b. Wind (e.g., windshear, mountain wave, factors affecting wind, etc.)
Meteorology applicable to the departure, en route, alternate, and destination under visual flight rules (VFR) in Visual Meteorological Conditions (VMC), including expected climate and hazardous conditions such as: b. Wind (e.g., windshear, mountain wave, factors affecting wind, etc.)
Bottom line
Turbulence, defined as a large variation in wind velocity over a short distance, can cause upset and loss of control in flight. Mountain wave activity may occur when strong winds blow perpendicular to mountain ranges, producing up-and-down or wave motions in the atmosphere. A crosswind that exceeds an aircraft's demonstrated maximum crosswind component or the pilot's ability may result in loss of control on the ground.
Key numbers
| Number | What it means |
|---|---|
| FL 290 (significant MWA occurs both below and above this level) | RVSM floor |
| approximately 200 feet (weather-induced altitude deviation triggering the Unable RVSM call) | RVSM deviation |
FAA references
- AFH ch. 5, Unusual Attitudes Versus Upsets; Environmental Factors (p. 5-2) — FAA-H-8083-3C
- AIM 4-6-6 (Guidance on Severe Turbulence and Mountain Wave Activity (MWA)) — AIM Basic 2/20/25 w/ Change 1 (8/7/25) & Change 2 (1/22/26)
- RMH ch. 3 (p. 3-7) — FAA-H-8083-2A
- AFH ch. 17 (pp. 17-7–17-8) — FAA-H-8083-3C
- AC 91-92, para. 7.6 — AC No: 91-92
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