Ground Reference Maneuvers

Understanding Wind & Wind Drift:

• As with water flowing down a river, air is a fluid in motion
• In order to maintain a desired path across a surface, an airplane must correct for wind (wind correction angle) in the same way a boat must does for current [Figure 1]
• The principles and techniques of varying the angle of bank to change the rate of turn and wind correction angle for controlling wind drift during a turn are the same for all ground track maneuvers involving changes in direction of flight

• 

• Wind Drift When Straight and Level:

  • Consider a flight with a wind velocity of 30 knots (knot=nautical mile per hour) from the left and 90° to the direction the airplane is headed
  • After 1 hour, the body of air in which the airplane is flying will have moved 30 nautical miles to the right
  • Since the airplane is moving within this body of air, it too will have drifted 30 NM to the right
  • In relation to the air, the airplane moved forward, but in relation to the ground, it moved forward as well as 30 NM to the right
  • In order to correct for this, the pilot applies a wind correction angle (into the wind) which is proportional to the wind velocity
  • When the drift has been neutralized, the airplane will follow the desired ground track



• Wind Drift During A Turn:

  • Wind effects are different in a turn [Figure 2]
  • Since the relative wind angle is constantly changing, so does ground speed, impacting the ground track and time it takes for the airplane to progress through any part of a turn
  • To follow a desired circular ground track, the wind correction angle must therefore be varied [Figure 3]
    • When the airplane is headed into the wind, the ground speed is decreased, reducing the required wind correction angle
    • When the airplane is headed away from the wind, the ground speed is increased, increasing the required wind correction angle
    • Through the crosswind portion of a turn, the airplane must be turned sufficiently into the wind to counteract drift
  • The amount of wind correction is dependent upon ground speed:
    • The faster the ground speed, the faster the wind correction angle must be established
    • The slower the ground speed, the slower the wind correction angle may be established
  • The steepest bank and fastest rate of turn should be made on the downwind portion of the turn and the shallowest bank and slowest rate of turn on the upwind portion
  • When there is no wind, it should be simple to fly along a ground track with an arc of exactly 180° and a constant radius because the flightpath and ground track would be identical
  • In order to determine the direction of the wind, pilots can observe flags, water, or perform a wind drift circle

Wind Drift Circle:

• The wind drift circle helps pilots determine wind direction and strength (velocity), while in flight and recognize the effect of wind on the airplane's ground track
• Primarily a training maneuver, the effects of wind during a turn can be seen by selecting a road, railroad, or other ground reference that forms a straight line parallel to the wind while flying a constant medium angle of bank for 360° of turn [Figure 3]
• The airplane will return to a point directly over the line but slightly downwind from the starting point, depending on the mount of wind velocity and the time required to complete the turn
• The path over the ground will be an elongated circle, although in reference to the air it is a perfect circle
• Straight flight during the upwind segment after completion of the turn is necessary to bring the airplane back to the starting position

• Wind Drift Circle Procedure:

  1. Perform clearing turns looking for traffic and ground obstructions
  2. Select a reference point in an area where an emergency landing can be made if necessary
  3. Establish and maintain traffic pattern speed and 800-1,000' AGL
  4. Enter the maneuver from any direction to the reference point
  5. Over the reference point, roll into a 30° bank and perform a 360° turn, maintaining a constant bank angle
     • Any error in AoB or coordination will have some degree of effect depending on how bad
  6. Initiate a roll-out at a point where the wings will be level when completing the turn
  7. Note any difference in position between the starting and finishing positions
     • The airplane will finish the maneuver downwind from the initial starting point by the magnitude of the wind
  8. Determine the approximate wind direction and strength based on any differences in the starting and finishing positions
  9. Upon completion of the maneuver, resume normal cruise and trim as necessary
  10. Complete cruise flow/checklist

• Wind Drift Circle Common Errors:

  • Failure to adequately clear the area
  • Skidding or slipping turns
  • Excessive gain or loss of altitude
  • Not entering the pylon turns into the wind
  • Failure to assume a heading that will compensate sufficiently for drift
  • Abrupt control usage

Turns Around a Point:

• Turns around a Point are an extension on S-Turns across a road where the airplane is flown in two or more complete circles of uniform radii or distance from a prominent ground reference point [Figure 4]
  • Further teaches the radius of a turn is a distance which is affected by the degree of bank used when turning with relation to a definite object
  • Perfects the ability to subconsciously control the airplane, while dividing attention between flight path and ground references in a turn
  • Develops a keen perception of altitude
• Use a maximum bank of 45° while maintaining altitude
• As experience and understanding of the effects of wind drift, bank angle, and wind correction angle improve, you may enter the maneuver from any point
• Take into account ground speed and wind velocity to determine the angle of bank required initially to maintain the proper ground track
• Radius distance must permit seeing the point throughout the maneuver, even in a bank
• In addition to varying the bank angle, "crabbing" is also necessary:
  • Crab in during the downwind half of the circle, crab out during the upwind half of the circle

• Turns Around a Point Procedure:

  1. Determine wind direction
     • This is important for the entry heading and reference point
  2. Perform clearing turns looking for traffic and ground obstructions
  3. Select a reference point in an area where an emergency landing can be made if necessary
     • Select a point easily distinguished and small enough to present precise reference
     • Isolated trees or crossroads work best
  4. Establish and maintain traffic pattern airspeed and 1,000' AGL
  5. Enter on a downwind to one side of the selected point at a distance equal to the desired radius of the turn
  6. Directly downwind and abeam the reference point, roll into the steepest bank to initiate maintaining a constant radius
     • This will be your highest ground speed
  7. Turn not to exceed 45°
  8. As the turn continues, begin to shallow the bank, as necessary, to continue maintaining a constant radius
     • Ground speed will decrease
  9. Directly upwind the bank should be at its shallowest
     • Ground speed will be slowest
  10. As the turn continues, begin to steepen the bank, as necessary, to continue maintaining a constant radius
      • Ground speed will begin to increase
  11. Continue the maneuver for another set of turns or depart on entry heading, as directed
  12. Upon completion of the maneuver, resume normal cruise, RPM
      • Trim as necessary
  13. Complete cruise flow/checklist

• Turns Around a Point Common Errors:

  • Failure to adequately clear the area
  • Failure to establish appropriate bank on entry
  • Failure to recognize wind drift
  • Excessive bank and/or inadequate wind correction angle on the downwind side of the circle, resulting in drift toward the reference point
  • Inadequate bank angle and/or excessive wind correction angle on the upwind side of the circle, resulting in drift away from the reference point
  • Skidding turns when turning from downwind to crosswind
  • Slipping turns when turning from upwind to crosswind
  • Gaining or losing altitude
  • Inadequate visual lookout for other aircraft
  • Inability to direct attention outside the airplane while maintaining precise airplane control

S-Turns:

• S-Turns develop the ability to compensate for drift during turns by flying semicircles of equal radii on each side of a reference line on the ground [Figure 5]
  • You may need to be creative but the end state is a straight line, approximately 1 mile or longer in length
• Builds wind drift skills developed with the rectangular course but introduces constant turns
• The maneuver is flown to arrive at a specified point, at specified headings, while compensating for drift, orienting the flight path with ground references by changing roll rate and angle of bank to establish correction to compensate for ground speed changes

• 

• S-Turns Procedure:

  1. Determine wind direction
     • This is important for the entry heading and reference line
  2. Perform clearing turns looking for traffic and ground obstructions
  3. Select a reference line perpendicular to the direction of the wind
     • Select an area where an emergency landing can be made if necessary
     • May be performed on any straight line such as a road, fence, or railroad
     • Select the point on upwind and turn back for a downwind entry
  4. Establish and maintain a cruise airspeed to enter the maneuver between 600-1,000' AGL
  5. Enter on a downwind to one side of the selected point, at a distance equal to the desired radius of the turn
  6. When abeam (perpendicular) or over the reference line (highest ground speed), begin the turn to roll into the upwind
     • Apply adequate wind-drift correction to track a constant radius turn on each side of the selected reference line
       • Start with a steep bank, as ground speed is highest
       • Transition to a moderate angle of bank around 90° as ground speed begins to slow
       • Shallow rolling out around 180° as ground speed is lowest
       • Roll wings level at 180° so as to be straight and level directly over and perpendicular to the reference line
       • Crabbing is also necessary (crab in during the downwind half of the circle, crab out during the upwind half of the circle)
  7. When abeam (perpendicular) or over the reference line (lowest ground speed), begin the turn to roll back into the downwind
     • Start with a shallow bank, as ground speed is lowest
     • Transition to a moderate angle of bank around 90° as ground speed begins to rise
     • Steepen the bank angle to roll out around 180° as ground speed is highest
     • Roll wings level at 180° so as to be straight and level directly over and perpendicular to the reference line
     • Crabbing is also necessary (crab in during the upwind half of the circle, crab out during the downwind half of the circle)
  8. Depart on entry heading and resume normal cruise
     • Trim as necessary
  9. Complete cruise flow/checklist

• S-Turns Common Errors:

  • Failure to adequately clear the area
  • Poor coordination
  • Gaining or losing altitude
  • Misjudging the rate of turn
  • Inability to visualize the half circle ground track
  • Poor timing in beginning and recovering from turns
  • Faulty correction for drift
  • Inadequate visual lookout for other aircraft
  • Inability to adequately divide attention between airplane control and maintaining ground track
  • Rolling into an angle of bank too quickly will not result in crossing perpendicular to the reference line
  • Rolling into an angle of bank too slowly will result in a portion of the maneuver being straight and level to return to profile

Rectangular Course:

• The rectangular course maneuver simulates the airport traffic pattern, demonstrating the effect of wind on an aircraft [Figure 6]
• The maneuver assists the student pilot in perfecting:
  • Practical application of the turn
  • The division of attention between the flightpath, ground objects, and the handling of the airplane
  • The timing of the start of a turn so that the turn will be fully established at a definite point over the ground
  • The timing of the recovery from a turn so that a definite ground track will be maintained
  • The establishing of a ground track and the determination of the appropriate "crab" angle
• It is unusual to find a situation where the wind is blowing exactly parallel to the field boundaries so slight wind corrections on all legs may be required
• It is important to anticipate the turns to correct for ground speed, drift, angle of bank (AoB), and turning radius
  • When the wind is behind the airplane, the turn requires a larger AoB due to the turn radius/rate and vice versa
    • Because of this, you will need to anticipate your turn at different points around the box pattern
    • The higher the ground speed, the earlier you must anticipate the turn
• Altitude and airspeed should be held constant
• Requires utilization of ground track with wind forming a "crab" angle to maintain an equidistant track from all sides of the rectangle
  • Approximately 1/4 to 1/2 mile away
  • For a Cessna, this will be when the edge of the rectangle bisects the wing strut
  • The closer you fly, the steeper the turns will have to be, the farther, the shallower
• Establish crab angles as necessary to maintain a uniform distance from the area boundaries for each leg of the maneuver

• 

• Rectangular Course Procedure:

  1. Note wind direction and strength, if able
     • Important for finding the downwind and anticipating ground speed
     • Can be determined by trees, water, flags, etc...
  2. Perform clearing turns looking for traffic and ground obstructions
  3. Pick a reference rectangle in an area where an emergency landing can be made if necessary
     • Fields or perpendicular roads are best as they provide reference lines
     • Distances should be about 1 mile in length and maintained at the same distance throughout the maneuver
  4. Establish and maintain downwind speed and 1,000' AGL (simulating traffic pattern) throughout the maneuver, maintaining 1/4th to 1/2 mile of lateral distance from the rectangular edges
  5. Enter the maneuver on a 45° mid-field downwind
     • Ground speed will increase as you enter the pattern
  6. Turn base at boundary:
     • AoB: Steep AoB, not to exceed 45°, transitioning to medium bank as the turn progresses
     • GS: Decrease, due to lost tailwind
     • Degrees: Turn greater than 90°, to compensate for wind, so as you roll out you have established a crab
  7. Turn upwind at boundary:
     • AoB: Medium AoB, transitioning shallow as the turn progresses
     • GS: Decrease, you are now flying directly into the wind
     • Degrees: Turn less than 90°, due to the crab already set prior to your turn
  8. Turn crosswind at boundary:
     • AoB: Shallow AoB, transitioning to medium as the turn progresses
     • GS: Increase, due to the loss of the complete headwind component
     • Degrees: Turn less than 90° to allow for wind correction
  9. Turn downwind at boundary:
     • AoB: Medium AoB transitioning to a much steeper AoB than earlier, not to exceed 45°
     • GS: Increase, due to the increasing tailwind
     • Degrees: Turn more than 90°
  10. Depart the maneuver on a 45° mid-field downwind
  11. Upon completion of the maneuver, resume normal cruise speed
      • Trim as necessary
  12. Complete cruise flow/checklist

• Rectangular Course Common Errors:

  • Failure to adequately clear the area
  • Failure to establish proper altitude prior to entry (typically entering the maneuver while descending)
  • Failure to establish appropriate wind correction angle, resulting in drift
  • Gaining or losing altitude
  • Poor coordination (Typically skidding in turns from a downwind heading and slipping in turns from an upwind heading)
  • Abrupt control usage
  • Inability to adequately divide attention between airplane control and maintaining ground track
  • Improper timing to beginning and recovering from turns
  • Inadequate visual lookout for other aircraft

Eights Along A Road:

• Consists of two complete adjacent circles of equal radii on each side of a straight road or other reference line on the ground [Figure 7]
• Develops the ability to maneuver the airplane accurately, while dividing your attention between the flight path and the selected points on the ground
• Should not be introduced until the student has a complete grasp on fundamentals (Rectangular Course, S-Turns, Turns Around a Point)
• Perfects the knowledge of the effect of angle of bank on radius of turn
• Demonstrate how wind affects the path of the airplane over the ground
• To gain experience in the visualization of the results of planning before the execution of the maneuver
• Trains the student to think and plan ahead of the airplane
• Performed with the wind either perpendicular or parallel to the reference line
• The measure of progress in the performance of eights along a road is the smoothness and accuracy of the change in bank used to counteract drift
  • The sooner the drift is detected and correction applied, the smaller will be the required changes
  • The more quickly the student can anticipate the corrections needed, the less obvious the changes will be and the more attention can be diverted to the maintenance of altitude and operation of the airplane
• Errors in coordination must be eliminated and a constant altitude maintained

• 

• Eights Along A Road Procedure:

  1. Determine wind direction
     • This is important for the entry heading and reference point
  2. Commence a clearing turn looking for traffic and ground obstructions
  3. Select 2 reference points on either side of the reference line in an area where an emergency landing can be made if necessary
  4. Establish and maintain 100 KIAS and 1,000' AGL
  5. Enter the maneuver parallel to the road
     • You may need to establish a crab to maintain a straight ground path
  6. Abeam the first point, roll into a 30° to 40° angle
     • Usually the first turn is made toward a downwind heading
     • As ground speed increases, the angle of bank will need to increase to increase the rate
     • As ground speed decreases after the first half of the turn, shallow the bank to arrive over the reference line on entry heading
  7. Perform the second turn
     • Ground speed will slow requiring a shallow angle of bank
     • After 180° of turn, ground speed will increase requiring an increase in angle of bank
  8. Depart the maneuver on the entry heading
  9. Complete cruise checklist

• Eights Along A Road Common Errors:

  • Failure to adequately clear the area
  • Skidding or slipping turns
  • Excessive gain or loss of altitude
  • Over concentration on the pylon and failure to observe traffic
  • Abrupt control usage

Eights Across A Road:

• Once the fundamentals of Rectangular Course, S-Turns, and Turns Around a Point are understood, next comes eights across a road
• The maneuver is a variation of eights along a road and involves the same principles and techniques
  • The primary difference is that at the completion of each loop of the figure eight, the airplane should cross an intersection of roads or specific point on a straight road
  • Wind should be perpendicular to the road
• Consists of two complete adjacent circles of equal radii on each side of a straight road or other reference line on the ground [Figure 8]
• Develops the ability to maneuver the airplane accurately, while dividing your attention between the flight path and the selected points on the ground
• Perfects the knowledge of the effect of angle of bank on radius of turn
• Demonstrate how wind affects the path of the airplane over the ground
• To gain experience in the visualization of the results of planning before the execution of the maneuver
• Trains the student to think and plan ahead of the airplane
• The measure of progress in the performance of eights along a road is the smoothness and accuracy of the change in bank used to counteract drift
  • The sooner the drift is detected and correction applied, the smaller will be the required changes
  • The more quickly the student can anticipate the corrections needed, the less obvious the changes will be and the more attention can be diverted to the maintenance of altitude and operation of the airplane
• Errors in coordination must be eliminated and a constant altitude maintained

• 

• Eights Across a Road Procedure:

  1. Determine wind direction
     • This is important for the entry heading and reference point
  2. Commence a clearing turn looking for traffic and ground obstructions
  3. Select 2 reference points on either side of the reference line in an area where an emergency landing can be made if necessary
  4. Establish and maintain an appropriate airspeed (generally 100 KIAS) and 1,000' AGL
  5. Enter the maneuver ~30° to the road
     • You may need to establish a crab to maintain a straight ground path
  6. Abeam the first point, roll into a 30° to 40° angle of bank
     • Usually the first turn is made toward a downwind heading
     • As ground speed increases, the angle of bank will need to increase to increase the rate
     • As ground speed decreases after the first half of the turn, shallow the bank to arrive over the reference line on entry heading
  7. Perform the second turn
     • Ground speed will slow requiring a shallow angle of bank
     • After 180° of turn, ground speed will increase requiring an increase in angle of bank
  8. Depart the maneuver on the entry heading
  9. Complete cruise checklist

• Eights Across a Road Common Errors:

  • Failure to adequately clear the area
  • Skidding or slipping turns
  • Excessive gain or loss of altitude
  • Over concentration on the pylon and failure to observe traffic
  • Abrupt control usage

Eights Around Pylons:

• Consists of a figure eight pattern at a pivotal altitude as two points, or pylons are used as references for turns [Figure 1]
  • Involves flying downwind between the pylons and upwind outside of the pylons
• Develops the ability to maneuver the airplane accurately, while dividing your attention between the flight path and the selected points on the ground
• Most advanced and most difficult of the low altitude flight training maneuvers
• Should not be introduced until the student has a complete grasp on fundamentals (Rectangular Course, S-Turns, Turns Around a Point)
• Perfects the knowledge of the effect of angle of bank on radius of turn
• Demonstrate how wind affects the path of the airplane over the ground
• To gain experience in the visualization of the results of planning before the execution of the maneuver
• Trains the student to think and plan ahead of the airplane

• Eights Around Pylons Procedure:

  1. Determine wind direction
     • This is important for the entry heading and reference point
  2. Commence a clearing turn looking for traffic and ground obstructions
  3. Select 2 reference points in an area where an emergency landing can be made if necessary
     • The pylons selected should be on a line 90° to the direction of the wind and should be in an area away from communities, livestock, or groups of people, to avoid possible annoyance or hazards to others
  4. Establish and maintain 100 KIAS (approx. 2200 RPM) and 1,000' AGL
  5. Enter the maneuver on a downwind heading when passing between the pylons
  6. Abeam the first point, roll into a 30° to 40° angle
     • The distance between the pylons and the wind velocity will determine the initial angle of bank required to maintain a constant radius from the pylons during each turn
     • Steepest banks will be required just after entry and just before roll-out from each turn as ground speed is highest with the tailwind
     • The bank will shallow as you continue through the 180° point where it will be the shallowest, gradually increasing
  7. Perform the second turn
     • the roll-out from each turn must be completed on the proper heading with sufficient wind correction angle to ensure that after brief straight-and-level flight, the airplane will arrive at the point where a turn of the same radius can be made around the other pylon
     • The straight-and-level flight segments must be tangent to both circular patterns
  8. Depart the maneuver on the entry heading
  9. Complete cruise checklist





• Eights Around Pylons Common Errors:

  • Failure to adequately clear the area
  • Poor choice of pylons
  • Improper entry to the maneuver
  • Incorrect initial bank
  • Skidding or slipping turns
  • Excessive gain or loss of altitude
  • Over concentration on the pylon and failure to observe traffic
  • Not entering the pylon turns into the wind
  • Failure to roll out of turns on proper heading
  • Failure to assume a heading when flying between pylons that will compensate sufficiently for drift
  • Failure to time the bank so that the turn entry is completed with the pylon in position
  • Abrupt control usage
  • Loss of orientation

Ground Reference Maneuvers Airman Certification Standards:

• To determine that the applicant exhibits satisfactory knowledge, risk management, and skills associated with ground reference maneuvering which may include a rectangular course, Sturns, and turns around a point
• Note: See Appendix 7: Aircraft, Equipment, and Operational Requirements & Limitations
• References: 14 CFR part 61; FAA-H-8083-2, FAA-H-8083-3

Conclusion:

• We usually think of air in the form of wind, like a stream flowing from one point long the surface to another however, air is more dynamic
• Air can also flow up, producing thermals used in gliding
• Air can also flow downwards, producing downdrafts like those seen in microbursts
• Consider practicing maneuvers on a flight simulator to introduce yourself to maneuvers or knock off rust
• Still looking for something? Continue searching:

References:

• Federal Aviation Administration - Pilot/Controller Glossary
• Airplane Flying Handbook - Eights Along A Road
• Airplane Flying Handbook - Eights Across A Road
• Airplane Flying Handbook - Elementary Eights
• Airplane Flying Handbook - Drift and Ground Track Control
• Airplane Flying Handbook - Rectangular Course
• Airplane Flying Handbook - S-Turns
• FAA - Airman Certification Standards
• AOPA - Understanding the most basic ground reference maneuver
• NASA - Cross Winds