The crab method is executed
by establishing a heading (crab) toward the wind with
the wings level so that the airplane's ground track
remains aligned with the centerline of the runway. [Figure
8-15] This crab angle is maintained until just prior
to touchdown, when the longitudinal axis of the airplane
must be aligned with the runway to avoid sideward contact
of the wheels with the runway. If a long final approach
is being flown, one option is to use the crab method
until just before the round out is started and then
smoothly change to the wing-low method for the remainder
of the landing.
The wing-low (sideslip) method compensates for a crosswind
from any angle, but more important, it keeps the airplane's
ground track and longitudinal axis aligned with the
runway centerline throughout the final approach, round
out, touchdown, and after-landing roll. This prevents
the airplane from touching down in a sideward motion
and imposing damaging side loads on the landing gear.
To use the wing-low method, align the airplane's heading
with the centerline of the runway, note the rate and
direction of drift, and promptly apply drift correction
by lowering the upwind wing. [Figure 8-16] The amount
the wing must be lowered depends on the rate of drift.
When the wing is lowered, the airplane tends to turn
in that direction. To compensate for the turn, it
is necessary to simultaneously apply sufficient opposite
rudder pressure to keep the airplane's longitudinal
axis aligned with the runway. In other words, the
drift is controlled with aileron and the heading with
rudder. The airplane is now side slipping into the
wind just enough that both the resultant flightpath
and the ground track are aligned with the runway.
If the crosswind diminishes, this crosswind correction
is reduced accordingly, or the airplane begins slipping
away from the desired approach path. [Figure 8-17]
To correct for strong crosswind, the slip into the
wind is increased by lowering the upwind wing a considerable
amount. As a consequence, this results in a greater
tendency of the airplane to turn. Since turning is
not desired, considerable opposite rudder must be
applied to keep the airplane's longitudinal axis aligned
with the runway. In some airplanes, there may not
be sufficient rudder travel available to compensate
for the strong turning tendency caused by the steep
bank. If the required bank is such that full opposite
rudder does not prevent a turn, the wind is too strong
to safely land the airplane on that particular runway
with those wind conditions. Since the airplane's capability
is exceeded, it is imperative that the landing be
made on a more favorable runway either at that airport
or at an alternate airport.
Flaps are used during most approaches since they tend
to have a stabilizing effect on the airplane. The
degree to which flaps are extended vary with the airplane's
handling characteristics, as well as the wind velocity.
