Definition
In a multi-engine airplane, VYSE is the airspeed that produces the greatest gain in altitude per unit of time when one engine is inoperative and the remaining engine is producing maximum available thrust. It is published in the Airplane Flight Manual and is marked on the airspeed indicator of most light twins by a blue radial line, commonly called the 'blue line.' VYSE is the speed that gives the best single-engine climb performance under standard conditions with the airplane configured per the manufacturer's procedures (typically gear up, flaps up, inoperative propeller feathered, and bank into the operating engine).
Plain English
On a twin-engine airplane, this is the speed that gives you the best climb rate when one engine has quit and the other is doing all the work. It is shown by a blue line on the airspeed indicator.
Context Anchor
You see VYSE on multiengine airplane airspeed indicators, in engine-out training, and in performance information for one-engine-inoperative flight.
Derivation
The label is built from V (velocity), Y (the standard symbol for best rate of climb), and SE (single engine). It is read directly as 'best rate of climb speed, single engine.'
Why Pilots Care
Flying at VYSE after an engine failure maximizes climb performance and may determine whether the airplane can reach a safe altitude or must land.
Grounding Statement
With one engine failed in a twin, VYSE is the target speed that gives the airplane its best chance to gain altitude.
Intuition Check
Do not read “best” as “safe in every situation” or “guaranteed to climb.” It means the best climb rate available with one engine inoperative under the airplane’s published conditions.
Example Sentence 1
After the right engine failed on climb-out, the pilot pitched for the blue line and held VYSE while securing the dead engine.
Example Sentence 2
The instructor had the student identify the blue line and state what VYSE represents before the engine-failure drill.