Accident Details
On March 10, 2022, at about 1430 Alaska daylight time, a Cessna 310R airplane, registration N3UR, was substantially damaged in an accident near McGrath, Alaska. The pilot and three passengers were not injured. The flight was operating under Title 14 Code of Federal Regulations Part 91 as a personal flight.
According to the pilot, he back-taxied along runway 16 to the departure end of runway at McGrath Airport (PAMC). Upon reaching the end, he began turning the airplane to align with the reciprocal runway. As the turn commenced, the right main landing gear collapsed, causing the wing, propeller, and right elevator to contact the runway. The right elevator was substantially damaged.
Examination Findings
A postaccident examination of the right main landing gear well by the pilot revealed fractures at the bellcrank lower arm fork, bellcrank pivot bolt, and the trunnion bellcrank lug. An NTSB materials laboratory review of photographs of the fracture surfaces showed fracture characteristics consistent with overstress. No evidence of fatigue was observed on any of the fracture faces; however, the quality of the photographs prevented observation of any small regions that may have exhibited fatigue cracking. According to the airplane manufacturer, an overstress failure of the bellcrank assembly at the trunnion is commonly an indication that the down lock side brace was not in the down and locked position.
Maintenance History
A logbook entry from the airplane's most recent annual inspection indicated that the right main landing gear door and gear strut were removed and replaced with new bolts. The landing gear was subsequently re-rigged in accordance with the maintenance manual before the airplane was returned to service. The accident pilot was also the certified airframe and powerplant mechanic responsible for completing the last annual inspection. According to his recount, after replacing the landing gear strut following a previous right main landing gear failure, he checked the down lock tension and discovered it was "too tight." He made an adjustment to reduce the tension, but found it out of tolerance. He made one final adjustment that placed the down lock tension within tolerance before returning the airplane to service, 22 flight hours prior to the accident.
The accident airplane maintenance manual provides specific instructions for adjusting main landing gear down lock tension (Chapter 32, Section 32-30-00). The procedure includes inspecting the down lock tension for proper adjustment (40 to 60 pounds) and adjusting by turning the push-pull tube in half-turn increments. The pilot recalled using a spring scale to measure the tension and adjusting the push-pull tube. He noted he was particular about following each step in the Cessna maintenance manual during this inspection, as he was new to maintaining the accident airplane make and model.