Introduction
Ground reference maneuvers and their related factors are
used in developing a high degree of pilot skill. Although
most of these maneuvers are not performed in normal
everyday fl ying, the elements and principles involved are
applicable to performance of the customary pilot operations.
The maneuvers aid the pilot in analyzing the effect of wind
and other forces acting on the aircraft and in developing
a fine control touch, coordination, and the division of
attention necessary for accurate and safe maneuvering of
the aircraft.
Ground Reference
Maneuvers
Chapter 9
The early part of a pilot’s training is conducted at relatively
high altitudes for the purpose of developing technique,
knowledge of maneuvers, coordination, feel, and the handling
of the aircraft in general. This training requires that most of
the pilot’s attention be given to the actual handling of the
aircraft, the results of control pressures on the action, and
attitude of the aircraft.
As soon as the pilot shows profi ciency in the fundamental
maneuvers, it is necessary that he or she be introduced to
ground reference maneuvers requiring attention beyond
practical application and current knowledge base.
It should be stressed that during ground reference maneuvers,
it is equally important that previously learned basic fl ying
technique be maintained. The fl ight instructor should not allow
any relaxation of the student’s previous standard of technique
simply because a new factor is added. This requirement
should be maintained throughout the student’s progress from
maneuver to maneuver. Each new maneuver should embody
some advanced knowledge and include principles of the
preceding maneuver in order to maintain continuity. Each
new skill introduced should build on one already learned so
that orderly, consistent progress can be made.
Maneuvering by Reference to Ground
Objects
Ground track or ground reference maneuvers are performed at
relatively low altitudes while applying wind drift correction
as needed to follow a predetermined track or path over the
ground. These maneuvers are designed to develop the ability
to control the aircraft and to recognize and correct for the
effect of wind, while dividing attention among other matters.
This requires planning ahead of the aircraft, maintaining
orientation in relation to ground objects, fl ying appropriate
headings to follow a desired ground track, and being
cognizant of other air traffi c in the immediate vicinity.
Ground reference maneuvers should be fl own at an altitude of
approximately 500 to 1,000 feet above ground level (AGL).
The actual altitude will depend on the ability to reach a safe
landing area if there is an engine failure during the maneuver
and the type of air in which the maneuvers are being fl own.
If there is signifi cant vertical movement of the air, higher
altitudes should be used to avoid the possibility of fl ying
below 400 feet AGL, the minimum altitude recommended
in the Practical Test Standards (PTS).
Overall, the following factors should be considered in
determining the appropriate altitudes for ground reference
maneuvers:
• The speed with relation to the ground should not be
so apparent that events happen too rapidly.
• The radius of the turn and the path of the aircraft over
the ground should be easily noted and changes planned
and effected as circumstances require.
• Drift should be easily discernable but should not
overtax the student in making corrections.
• Objects on the ground should appear in their proportion
and size.
• The altitude should be low enough to render any gain
or loss apparent to the student, but not recommended
lower than 400 feet above the highest obstruction
and in no case lower than 500 feet above any person,
vessel, vehicle, or structure.
During these maneuvers, both the instructor and the student
should be alert for available forced-landing fi elds. The
area chosen should be away from communities, livestock,
or groups of people to prevent becoming an annoyance or
hazard. Due to the altitudes at which these maneuvers are
performed, there is little time available to search for a suitable
fi eld for landing in the event the need arises.
Drift and Ground Track Control
Whenever an object is free from the ground, it is affected
by the medium surrounding it. This means that a free object
moves in whatever direction and speed that the medium
moves.
For example, if a powerboat were crossing a still river, the
boat could head directly to a point on the opposite shore
and travel on a straight course to that point without drifting.
However, if the river were fl owing swiftly, the water current
would require consideration. That is, as the boat progresses
forward on its own power, it must also move upstream at
the same rate the river is moving it downstream. This is
accomplished by angling the boat upstream suffi ciently to
counteract the downstream fl ow. If this is done, the boat
follows the desired track across the river from the departure
point directly to the intended destination point. If the boat
is not headed suffi ciently upstream, it would drift with the
current and run aground at some point downstream on the
opposite bank. [Figure 9-1]
As soon as an aircraft becomes airborne, it is free of ground
friction. Its path is then affected by the air mass in which it is
fl ying; therefore, the aircraft (like the boat) does not always
track along the ground in the exact direction that it is headed.
When fl ying with the longitudinal axis of the aircraft aligned
with a road, it may be noted that the aircraft gets closer to or
farther from the road without any turn having been initiated
by the pilot. This would indicate that the air mass is moving
sideward in relation to the aircraft. Since the aircraft is fl ying
Wind
Wind
Current
Current
Figure 9-1. Wind drift and wind correction angle (crab angle).
within this moving body of air (wind), it moves or drifts with
the air in the same direction and speed, just like the boat
moved with the river current.
When fl ying straight and level and following a selected ground
track, the preferred method of correcting for wind drift is to
head the aircraft (wind correction angle) suffi ciently into the
wind to cause the aircraft to move forward into the wind at the
same rate the wind is moving it sideways. Depending on the
wind velocity, this may require a large wind correction angle
or one of only a few degrees. This wind correction angle is also
commonly known as the crab angle. When the drift has been
neutralized, the aircraft follows the desired ground track.
To understand the need for drift correction during fl ight,
consider a fl ight with a wind velocity of 20 knots from the
left and 90° to the direction the aircraft is headed. After
1 hour, the body of air in which the aircraft is fl ying has
moved 20 nautical miles (NM) to the right. Since the aircraft
is moving with this body of air, it too has drifted 20 NM to
the right. In relation to the air, the aircraft moved forward;
but in relation to the ground, it moved forward as well as 20
NM to the right.
There are times when the pilot needs to correct for drift
while in a turn. [Figure 9-2] Throughout the turn, the wind
is acting on the aircraft from constantly changing angles. The
relative wind angle and speed govern the time it takes for the
aircraft to progress through any part of a turn. This is due to
the constantly changing groundspeed. When the aircraft is
headed into the wind, the groundspeed is decreased; when
headed downwind, the groundspeed is increased. Through
the crosswind portion of a turn, the aircraft must be turned
suffi ciently into the wind to counteract drift.
To follow a desired circular ground track, the wind correction
angle must be varied in a timely manner because of the
varying groundspeed as the turn progresses. The faster the
groundspeed, the faster the wind correction angle must be
established; the slower the groundspeed, the slower the wind
correction angle may be established. It can be seen then that
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.
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 fl ight.
When there is no wind, it should be simple to fl y along a
ground track with an arc of exactly 180° and a constant
radius because the fl ightpath and ground track would be
identical. This can be demonstrated by approaching a road
at a 90° angle and, when directly over the road, rolling into
a medium-banked turn. Then, maintaining the same angle of
bank throughout the 180° of turn. [Figure 9-2]
To complete the turn, the rollout should be started at a point
where the wings become level as the aircraft again reaches
the road at a 90° angle and is directly over the road just as the
Intended ground path
Actual ground path
No wind
20 knot wind
Figure 9-2. Effect of wind during a turn.
turn is completed. This would be possible only if there were
absolutely no wind and if the angle of bank and the rate of
turn remained constant throughout the entire maneuver.
If the turn were made with a constant angle of bank and a wind
blowing directly across the road, it would result in a constant
radius turn through the air. However, the wind effects would
cause the ground track to be distorted from a constant radius
turn or semicircular path. The greater the wind velocity, the
greater the difference between the desired ground track and
the fl ightpath. To counteract this drift, the fl ightpath can be
controlled by the pilot in such a manner as to neutralize the
effect of the wind and cause the ground track to be a constant
radius semicircle.
The effects of wind during turns can be demonstrated after
selecting a road, railroad, or other ground reference that forms
a straight line parallel to the wind. Fly into the wind directly
over and along the line and then make a turn with a constant
medium angle of bank for 360° of turn. [Figure 9-3] The
aircraft returns to a point directly over the line but slightly
downwind from the starting point, the amount depending on
the wind velocity and the time required to complete the turn.
The path over the ground is an elongated circle, although in
reference to the air it is a perfect circle. Straight fl ight during
the upwind segment after completion of the turn is necessary
to bring the aircraft back to the starting position.
A similar 360° turn may be started at a specifi c point over the
reference line, with the aircraft headed directly downwind.
In this demonstration, the effect of wind during the constant
banked turn drifts the aircraft to a point where the line is
re-intercepted, but the 360° turn is completed at a point
downwind from the starting point.
Another reference line which lies directly crosswind may be
selected and the same procedure repeated. If wind drift is not
corrected, the aircraft is headed in the original direction at
the completion of the 360° turn, but has drifted away from
the line a distance dependent on the amount of wind.
From these demonstrations, it can be seen where and why
it is necessary to increase or decrease the angle of bank and
the rate of turn to achieve a desired track over the ground.
The principles and techniques involved can be practiced and
evaluated by the performance of the ground track maneuvers
discussed in this chapter.
Rectangular Course
Normally, the fi rst ground reference maneuver introduced
to the pilot is the rectangular course. Reference Figure 9-4
throughout this rectangular course section. The rectangular
course is a training maneuver in which the ground track
of the aircraft is equidistant from all sides of a selected
rectangular area on the ground. The maneuver simulates the
conditions encountered in an airport traffi c pattern. While
performing the maneuver, the altitude and airspeed should
be held constant.
The maneuver assists the student pilot in perfecting:
• Practical application of the turn.
Wind
Track with no wind correction
Track with no wind correction
Base
Crosswind
Downwind
Upwind
No wind correction
Turn more than 90°
Complete turn at boundary
Start turn
at boundary
Exit
Turn into wind
Start turn at boundaryNo wind correctionComplete turn at boundary
Start turn
at boundary
Turn into wind
Complete turn at boundary
roll out with wind
correction established
Turn more than 90°
Start turn at boundary
Turn less than 90°
Enter 45° to downwind
Turn less than 90°
Complete turn at boundary
roll out with wind
correction established
Figure 9-4. Rectangular course.
Start and finish
No wind
Wind Wind
Wind
Figure 9-3. Effect of wind during turns.
• Division of attention between the fl ightpath, ground
objects, and the handling of the aircraft.
• Timing of the start of a turn so that the turn is fully
established at a defi nite point over the ground.
• Timing of the recovery from a turn so that a defi nite
ground track is maintained.
• Establishing a ground track and determining the
appropriate “crab” angle.
As for other ground track maneuvers, one of the objectives
is to develop division of attention between the fl ightpath
and ground references while controlling the aircraft and
watching for other aircraft in the vicinity. Another objective
is to develop recognition of drift toward or away from a
line parallel to the intended ground track. This is helpful in
recognizing drift toward or away from an airport runway
during the various legs of the airport traffi c pattern.
For this maneuver, a square or rectangular fi eld (bound on
four sides by section lines or roads that are approximately
one-half mile in length) should be selected away from other
air traffi c. The aircraft should be fl own parallel to and at a
uniform distance just to the outside of the fi eld boundaries,
not quite above the boundaries so that the fl ightpath may be
easily observed from either seat by looking out the side of
the aircraft. The closer the track of the aircraft is to the fi eld
boundaries, the steeper the bank necessary at the turning
points. The distance of the ground track from the edges of
the fi eld should be the same regardless of whether the course
is fl own to the left or right. Turns should be started when
the aircraft is abeam the corner of the fi eld boundaries, and
the bank normally should not exceed 45°. These should be
the determining factors in establishing the distance from the
boundaries for performing the maneuver.
Although the rectangular course may be entered from any
direction, this discussion assumes entry on a downwind.
On the downwind leg, the wind is a tailwind and results in
increased groundspeed. Consequently, the turn onto the next
leg is entered with a fairly fast rate of roll-in with relatively
steep bank. As the turn progresses, the bank angle is reduced
gradually because the tailwind component is diminishing,
resulting in a decreasing groundspeed.
During and after the turn onto this leg (the equivalent of the
base leg in a traffi c pattern), the wind tends to drift the aircraft
away from the fi eld boundary. To compensate for the drift,
the amount of turn is more than 90°.
The rollout from this turn must be such that as the wings
become level, the aircraft is turned slightly toward the fi eld
and into the wind to correct for drift. The aircraft should
again be the same distance from the fi eld boundary and at
the same altitude as on other legs. The base leg should be
continued until the upwind leg boundary is being approached.
Once more, the pilot should anticipate drift and turning
radius. Since drift correction was held on the base leg, it is
necessary to turn less than 90° to align the aircraft parallel
to the upwind leg boundary. This turn should be started with
a medium bank angle with a gradual reduction to a shallow
bank as the turn progresses. The rollout should be timed
to assure paralleling the boundary of the fi eld as the wings
become level. [Figure 9-5]
While the aircraft is on the upwind leg, the next fi eld boundary
should be observed as it is being approached to plan the turn
onto the crosswind leg. Since the wind is a headwind on this
leg, it reduces the aircraft’s groundspeed and tries to drift the
aircraft toward the fi eld during the turn onto the crosswind
leg. For this reason, the roll-in to the turn must be slow and
the bank relatively shallow to counteract this effect. As the
turn progresses, the headwind component decreases, allowing
the groundspeed to increase. Consequently, the bank angle
and rate of turn are increased gradually to assure that upon
completion of the turn, the crosswind ground track continues
the same distance from the edge of the fi eld. Completion of
the turn with the wings level should be accomplished at a
point aligned with the upwind corner of the fi eld.
As the wings are rolled level, the proper drift correction
is established with the aircraft turned into the wind with a
change in heading of less than 90°. If the turn has been made
properly, the fi eld boundary will again be the same distance
as it was in the previous legs. While on the crosswind leg,
the wind correction angle should be adjusted as necessary to
maintain a uniform distance from the fi eld boundary.
As the next fi eld boundary is being approached, the pilot
should plan the turn onto the downwind leg. Since a wind
correction angle is being held into the wind and away from the
fi eld while on the crosswind leg, this next turn requires a turn
of more than 90°. Since the crosswind becomes a tailwind,
causing the groundspeed to increase during this turn, the bank
initially should be medium and progressively increased as
the turn proceeds. To complete the turn, the rollout must be
timed so that the wings become level at a point aligned with
the crosswind corner of the fi eld just as the longitudinal axis
of the aircraft again becomes parallel to the fi eld boundary.
The distance from the fi eld boundary should be the same as
from the other sides of the fi eld.
Usually, drift should not be encountered on the upwind or the
downwind leg, but it may be diffi cult to fi nd a situation where
the wind is blowing exactly parallel to the fi eld boundaries.
This would make it necessary to use a slight wind correction
Figure 9-5. Pilot’s view coming out of a left turn to straighten out for the rectangular leg on the lower left. The next left turn of the
rectangular course is shown by the red line for reference.
angle on all the legs. It is important to anticipate the turns
to correct for groundspeed, drift, and turning radius. When
the wind is behind the aircraft, the turn must be faster and
steeper; when it is ahead of the aircraft, the turn must be
slower and shallower. These same techniques apply while
fl ying in airport traffi c patterns.
Common errors in the performance of rectangular courses
are:
• 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 gaining or losing airspeed
during the turns).
• Abrupt control usage.
• Inability to divide attention adequately between
aircraft control and maintaining ground track.
• Improper timing in beginning and recovering from
turns.
• Inadequate visual lookout for other aircraft.
S-Turns Across a Road
An S-turn across a road is a practice maneuver in which the
aircraft’s ground track describes semicircles of equal radii on
each side of a selected straight line on the ground. Reference
Figure 9-6 throughout this S-turn across the road section. The
straight line may be a road, fence, railroad, or section line
that lies perpendicular to the wind and should be of suffi cient
length for making a series of turns. A constant altitude should
be maintained throughout the maneuver.
S-turns across a road present one of the most elementary
problems in the practical application of the turn and in the
correction for wind drift in turns. While the application of this
maneuver is considerably less advanced in some respects than
the rectangular course, it is taught after the student has been
introduced to that maneuver in order that the student may
have a knowledge of the correction for wind drift in straight
fl ight along a reference line before the student attempts to
correct for drift by playing a turn.
Reference Line
Figure 9-7. Pilot’s view of crossing a reference line (road) at 90°
wings level starting the S-turn maneuver.
Wind
Wings Level
Shallowest Bank
Moderate Bank
Steepest Bank
Moderate Bank
Shallowest Bank
Steepest Bank
Entry
Wings Level to
Start Maneuver
Figure 9-6. S-Turn.
The objectives of S-turns across a road are to develop
the ability to compensate for drift during turns, orient the
fl ightpath with ground references, follow an assigned ground
track, arrive at specifi ed points on assigned headings, and
divide the pilot’s attention. The maneuver consists of crossing
the road at a 90° angle and immediately beginning a series
of 180° turns of uniform radius in opposite directions,
re-crossing the road at a 90° angle just as each 180° turn
is completed. The maneuver can be started with either a
left hand turn or a right hand turn to go in either direction.
Figure 9-6 starts the turn in a left hand turn as an example.
Accomplishing a constant radius ground track requires
a changing roll rate and angle of bank to establish the
wind correction angle. Both increase or decrease as the
groundspeed increases or decreases.
The bank must be steepest when beginning the turn on the
downwind side of the road and must be shallowed gradually
as the turn progresses from a downwind heading to an upwind
heading. On the upwind side, the turn should be started with
a relatively shallow bank and then gradually steepened as
the aircraft turns from an upwind heading to a downwind
heading. In this maneuver, the aircraft should be rolled from
one bank directly into the opposite just as the 90° reference
line on the ground is crossed.
Before starting the maneuver, a straight ground reference
line or road that lies 90° to the direction of the wind
should be selected, then the area checked to ensure that no
obstructions or other aircraft are in the immediate vicinity.
The road should be approached from the upwind side at the
selected altitude on a downwind heading. When directly
over the road, the fi rst turn should be started immediately.
[Figure 9-6, position 1 and Figure 9-7] With the aircraft
headed downwind, the groundspeed is greatest and the rate
of departure from the road is rapid; the roll into the steep
bank must be fairly rapid to attain the proper wind correction
angle. [Figure 9-6, position 2] This prevents the aircraft from
fl ying too far from the road and from establishing a ground
track of excessive radius.
During the latter portion of the fi rst 90° turn, when the
aircraft’s heading is changing from a downwind heading
to a crosswind heading, the groundspeed becomes
less and the rate of departure from the road decreases.