A steady-sideslip landing can be performed safely (i.e., while retaining significant margins relative to geometry or roll / rudder limits).
Figure 3shows that with a 30 kt steady crosswind component:
.
Achieving a steady-sideslip landing (i.e., with zero crab angle) requires nearly a 9-degree into-wind bank angle, placing the aircraft closer to its geometry and roll /r udder limits ( point A on the graph ); or,
.
Achieving a wings-level touchdown (i.e., with no decrab) would result in a 13-degree crab angle at touchdown, potentially resulting in landing gear damage ( point B ).
With 30 kt crosswind, adopting a combination of sideslip and crab-angle (i.e., moving from point A to point C ) restores significant margins relative to geometry and roll / rudder limits while eliminating the risk of landing gear damage). This requires, typically:
.
5 degrees of crab angle; and,
.
5 degrees of bank angle,
On aircraft models limited by their geometry characteristics, increasing the final approach speed (i.e., by applying a wind correction on the final approach speed, even under full crosswind, thus moving from point A to point D ) increases the margin with respect to the geometry limitation.
Getting to Grips withApproach-and-Landing Accidents Reduction
Operational recommendations and handling techniques
Figure 2 and Figure 3 shows that:
. With low crosswind ( typically up to 15 kt to 20 kt crosswind component ), a safe crosswind landing (i.e., flare and touchdown) can be performed with either:
- A steady-sideslip (i.e., no crab angle); or,
- Wings-level, with no decrab prior to touchdown.
. With higher crosswind ( typically above 15 kt to 20 kt crosswind component ), a safe crosswind landing requires:
- a crabbed-approach; and,
- a partial decrab prior to touchdown, using a combination of bank angle and crab angle (achieved by applying cross-controls).
On most Airbus models, this requires touching down with:
- 5 degrees of crab angle; and,
- 5 degrees of bank angle.
The decision to perform the flare with no decrab, with partial decrab or with complete decrab should depend upon the prevailing crosswind component but also on the following factors (or as specified by company’ SOPs):
.
Wind gustiness;
.
Runway length;
.
Runway surface condition;
.
Type of aircraft; and,
.
Pilot experience on type.
Crosswind Landings
Page 5
AIRBUS INDUSTRIE Getting to Grips with
Flight Operations Support Approach-and-Landing Accidents Reduction
Touchdown – Friction Forces
Assuming a crabbed-approach with no decrab or with partial decrab during flare, upon touchdown the flight should be on the up-wind side of the runway centerline to ensure that the left and right main landing gears are on their respective sides of the runway centerline.
Upon touchdown of the main landing gear, the aircraft transitions from the “ laws of flight dynamics “ to the “ laws of ground dynamics “.
The following are among the events that occur upon touchdown:
. Wheel rotation, unless hydroplaning is experienced.
Wheel rotation is the trigger for:
-Automatic ground spoilers extension;
-Autobrake operation; and,
-Anti-skid operation.
To minimize the risk of hydroplaning and ensure a positive spin up of wheels, it is recommended to perform a firm touchdown when landing on a contaminated runway.
. Buildup of friction forces between the wheel tires and the runway surface, under the combined effect of:
- Wheels/tires-braking forces; and,
- Tire-cornering forces.
Figure 4 illustrates these friction forces.
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