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the “aiming point.” [Figure 11-18] It is the point on the
ground at which, if the aircraft maintains a constant glidepath
and was not rounded out for landing, it would strike the
ground. To a pilot moving straight ahead toward an object,
it appears to be stationary. This is how the aiming point can
be distinguished—it does not move. However, objects in
front of and beyond the aiming point do appear to move as
the distance is closed, and they appear to move in opposite
directions. During instruction in landings, one of the most
important skills a student pilot must acquire is the use of
visual cues to accurately determine the true aiming point
from any distance out on fi nal approach. From this, the pilot
is able not only to determine if the glidepath results in an
undershoot or overshoot, but also to predict the touchdown
point to within a few feet taking into account fl oat during
roundout.
11-11
34
Final Approach
Roundout starts
Distance Traveled Past Aiming
Point to Touchdown Touchdown
Aiming point is
where descent angle
intersects ground
Figure 11-18. Stabilized approach.
For a constant angle glidepath, the distance between the
horizon and the aiming point remain constant. If a fi nal
approach descent has been established but the distance
between the perceived aiming point and the horizon
appears to increase (aiming point moving down, away from
the horizon), then the true aiming point and subsequent
touchdown point is farther down the runway. If the distance
between the perceived aiming point and the horizon decreases
(aiming point moving up toward the horizon), the true aiming
point is closer than perceived.
When the aircraft is established on fi nal approach, the shape
of the runway image also presents clues regarding what
must be done to maintain a stabilized approach to a safe
landing. A runway is normally shaped in the form of an
elongated rectangle. When viewed from the air during the
approach, perspective causes the runway to assume the shape
of a trapezoid with the far end appearing narrower than the
approach end, and the edge lines converging in the distance.
If the aircraft continues down the glidepath at a constant angle
(stabilized), the image the pilot sees is still trapezoidal but
of proportionately larger dimensions.
During a stabilized approach, the runway shape does not
change. [Figure 11-19] If the approach becomes shallower,
the runway appears to shorten and become wider. Conversely,
if the approach is steepened, the runway appears to become
longer and narrower. [Figure 11-20]
The objective of a stabilized approach is to select an
appropriate touchdown point on the runway and adjust
the glidepath so that the true aiming point and the desired
touchdown point coincide. Immediately after rolling out of
base leg and onto fi nal approach, the pilot should adjust the
speed so that the aircraft descends directly toward the aiming
point. With the approach set up in this manner, the pilot is
free to devote full attention to outside references. The pilot
should not stare at any one place, but rather scan from one
area to another, such as from the aiming point to the horizon,
to the trees and bushes along the runway, to an area well
short of the runway, and back to the aiming point. In this
way, the pilot is more apt to perceive a deviation from the
desired glidepath and whether or not the aircraft is proceeding
directly toward the aiming point.
If the pilot perceives any indication that the aiming point
on the runway is not where desired, an adjustment must be
made to the glidepath. This in turn moves the aiming point.
For instance, if the pilot perceives that the aiming point
is signifi cantly short of the desired touchdown point and
results in an undershoot, an increase in power is warranted.
The minimum airspeed recommended by the manufacturer
must be maintained. This results in a shallowing of the
glidepath with the resultant aiming point moving toward the
desired touchdown point. Conversely, if the pilot perceives
that the aiming point is farther down the runway than the
desired touchdown point and results in an overshoot, the
glidepath should be steepened by an increase in speed with
the throttle at idle. It is essential that deviations from the
desired glidepath be detected early, so that only slight and
infrequent adjustments to glidepath are required.
If a situation arises in which the required corrections become
larger (and possibly more frequent) as the aircraft draws closer
to the runway, an unstabilized approach results.
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Weight-Shift Control Aircraft Flying Handbook(119)
