The cross-wind component is the component of surface wind perpendicular to the runway.
Formulas
code
Crosswind = wind speed × sin(α)
Headwind = wind speed × cos(α)
Tailwind = − headwind (when α > 90°)
Where α = angle between wind direction and runway magnetic bearing (e.g. RWY 22 = 220° magnetic, wind from 250° → α = 30°).
Quick estimate — sine values for common angles
| Angle α | sin(α) ≈ | Wind portion as crosswind |
|---|---|---|
| 10° | 0.17 | ~ 17 % |
| 20° | 0.34 | ~ 34 % |
| 30° | 0.50 | ~ 50 % (rule of thumb) |
| 45° | 0.71 | ~ 70 % (rule of thumb) |
| 60° | 0.87 | ~ 87 % |
| 70° | 0.94 | ~ 94 % |
| 90° | 1.00 | 100 % (pure crosswind) |
Example
Wind 250°/20 kt, runway 22:
- α = 250° − 220° = 30°
- Crosswind = 20 × sin(30°) = 20 × 0.50 = 10 kt
- Headwind = 20 × cos(30°) = 20 × 0.87 = 17 kt
Demonstrated cross-wind
The AFM lists the demonstrated cross-wind component — the maximum value successfully landed by a test pilot during certification.
| Important point | Note |
|---|---|
| Demonstrated = a value that has been shown — not an operating limit (for standard CS-23 types) | |
| AFM limit only if explicitly so labelled (some types, especially STC'd ones, have actual limits) | |
| PIC responsibility — the PIC is ultimately responsible for accepting a cross-wind based on own competence and conditions |
Typical demonstrated values:
- Cessna 172: 15 kt
- Piper PA-28-161: 17 kt
- Aquila A210: 15 kt
Rule of thumb (established pilot training): students should not exceed half of their demonstrated value until they have proven experience.
When crosswind is too strong
- Choose another runway (if available).
- Divert to another airfield.
- Wait for wind to subside (often in late afternoon as thermal activity decreases).
- Sideslip / wing-low technique on approach, or crab + kick.