Which speed is Best rate-of-climb speed with one engine inoperative for a light twin-engine airplane?

• A. VYSE
• B. VXSE
• C. VY
• D. VS1

Answer: (A)

When one engine fails in a light twin, you want the speed that gives the greatest increase in altitude per unit time, i.e., the greatest climb rate with the remaining engine. That speed is VYSE—the best rate-of-climb speed with one engine inoperative. It’s chosen because it provides the maximum excess power available after the engine-out event: the remaining engine’s thrust, minus the drag, at a speed where that difference translates into the fastest climb.

VXSE, by contrast, is the best angle of climb with one engine out, which maximizes altitude gained per horizontal distance and is useful for obstacle clearance, not for maximum climb rate. VY is the best rate of climb with both engines operating, which is higher than VYSE. VS1 is the stall speed in a specified configuration, unrelated to climb performance.