曝光臺 注意防騙 網曝天貓店富美金盛家居專營店坑蒙拐騙欺詐消費者

approach, however, will increase landing distance and
should be avoided. For example, an approach angle of
2° instead of a recommended 3° will add 500 feet to
landing distance.
A more common error is excessive height over the
threshold. This could be the result of an unstable
approach, or a stable but high approach. It also may
occur during an instrument approach where the missed
approach point is close to or at the runway threshold.
Regardless of the cause, excessive height over the
threshold will most likely result in a touchdown
beyond the normal aiming point. An extra 50 feet of
height over the threshold will add approximately 1,000
feet to the landing distance. It is essential that the
airplane arrive at the approach threshold window
exactly on altitude (50 feet above the runway).
THE FLARE
The flare reduces the approach rate of descent to a
more acceptable rate for touchdown. Unlike light
airplanes, a jet airplane should be flown onto the
runway rather than “held off” the surface as speed
dissipates. A jet airplane is aerodynamically clean
even in the landing configuration, and its engines still
produce residual thrust at idle r.p.m. Holding it off
during the flare in a attempt to make a smooth landing
will greatly increase landing distance. A firm landing
is normal and desirable. A firm landing does not mean
a hard landing, but rather a deliberate or positive
landing.
For most airports, the airplane will pass over the end
of the runway with the landing gear 30 – 45 feet above
the surface, depending on the landing flap setting and
the location of the touchdown zone. It will take 5 – 7
seconds from the time the airplane passes the end of
Figure 15-24. Stabilized approach.
Stop Rollout Touchdown
1,000'
Threshold
Window
50' VREF
500'
Window
Check for
Stabilized
Approach
Stabilized Approach
on Course on Speed
2.5° - 3° Glidepath
500 - 700 FPM
Descent
1,000'
Window
Flare
Ch 15.qxd 5/7/04 10:22 AM Page 15-22
15-23
the runway until touchdown. The flare is initiated by
increasing the pitch attitude just enough to reduce the
sink rate to 100 – 200 feet per minute when the landing
gear is approximately 15 feet above the runway
surface. In most jet airplanes, this will require a pitch
attitude increase of only 1° to 3°. The thrust is
smoothly reduced to idle as the flare progresses.
The normal speed bleed off during the time between
passing the end of the runway and touchdown is 5
knots. Most of the decrease occurs during the flare
when thrust is reduced. If the flare is extended (held
off) while an additional speed is bled off, hundreds or
even thousands of feet of runway may be used up.
[Figure 15-25] The extended flare will also result in
additional pitch attitude which may lead to a tail strike.
It is, therefore, essential to fly the airplane onto the
runway at the target touchdown point, even if the
speed is excessive. A deliberate touchdown should be
planned and practiced on every flight. A positive
touchdown will help prevent an extended flare.
Pilots must learn the flare characteristics of each model
of airplane they fly. The visual reference cues observed
from each cockpit are different because window
geometry and visibility are different. The geometric
relationship between the pilot’s eye and the landing
gear will be different for each make and model. It is
essential that the flare maneuver be initiated at the
proper height—not too high and not too low.
Beginning the flare too high or reducing the thrust too
early may result in the airplane floating beyond the
target touchdown point or may include a rapid pitch up
as the pilot attempts to prevent a high sink rate
touchdown. This can lead to a tail strike. The flare that
is initiated too late may result in a hard touchdown.
Proper thrust management through the flare is also
important. In many jet airplanes, the engines produce a
noticeable effect on pitch trim when the thrust setting
is changed. Arapid change in the thrust setting requires
a quick elevator response. If the thrust levers are
moved to idle too quickly during the flare, the pilot
must make rapid changes in pitch control. If the thrust
levers are moved more slowly, the elevator input can
be more easily coordinated.
Touchdown
On Target
Extended
Flare
10 Knots Deceleration
on Ground (Maximum Braking)
10 Knots Deceleration
in Flare
　
中國航空網 www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：AIRPLANE FLYING HANDBOOK 飛機飛行手冊下(87)