Dead Reckoning, Plotting and the Navigation Computer
Dead reckoning and the wind triangle
Dead Reckoning, Plotting and the Navigation Computer tests your ability to turn heading, time, wind and distance into a position and an ETA. Heading is where the aircraft nose points; track is the path over the ground. True airspeed (TAS) combined with wind gives ground speed (GS) and drift. The wind triangle relates heading/TAS to track/GS: wind direction is given as the direction the wind comes from, so a 270/30 wind blows toward 090°. Drift is the angle between heading and track. The 1-in-60 rule approximates: track error in degrees = (distance off track ÷ distance flown) × 60.
Plotting and the computer
Plot tracks from known positions, mark wind vectors, and label headings, times and fuel. Use the navigation computer for fuel, time, distance, TAS and wind-side calculations. Check units: the computer may use nautical miles, gallons, litres, pounds or kilograms. Round only at the end; early rounding accumulates error.
Worked example
You plan 120 nm at a GS of 90 kt, so ETA is 120 ÷ 90 = 1.33 h, or 1 h 20 min. After 30 nm, you are 2 nm right of track. The 1-in-60 rule gives (2 ÷ 30) × 60 = 4°. Alter heading 4° left to parallel the track, then use a closing alteration to regain the original track. If the remaining 90 nm is flown at 90 kt, the remaining time is 1 h.
Traps
Do not confuse heading with track or TAS with IAS. Wind direction is “from”, not “toward”. Watch drift sign: right drift requires a left heading correction. Keep true and magnetic values separate. A computer answer is only as good as the input units and the wind actually used.