At times, it is necessary to correct for wind drift by crabbing  on the final approach. If the round out and touchdown are  made while the airplane is drifting or in a crab, it contacts  the ground while moving sideways. This imposes extreme  side loads on the landing gear and, if severe enough, may  cause structural failure. swerve tends to make the airplane ground loop, whether it is  a tailwheel-type or nose-wheel type.  [Figure 8-39] Nose-wheel type airplanes are somewhat less prone to  ground loop than tailwheel-type airplanes. Since the center  of gravity (CG) is located forward of the main landing gear  The most effective method to prevent drift is the wing-low  method. This technique keeps the longitudinal axis of the  airplane aligned with both the runway and the direction of  motion throughout the approach and touchdown. There are three factors that cause the longitudinal axis and  the direction of motion to be misaligned during touchdown:  drifting, crabbing, or a combination of both. A ground loop is an uncontrolled turn during ground operation  that may occur while taxiing or taking off, but especially  during the after-landing roll. Drift or weathervaning does  not always cause a ground loop, although these things may  cause the initial swerve. Careless use of the rudder, an uneven  ground surface, or a soft spot that retards one main wheel of  the airplane may also cause a swerve. In any case, the initial  Figure 8-39.  Start of a ground loop. Figure 8-38.  Drifting during touchdown. Touchdown in a Drift or Crab Ground Loop 8-34 W i n$_{d}$ Weight Inertia force Center of gravity Force resisting side motion Wind force Roundout Roundout Touchdown Airplane tips and swerves CG continues moving in same direction of drift Wind If the pilot does not take adequate corrective action to avoid  drift during a crosswind landing, the main wheels’ tire tread  offers resistance to the airplane’s sideward movement in  respect to the ground. Consequently, any sidewise velocity  of the airplane is abruptly decelerated, resulting in the aircraft  being shifted to the right due to the inertia force which is  shown in  Figure 8-38 . This creates a moment around the  main wheel when it contacts the ground, tending to overturn  or tip the airplane. If the windward wingtip is raised by the  action of this moment, all the weight and shock of landing is  borne by one main wheel. This could cause structural damage. Not only are the same factors present that are attempting  to raise a wing, but the crosswind is also acting on the  fuselage surface behind the main wheels, tending to yaw  (weathervane) the airplane into the wind. This often results  in a ground loop.