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the descent with reduced power and airspeed of
approximately 1.4 VSO. (VSO—the stalling speed
with power off, landing gears and flaps down.) For
example, if VSO is 60 knots, the speed should be 1.4
times 60, or 84 knots. Landing flaps may be partially
lowered, if desired, at this time. Full flaps are not
recommended until the final approach is established.
Drift correction should be established and
maintained to follow a ground track perpendicular
to the extension of the centerline of the runway on
which the landing is to be made. Since the final
approach and landing will normally be made into
the wind, there will be somewhat of a crosswind
during the base leg. This requires that the airplane be
angled sufficiently into the wind to prevent drifting
farther away from the intended landing spot.
The base leg should be continued to the point where a
medium to shallow-banked turn will align the
airplane’s path directly with the centerline of the
landing runway. This descending turn should be
completed at a safe altitude that will be dependent
upon the height of the terrain and any obstructions
along the ground track. The turn to the final approach
should also be sufficiently above the airport elevation
to permit a final approach long enough for the pilot to
accurately estimate the resultant point of touchdown,
while maintaining the proper approach airspeed. This
will require careful planning as to the starting point
and the radius of the turn. Normally, it is recommended
that the angle of bank not exceed a medium bank
because the steeper the angle of bank, the higher the
airspeed at which the airplane stalls. Since the base-tofinal
turn is made at a relatively low altitude, it is
important that a stall not occur at this point. If an
extremely steep bank is needed to prevent
overshooting the proper final approach path, it is
advisable to discontinue the approach, go around, and
plan to start the turn earlier on the next approach rather
than risk a hazardous situation.
FINAL APPROACH
After the base-to-final approach turn is completed, the
longitudinal axis of the airplane should be aligned with
the centerline of the runway or landing surface, so that
drift (if any) will be recognized immediately. On a
normal approach, with no wind drift, the longitudinal
axis should be kept aligned with the runway centerline
throughout the approach and landing. (The proper way
to correct for a crosswind will be explained under the
section, Crosswind Approach and Landing. For now,
only an approach and landing where the wind is
straight down the runway will be discussed.)
After aligning the airplane with the runway centerline,
the final flap setting should be completed and the pitch
attitude adjusted as required for the desired rate of
descent. Slight adjustments in pitch and power may
be necessary to maintain the descent attitude and the
desired approach airspeed. In the absence of the
manufacturer’s recommended airspeed, a speed
equal to 1.3 VSO should be used. If VSO is 60 knots,
the speed should be 78 knots. When the pitch
attitude and airspeed have been stabilized, the
airplane should be retrimmed to relieve the
pressures being held on the controls.
The descent angle should be controlled throughout the
approach so that the airplane will land in the center
of the first third of the runway. The descent angle is
affected by all four fundamental forces that act on an
airplane (lift, drag, thrust, and weight). If all the
forces are constant, the descent angle will be constant
in a no-wind condition. The pilot can control these
forces by adjusting the airspeed, attitude, power, and
drag (flaps or forward slip). The wind also plays a
prominent part in the gliding distance over the
ground [Figure 8-2]; naturally, the pilot does not have
control over the wind but may correct for its effect
on the airplane’s descent by appropriate pitch and
power adjustments.
Increased Airspeed Flightpath
Normal Best Glide Speed
Flightpath
Figure 8-2. Effect of headwind on final approach.
8-2
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8-3
Considering the factors that affect the descent angle on
the final approach, for all practical purposes at a given
pitch attitude there is only one power setting for one
airspeed, one flap setting, and one wind condition.
A change in any one of these variables will require
an appropriate coordinated change in the other controllable
variables. For example, if the pitch attitude
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(78)
