Crosswind with gusts

What the G means

In a METAR the wind is a group like 30018G26KT: direction, speed, then the gust. The Aeronautical Information Manual describes the group this way:

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]

So 30018G26KT is wind from 300° (true) at 18 knots, gusting to 26. The gust is the highest one reported.

The calculation

Crosswind = gust speed × sin Δ, where Δ is the wind direction minus the runway heading, exactly as in the formula. The same goes for the headwind. Do the sum twice, once with the steady speed and once with the gust, and you have the range.

Example: wind 300° at 18 knots gusting to 26, runway 27. Angle = 300 − 270 = 30°, sin 30° = 0.5000.

• Steady: 18 × 0.5000 = 9.0 → 9 knots of crosswind from the right, with a headwind of 15.6 → 16.
• Gust: 26 × 0.5000 = 13.0 → 13 knots of crosswind from the right, with a headwind of 22.5 → 23.

The gust adds 4 knots of crosswind. Because the crosswind is the speed times a fixed number for that angle, it grows in step with the speed.

Where your own limits fit

This page gives you the numbers. Whether they are acceptable is a decision for the pilot. The Pilot’s Handbook of Aeronautical Knowledge describes setting limits of your own:

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]

The calculator has a box for your maximum crosswind. It flags a crosswind that is within 80 percent of that number, and one at or above it, in whole knots. The 80 percent is this tool’s own convention, not an FAA figure, and it compares your number only; it does not know your airplane.