AA.I.D.K6FAA-S-ACS-11A · Nov 2023Knowledge
Maximum Operating Speed - Knots (VMO) / Maximum Operating Speed - Mach (MMO) convergenc...
Maximum Operating Speed - Knots (VMO) / Maximum Operating Speed - Mach (MMO) convergence and stall angle of attack.
Bottom line
VMO/MMO is defined as the maximum operating limit speed, and VMO is expressed in knots calibrated airspeed (KCAS). The VMO limit is usually associated with lower altitudes and structural loads and flutter, while the MMO limit is associated with higher altitudes and compressibility effects and flutter. Above approximately FL 310 on a standard day, an MMO of 0.82 always equaled a KCAS less than 306 KCAS and became the operating limit, because the VMO limit could not be reached without first reaching the MMO limit.
Key numbers
| Number | What it means |
|---|---|
| 306 KCAS ≈ 0.82 MMO at approximately FL 310 on a standard day (early civilian jet example) | VMO/MMO converge |
| 0.82 MMO = 261 KCAS at FL 380 | MMO at FL 380 |
| At 51,000 ft MSL and 1.0 G, Mach buffet slightly above MMO 0.82 and low-speed buffet at 0.60 Mach (typical turbojet) | Buffet at 51,000 ft |
FAA references
- PHAK ch. 5 (p. 5-45) — FAA-H-8083-25C (2023)
- AC 61-107, para. 3-2 — AC No: 61-107B
- AFH ch. 16 (p. 16-6) — FAA-H-8083-3C
- AC 61-107, para. 1-4 — AC No: 61-107B
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