introduction to ground reference

Ground Reference

Skill in performing ground reference is essential to airport flying
Be able to describe the complexities of ground reference manoeuvres before and during the performance.
The PTS requires ground reference manoeuvres and explanation as to 'why' you do what you do
Pilot should be able to relate how ground manoeuvres are related to specific flight conditions
The IFR circle to land instrument requirement is related to turns about a circle.
The pilot must be able to demonstrate and explain how the wind is influencing the ground pattern
Ground reference requirements are 100 feet of altitude and 10 knots of airspeed.
Division of attention inside and outside the aircraft are expected of the pilot during all manoeuvres
The ground track requires constant consideration of effective drift caused by wind velocity and direction
A traffic watch at all times is a requirement. Demonstrate by obvious head movement and remarks
The pilot must know the latest changes and version expected by the current PTS and how to perform
The Airplane Flying Handbook (FAA-H-8083) and the PTS define how to perform manoeuvres
For example the entry and exit from the rectangular pattern are related to acceptable pattern entries
The use of a variable bank is used to correct drift in a turn
Know how to find and select suitable practice area.
Know the difference between private pilot and commercial manoeuvres

Why Ground Reference?

One of the weakest parts of flight instruction is the failure of the instructor to let the student know the 'why' of some of the manoeuvres as they relate to actual flight operations. Ground reference is but one of these areas of weakness. Every ground reference manoeuvre has the potential of being applied in a real situation in the vicinity of an airport. The apex of all ground reference manoeuvres is the landing.

Flying relatively close to the ground greatly reduces the options you have in event of an emergency. It's not all bad since in case of a fire you can get to the ground more quickly. Select your area for ground reference in a sparsely inhabited area with plenty of emergency fields. At altitude we have always cleared prior to every turn. There is no reason not to clear for ground reference turns and every reason to continue what should be an ongoing habit. Once you have cleared, look over the nose during the turn.

As with airports you are learning to divide your attention between the ground and the airplane while maintaining control. If you do not properly divide your attention you will have difficulty maintaining a constant altitude and the desired ground track. At 4500' a hundred-foot altitude deviation is not as significant as it is at 500'. As changes in altitude and flight path occur you will be making cockpit adjustments using the division of attention skills required close to the ground. Ground reference manoeuvres are performed to increase your comfort level with ground proximity before you begin intensive training with landings.

Any inability to understand and perform ground reference will appear again during the instructional phase on landings. Winds are never, but never, what ATC says they are or will be. The performance of the airplane in relation to the ground track and speed tells you the wind. When the airplane does not point where it is going, it is because of the wind. When the ground speed on a stabilized approach (correct airspeed) is seemingly too fast or slow, high or low, it is because of the wind. You must learn to fly airspeeds during landing approaches and interpret any variations in pattern and approach angle as due to wind.

When you have soloed and have an opportunity to practice ground reference on you own you enter a new world of practice. Only practice of the right kind will lead you beyond rote performance to competence and finally to confidence. You may recognize that you are having difficulty, and you may not. Contact the instructor and talk/walk through the manoeuvre to make sure you understand the mechanics involved. This may solve the problem, but if it doesn't, a flight lesson is going to be the most economic solution. There is nothing worse you can do in flying than practicing a procedure incorrectly.

Cross-country flying not so apparently utilizes ground reference skills To fly a given course in any wind you will be required to make heading adjustments and bank adjustments. The higher altitudes of cross country make ground track adjustments more difficult to determine. The more readily you can make heading corrections for a desired ground track the more efficient will be your cross-country flying. Some examiners hold a pilot to 1/8 mile of his selected course.

Ground Reference

More often than not ground reference is taught as though it were the end itself and not a tool for use. We are not trying to teach how to buzz your friend's front yard. The purpose of ground reference training is to be able to control the aircraft in coordinated flight while dividing attention between aircraft control, altitude, and the ground track. The application of ground reference skills and perceptions enable the pilot to safely manoeuvre and fly a selected ground track while landing. The key to landing is getting the aircraft configured, keeping visual track with both headings and reference points, while making wind corrections. Being able to fly an accurate ground track and altitude about an airport in a strong wind is an essential skill. As a preliminary exercise, the patterns can be done by driving around light poles or making patterns on a large parking lot.

Due to wind, where the nose of the airplane points is not, necessarily, where it goes. When wind velocities permit a demonstration of how an airplane is moved by the wind can be done by holding a 360-degree; turn in a 30-degree; bank and noting that you do not make a circle over the ground but are moved by the wind into an ellipse. Banks used during ground reference are not all or nothing. Banks should be smoothly and continuously entered and removed. Aileron pressure must continuously be both held into the bank or against the bank any time it leaves 30-degrees. Coordinated rudder either in anticipation or application is a must. As the lessons proceed we will devote ever more attention outside the aircraft. Rectangles require about a 50-50 split. S-turns about 80-20. Eights on pylons for the commercial require near total outside attention.

When you make a turn that is going to be affected by the wind, and they all are, you are going to vary your roll rate and bank angle. How fast and how much takes practice. This practice is best noted close to the ground. Since entries are usually with the wind behind you, you must be quicker into the bank and perhaps with greater angle. Ground track is determined by ground speed and you have the wind adding to your airspeed. You must get around further and faster, hence you begin sooner, react more quickly and bank more. Failure to do so will bend your path around the turn and require additional corrections further on.

When you are making your turn into a headwind you will again vary your roll rate and bank angle. This time you will begin later, react more slowly, and use less bank angle. Because of the wind you will be flying with a lower ground speed so everything happens more slowly.

Ground proximity flying creates problems more psychological than real. All aircraft controls function the same but the ground movement gives an impression of speed not available at altitude. This impression is sometimes a deceptive illusion. One real hazard is a bird. At ground reference altitudes the possibility of a bird strike is greatly increased. The pilot should become aware of the seasonal migratory flight of birds and of their presence. A bird instinctively reacts to an airplane as a 'hawk'. It will dive. The pilot's best reaction is to climb in the presence of birds. A defence is to fly with the landing light on. Birds will react to the light before reacting to the airplane. There is no practical need to do any ground reference below 300' and during duck hunting season 500' should be a minimum. 700' is a good student minimum. There will be little benefit if ground reference is practiced at altitudes over 1000'.

The student must learn to look for and find wind direction and velocity indicators. Waves, smoke, tractor dust, windmills, even the way heard animals face can be indicative of wind direction. Wind becomes a variable factor which must be anticipated and estimated to secure a desired ground track. Wind strength normally varies with altitude, becoming less as altitude decreases. Turbulence, if encountered, should be introduced gradually both as to duration and violence.

The FAR's relative to low level operations and altitudes are covered. Requirements are 500' clear of any person or residence and always able to make a safe landing without injury to persons or property. The last part of the FAR makes possible simulated emergencies from ground reference altitudes as long as a safe landing area is available. With the mastery of the 'go around' the student is ready for the low level situations that utilize that particular skill.

An area with curved roads, rectangles, and straight lines that is further away may be more effective for teaching. There are many skills to teach during en route flying. The instructor must know about any obstructions, wires or other hazards. It is seldom possible to find exactly the size and shape pattern required. Be prepared to adapt. The instructor should have several different practice areas. This is because on a given day you want to have the best possible wind direction for doing the patterns. Calm morning winds are best for the introductory ground reference flight but the stronger afternoon winds are best for student pilot recognition of the wind effects.

The only real difference between ground reference and other flying is the difference, caused by wind, between your ground track and your heading is more apparent. In a wind your ground speed and track will result from the sum of the vectors with respect to the ground. First, you must determine the wind using whatever ground source is available. Second, you must make a decision as to how much "wind correction" you will apply. Third, you compare your ground track with the one you want. Fourth, you make a series of changes in one and two, to get the three you want. Finding the "drift" is a matter of training your eye to differentiate between where you are heading and where you are going.

Wind and Groundspeed

Turning as low levels from a crosswind path to a downwind path can be hazardous. It leads to the terrible downwind turn stall accident. When the aircraft turns from a crosswind to a downwind direction at low altitudes, all at once the ground seems to go by much faster. In actuality, it is, but the reaction to the sensation-illusion is that the airspeed has changed as well. It has not and should not. The wind speed added to your airspeed has caused an increase in your ground speed. Close to the ground fly the airspeed not the ground speed. To allow for student errors in this regard all ground reference should be flown a cruise power in trainers. The downwind turn illusion will be exacerbated if the pilot has developed a (bad) habit of trying to look around the cockpit window post during the turn.

As a private pilot you are expected to perform a turn about a point. This means a circle at a constant altitude, of a constant radius with ground speed a variable as affected by the wind. As a commercial pilot you are expected to do a turn on a point. The turn on a point has a constant radius but you are expected to keep the wing tip on the point while flying the circle. This can only be done if you fly a constant ground speed. You should know the difference between the two.

Every ground speed has a critical altitude at which a given radius circle will allow the pilot to keep the wingtip on a point. As the circle is flown the wind affects the ground speed differently at every point. To keep the tip on the point the pilot must vary his altitude. Changing altitude will vary the ground speed. Enter a slight dive when the point moves ahead of the wingtip (tailwind component) and a slight climb when the point moves behind the wingtip.

Practicing turns on a point at about 640' in a C-150 will give you an idea of how the wind affects ground speed. With this knowledge you will be better prepared to cope with the sensations present in the downwind turn. The best defence is to fly a wide downwind if the wind direction is forcing you toward the runway. When you slow the aircraft on the downwind add some more wind correction.

Turns About a Point

Some students do better if the point is selected at the intersection of to right angle roads. This, instead of a lone tree helps maintain orientation. It is important that the student not try to see under a wing or around the windshield to see the point. The student must learn to give the wing a quick flip for a look and then put the wing back down for the turn. Keeping the circle with a 1/4 mile radius works well.

Water is a good way to tell if any wind exists. Turns to the left are easier because of pilot position.

Draw your own diagram using the words.

Left turns about a point entry
Shallow banks going upwind
Steep banks going downwind
Aircraft headings to make circle instead of ellipse.

With a wind, the first turn will require more than a 90-degree angle of turn. The angle beyond 90-degrees is used to set up the crab required by the crosswind. The upwind turn will be gradually decreased so that when directly upwind the wings will be most nearly level. This is where the ground speed is slowest. The bank is gradually increased but crab must be held into the crosswind to keep the circle from flattening on the top. Once across the top of the circle, the bank must be gradually increased to make the circle conform to the added ground speed caused by the tail wind. The steepest bank is held when we are directly downwind. All banks are gradually increased and gradually decreased.

Often the student will try to look under or around the wing while in the turn. Any such tilting or twisting of the head may disrupt the fluids in the inner ear and often affect altitude control.

Turns about a point have an airspeed and altitude combination that keeps the wing tip on the point. In this situation the turn about a point becomes a turn on a point. The difference is one of focus. The turn about a point is at a constant altitude while the turn on a point is made at a constant ground speed.

In a dead calm condition both turns can be the same only if the pivotal groundspeed and altitude are matched. A between the wingtips should intersect the desired ground point and stay there throughout the 360 turn. A coordinated turn will balance all the factors of speed, angle of bank, radius of turn and altitude. At a constant ground speed there is an altitude that keeps the sight angle on the point. If the point moves forward or back because of wind variations, then the altitude becomes the variable to modify the ground speed. Any change of radius will require that the angle of bank be modified.

Chart of ground speed in knots and altitude in feet AGL for Turns On A Point. (Commercial Manoeuvre)
70 kt 433 ft
80 ---565
90 ---716
100 --883

The turn about a point can occur in tower controlled situations as when ATC might require a 360 on downwind or as in a SVFR arrival clearance which might require reporting over a specific checkpoint while remaining clear of the airport Class D surface area. The turn about a point should be basic to many uncontrolled airport arrivals which require circling over the field at twice pattern altitude while determining active runway and traffic patterns.

There are two different kinds of turns related to a point. The private level is 'turns about a point'. in this instance the turns are to be constant in radius. In this case you can visualize points at a constant distance from the point and use these to fly your circle. Wind affects your ability to maintain this circle. The first lesson is best done in a calm wind. Subsequent flights require constant adjustment of bank to maintain your wind correction for flying the circle.

The commercial level is a turn on a point'. The turn on a point requires that you fly around the point with a constant ground speed. To fly this constant ground speed you must dive lower in a head wind and climb in a tailwind. The C-150 has a critical pivot altitude of about 620 feet. This means that in calm conditions you can fly a turn on a point which keeps the wing tip on that point. You know where you are flying too fast, slow, or just right by the tip position relative to the point. Every plane will have a different critical altitude at any given speed. Find the critical altitude for the speed you select and then vary your altitude to keep the tip on your selected point. Climb if the point falls behind the tip and dive if the point gets ahead of the tip. How much you vary your altitude will depend on wind velocity.

Turns around a point

Selection of altitude
Speed from approach to cruise
Entry from downwind with maximum bank
Angle of bank from 30 to 45
Angle of bank to vary with ground speed

Cheating Your Way to a Circle

Turns about a point are constant radius, constant airspeed, and constant *altitude* manoeuvres. It's the commercial 8-s on pylons that are changing altitude. The initial bank for the downwind entry of a turn about a point is a maximum of 45-degrees, the ideal distance away will be the same as you height above the ground. Turns about a point are the most difficult student manoeuvre because of the precision required and the division of attention needed. Set up your entry for airspeed, altitude and trim before beginning it and fly it looking mostly out the window.

If you are having difficulty maintaining altitude, you might try covering the altimeter. This requires that maximum attention be paid to the nose pitch attitude. Remember that you must understand the theory of the manoeuvre that the steepest bank on entry is followed by varying bank and crab depending on wind direction and velocity.

Visualize the ground track that will give you your selected radius. Pick points on the ground that give you a predetermined radius circle about the centre and adjust to fly over these points. It is just like connecting the dots of a drawing to make a circle.

Spirals Around a Point

Start at least at 3000' AGL
Use constant approach to landing speed
Expect a wind shift during descent
--Use 90 degree arc checkpoints
Works great using ADF around a radio tower

Pylon, on a point and about a point turns

In turns on a pylon, altitude, airspeed, bank angle, and distance from the pylon all change throughout the manoeuvre. In turns about a point, altitude and airspeed are supposed to remain constant. It requires sometimes steep turns at low altitude, keeping the projected line of the wing through the pivot point, and maintaining coordination through the varied airspeed that occurs with changes of altitude.

The two manoeuvres converge when there is no wind, but the whole point of turns about a point is to practice and demonstrate using different bank angles to correct for wind during a turn.

Course Reversal

The course reversal is a new addition to the Private Pilot Practical Test standards. After the completion of a ground reference pattern in one direction it is desirable to do the pattern in the opposite direction. A pilot must be able to manoeuvre equally well in either direction. The course reversal is the most efficient way to do this. The course reversal can be performed at any degree of bank as long as the bank is constant throughout the reversal.

Initially we will fly upwind beyond the ground pattern for about one minute. For instance, if we have flown a heading such as 030 (Headings are always said as three digits.) At one minute we will make a left/right 90- degree turn at 30 degrees of bank. 90 degrees from 030 will be either 300 to the left or 120 to the right. At the 90-degree point reverse the bank for a turn of 270 degrees in the opposite direction. Come out of this turn when on the downwind heading. This heading, originally to our rear, is 210 degrees.

210 degrees will be our final downwind heading taking us into the previous ground reference manoeuvre in the opposite direction. In a no wind condition we should be tracking back over our original route regardless of direction. If the manoeuvre is initiated directly up wind then the completed course reversal should be downwind over the reverse course. The accuracy of the reversal is directly related to how well the headings correspond to wind direction. All banks are at the same angle.

The aircraft should now be entering downwind to the left of the original point. Abeam the point the right turn is commenced. If there is a wind this will be the steepest turn. For the student the right turns are more difficult because the point must be viewed across the cockpit. If the circle is made too small the point becomes even more difficult to see. Since there are a number of other figures to fly, only two or three full circles should be flown.

To change direction of turns about the point a course reversal is required. A course reversal is a 90-degree constant angle bank in one direction followed by a 270-degree constant angle bank in the other. For best use of space begin the reversal about one minute flight time upwind of the pattern.

Exit is same line as entry from pattern area

The course reversal procedure in ground reference is used in uncontrolled airport arrivals as part of the 45-degree entry. This can be part of a no radio (NORDO) arrival procedure as when landing at an airport with a tower. It is used as a (not-recommended by FAA) procedure turn manoeuvre and can be used to enter traditional teardrop and parallel entry holding patterns in instrument flying.

Rectangular Patterns

In the latest PTS the rectangular pattern entry has been revised. You are expected to enter on a 45-degree entry to the downwind as though for landing. You can expect to be required to fly two rectangles in each turning direction.. There are various ways to get the aircraft going in the other direction from a 45-degree entry. To do this would require that on your second complete left circuit you would go outbound at right angles to your original entry. You would proceed outbound, perform a course reversal and go around twice in right turns. This process is not difficult to understand when done by diagram.

Under calm conditions almost any rectangle can be used. If there is a wind, the longest leg of the rectangles should be planned to be with the wind. The less wind there is the lower the altitude flown so wind effect and crab angle is more discernible. This gives greater practice in selecting the crab angle needed to hold a given ground track. The ground track should held a constant distance outside the rectangle sides and around the corners. 700 feet is considered a good altitude.

Usually only a couple of left turn rectangles are needed before doing a course reversal and entering two or more right turns. It is again important to do as many left turns as right turns. In the beginning accept some variation of altitude and tracking distance. On the second and any subsequent lessons be very specific and critical of variations. Do this because ground reference is one of the skill lessons that require mastery. Mastery will allow the pilot to manoeuvre about an airport pattern on track and at altitude. This skill must exist to allow sufficient intellectual energy left over for radio and reconfiguration of the aircraft for landing.

The rectangular pattern should be flown as though the runway is parallel with the opposite side of the field. In calm winds heading and course are the same. It is in crosswinds where we use the ground reference skills of heading/course differences to make a desired ground track. The ideal of flying a pattern is that it be kept rectangular and tight to the airport. Properly flown the airport traffic pattern provides maximum safe separation of aircraft in the pattern, arriving aircraft and departing aircraft.

The corners of a ground reference rectangle exactly conform to the four wind quadrants of the ground reference circle. The execution of the downwind and upwind turns are performed exactly the same for the rectangle as for the circle. Downwind straight legs will have crab angles between ground track (course) and heading to compensate for wind effect.

Rectangular patterns are flown to the outside of a selected rectangle so as to give smooth turns at the corners. For best wind correction practice make the long side of the rectangle 90 degrees to the wind.

course reversal
entry direction
wind wind

It is important that the student be aware that flying the rectangular pattern has a direct relationship with the typical traffic pattern scenario. A low time pilot in the low and relatively slow pattern speed is more likely to be turning final too late. The bank angle seems steeper because the turn radius is tighter at slow speed. When the final approach line is overshot, rather than make the apparently steep turn even more so, the pilot hastens the turn with rudder. This rudder application while increasing the rate of turn will cause the nose to drop. The back pressure is added to lower the pitch, the speed drops, and aileron is trying to decrease the bank angle. At stall the airplane will roll to the inside of the turn and spin with the rudder. All of the stall symptoms are the result of sensory illusions too real to be recognized or corrected. It is too low and too late, you're dead.

The purpose of rectangular patterns is to teach the student that the turns around a pattern must be planned, adjusted, and shaped with their straight legs to prevent the initial cause of the accident above. You must be able to position the aircraft on to the final approach course without overshooting. Or, if overshooting, the bank must not be increased nor the airspeed allowed to drop.

You should learn to use "sum of the digits" in than all four headings at 90 degrees from each other are equal. Using the four cardinal headings we see that the sum of the digits for every 90, 180, or 270 degrees are always equal.

North 3 + 6 + 0 = 9
East 0 + 9 + 0 = 9
South 1 + 8 + 0 = 9
West 2 + 7 + 0 = 9

This is also true for headings at 90 degrees to each other as with 045, 135, 225, 315


The two downwind and two upwind turns of the S-turn combine the four quadrants of the left and right turns about a point. The technique calls for the wings to be momentarily level at the moment of crossing the reference line. The bank angle used just before levelling the wings will be the same angle but opposite bank after crossing the reference line. It is important to get as long a reference line as possible. It helps if the line happens to have regular division lines to help the student keep the S as symmetrical as possible. It is a good practice to work the S to and from both ends of the reference line. In a strong wind the downwind turns and reversal of bank will need to be quite abrupt and steep. The upwind turns will be proportionately gradual and shallow.

Common mistakes in making S-turns are such as not varying the bank angle and forgetting to change the bank angle to correct for the wind effect. If the pilot does not alternate his scan in and out of the cockpit then there may be wide variations in altitude. Keeping track of the wind direction is important in the correct performance of S-turns.

Pick a straight road at right angles to the prevailing wind
Save emergency options must be available throughout the manoeuvres.
Make clearing turns and remember to divide attention inside and outside
Watching the horizon will help maintaining altitude
Fly across one end of the road at 700' AGL In emergencies you are on base leg for landings.
PTS calls for first turn to the left so select end of road accordingly
Since downwind turn will be steepest begin at about 40/45 degree bank
Gradually shallow the bank to cross road at right angles on completion of half circle
You use the same angle of bank leaving the road as you did on arrival.
Your bank angle on the second half of the S will gradually increase until reaching the road.
You reverse this steeper bank at the road and begin the second S with a steep bank again.
Performed correctly the S will have the same radius half-circle on each side of the road.

River Flying with Steep Turns

On some subsequent lesson, it is well to select an upwind track along a very S shaped course. By flying upwind the relative ground speed can be reduced with no reduction in airspeed. This permits relatively steep turns. Any gain in altitude during a steep turn has a dramatic effect on airspeed and can precipitate an accelerated stall. On completion of the turn the power is again reduced to cruise.

Spiral Descents

This particular manoeuvre is the most difficult of the ground reference manoeuvres. It requires that the student descend over a selected point, such as the approach end of a runway, The angle of bank will be constantly changing to adapt to the wind. The airspeed must be constant. If the spiral is made too tight the banks become so steep that the student can't control the airspeed. Just pulling back to reduce airspeed has the effect of increasing the bank angle and tightening the spiral. This is an interesting manoeuvre to do in both left and right turns to show the student why the left turns are more desirable.

This manoeuvre and its requirements can best be demonstrated in an aircraft equipped with an ADF. Arrive at an altitude of several thousand feet over a radio station. Reduce power and initiate a descent at best glide speed. Turn the aircraft so that the ADF needle is pointed to the 270 bearing to the station. The spiral descent is made in left turns in such a manner as to keep the needle of the ADF on or near the 270 bearing. This gives a reference for the student and instructor to gauge the accuracy of the spiral over the point. Errors show up immediately.

The second descent should be done in right turns with the ADF on the 090 bearing. Climbs could be made in square patterns so as to demonstrate the movement of the ADF needle from the front 45 degree position to the rear 45 degree position at the corners of the square. This is a excellent learning technique for demonstrating the wind effect and the required flight corrections.

On completion of the above ground reference manoeuvres the student is advised that he should expect and be prepared for 'emergencies' on any subsequent flight. The student should be advised that when soloed he will be allowed and expected to practice the ground reference manoeuvres but never emergencies or off airport landings. The limits of the practice area, the practice altitudes and any radio procedures and assigned. We are now ready to put the skills learned in ground reference to work. About this time the student should realize that he has been practicing the skills needed for takeoff and landings from the very beginning.

Should you be flying an aircraft equipped with an ADF, it is rather interesting to perform the spiral about a radio station antenna. Tune the ADF to the radio station, switch to ADF and try to perform both turns and spiral that keep the ADF needle on your wingtip. Not easy but 'do-able'.