Navigation for Agricultural Operations
Navigating a spray block
Agricultural navigation is not airway navigation; it is precise, repetitive track-keeping over a field. The pilot must know the field boundaries, the swath width, the spray lines, and the turn pattern. Dead reckoning, map reading, GPS and GNSS-based guidance all play a part, but the pilot must always maintain visual reference and avoid obstacles.
Concepts to command
Understand heading, track and drift, and how wind correction keeps the spray lines parallel. Know how to compute time and distance for a run, and how to plan turns that avoid obstacles and overspray. Understand the use of GPS waypoints and the risk of over-reliance on automation. Know the magnetic variation and its effect on heading. Understand the meaning of AGL altitude and how to maintain a constant height over undulating terrain. Know the local area: power lines, towers, houses, water bodies and livestock.
Traps
Questions often test the difference between heading and track, or ask how to correct for drift. Another trap: assuming GPS guidance removes the need for a visual scan. Watch for items on magnetic variation and on the effect of terrain on AGL height.
Rule of thumb
Plan the field on the ground: draw the boundary, mark obstacles, set the swath and the number of runs, and note the wind. In the air, fly the line and let the wind correction angle do the work; do not chase the GPS needle.
Worked example: A field is 900 m long and the helicopter flies at 40 m/s. Time per run = 900 / 40 ≈ 22.5 s. With a 20 m swath and a 100 m field width, five runs cover the field. Add turn time and check the total against the fuel and product load.