Multi-engine flying introduces several V-speeds that have no equivalent in single-engine airplanes. Memorize their definitions exactly — examiners probe them hard.
The Engine-Out Speeds
- Vmc — Minimum Control Speed (air): the minimum airspeed at which directional control can be maintained with the critical engine inoperative, under the CFR 23 certification conditions. Marked with a red radial line.
- Vyse — Best Rate of Climb, Single Engine ("blue line"): gives the greatest altitude gain per unit time on one engine. Marked blue.
- Vxse — Best Angle of Climb, Single Engine: gives the greatest altitude gain per unit distance on one engine — used to clear obstacles.
- Vsse — Safe, Intentional One-Engine-Inoperative Speed: the lowest speed at which an instructor will intentionally fail an engine. It provides a margin above Vmc so that an inadvertent stall/Vmc roll is avoided.
How They Relate
For a normally-aspirated light twin near sea level, the typical ordering is:
Vmc (red) < Vsse < Vxse < Vyse (blue)
Vyse is the airspeed you pitch for whenever an engine quits in the climb or cruise — it buys the best single-engine rate of climb and keeps you safely above Vmc.
Other Relevant Speeds
- Va — Maneuvering speed, Vno/Vne, Vfe, Vle/Vlo apply as in any complex airplane.
- Blue line is your friend: "If in doubt, pitch for blue line" is the single most useful engine-out reflex.
Note that Vmc decreases with altitude (less thrust asymmetry as the engine loses power), while stall speed (in IAS) stays roughly constant — at high density altitude they can converge, which has dangerous implications covered later.