Mitsubishi MU-2B-20 N52CD incident near Walterboro, South Carolina

Probable cause

The inadequate inspection and rigging of the nose landing gear downlock mechanism by maintenance personnel, which resulted in the failure of a bolt and the subsequent collapse of the nose gear during the landing roll.

NTSB analysis

The pilot reported hearing a “pop” sound from the nose gear area when the gear was extended for the landing. Toward the end of the landing roll, the nose gear collapsed. A postaccident examination of the nose gear revealed that the bolt that holds the downlock drag brace joint link to the airframe structure had fractured. A metallurgical examination revealed that the bolt failed in reverse bending fatigue, which is associated with the bolt having insufficient clamping pressure (looseness). The airplane’s last required inspection was about 70 flight hours and 40 gear cycles before the nose gear collapsing, and the nose gear downlock system rigging should have been inspected at that time.

Text from the NTSB. Open the NTSB docket for ERA11IA172 for the full record.