Chapter 6: Ground Reference Maneuvers
To master ground reference maneuvers, a pilot must develop coordination, timing, and division of attention to accurately maneuver the airplane in reference to flight attitudes and specific ground references. With these enhanced skills, the pilot significantly strengthens his/her competency in everyday flight maneuvers, such as straight-and-level, turns, climbs, and descents.
Ground reference maneuvers are the principal flight maneuvers that combine the four fundamentals (straight-and-level, turns, climbs, and descents) into a set of integrated skills that pilots use in everyday flight activity.
Skills acquired with ground reference maneuvers become the basis for traffic patterns, survey and photographic flights, sightseeing trips, aerial applications (such as cropdusting and powerline inspections), and various other flight profiles requiring specific flightpaths referenced to points on the surface.
Instructors should introduce student pilots to ground reference maneuvers as soon as the student shows proficiency in the four fundamentals.
Maneuvering by Reference to Ground Objects
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.
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. Fixation on any one reference eliminates the ability to determine rate, which significantly degrades a pilot's performance. Multiple references are required to precisely control the airplane in reference to the ground
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.
Ground reference maneuvers place the airplane in an environment where heightened awareness is needed. Division of attention is an important skill that a pilot must develop. The pilot must track a specific path while also avoiding other aircraft, watching for hazards, and scanning the flight and engine instruments.
A ground reference maneuver should not exceed a bank angle of 45° or an airspeed greater than maneuvering speed (Va). 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.
Drift and Ground Track Control
Whenever the airplane is in flight, the movement of the air directly affects the actual ground track of the airplane. Wind direction and velocity variations are the primary effects requiring corrections of the flightpath during ground reference maneuvers.
Ground reference maneuvers are generally flown at altitudes between 600 and 1,000 feet above ground level (AGL). The pilot must consider the following when selecting the maneuvering altitude:
- The lower the maneuvering altitude, the faster the airplane appears to travel in relation to the ground.
- Drift should be easily recognizable from both sides of the airplane.
- The altitude should provide obstruction clearance of no less than 500 feet vertically above the obstruction and 2,000 feet horizontally.
- In case of an engine failure, the pilot must plan, consider, and be alert for forced landing areas while understanding that the lower the airplane's altitude, the less time there is to configure the airplane for an emergency landing and the shorter the glide distance.
- Any specific altitude required by test standards.
The preferred method of correcting for wind drift is to angle the airplane sufficiently into the wind to cancel the effect of the sideways drift.
The amount of wind correction angle required is dependent on the forward speed of the airplane and the speed of the wind. The slower the forward speed of the airplane and/or the faster speed of the wind, the greater the angle must be to counteract the drift. The converse is also true.
Airplanes correct for wind drift to maintain a track over the ground. Boats angle into a river current to reach a point on the opposite shore. The principles are identical.
Any wind not directly on the nose or tail of the airplane will drift the airplane sideways at a speed up to the speed of the wind. Pilots do not calculate the required drift correction angles for ground reference maneuvers. Instead, they use visual references and adjust the airplane's relationship to those references to cancel any drift.
The groundspeed of the airplane is affected by the wind. When the wind is blowing straight into the nose of the airplane, the groundspeed will be less than the airspeed. When the wind is blowing from directly behind the airplane, the groundspeed will be faster than the airspeed. Wind from any angle will affect groundspeed to a degree.
Constant Radius During Turning Flight
In a no-wind condition, the pilot can perform a ground-based constant radius turn by accurately maintaining a constant bank angle throughout the turn. When wind is present, during ground reference maneuvers involving turns, the pilot must correct for wind drift
Throughout the turn, the wind is acting on the airplane from a constantly changing angle. To follow a circular, constant radius ground track, the bank angle must vary to compensate for wind drift throughout the turn.
The airplane's ground-based turn radius is affected by the airplane's groundspeed. The faster the groundspeed, the steeper the airplane must be banked to maintain a ground-based constant radius turn. To maintain the constant radius over the ground, the bank angle is proportional to ground speed.
To demonstrate, the airplane would be flown into the wind and directly over a selected straight-line ground reference that is parallel to the wind (a road, railroad track, or powerline). As the airplane completes a 360° turn, it should return directly over the straight-line ground reference but downwind from the starting point, due to the direct headwind.
A turn over a straight-line ground reference that has a crosswind, using the same 360° constant medium-banked turn, will demonstrates how the airplane drifts away from the reference. This is due to the crosswind..
In both examples, the airplane flies a perfect continuous radius through the air. However, the path over the ground is an elongated circle.
In order to compensate for the elongated, somewhat circular path over the ground, the pilot must adjust the bank angle as the groundspeed changes throughout the turn. Where groundspeed is the fastest, such as when the airplane is headed downwind, the turn bank angle must be steepest (the steeper bank neutralizes the faster groundspeed.) Where groundspeed is the slowest, such as when the airplane is headed upwind, the turn bank angle must be shallow.
Ground reference maneuvers should always be entered from a downwind position. This allows the pilot to establish the steepest bank angle required to maintain a constant radius ground track.
Tracking Over and Parallel to a Straight Line
Student pilots should first be introduced to ground reference maneuvers by correcting for the effects of a crosswind over a straight-line ground reference. Multiple visual references can also be used to create an imaginary straight line. The pilot should angle the airplane's longitudinal axis into the wind sufficiently enough to cancel the effect of drift.
The student pilot should then practice flying a straight parallel path that is offset from the ground reference. The offset parallel path should not be more than three-fourths of a mile from the reference line.
Rectangular Course
The rectangular course (kneeboard) is a training maneuver in which the airplane maintains an equal distance from all sides of the selected rectangular references. This replicates the airport traffic pattern. The pilot should maintain a constant altitude, airspeed, and distance from the ground references.
The rectangular course covers the following skill areas:
- Maintaining a specific relationship between the airplane and the ground.
- Dividing attention between the flightpath, ground-based references, manipulating the flight controls, and scanning for outside hazards and instrument indications.
- Adjusting the bank angle during turns to correct for groundspeed changes in order to maintain constant radius turns.
- Rolling out from a turn with the required wind correction angle to compensate for any drift cause by the wind.
- Establishing and correcting the wind correction angle in order to maintain the track over the ground.
- Preparing the pilot for the airport traffic pattern and subsequent landing pattern practice.
A square, rectangular field, or an area with suitable ground references on all four sides should be selected consistent with safe practices. The airplane should be flown parallel to and at an equal distance between one-half to three-fourths of a mile away from the field boundaries.
The entry is downwind, which increases groundspeed (a wind-correction angle for drift may be necessary). The turn from the downwind leg onto the base leg is entered with a relatively steep bank angle. As the airplane turns onto the upwind leg, the crosswind lessens and becomes a headwind (again, with correction for drift). The pilot should slowly roll the airplane into a shallow-banked turn when entering the crosswind leg, since the crosswind drifts the airplane into the inside of the rectangular course.
Each turn in the rectangular course requires the bank angle to be adjusted to compensate for the changing groundspeed. The higher the groundspeed, the steeper the bank. This will maintain a constant ground-based radius.
Common errors made while performing rectangular courses include:
- Failure to adequately clear the area above, below, and on either side of the airplane for safety hazards, initially and throughout the maneuver.
- Failure to establish a constant, level altitude prior to entering the maneuver.
- Failure to maintain altitude during the maneuver.
- Failure to properly assess wind direction.
- Failure to establish the appropriate wind correction angle.
- Failure to apply coordinated aileron and rudder pressure, resulting in slips and skids.
- Failure to manipulate the flight controls in a smooth and continuous manner.
- Failure to properly divide attention between controlling the airplane and maintaining proper orientation with the ground references.
- Failure to execute turns with accurate timing.
Turns Around a Point
The turn around a point maneuver (kneeboard) is a 360° constant-radius turn around a single ground-based reference point. As with all ground reference maneuvers, higher groundspeeds require steeper banks and slower ground speeds require shallower banks.
While one turn may be sufficient for demonstration, to properly assess wind direction, velocity, bank required, and other factors related to turns in wind, the pilot should complete two or more turns. The pilot should make bank angle (and the resulting rate of turn) adjustments by applying coordinated aileron and rudder pressure throughout the turn.
The pilot should ensure that the reference point is visible at all times throughout the maneuver, even with the wing lowered in a bank. In a high-wing airplane, the pilot may need to change the maneuvering altitude or the desired turn radius.
When applying wind correction angles for any maneuver, the airplane's heading should be ahead of its position over the ground during the downwind half of the turn behind its position during the upwind half. This can be thought of as "overshoot into a headwind, undershoot with a tailwind."
The pilot should enter the maneuver downwind, where the groundspeed is at its fastest, at the appropriate radius of turn and distance from the selected ground-based reference point.
Upon entering the maneuver, it may be necessary to roll into the initial bank at a rapid rate so that the steepest bank is set quickly to prevent the airplane from drifting outside of the desired turn radius. The pilot should progressively adjust the airplane's heading toward the inside of the turn. Thereafter, the pilot should gradually decrease the angle of bank until the airplane is headed directly upwind.
During the upwind half of the turn, the pilot should progressively adjust the airplane's heading toward the outside of the turn.
The following are the most common errors in the performance of turns around a point:
- Failure to adequately clear the area above, below, and on either side of the airplane for safety hazards, initially and throughout the maneuver.
- Failure to establish a constant, level altitude prior to entering the maneuver.
- Failure to maintain altitude during the maneuver.
- Failure to properly assess wind direction.
- Failure to properly execute constant radius turns.
- Failure to manipulate the flight controls in a smooth and continuous manner.
- Failure to establish the appropriate wind correction angle.
- Failure to apply coordinated aileron and rudder pressure, resulting in slips or skids.
S-Turns
S-turns (kneeboard) is a ground reference maneuver in which the airplane's ground track resembles two opposite but equal half-circles on each side of a selected ground-based straight-line reference. The maneuver requires arriving at specific points on required headings.
With the airplane in the downwind position, the maneuver consists of crossing a straight-line ground reference at a 90° angle and immediately beginning a 180° constant-radius turn. Bank angle and roll rate are adjusted for drift effects and changes in groundspeed. The straight line is re-crossed in the opposite direction just as the first 180° constant radius turn is completed.
The first 180° constant-radius turn is immediately followed by a second 180° turn in the opposite direction. Because the airplane is now upwind, the roll into this second turn should be smooth and gentle. The initial bank angle should be shallow. As the airplane turns downwind, groundspeed increases and the bank angle should increase.
If the straight-line ground reference is of sufficient length, the pilot may complete as many S-turns as can be safely accomplished.
It is standard practice to enter ground-based maneuvers downwind where groundspeed is greatest. The roll into the S-turn must be rapid, but not aggressive, and the angle of bank must be steepest when initiating the turn.
As the turn progresses, the bank angle and the rate of rollout must be decreased as the groundspeed decreases to ensure that the turn's radius is constant.
The following are the most common errors made while performing S-turns across a road:
- Failure to adequately clear the area above, below, and on either side of the airplane for safety hazards, initially and throughout the maneuver.
- Failure to establish a constant, level altitude prior to entering the maneuver.
- Failure to maintain altitude during the maneuver.
- Failure to properly assess wind direction.
- Failure to properly execute constant radius turns.
- Failure to manipulate the flight controls in a smooth and continuous manner when transitioning into turns.
- Failure to establish the appropriate wind correction angle.
- Failure to apply coordinated aileron and rudder pressure, resulting in slips or skids.
Elementary Eights
Elementary eights are a family of maneuvers in which each individual maneuver is one that the airplane tracks a path over the ground similar to the shape of a figure eight. Eights develop a pilot's flight control coordination skills, improve awareness of ground references, and enhance division of attention. With practice, flying becomes more instinctive than mechanical.
Elementary eights include eights along a road, eights across a road, and eights around pylons. Each of these maneuvers is a variation of a turn around a point. These maneuvers are not included as part of of the Private Pilot Airman Certification Standards (ACS). See the Airplane Flying Handbook for details on these maneuvers.
Eights-on-pylons (kneeboard) is a maneuver established in the Commercial Pilot Airman Certification Standards. The eights-on-pylons is the most advanced and difficult of the ground reference maneuvers, unmatched for developing intuitive control of the airplane.
The goal of the eights-on-pylons is to have an imaginary line that extends from the pilot's eyes to the pylon. Altitude is varied to maintain a specific visual reference to the pivot points.
The imaginary line is parallel to the airplane's lateral axis. If a taut string were extended from the airplane to the pylon, the string would remain parallel to lateral axis as the airplane turned around the pylon. At no time should the string be at an angle to the lateral axis.
High-wing, low-wing, swept-wing, and tapered wing airplanes, as well as those with tandem or side-by-side seating, all present different angles from the pilot's eye to the wingtip. Thus, a "wingtip" visual reference in this maneuver is not necessarily correct. The pilot should use a visual reference line that, from eye level, parallels the lateral axis of the airplane.
The altitude that is appropriate for eights-on-pylons is called the pivotal altitude and is determined by the airplane's groundspeed.
At the pivotal altitude, the projection of the visual reference line to the pylon appears to pivot.
With most ground reference maneuvers, the airplane flies a prescribed path over the ground. The pilot attempts to maintain the track by correcting for the wind.
With eights-on-pylons, the pilot maintains lateral orientation to a specific spot on the ground. This develops accurate maneuvering while the pilot's attention is divided between the flightpath and the pylons.
Pivotal altitude is determined by finding the square of the groundspeed. If this is in miles per hour (MPH), the square is divided by 15. If this is in knots, the square is divided by 11.3. The result is then added to the pylon's mean sea level (MSL) altitude.
- Groundspeed: 90 knots.
- Square of groundspeed: 8100
- Square of groundspeed divided by 11.3: 717.
- MSL elevation of pylon: 200 feet.
- Pivotal altitude: 917 feet MSL.
Pivotal altitude should be estimated during preflight planning. Wind direction and velocity can be estimated to calculate the appropriate pivotal altitudes for upwind, downwind, and crosswind.
At any altitude above the pivotal altitude, the projected visual reference line appears to move backward across the ground, while pylon moves forward ("fly high, fall back"). When the airplane is below the pivotal altitude, the projected visual reference line appears to move forward across the ground, while pylon moves back ("fly low, let's go").
Pilots can fly above and below pivotal altitude to demonstrate the change in visual reference to the pylon. The altitude at which the visual reference line ceases to move across the ground is the pivotal altitude.
Pivotal altitude does not vary with the angle of bank unless the bank is steep enough to affect the groundspeed. Angle of bank varies based on the distance from the pylon.
Proper pivotal altitude will vary slightly throughout the turn, due to variations in groundspeed caused by wind. The pilot should adjust for this by climbing or descending, as necessary, to hold the visual reference line on the pylons.
Selected pylons should also be adequately spaced to provide time for planning the turns, but not spaced so far apart that they cause unnecessary straight-and-level flight between the pylons. The distance between the pylons should allow for the straight-and-level flight segment to last from three to five seconds. The pylons should be at the same elevation.
The pilot should begin the eight-on-pylons maneuver by flying diagonally crosswind between the pylons to a point downwind from the first pylon so that the first turn can be made into the wind. As the airplane approaches a position where the pylon appears to be just ahead of the wingtip, the pilot should begin the turn by lowering the upwind wing to the point where the visual reference line aligns with the pylon.
As the airplane heads upwind, the groundspeed decreases, which lowers the pivotal altitude. The pilot must descend to hold the visual reference line on the pylon.
Since this maneuver does not require the turn to be completed at a constant radius, the pilot does not need to apply drift correction to complete the turn.
If the visual reference line appears to move ahead of the pylon, the pilot should increase altitude (fly high to fall back"). If the visual reference line appears to move behind the pylon, the pilot should decrease altitude ("fly low, let's go").
It is important to understand that variations in pylon position are according to the apparent movement of the visual reference line. Attempting to correct pivotal altitude by the use of the altimeter is ineffective.
Common errors in the performance of eights-on- pylons include:
- Application of inside rudder pressure to yaw the wing backward when the projection of the visual reference line moves forward.
- Failure to adequately clear the area above, below, and on either side of the airplane for safety hazards, initially and throughout the maneuver.
- Poor selection of ground references.
- Failure to establish a constant, level altitude prior to entering the maneuver.
- Failure to maintain adequate altitude control during the maneuver.
- Failure to properly assess wind direction. Failure to properly execute constant radius turns.
- Failure to manipulate the flight controls in a smooth and continuous manner.
- Failure to establish the appropriate wind correction angles.
- Failure to apply coordinated aileron and rudder pressure, resulting in slips or skids.
- Failure to maintain orientation as the maneuver progresses.
Commercial Pilot & Flight Instructor Test Questions
Rectangular Course
When beginning a rectangular course, the determining factor in deciding the distance from the field boundary at which an aircraft should be flown is the steepness of the bank desired in the turns.
In flying the rectangular course, which would describe the proper angle of bank? Corner 1 (upwind to crosswind) shallow to medium, corner 2 medium to steep, corner 3 steep to medium, and corner 4 medium to shallow.
— There has to be a change in bank at all four corners.
In flying the rectangular course, when would the aircraft be turned less than 90°? Turn from base to upwind; turn from upwind to crosswind.
— On the test diagram, this may be shown as positions 1 and 4.
Turns Around a Point
During turns around a point, an imaginary line from the pilot's eye and parallel to the lateral axis should point to the pylon when the aircraft is abeam the point heading directly upwind or downwind.
— The wings are aligned with the pylon only when the aircraft is flying upwind or downwind. At all other times, the airplane is crabbed.
During turns around a point, the groundspeed will be equal in which positions? Groundspeeds are equivalent at the reciprocal points, with the exception of directly upwind vs. directly downwind.
— The quiz diagram may present directly upwind and directly downwind as positions 3 and 7.
At which points will the wing (lateral axis) be in alignment with the pylon during turns around a point? No crabbing is required when directly into the wind or with the wind. The airplane's lateral axis will intersect the pylon.
— The quiz diagram may present directly upwind and directly downwind as positions 3 and 7.
During turns around a point, the bank angle will most nearly equal in which positions? The crosswind positions.
— The quiz diagram may present directly crosswind as positions 1 and 5.
S-Turns Across a Road
During S-turn practice, which positions require the steeper angle of bank? The change of direction over the road when flying downwind will have the two steepest banks.
— The quiz diagram may present these as positions 3 and 4.
Proper execution of S-turns across a road requires that the aircraft be crabbed into the wind the greatest amounts at which points? At the crosswind positions.
— Flying crosswind requires crabbing, while flying directly upwind or downwind does not. The quiz diagram may present the crosswind points as positions 2 and 5.
While practicing S-turns, a consistently smaller half-circle is made on one side of the road than on the other, and this turn is not completed before crossing the road or reference line. This would most likely occur in turn... 4-5-6 because the bank is increased too rapidly during the early part of the turn.
— This is an easy question to get wrong because turning too slowly on the upwind side appears that it would push the airplane back across the road before the turn is completed. However, the test question suggests that the bank is increased too rapidly, which results in a smaller half-circle.
While practicing S-turns, which positions require the steepest angle of bank? 3 and 4.
— Positions 3 and 4 are adjacent — the "big flop" in the wind.
Eights-on-Pylons
In properly coordinated eights-on-pylons, if the reference point is behind the pylon, it means the airplane is above the pivotal altitude.
— The airplane needs to reduce altitude to create the "catch up" effect. Flying high has caused the reference point to "fall back."
If the wing moves behind the pylon during properly coordinated eights-on-pylons, the airplane is above pivotal altitude.
The pivotal altitude for eights-on-pylons is dependent upon the groundspeed.
Misuse of rudder in attempting to hold the pylon during the performance of eights-on-pylons will result in which turn-and-slip indication? A slip when above pivotal altitude; a skid when below pivotal altitude.
— It's easiest to visualize this with a small airplane and a pylon. When the wing is behind the pylon, the pilot can improperly move the wing forward with the rudder by applying outside rudder, which slipping the airplane (the ball falls to the inside of the turn). The pilot also can bring the wing forward by lowering altitude to create the "catch up" effect. Thus, if the pilot is improperly slipping the airplane to hold the pylon, the airplane is above pivotal altitude and should reduce altitude.