Calculating cross wind and headwind

Posted on November 17, 2025 by - IMC rating, Navigation - PPL, Tips

We need to calculate or estimate cross winds for several reasons

  1. To check whether the cross wind is within limits for take-off and landing
  2. To calculate wind drift (the difference between heading and track) on a cross-country flight
  3. To estimate wind drift for an unplanned diversion
  4. To calculate wind drift / heading correction on an instrument approach

There are several ways we can go about this this.

    • For a cross country flight, calculate the required heading (and implicitly the drift) before flight using our trusty CRP-1 (Whizz wheel) or with a planning app like SkyDemon, or with a wind protractor.
    • Use an app like Windstar to calculate headwind / tailwind, cross wind and cross wind drift, so we have the info ready to use when needed
    • Use a graphical calculator, on the fly, like the one which I present on my VFR reference card
    • Calculate the maximum cross wind drift using this formula: Drift = wind speed x 60 / TAS
TAS –> 60 kt 90 kt 100 kt 120 kt 
Max drift 1x 2/3 x 3/5 x 1/2 x
Wind speed in kt
  • And then estimate the actual drift, on the fly, using a simple rule of thumb
Roughly, ‘nothing, half, all’ rule wind 30o off, cross wind = ½ x wind speed and drift is ½ x max drift;

wind 60 o off, x-wind = full wind and drift = max drift
More precisely, ‘rule of sixths’  Take one sixth of the drift or wind

for every 10o the wind is different to the runway or track direction.

And finally, how do we record the information we’ve derived? We could

  • mark the wind and max drift on the chart and do the rest in our heads
  • look at the app
  • put the info on a paper windstar and paper-clip it to the chart
  • write the info on the instrument approach plate (thanks to one of my students for inventing this!)