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. It is not always caused by drift or weathervaning 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 swerve tends to make the airplane ground loop, whether it be a tailwheel type or nosewheel type.
 

As explained in the chapter on Landing Approaches, due to the characteristics of an airplane equipped with a tailwheel, the forces that cause a ground loop increase as the swerve increases. The initial swerve develops centrifugal force and this, acting at the center of gravity (which is located behind the main wheels), swerve the airplane even more. If allowed to develop, the centrifugal force produced may become great enough to tip the airplane until one wing strikes the ground (Fig. 10-7).    Airplanes having a nosewheel are somewhat less prone to ground loop. Since the center of gravity is located forward of the main landing gear on these airplanes, any time a swerve develops, centrifugal force acting on the center of gravity will tend to stop the swerving action. If the airplane touches down while drifting or in a crab, the pilot should apply aileron toward the high wing and stop the swerve with the rudder. Brakes should be used to correct for turns or swerves only when the rudder is inadequate. The pilot must exercise caution when applying corrective brake action because it is very easy to over control and aggravate the situation.    If brakes are used, sufficient brake should be applied on the low wing wheel (outside of the turn) to stop the swerve. When the wings are approximately level, the new direction must be maintained until the airplane has slowed to taxi speed or has stopped.

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