- Critical engine
- The engine whose failure hurts control and performance the most. On a conventional twin, the left.
- Vmc
- Slowest speed where full rudder can still hold heading with the critical engine out, under certification conditions. Directional control only, not climb.
- Vyse · blue line
- Best rate of climb on one engine.
- Vsse
- Safe single-engine speed. Never fail an engine on purpose below it.
- Accelerate-stop distance
- Runway to reach rotation, lose an engine there, and stop.
- Accelerate-go distance
- Runway to reach rotation, lose an engine there, and climb to 50 ft at the departure end.
- Service ceiling
- Density altitude where both engines give 100 fpm at Vy, clean.
- Single-engine service ceiling
- Density altitude where one engine gives 50 fpm at Vyse, clean, other prop feathered.
- Absolute ceiling
- Highest altitude you can hold level on both engines.
- Single-engine absolute ceiling
- Highest altitude you can hold level on one. Lose an engine above it and you drift down to it.
- Critical altitude
- Highest altitude a turbocharged engine still makes rated power, standard day.
