What happened
On March 7, 2025, at approximately 1400 Alaska standard time, a Cessna 185 aircraft, N1718R, was taxiing for takeoff from a remote, snow-covered lake near Skwentna, Alaska. During the taxi, the right landing gear leg collapsed, causing the gear leg to separate from the landing gear box assembly and fold underneath the aircraft. The accident resulted in substantial damage to the landing gear box assembly and the door post assembly. The pilot and two passengers were not injured.
The investigation
An examination of the right landing gear leg assembly showed that while the bolt securing the gear leg to the box assembly remained in place, the nut had fallen into the belly of the aircraft.
Investigators reviewed maintenance records, which showed the aircraft had flown approximately 83 hours between May 2023 and the accident. Records indicated that in October 2023, the floats and float rigging were removed and main landing gear with wheels were installed, though this specific alteration was not documented in the maintenance logs. In December 2023, wheels were replaced with skis. The mechanic responsible for the October 2023 gear change stated he used hardware provided by the owner and noted that no logbook entry was made because the owner had not provided the logs for signature.
Physical inspection of the hardware on the main landing gear spring revealed the use of an AN7-20 bolt with a cross-drilled hole and an MS20365-720A nylon locking nut. This differed from the manufacturer's parts catalog, which specifies an AN7-20A bolt (without a cross-drilled hole), an MS20365-70C all-metal locking nut, and a spring adjustment shim.
Laboratory examination of the bolt and nut showed patchy, worn cadmium plating. Both components exhibited worn threads. The wear on the nylon locking insert of the nut was consistent with progressive wear over time rather than a single instance of overload.