In general slang “crab” refers to a bad tempered person or in the plural form an infestation of pubic lice. In aviation lingo, “crab” means to fly an aircraft with the nose pointed into a crosswind to compensate for drift. The aircraft looks like a crab scuttling sideways across the sand.
Today I came across an entertaining video compilation of commercial airliners landing or taking off in strong crosswinds that require crabbing into the wind to maintain a straight track down the runway. The maneuver looks scary but crabbing is one of two simple techniques for handling crosswinds that every pilot is taught in basic flight school. Once the plane touches down, the pilots use the rudder to get the nose pointing straight down the runway.
In terms of success rate, crosswind landings are easier than making a lay up in basketball. Even pros miss uncontested layups from time to time. Airline Transport Pilots don’t ” make successful crosswind landings all the time even when they might have to go around or perform a touch and go.
The other crosswind landing technique is called a slip or slipping. In a slip approach, the pilot lowers a wing into the crosswind while using opposite rudder to keep the nose of the plane pointed straight ahead. This method works well in small aircraft. Most commercial airliners don’t use this method because most large airplanes have long wings with engines underneath. In those aircraft, landing in a slip with a wing down could result in a wingtip or engine contacting the runway.
Many years ago on a flight to Chicago O’Hare Airport (ORD) the pilots of the Boeing 727 I was on used the slip method for landing in a strong crosswind. A 727 has relatively short wings and the engines are mounted on the tail. The pilots had to dip the starboard (right) wing considerably to compensate for the crosswind. After touchdown, the port (left) wing and landing gear came crashing down so forcefully that all of the oxygen masks came down and the overhead bins popped open.
The stronger the crosswind the more the nose must point into it in a crab and the more the wing must be lowered in a slip. Interestingly, the size of the plane doesn’t matter. A crosswind is like an ocean current, which affects all vessels equally. Approach speed, not size or weight, determines the amount of crab angle or slip required to maintain a track down the center of the runway.
The next time you are on a flight that seems to be landing cockeyed, don’t worry. The pilots aren’t drunk. Have you encountered any harrowing crosswind landings in your travels?