Crab, sideslip . . . or both?
INADEQUATE CROSSWIND SKILLS ARE one of the primary pilot deficien-cies observed most often during pilot certificate checkrides,
according to a panel of designated pilot examiners at the flight
instructor refresher clinic last year at Rantoul, Illinois.
Although crosswind landings are an enjoyable challenge for some
pilots, others view them like a recent flight review candidate who
said, “I try to avoid crosswind landings like the plague!” Realistically,
flying an approach and landing during crosswinds is inevitable.
When it happens, pilots have a choice of which technique to use
during final approach to eliminate side drift: the sideslip or the crab.
Both techniques are acceptable; however, if the crab is used, it
must be removed prior to touchdown for most general aviation aircraft designs, according to the FAA Airplane Flying Handbook.
Which method do EAA members prefer? According to the recent
“2010 Survey of the Average Aviator” (see article on p. 46), 72 percent prefer the sideslip. To help determine which method should be
used on final approach and when, consider the following.
The sideslip eliminates left or right drift by lowering the upwind wing
with aileron, while using rudder to maintain aircraft heading (
longitudinal axis) alignment with the runway centerline. To set up the
sideslip after turning to final approach, the upwind wing is lowered as
necessary to stop the drift (i.e., if drifting left, lower the right wing,
etc.). However, when a wing is lowered, the aircraft tends to turn in
that direction, requiring prompt input of opposite rudder to compensate and to align the aircraft with the runway. The sideslip requires
constant aileron and rudder control inputs throughout the final
approach, round-out, touchdown (often made on the upwind wheel
first, then the downwind wheel in strong crosswinds), and roll-out.
Using the sideslip increases the aircraft’s rate of descent, which
shortens the final approach unless power is added. After touchdown,
particular attention should be given to maintaining directional control
with the rudder or nose wheel steering, while following through with
the aileron to full deflection to prevent the upwind wing from lifting.
The crab is executed by turning to a heading that incorporates a
wind correction angle (crab) slightly toward where the wind is coming from so that the aircraft’s ground track remains aligned with the
runway centerline throughout the final approach.
If the crab is used, it must be removed before touchdown by
applying rudder to align the aircraft with the runway. At the same
time, the upwind wing must be lowered sufficiently to prevent side
drift. This requires a timely and accurate action that pilots
sometimes attempt during their round-out
when a lot is happening. Safer, more effective
timing would be to convert to a sideslip before
short final (several hundred feet above ground
level), not during round-out. Failure to prop-
erly convert from a crab to a sideslip could
result in severe side loads being imposed on the
landing gear, which, on a tailwheel aircraft,
could also cause a ground loop or worse,
because its center of gravity is located behind
the main landing gear.
Robert O’Quinn, EAA 742434, is a part-time certificated
flight instructor whose primary focus is on tailwheel training.
He enjoys sharing those skills and other pilot improvement
techniques through newsletter articles and presentations to
his local EAA Chapter 790 in Barrington, Illinois.
ILLUSTRATION BY PIERRE KOTZE