Crosswind calculator FAQ

How do you calculate crosswind?

Multiply the wind speed by the sine of the angle between the wind direction and the runway heading. For wind 300 degrees at 20 knots on runway 27 (270 degrees) the angle is 30 degrees and the crosswind is 20 × sin 30° = 10.0 knots. The formula.

How do you calculate headwind?

Multiply the wind speed by the cosine of the same angle. In the same example the headwind is 20 × cos 30° = 17.3 knots. If the answer is negative, it is a tailwind. The formula.

What angle do I use?

The wind direction (where the wind blows from) minus the runway heading, in the same kind of degrees. If the result is outside −180 to 180, add or subtract 360. The sign tells you the side: positive is a crosswind from the right, negative from the left. Finding the angle.

What heading does a runway number mean?

The number is the runway's magnetic azimuth rounded to the nearest 10 degrees, divided by 10, so runway 27 is about 270 degrees magnetic. The calculator uses the number times ten, which can differ from the real centerline by up to 5 degrees.

Runways are identified by numbers that indicate the nearest 10-degree increment of the azimuth of the runway centerline. For example, where the magnetic azimuth is 183 degrees, the runway designation would be 18; for a magnetic azimuth of 87 degrees, the runway designation would be 9. [AIM 4-3-6 a]

Is a METAR wind true or magnetic?

True. The AIM says the first three digits of the wind group are in tens of degrees referenced to true north. Runways are numbered magnetically, so a METAR wind has to be converted before it is used against a runway. METAR wind and your runway.

The first three digits are the direction the wind is blowing from, in tens of degrees referenced to true north, or “VRB” if the direction is variable. The next two digits is the wind speed in knots, or if over 99 knots, the next three digits. If the wind is gusty, it is reported as a “G” after the speed followed by the highest gust reported. [AIM 7-1-29 b 5]

Is the tower or ATIS wind true or magnetic?

Magnetic. The AIM says the wind direction issued by the tower is magnetic, and that ATIS, ASOS and AWOS voice broadcasts report wind direction relative to magnetic north. METAR wind and your runway.

Wind direction issued by the tower is also magnetic and wind velocity is in knots. [AIM 4-3-6 a]

Wind direction is reported relative to magnetic north in ATIS as well as ASOS and AWOS radio (voice) broadcasts. [AIM 7-1-10 d 3 (c) note]

How do I calculate the crosswind in a gust?

Use the gust speed in place of the steady speed. The angle does not change, so the crosswind in the gust is the gust speed times the same sine. Crosswind with gusts.

What is the maximum crosswind for my airplane?

This calculator does not know. The PHAK says the maximum demonstrated crosswind component is published in the airplane's AFM or POH, and the AFH says the demonstrated crosswind velocity is on a placard in airplanes certificated after May 3, 1962. Look in your own airplane's documents.

The maximum demonstrated crosswind component is published in the AFM/POH. The crosswind and headwind component chart allows for figuring the headwind and crosswind component for any given wind direction and velocity. [PHAK p. 11-25]

The demonstrated crosswind velocity is included on a placard in airplanes certificated after May 3, 1962. [AFH p. 9-19]

It is imperative that pilots determine the maximum crosswind component of each airplane they fly and avoid operations in wind conditions that exceed the capability of the airplane. [AFH p. 9-19]

How is the demonstrated crosswind decided?

The PHAK describes a test flown in 90 degree crosswinds up to 0.2 times the stalling speed, with power off, gear down and flaps down.

The aircraft is tested by a pilot with average piloting skills in 90° crosswinds with a velocity up to 0.2 VS0 or two-tenths of the aircraft’s stalling speed with power off, gear down, and flaps down. [PHAK p. 11-25]

What is a personal minimum?

A limit you set for yourself, based on your own experience and proficiency. The PHAK's example is a pilot with experience in 10 knots of direct crosswind setting that as the personal limit until further training.

One way a pilot can control the risks is to set personal minimums for items in each risk category. These are limits unique to that individual pilot’s current level of experience and proficiency. [PHAK p. 2-8]

For example, the aircraft may have a maximum crosswind component of 15 knots listed in the aircraft flight manual (AFM), and the pilot has experience with 10 knots of direct crosswind. It could be unsafe to exceed a 10 knot crosswind component without additional training. [PHAK p. 2-8]

Does the calculator tell me whether it is safe to land?

No. It computes the components and, if you enter a maximum crosswind of your own, says whether the result is within 80 percent of it or at or above it. Whether to take off or land is the pilot's decision. It is a training and planning aid, not for primary flight operations.

What does the "best runway" ranking mean?

It ranks the 36 runway headings for your wind. Headings with a tailwind go below those without; within each group, the smaller crosswind comes first, then the larger headwind. It ranks headings, not the runways at a given airport.

What if the METAR says VRB?

VRB means the direction is variable, so the report has no single direction to enter and one set of components cannot be worked out from it.

The first three digits are the direction the wind is blowing from, in tens of degrees referenced to true north, or “VRB” if the direction is variable. The next two digits is the wind speed in knots, or if over 99 knots, the next three digits. If the wind is gusty, it is reported as a “G” after the speed followed by the highest gust reported. [AIM 7-1-29 b 5]

Does it work in miles per hour or kilometers per hour?

No. The speeds are in knots, the unit the METAR and the tower's wind use.

Is it the same math as the app?

Yes. The calculator runs the same wind-triangle code as the Crosswind Calculator iOS app, and an automated test compares it with the app's own Swift code on a grid of winds and runways.