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Aviation Words — Crab
By Ian Brown, Editor
July 2019 - This is the use of rudder and ailerons to yaw the aircraft towards the crosswind allowing the pilot to maintain a flight path in line with the runway in a landing approach. The purpose is to correct for lateral drift from winds perpendicular to the runway.
Since most GA aircraft do not have castering main gear, the pilot must de-crab the aircraft just before the flare using opposite rudder while keeping the wings level with the ailerons. Once the wheels touch, the pilot keeps the aircraft on the centerline with the rudder and nose wheel or tail wheel as appropriate, countering the crosswind.
For entertainment you might like to look at some crabbed landings in aircraft that do have a castering undercarriage. Click here.
One assumes that the idea comes from the motion of a crab which is sideways, although if you're really flying sideways you might have been better off staying on the ground.