How the crosswind component works
Any wind that is not straight down the runway splits into two parts. The crosswind component pushes the airplane sideways across the runway; the headwind component (or tailwind) acts along it. With the wind angle measured between the wind direction and the runway heading:
- crosswind = wind speed × sin(wind angle)
- headwind = wind speed × cos(wind angle)
The worked example is PHAK Sample Problem 10 (FAA-H-8083-25C, chapter 11): runway 17 with the wind from 140° at 25 knots. The wind angle is 30°, so the crosswind is 12.5 knots from the left and the headwind is 21.7 knots. The handbook's chart reading is 13 and 22 knots, the same as the rounded result above.
Runway numbers, headings and wind references
Enter the runway designator (17, 09L, 27R) and the calculator uses ten times the number: runway 17 becomes 170°. For more precision, type the published three-digit heading instead, such as 173. Runway numbers are magnetic. Tower, ATIS and AWOS winds are magnetic too, so they compare directly. METAR and TAF winds are true: with 10° of east variation, a METAR wind of 140° is about 130° magnetic.
Gusts and your personal limit
A gust adds to the speed, not the direction, so the gust crosswind uses the same angle. With the wind from 140° at 25 gusting 35, the gust crosswind is 17.5 knots. Enter your crosswind limit and the result is checked against the gust value when you give one, the steady value otherwise.
The maximum demonstrated crosswind in a POH is the value shown during certification, not a structural limit. Many instructors recommend a lower personal limit, especially for new pilots and gusty days.
Quick estimates without a calculator
Pilots often estimate the crosswind from the wind angle using a clock-face rule:
| Wind angle | Crosswind, fraction of wind speed | Exact sine |
|---|---|---|
| 15° | about 1/4 | 0.26 |
| 30° | about 1/2 | 0.50 |
| 45° | about 3/4 | 0.71 |
| 60° or more | nearly all of it | 0.87 |
The rule is conservative at 45° and slightly low between 15° and 30°. Use it for a quick check against the calculator.
Crosswind on the E6B wind side
- Turn the rose until the runway heading (170° for runway 17) is under the TRUE INDEX.
- Mark the wind direction and speed as a dot: find 140° on the rose and count 25 knots out from the grommet along that line.
- Read the crosswind as the dot's distance left or right of the center line, and the headwind as its distance above the grommet.
Questions pilots ask
How do you calculate a crosswind component?
Multiply the wind speed by the sine of the angle between the wind and the runway. With the wind 30 degrees off the runway at 25 knots, the crosswind is 25 × sin 30° = 12.5 knots. The headwind is 25 × cos 30° = 21.7 knots.
Should I use the gust or the steady wind?
Check both. The steady component tells you what to hold most of the time; the gust component is the worst case. The calculator flags your limit against the gust value when you enter one.
Is the wind in a METAR true or magnetic?
METAR and TAF winds are relative to true north. ATIS, AWOS broadcasts and tower winds are magnetic, like runway numbers. For a METAR wind, convert the direction to magnetic before comparing it with the runway, or use the runway's true heading.
What does a negative headwind mean?
A tailwind. The calculator labels it as a tailwind and flags it as a caution, because a tailwind lengthens the takeoff and landing roll.