How to use the crosswind calculator
- Get the wind. Paste a METAR (or just its wind group, such as 31018G27KT) and the calculator fills it in. Or type the direction, speed and any gusts from the tower, the ATIS or your sim's weather.
- Say where the wind came from. Tower and ATIS winds are magnetic, like runway numbers, so nothing needs converting. A METAR or TAF wind is true; enter the airport's magnetic variation for an exact answer.
- Enter the runways. A runway number (27, 09L), both ends (09/27) or the exact magnetic heading from the airport chart (273). Add up to four runways. Each one is checked in both directions.
- Read the answer. The runway most into the wind comes first, with its headwind and crosswind and which side the wind comes from. The table lists every runway end; tailwinds show in amber.
- Optional: your aircraft's demonstrated crosswind. Enter it from the aircraft's manual and any runway end above it is flagged.
How the crosswind is worked out
The wind is split into two parts. The part along the runway is the headwind (or a tailwind, if it comes from behind). The part across the runway is the crosswind.
- Crosswind = wind speed × sine of the angle between the wind and the runway
- Headwind = wind speed × cosine of that angle
The FAA's Pilot's Handbook of Aeronautical Knowledge works this example with its crosswind chart: runway 17, wind from 140° at 25 knots. The angle is 30°, so the headwind is 22 knots and the crosswind 13 knots. The calculator opens on that example and gives the same answer.
Without a calculator, the angle tells you roughly how much of the wind is crosswind:
| Wind off the runway | Share that is crosswind | 20 kt wind |
|---|---|---|
| 10° | about a sixth (0.17) | 3 kt |
| 20° | about a third (0.34) | 7 kt |
| 30° | half (0.5) | 10 kt |
| 45° | about seven tenths (0.71) | 14 kt |
| 60° | about nine tenths (0.87) | 17 kt |
| 90° | all of it (1.0) | 20 kt |
Past 90° the wind is behind you: the crosswind shrinks again and the headwind turns into a tailwind.
True or magnetic wind?
Runway numbers are magnetic: runway 27 points about 270° on a magnetic compass. The wind in a METAR or TAF is measured from true north, while the wind the tower or the ATIS gives you is magnetic.
The difference between the two is the magnetic variation, printed on the airport chart. To turn a true wind into a magnetic one, subtract an east variation and add a west one; pilots remember it as "east is least, west is best". For example, a METAR wind from 150° with 10° east variation is 140° magnetic.
Where the variation is a few degrees, it barely changes the answer. Where it is large, it can move several knots between headwind and crosswind. A runway number is also rounded to the nearest 10°, so for an exact answer enter the runway's heading from the chart (273 rather than 27).
Gusts and a varying wind
Gusts. A wind of 15 gusting 25 knots has a gust factor of 10 knots: how far the gusts rise above the steady wind. The calculator gives the crosswind for both, because the gusts are what you have to hold on short final. The FAA's Airplane Flying Handbook adds no more than half the gust factor to the approach speed in gusty air, so 5 knots in this example. Your aircraft's manual comes first.
A varying wind. A METAR such as 31018KT 280V340 means the wind is from 310° but swinging between 280° and 340°. The calculator checks every direction in that range, at the gust speed if there is one, and gives the worst crosswind you could meet.
A variable wind (VRB) has no direction at all, so no runway is better than another. For a safe planning figure, treat the whole wind speed as crosswind.
How much crosswind is too much?
Most light-aircraft manuals list a maximum demonstrated crosswind. The FAA's safety team explains that it is not a limitation: it is the strongest crosswind met during the aircraft's flight tests for certification. The aircraft may handle more, but nobody has shown it.
Certification also sets a floor. Under the FAA's certification rules, airplanes must handle safely on the ground in a 90° crosswind of 0.2 times their landing-configuration stall speed: an airplane that stalls at 49 knots has to cope with just under 10 knots.
In a sim, the demonstrated figure is a good target: practise up to it, then past it, and you'll learn where the aircraft runs out of rudder.
Flying crosswind landings in a sim
The FAA's Airplane Flying Handbook describes two ways to land in a crosswind:
- Crab: point the nose into the wind so the aircraft tracks the centerline, then straighten it with rudder the instant before touchdown. Easier on final, but the timing at the end is hard.
- Wing-low (sideslip): line the nose up with the runway using rudder, and lower the upwind wing just enough to stop the drift. The handbook recommends it in most cases. It also describes a mix: crab on final, then change to the wing-low method before the flare.
Both need steady rudder. On a twist-grip stick, rudder and roll share one hand; rudder pedals put rudder under your feet, so hands and feet each do one job.
To practise, set a wind in your sim's weather settings: start at 5 knots straight across the runway and add 5 knots at a time. Or fly live weather, decode the airport's METAR, and use this calculator to pick the runway and know what's coming before you start the approach.