McCall Air Cessna 206 TU206F accident

The airplane was routinely used to transport passengers to and from remote unpaved, and sometimes rough, landing strips. The pilot reported that the landing at one of those unpaved strips was uneventful. Several passengers and their baggage were boarded, and the airplane then departed uneventfully. After a normal touchdown on the smooth, paved runway at the airplane's destination, when the pilot lowered the nose, the airplane began to vibrate severely, and the pilot was unable to maintain directional control. The airplane veered to the left, the nose landing gear collapsed, and the right wing contacted the runway before the airplane came to a stop near the edge of the runway. Examination of the nose landing gear components did not reveal any preimpact damage that could be associated with the vibration or failure of the nose landing gear. Although not causal to the nose landing gear failure, the nose landing gear steering collar was found to contain a high-cycle fatigue crack, but no further information was available to determine the age of the crack or the effectiveness of the previous inspection.

Nose gear shimmy, which is an abnormal, and often violent, vibration of the nose wheel, can result in failure of the nose landing gear. It is usually caused by looseness of the nose wheel support mechanism or an unbalanced wheel. However, there were no reports of recent nose gear shimmy on the airplane, and damage precluded any postaccident determination of the airplane's susceptibility to shimmy. Although operations on rough, unpaved runways can induce higher and different nose landing gear loads than do operations from smooth, paved runways, there was no evidence to directly link the operator's use of unpaved runways with the failure of the nose landing gear.

Verbatim NTSB analysis and probable cause from the NTSB dataset