Crosswind components

A wind that is not straight down the runway pushes you sideways, and knowing exactly how much sideways turns a vague unease into a number you can act on.

This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.

Splitting the wind into two

A reported wind has a direction and a speed, but for a runway what matters is how that wind splits into the part blowing along the runway (the headwind component, which helps you) and the part blowing across it (the crosswind component, which you have to control). The split is pure trigonometry, set out in the FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25) and the FAA Airplane Flying Handbook (FAA-H-8083-3), which give a chart that does the same job graphically.

With the angle between the wind and the runway called the wind angle:

• Crosswind component = wind speed x sine (wind angle).
• Headwind component = wind speed x cosine (wind angle).

The geometry is universal: it does not change by authority or aircraft. What changes is how much crosswind your aircraft and you can handle.

A worked example

Runway 36 points to a magnetic heading of 360 degrees (the number is the heading to the nearest ten, with the last zero dropped). The tower reports the wind as 060 degrees at 20 knots.

First the angle: the wind is from 060, the runway points to 360, so the wind is 60 degrees off the nose. Then the components:

• Crosswind = 20 x sine(60) = 20 x 0.87 = 17 knots (rounded).
• Headwind = 20 x cosine(60) = 20 x 0.5 = 10 knots.

So that 20-knot wind gives you a 17-knot crosswind and a 10-knot headwind. If your aircraft's maximum demonstrated crosswind is 15 knots, this runway in this wind is already beyond the demonstrated figure, and you would look for a more favourable runway or reconsider the flight.

The sine rule of thumb

You will not always have a calculator on short final, so pilots carry the relationship in their head. Because the crosswind is the wind speed times the sine of the angle, and the sine of a few key angles is easy to remember, the clock-code estimate follows:

• about 15 degrees off: roughly a quarter of the wind as crosswind;
• about 30 degrees off: roughly half;
• about 45 degrees off: roughly seventy per cent;
• about 60 degrees off: nearly all of it (the true figure is about eighty-seven per cent, so treating it as ninety per cent is a slight, safe over-estimate);
• 90 degrees off: all of the wind is crosswind.

It is an approximation of the trigonometry, handy for a quick mental check, not a replacement for working the numbers or reading the chart.

What "maximum demonstrated crosswind" means

Many pilots treat the figure in the flight manual as an absolute limit, and for some aircraft it is, but the term is precise. The maximum demonstrated crosswind component is the value a test pilot of average skill demonstrated the aircraft could be safely landed and taken off in during certification, then published in the manual or on a placard. As the FAA Airplane Flying Handbook explains, for many light aircraft it is a demonstrated value rather than a regulatory limit, so exceeding it is not necessarily prohibited, but it is well beyond what was tested and your skill, the conditions, and your operator's rules all bear on the decision. Check your own aircraft's flight manual, because for some types it genuinely is a limit.

Common pitfalls

• Tower wind is magnetic; the METAR is true. The wind read to you for take-off and landing is in degrees magnetic, matching the runway numbers, while the written METAR is degrees true, so do not mix the two when working the angle.
• Use the gust, not the mean. A gusting wind can put the crosswind over your limit at the worst moment, so base the component on the gust value.
• A negative headwind is a tailwind. If the wind is more than 90 degrees off the nose, the cosine goes negative, and you are looking at a tailwind component that lengthens your landing.
• Demonstrated is not always a limit, but treat it with respect. Knowing the difference is not licence to ignore the figure.

In Pilot EFB

Pilot EFB includes a crosswind and headwind calculator among its quick tools, and it shows you the decoded wind in the METAR, alongside your weather, NOTAMs, flight time, and logbook in one offline-first place. It is a study and planning aid, not a certified Electronic Flight Bag, and it does not know your aircraft's published crosswind figures or your operator's policy. Treat its output as a cross-check, work the limit from the reported wind and your own aircraft data, and follow your operator's crosswind policy. Saved weather stays readable offline; pulling a fresh observation needs a connection.