How to calculate crosswind

The crosswind component is the part of the wind blowing across the runway centreline. It helps with briefing, but the number must always be considered alongside the aircraft limitation, runway condition and your experience.

The short answer

Find the angle between wind direction and runway heading. Multiply wind speed by the sine of that angle for crosswind; use the cosine for headwind or tailwind. Make sure your calculator is set to degrees.

A simple example

With wind from 300 degrees at 20 knots and a runway heading of 270 degrees, the difference is 30 degrees. Crosswind is approximately 10 knots and headwind is approximately 17 knots.

The sign tells you whether it comes from the left or right; the magnitude tells you how much lateral wind to consider.

As a mental check, 30 degrees is roughly half the wind, 45 degrees is roughly 70 percent and 90 degrees is the full wind speed. The Pilot One crosswind calculator can verify the result.

From number to decision

Check the POH or AFM value, gusts, runway surface and width, turbulence, variable wind and your current experience. A wet runway and a strong gust may justify stopping even when a simple calculation is below a published demonstration value.

Common PPL mistakes

• Using the runway direction without checking the reciprocal.
• Taking the wrong angle between headings.
• Confusing crosswind with tailwind.
• Ignoring gusts.
• Treating a demonstrated value as a universal operational limit.

Conclusion

Crosswind calculation is simple when you respect angle, units and source. The number informs the briefing; operational judgement makes the decision.