The purpose of ground reference maneuvers is to train pilots to accurately place the airplane in relationship to specific references and maintain a desired ground track. Such precision requires that a pilot simultaneously evaluate the airplane’s attitude, reference points along the desired path, and the natural horizon. Vision is the most utilized sense in maneuvering in orientation to ground-based references; however, all senses are actively involved at different levels. For example, touch provides tactile feedback as to the required flight control pressures to overcome flight control surface forces that indirectly indicate the airplane’s airspeed and aerodynamic load.
It is a common error for beginning pilots to fixate on a specific reference, such as a single location on the ground or the natural horizon. To be effective, the pilot must scan between several visual references to determine relative motion and to determine if the airplane is maintaining, or drifting to or from, the desired ground track. A pilot fixating on any one reference eliminates the ability to determine rate, which significantly degrades a pilot’s performance. Visual scanning across several references allows the pilot to develop the important skill of determining the rate of closure to a specific point. Consider a skilled automobile driver in a simple intersection turn; the driver does not merely turn the steering wheel some degree and hope that it will work out. The skilled driver picks out several references, such as an island to their side, a painted lane line, or the opposing curb, and they use those references to make almost imperceptible adjustments to the amount of deflection on the steering wheel, as well as the pressure on the accelerator pedal to smoothly join the lane into which they are turning. In the same manner, multiple references are required to precisely control the airplane in reference to the ground.
Not all ground-based references are visually equal and some understanding of those differences is important for their selection and use. For example, larger objects or references may appear closer than they actually are when compared to smaller objects or references. Also, prevailing visibility has a significant effect on the pilot’s perception of the distance to a reference. Excellent visibilities with clear skies tend to make an object or reference appear closer than when compared to a hazy day with poor visibility. Another example is that rain can alter the visual image in a manner that an illusion of being at a higher altitude may be perceived, and brighter objects or references may appear closer than dimmer objects. Being aware of typical visual illusions helps a pilot select the best references for ground reference maneuvers. It is best, however sometimes impracticable, to find ground-based references that are similar in size and proportion.
Ground-based references can be numerous. Excellent examples are breakwaters, canals, fence lines, field boundaries, highways, railroad tracks, roads, pipe lines, power lines, water-tanks, and others; however, choices can be limited by geography, population density, infrastructure, or structures. Selecting a ground-based reference requires prior consideration, such as the type of maneuver being performed, altitude at which the maneuver will be performed, emergency landing requirements, density of structures, wind direction, visibility, and the type of airspace.
Division of attention is an important skill that a pilot must develop. A pilot must be able to fly the airplane affecting the flight controls in a manner they will place the airplane in the needed attitude while tracking a specific path over the ground. In addition, the pilot must be able to scan for hazards such as other aircraft, be immediately prepared for an emergency landing should the need arise, and scan the flight and engine instruments at regular intervals to ensure that a pending situation, such as decreasing oil pressure, does not turn into an unexpected incident.
Safety is paramount in all aspects of flying. Awareness and practice of safety-enhancing procedures must be constantly exercised. Ground reference maneuvers place the airplane in an environment where heightened awareness is needed. Pilots should be looking for other aircraft, including helicopters, radio towers, and assessing locations for emergency landings. Pilots should always clear the area with two 90° clearing turns looking to the left and the right, as well as above and below the airplane. The maneuver area should not cause disturbances and be well away from groups of people, livestock, or communities. Before performing any maneuver, the pilot should complete the required checklist items, make any radio announcements (such as on a practice area frequency), and safety clearing turns. As a general note, a ground reference maneuver should not exceed a bank angle of 45° or an airspeed greater than maneuvering speed. As part of preflight planning, the pilot should determine the predicted (POH/AFM) stall speed at 50° or the highest bank angle planned plus some margin for error in maneuvering.