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There are several crosswind landing techniques described on Wikipedia, including crabbing (straightening out after touchdown) and de-crabbing (straightening out just before touchdown).

For airline pilots, are there specific conditions that favor the use of the crab method over the de-crab method for crosswind landings, despite the excessive side load the crab method may incur? When airline pilots use crabbing for crosswind landings, what are the reasons?

(This question is not about the general crosswind landing techniques dealt with in this great post but more about airline pilots' crosswind landing techniques. More specifically, my question addresses some possible conditions where the airline pilots would prefer the crab technique to the de-crab technique.)

Pondlife
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lemonincider
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    Take the runway that better aligned into the wind. – ratchet freak Aug 04 '17 at 09:29
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    Most airliners are low-wing, hence sideslipping near the ground is not advisable. Thus, crabbing with a last-second de-crab is the best option. – xxavier Aug 04 '17 at 10:14
  • @xxavier Thank you for your reply. Then what's your opinion on my second question? Watching several crosswind landing videos on Youtube, I found a small number of airliners landed crabbing all the way down onto the runway without a last-second decrab. – lemonincider Aug 04 '17 at 10:22
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    You can embed links with [link text](url). – David Richerby Aug 04 '17 at 10:45
  • @lemonincider With a crosswind, in order that the plane may follow the axis of the runway in final, you approach with the wings level and an big angle between the plane's axis and the runway. That angle has to be corrected at the last moment, before the wheels touch the ground. That 'instant' has to be as brief as possible, because during that small time, the plane moves sideways. Now, in order to reduce that angle (even to zero if the crosswind is not to strong) you may also roll the plane slightly to the crosswind. That may be advisable with high-wing planes, but no with low wing ones... – xxavier Aug 04 '17 at 11:44
  • @xxavier So are you implying a touchdown on the runway in a crab attitude is the wrong crosswind landing technique? But I saw it used on some videos, and most of all, Boeing introduces it as one of the three crosswind landung techniques (although Airbus discourages using it). – lemonincider Aug 04 '17 at 11:55
  • @lemonincider No... I'm not implying anything... Please read my last comment. I know quite well what I'm talking about, having done thousands of landings, some of them under very difficult wind conditions. – xxavier Aug 04 '17 at 14:13
  • @xxavier I apologize if I was misunderstood. I didn't write my previous comment because I suspected your level of knowledge about flight but because I just wanted to emphasize that those techniques are being actually used by some airline pilots and get your opinion on that. – lemonincider Aug 04 '17 at 14:29
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    FWIW, in the 1990s in 747-100/200 aircraft I handled all crosswinds regardless of strength in the same manner: Maintain a crab down final, at the 50 foot call (radar altimeter) decrab as much as possible while lowering the upwind wind to not more than 5 degrees. That meant that in a heavy crosswind, I'd still have some crab left at touchdown. – Terry Aug 04 '17 at 19:12

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First, I would say that the question should be between Crab technique vs sideslip technique. What the wikipedia article describes as De-crab technique is simply a quick transition from crabbing to a momentary sideslip as the wheels touch down. Generally, landing while crabbed is bad form, regardless of type or size of aircraft due to the side load on the landing gear at touchdown.

I was taught that side slip technique (where you fly with the down wind wing slightly elevated and use rudder to keep fuselage and wheels lined up with the centerline) is preferred because you don't have to do any last second adjustments right before touchdown. If you do this correctly, the turning tendency of the aircraft is mostly cancelled out by the cross wind component. Also, if you do this right, you touch down with upwind mains first, then downwind mains.

However, I was also taught that side slip makes passengers feel uncomfortable, and that is why airliners stay in the "crab" until last second.

As to your comment about airliners failing to de-crab, I've seen that too, I argue its just bad technique. Its difficult to properly execute the de-crab, it takes finesse and good timing.

Devil07
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    Actually, landing while crabbed is a preferred technique with some airlines. – GdD Aug 04 '17 at 16:02
  • I could see that, assuming the crab is not too severe. I've felt it many times when traveling as a passenger. What airlines are you referring to? I'm curious to know if there is a threshold of crab angle. – Devil07 Aug 04 '17 at 17:24
  • I suspect @Terry's comment on the OP's question is the reason for some airlines landing with crab. The bank angle is limited to a certain angle that might not be sufficient for strong crosswind. I don't know if its preferred technique, but when I'm a passenger in an airliner that lands without de-crabing or whatever you want to call it, I always think to myself, "amateur." :) Terry explained it exactly right. – Devil07 Aug 04 '17 at 20:40
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Most airliners are designed to accommodate reasonable sideloads on the landing gear during touchdown per the Part 23 requirements for transport aircraft. Sideslippimg at touchdown creates a risk of contact with the engine nacelles and FOD ingestion. Therefore most manufacturers and airline SOPs suggest touching down in a crab, then aligning with the runway centerline after touchdown.

Romeo_4808N
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  • It's surprising most manufacturers and airline SOPs suggest touching down in a crab. Do they provide any conditions where that method should be used, like a specific crosswind component? – lemonincider Aug 04 '17 at 17:42