Crosswind landing
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A crosswind landing is a landing maneuver in which a significant component of the prevailing wind is perpendicular to the runway centerline.
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[edit] Significance
Aircraft are generally directionally stable and have a tendency to point into the wind direction. In situations where a crosswind is present, the aircraft will adopt a yaw orientation with respect to the runway and will drift laterally as it approaches the runway. These pose significant safety issues when safe operation of the undercarriage requires the body and the velocity of the aircraft to be aligned with the runway at touch down. The landing gear on the B-52 included an unusual feature to counteract the problem: all landing gear bogies could be steered, allowing the aircraft to land with the wheels facing the direction of travel even if the nose was not pointed in the same direction.
To meet these conflicting requirements, three standard procedures are used for executing a safe landing in a cross wind situation. These landings are called the Crab, De-Crab and Sideslip techniques.
[edit] Techniques
The following guidelines are advised by Boeing for a crosswind landing. These guidelines assume steady wind (no gusting). These winds are measured at 33 foot (10 m) tower height for a runway 148 feet (45 m) in width. Basically, there are 3 landing techniques which may be used to correct for cross winds: De-Crab, Crab, and Sideslip.
[edit] De-Crab
The objective of this technique is to maintain wings level and the aircraft position near the runway centerline during approach. The nose points into the wind so that the aircraft approaches the runway slightly skewed with respect to the runway centerline (crabbing). This gives the impression of approaching the runway flying sideways, which can be disorienting for the pilot. Position is maintained by balancing the crosswind component, or more accurately the drag force arising from it, with engine thrust. Wings are maintained level throughout the approach. Just before the flare, opposite rudder (downwind rudder) is applied to eliminate the crab, with a simultaneous application of opposite aileron to maintain a wings-level attitude, so that at touch down, the body, velocity vector, and bank angle are all aligned with the runway, and the aircraft is positioned near the center.
[edit] Crab
This is similar to the De-Crab technique. The principal difference is the aircraft touches down whilst still crabbing. The position on the runway is corrected after touch down. This applies significant slip angle to the tires, and increases the lateral loads on the undercarriage, so this technique is bounded by speed restrictions and is not generally recommended.
[edit] Sideslip
This requires a higher level of skill. The purpose of this technique is to maintain heading aligned with the centerline. The initial phase of the approach is flown using the Crab technique to correct for drift. The aircraft heading is adjusted using rudder and ailerons to align with the runway. This places the aircraft at a constant sideslip angle, which its natural stability will tend to correct. Sufficient rudder and aileron must be applied continuously to maintain the sideslip at this value. The dihedral action of the wings has a tendency to cause the aircraft to roll, so aileron must be applied to check the bank angle.
With a slight residual bank angle, a touchdown is typically accomplished with the upwind main wheels touching down just before the downwind wheels. Excessive control must be avoided because over-banking could cause the engine nacelle or outboard wing flap to contact the runway/ground.
In strong crosswind conditions, it is sometimes necessary to combine the crab technique with the sideslip technique.
[edit] References
- Boeing Flight Crew Training Manual
[edit] External links
- Videos can be found here .
- Crosswind landing test of A380
- FAA - Airplane Flying Handbook FAA 2004
- Private Pilot Pratical Test Standards for Airplane FAA August 2002
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