05 · Performance · Wind components
Crosswind and headwind components .
Wind direction and speed plus runway heading → the headwind and crosswind your aircraft will see on landing or takeoff. The two numbers every preflight verdict ultimately depends on.
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Section 01
Compute
Section 02
The geometry
Wind has a direction and a speed; a runway has a heading. The component of the wind that lies
along the runway centreline is the headwind (or, when negative, a tailwind); the perpendicular
component is the crosswind. Both are derived from the same right-triangle geometry — HW = wind × cos(θ), XW = wind × sin(θ), where θ is the signed angle between the wind direction and
the runway heading.
A few rules of thumb make this tractable in your head: 0° = pure headwind, 30° = half-crosswind, 60° = mostly crosswind, 90° = pure crosswind. For a 20 kt wind at 30° off the runway, you get about 17 kt of headwind and 10 kt of crosswind. At 45°, you get 14 kt of each.
One subtlety: the wind direction in a US METAR is given true; the runway designator is magnetic. For most of CONUS the magnetic variation is under 15°, and the calculator does not correct for it — pilots usually do the math in one frame and accept the small error. If you're operating in a part of the world with large variation (Alaska, the high latitudes, the East Pacific) you may want to correct manually.
Section 03
A worked example
A 20 kt wind 45° to the left of the runway centreline. The headwind and crosswind components are equal — each about 14 kt — because cos(45°) = sin(45°). If your personal-minimums max crosswind is 12 kt, this departure is a no-go even though the wind itself is well within most aircraft demonstrated limits.
Inputs
- Wind
- 235° at 20kt
- Runway
- 28 (280°)
Output
- Headwind
- 14.0kt
- Crosswind
- 14.0kt
- Crosswind side
- left
Section 04
Common pitfalls
- 01Runway designators are magnetic, METARs are true. Variation is < 15° for most of CONUS — but it matters at high latitudes.
- 02A "20 kt gust 35" METAR (`G35`) means peak gusts of 35 kt, not an additional 35 kt. Use the gust value, not the difference.
- 03A tailwind on takeoff (negative headwind) lengthens the ground roll dramatically; many POHs cap tailwind at 5–10 kt.
- 04Demonstrated max crosswind is not a regulatory limit. Personal minimums always live below the demonstrated number — by a margin you set, not the aircraft.
- 05Wet, gusty, or short runways shift the crosswind margin down. The number that matters is the one you can hold the upwind wheel down at, not the one the POH advertises.
Download
Free on the App Store. iOS 18 and up.
The iOS app computes wind components per runway for each watched station and surfaces the best-runway recommendation directly on the station detail screen.