By lex, on November 18th, 2007
Best case is winds down the runway at 5-15 knots. Runways are typically constructed with a view towards the predominant winds. That doesn’t mean that winds are always down centerline, however. When a weather front comes in, sometimes they’re offset as much as 45 degrees. Sometimes more.
Generically speaking there are two crosswind landing techniques: The “wing down, top rudder” landing, and the crab.
In a wing down, top rudder landing, you align yourself on the runway centerline. As the cross wind pushes you off the runway you correct back to centerline and once there, ease out about half the angle of bank – to fight the crosswind – and then add “top rudder,” or rudder opposite the bank angle direction. Essentially, this “cross-controlled” setting – called so because the ailerons and rudders appear to work at cross purposes – aligns the fuselage more or less with the runway, causing the plane to land low main landing gear first, in a bit of an angle of bank.
The crabbed landing is a flight path flown at an angle to the runway heading. This is the approved technique in the FA-18, since a wing down, top rudder approach could cause the flight control computers to question the pilot’s commitment to controlled flight. Just prior to landing, FA-18 pilots are taught to take half the crab out with a stab of rudder, to more closely align the jet to runway heading. Otherwise he might encounter what the book dryly calls “mildly objectionable” directional oscillations.
Which, as a young aviator, led me to the understanding that what a test pilot calls “mildly objectionable” could well be called pretty dern frightening to a nugget pilot.
For a pretty impressive look at a crabbed approach to landing, check out these Boeing clips. I can only assume they were done under test circumstances, without paying customers aboard.