PA.X.B.K1FAA-S-ACS-6C · Nov 2023Knowledge
Factors affecting VMC and how VMC differs from stall speed (VS).
Factors affecting VMC and how VMC differs from stall speed (VS).
Bottom line
VMC is the minimum flight speed at which a light, twin-engine airplane can be satisfactorily controlled when an engine suddenly becomes inoperative and the remaining engine is at takeoff power. With normally aspirated engines, VMC decreases with altitude, but stalling speed (Vs) remains the same. At some altitude, VMC and Vs are the same, and where Vs is encountered at or before VMC, the departure from controlled flight may be quite sudden.
Key numbers
| Number | What it means |
|---|---|
| not more than 5° to maintain straight flight at VMC (static determination) | Max bank |
| within 20 degrees of the original heading after the critical engine is suddenly made inoperative | Heading change |
| published Vmc is almost always higher than Vs, except for a few models | VMC vs Vs |
FAA references
- PHAK Glossary (p. G-33) — FAA-H-8083-25C (2023)
- FAA-P-8740-66, Flying Light Twins Safely — FAA-P-8740-66
- AFH ch. 13 (pp. 13-23–13-24) — FAA-H-8083-3C
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