Ground Reference Maneuvers: Flying a Track Over the Ground

Ground reference maneuvers train you to fly a chosen path over the ground while the wind constantly tries to blow you off it. Because the air mass itself is moving, the airplane’s track over the ground is the sum of its motion through the air and the wind’s motion — the same effect that makes a boat crossing a river drift downstream. Two things change as you turn through the wind. First, groundspeed changes: headed upwind the groundspeed is less than the airspeed, and headed downwind it is greater. Second, to hold a straight ground track you must angle the nose into the wind just enough to cancel the sideways drift — a wind correction angle, or crab — with no correction needed only when the wind is directly on the nose or tail. To hold a constant radius while turning over the ground, the bank angle must vary with groundspeed: steepest where the groundspeed is highest (the downwind side) and shallowest where it is lowest (the upwind side), because a higher groundspeed leaves less time to get around the arc. For that reason these maneuvers are entered from the downwind position, where the steepest bank is set first. Pilots do not calculate correction angles in flight; they watch the reference and adjust the airplane’s relationship to it. Three maneuvers build the skill. The rectangular course flies an equal distance from all four sides of a rectangular field to replicate the airport traffic pattern, using varying wind correction and bank on each leg. S-turns fly a series of equal half-circles on alternating sides of a straight line such as a road, reversing the turn each time the line is crossed. Turns around a point fly consecutive 360-degree constant-radius turns around a single ground reference, continuously adjusting bank for the changing groundspeed. These maneuvers are flown at low altitude — generally 600 to 1,000 feet above the ground — so drift is easy to see, and are limited to a bank angle no steeper than 45 degrees and a speed no greater than the maneuvering speed, with obstruction clearance of at least 500 feet, because the low-altitude environment leaves little margin if the engine quits.