The headwind or tailwind can be worked out mentally, similar to how we calculated the crosswind component in the previous lesson. We can then work out our ground speed by applying the headwind or tailwind to our true airspeed.
If the wind is directly on the nose or tail, the headwind/tailwind component will be the full wind speed.
If the wind is 90° to the nose, it will be all crosswind and our groundspeed will not change.
For any angle in between, the ‘clock code’ method is again used. However, this time we need to see how far the angle differs from a direct crosswind. Let’s look at an example:
You are flying on a heading of 320° with a true airspeed (TAS) of 90 knots. The wind is 170/20. What is your groundspeed?
1 Calculate the shortest angle between a direct crosswind and the actual wind:
Your heading is 320° so a direct crosswind would be 230° (320° – 90°)
The angle between 230° (a direct crosswind) and 170° is 60°
2 Use the clock code to determine how much of the wind is headwind or tailwind (see the previous lesson to learn about the clock code)
The wind is 60° off a direct crosswind, so the headwind/tailwind component is the full 20 knot wind speed.
From the diagram, we can see the wind is coming from behind the aircraft, so we have a 20 knot tailwind.
(always draw a diagram to help you visualise!)
3 Add the tailwind to or subtract the headwind from the true airspeed (TAS) to get the groundspeed
TAS = 90 knots
Tailwind = 20 knots
Groundspeed = 90 + 20 = 110 knots