Heading and Track Conversions in Practice
Track, heading, drift
Track is the path over the ground; heading is where the nose points. The difference is drift, produced by the crosswind component, and the heading always points into wind to make good the required track. The conversion sequence is: solve the wind triangle on track and TAS to obtain heading (true) and groundspeed; then convert true heading to magnetic by applying variation; then to compass by applying deviation. Converting back runs the chain in reverse: compass to magnetic to true heading, then subtract drift to recover track.
Techniques worth knowing
- Estimate drift with max drift (wind speed / TAS x 60) multiplied by the sine of the wind angle; refine with the sine rule when accuracy matters.
- To regain a parallel track after a known track error, apply twice the error for the same time flown, then reduce to the corrected heading.
- To intercept a track, use the closing angle as well as the track error; the sum is the heading change needed.
- Rate-one turns take 2 minutes for 360 degrees, or 3 degrees per second, which sets the lead for intercepting a radial or localizer.
- Groundspeed from the triangle is what belongs in the time calculation, not TAS.
Worked example
Track 180T, TAS 100 kt, wind 270/20, variation 20E, deviation 2E. Wind angle is 90 degrees, so drift is full crosswind: sin(drift) = 20/100, drift 11.5 degrees. The wind is from the right, so the heading is 180 minus 11.5 = 168T, and groundspeed stays near 100 kt because there is no head or tail component. Magnetic = 168 minus 20 = 148M. Compass = 148 minus 2 = 146C.
Traps
Applying drift to track to get track; converting to compass before the wind is solved; using the wrong drift direction; and forgetting that the groundspeed in the log differs from TAS whenever the wind is not purely across track.