraft can safely continue flight after an engine failure on takeoff or climb.
Intuition Check
Do not read single-engine here as meaning a single-engine airplane. It means a multiengine airplane operating with only one engine producing power. Best means best climb rate, not best glide, best angle, or best speed for every situation.
Example Sentence 1
After the right engine failed, the pilot pitched for the blue line and held best single-engine rate-of-climb to clear the rising terrain ahead.
Example Sentence 2
The blue line on the ASI marks the best single-engine rate-of-climb speed for this twin-engine airplane.