STABILIZED APPROACH CONCEPT

A stabilized approach is one in which the pilot establishes
and maintains a constant angle glidepath
towards a predetermined point on the landing runway.
It is based on the pilot's judgment of certain visual
clues, and depends on the maintenance of a constant
final descent airspeed and configuration.

An airplane descending on final approach at a constant
rate and airspeed will be traveling in a straight line
toward a spot on the ground ahead. This spot will not
be the spot on which the airplane will touch down,
because some float will inevitably occur during the
roundout (flare). [Figure 8-9] Neither will it be the spot
toward which the airplane's nose is pointed, because
the airplane is flying at a fairly high angle of attack,
and the component of lift exerted parallel to the Earth's
surface by the wings tends to carry the airplane forward
horizontally.

For a constant angle glidepath, the distance between
the horizon and the aiming point will remain constant.
If a final 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 airplane is established on final approach, the
shape of the runway image also presents clues as to
what must be done to maintain a stabilized approach
to a safe landing.

Figure 8-9. Stabilized approach.

The point toward which the airplane is progressing is
termed the "aiming point." [Figure 8-9] It is the point
on the ground at which, if the airplane maintains a
constant glidepath, and was not flared for landing, it
would strike the ground. To a pilot moving straight
ahead toward an object, it appears to be stationary. It
does not "move." 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 how to use visual cues to accurately determine the
true aiming point from any distance out on final
approach. From this, the pilot will not only be able to
determine if the glidepath will result in an undershoot
or overshoot, but, taking into account float during
roundout, the pilot will be able to predict the touchdown
point to within a very few feet.

If the airplane continues down the glidepath at a
constant angle (stabilized), the image the pilot sees
will still be trapezoidal but of proportionately larger
dimensions. In other words, during a stabilized
approach the runway shape does not change. [Figure
8-10]

If the approach becomes shallower, however, the
runway will appear to shorten and become wider.
Conversely, if the approach is steepened, the runway
will appear to become longer and narrower.
[Figure 8-11]

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 basically coincide.