Originally Posted by
PearlPilot
Almost always I have seen big jets like the 757, 747, 737 using the crab method on x-wind landings. Why not use the down wing method instead? Is the crab method more preferable than the down wing method? Also, at the last minute when the rudder is being kicked to align the nose with the centerline, I have noticed that sometimes the nose isn't exactly aligned with the runway. I see some side loading. Are landing gears on big jets designed to be "twisted" like this without causing damage? On a 172 you really feel the side load and it is no bueno as you know.
Q. Why not use the down wing method?
A. One big reason is for ground clearance: the wings are long on big jets and the engines are slung low, so you run the risk of having something scrape the ground. The other big reason is aerodynamic: in the "wing down" scenario, the airplane is in a sideslip, which risks having the air flowing around the fuselage "blank out" the tail, causing you to lose elevator effectiveness, which is not good at low speed. In a crab, the airplane is not side-slipping.
Q. What about side loading on the gear?
A. While it's not ideal to land with side load, the main gear on large jets can handle some side loading. In fact, some large aircraft like B-52's, have steering mechanisms that can be steered to land in a crab.