Definition
In a multi-engine airplane, the airspeed that produces the greatest gain in altitude per unit of time when one engine is inoperative and the remaining engine is producing takeoff or maximum continuous power. VYSE is published by the manufacturer in the Airplane Flight Manual and is marked on the airspeed indicator with a blue radial line, commonly called the 'blue line.'
Plain English
The speed that gives a twin-engine airplane its best climb when one engine has quit and the other is doing all the work. Flown correctly, it gets the airplane up as fast as possible with the power available.
Context Anchor
You will see VYSE in multiengine training, emergency procedures, performance charts, and on the airspeed indicator as the blue line.
Derivation
V stands for Velocity (speed). Y is the standard FAA code letter for best rate of climb. SE stands for Single Engine — meaning only one engine is producing power. OEI (One Engine Inoperative) describes the condition: one engine has failed or been shut down. Put together: the speed for best rate of climb when only one engine is working.
Why Pilots Care
Maintaining VYSE after an engine failure maximizes the chance of climbing above obstacles or reaching a suitable landing site before altitude is lost.
Intuition Check
“Best” does not mean best for every situation. Here it specifically means the speed that gives the best rate of climb with one engine not producing usable power.
Example Sentence 1
After the simulated engine failure, the student pitched for blue line and held VYSE all the way to a safe altitude.
Example Sentence 2
The handbook shows that at 4,000 pounds and 20 degrees Celsius, VYSE is 88 knots indicated airspeed.