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constantly evaluate the situation.
It must be emphasized that, although accurate spot
touchdowns are important, safe and properly executed
approaches and landings are vital. The pilot must never
sacrifice a good approach or landing just to land on the
desired spot.
90° POWER-OFF APPROACH
The 90° power-off approach is made from a base leg and
requires only a 90° turn onto the final approach. The
approach path may be varied by positioning the base leg
closer to or farther out from the approach end of the runway
according to wind conditions. [Figure 8-25]
The glide from the key position on the base leg through
the 90° turn to the final approach is the final part of all
accuracy landing maneuvers.
The 90° power-off approach usually begins from a
rectangular pattern at approximately 1,000 feet above
the ground or at normal traffic pattern altitude. The
airplane should be flown onto a downwind leg at the
same distance from the landing surface as in a normal
traffic pattern. The before landing checklist should be
completed on the downwind leg, including extension
of the landing gear if the airplane is equipped with
retractable gear.
After a medium-banked turn onto the base leg is completed,
the throttle should be retarded slightly and the
airspeed allowed to decrease to the normal base-leg
speed. [Figure 8-26] On the base leg, the airspeed,
wind drift correction, and altitude should be maintained
while proceeding to the 45° key position. At this
position, the intended landing spot will appear to be
on a 45° angle from the airplane’s nose.
The pilot can determine the strength and direction of
the wind from the amount of crab necessary to hold the
desired ground track on the base leg. This will help in
planning the turn onto the final approach and in lowering
the correct amount of flaps.
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At the 45° key position, the throttle should be closed
completely, the propeller control (if equipped)
advanced to the full increase r.p.m. position, and altitude
maintained until the airspeed decreases to the
manufacturer’s recommended glide speed. In the
absence of a recommended speed, use 1.4 VSO. When
this airspeed is attained, the nose should be lowered to
maintain the gliding speed and the controls retrimmed.
The base-to-final turn should be planned and accomplished
so that upon rolling out of the turn the airplane
will be aligned with the runway centerline. When on
final approach, the wing flaps are lowered and the
pitch attitude adjusted, as necessary, to establish the
proper descent angle and airspeed (1.3 VSO), then the
controls retrimmed. Slight adjustments in pitch attitude
or flaps setting may be necessary to control the glide
Light Wind
Medium Wind
Strong Wind
Figure 8-25. Plan the base leg for wind conditions.
Figure 8-26. 90° power-off approach.
8-22
45°
Power Reduced
Base Leg Speed
Close Throttle
Established 1.4 V
Base Key
Position
Lower Partial Flaps
Maintain 1.4 V
Lower Full Flaps
(As Needed)
Establish 1.3 V
S0
S0
S0
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angle and airspeed. However, NEVER TRY TO
STRETCH THE GLIDE OR RETRACT THE FLAPS
to reach the desired landing spot. The final approach
may be made with or without the use of slips.
After the final approach glide has been established, full
attention is then given to making a good, safe landing
rather than concentrating on the selected landing spot.
The base-leg position and the flap setting already
determined the probability of landing on the spot. In
any event, it is better to execute a good landing 200
feet from the spot than to make a poor landing precisely
on the spot.
180° POWER-OFF APPROACH
The 180° power-off approach is executed by gliding
with the power off from a given point on a downwind
leg to a preselected landing spot. [Figure 8-27] It is an
extension of the principles involved in the 90° poweroff
approach just described. Its objective is to further
develop judgment in estimating distances and glide
ratios, in that the airplane is flown without power from
a higher altitude and through a 90° turn to reach the
base-leg position at a proper altitude for executing the
90° approach.
The 180° power-off approach requires more planning
and judgment than the 90° power-off approach. In the
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(95)
