Landing in Crosswinds

07/02/2014

Not long ago, this video went viral on YouTube, racking up more than 8½ million views. Apart from the fact that the 1,200-millimetre telephoto lens thoroughly flattens both the foreground and background, making the airplanes seem suspended in midair, what on earth are these pilots up to? Specifically, what’s up with the bizarre landing technique?

Believe it or not this technique is standard, by-the-book practice when there are strong lateral winds present during landing – aka a crosswind.

If wind is absent, or blowing parallel to the runway, aircraft are able to align themselves directly from many miles out. Pilots need to monitor altitude and minor lateral displacements, but the longitudinal axis of incoming aircraft basically coincides with the direction in which they are traveling.

It’s quite a different matter when winds of significant speed are blowing in a lateral direction across a runway. In this case if pilots were to attempt landing in a normal manner, these winds would push the aircraft completely off the runway axis. Drift of this type can be corrected in two ways:

The first, more commonly utilised in general aviation (that is, smaller planes), is to counter the wind’s effects by deploying the ailerons (hinged wing flaps), keeping the wing that’s toward the source of the wind down, and correcting the ensuing turn with the vertical aileron, controlled by the pedals. This operation is known as sideslip, as the plane is in effect slipping against the wind, and at a greater than normal rate of descent for a given speed. It’s a delicate (but not dangerous) maneuver which requires some practice. When the plane is about to touch ground, it’s necessary to level it out smoothly so as not to make contact with the tip of the wing, even while continuing to maintain a slight sideslip. And it’s even normal to touch down with just one wheel first. 

The second crosswind tactic is more common to larger aircraft such as commercial jets. This is called a “crab landing,” and that’s what you see in the above video. It’s performed by positioning an aircraft at a certain angle with respect to the flight trajectory so that the nose points in the direction of the wind, but the line it draws on the ground is exactly that of the axis of the runway. If the angle formed is less than 10 degrees, usually the landing is continued just like that, and any additional necessary course correction is performed once in contact with the runway. If greater than 10 degrees, however, it’s necessary to “de-crab,” or straighten out, just before touching down in order to prevent lateral stresses on the landing gear.

The reason this type of landing technique, more complicated and requiring more training, is used with large aircraft is that almost all such planes have engines under the wings, proportionately much closer to the ground, and so lowering them in a sideslip maneuver is not really feasible.

Although windless or parallel-wind landings are simpler, and the images these crosswind landings provide can be somewhat startling for the uninitiated, they involve little risk, and are part of all pilots’ standard training – above all if they fly for commercial airlines. You might say that for them it’s a piece of crab cake. 😉

 

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