Accident Overview
On March 25, 2024, at approximately 1853 central daylight time, a Cozy Mark IV experimental airplane, registration N20MN, was substantially damaged during a forced landing near Gonzales, Texas. The pilot, the sole occupant, was not injured. The flight was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Sequence of Events
According to the pilot's report, while en route at an altitude of about 9,500 ft mean sea level, the engine experienced a total loss of power. Despite multiple restart attempts, the engine could not be restored. The pilot executed a forced landing to a nearby airport. The airplane touched down short of the runway threshold, and during the transition onto the asphalt runway, the nose landing gear separated. The left wing and left canard sustained substantial damage.
Postaccident Examination
Postaccident examination of the engine revealed no valvetrain continuity when the engine was rotated at the propeller. Further inspection showed that the left crankshaft idler gear had disengaged from the crankshaft and camshaft gears. The 5/16-inch stud, slotted shear nut, and capscrew fasteners that attached the crankshaft idler gear shaft to the crankcase were abraded and separated into two sections. The capscrew was lockwired to the idler shaft, but no lockwire was observed through the stud and slotted shear nut, and no separated sections of lockwire were found in the oil sump. The heads of the capscrew and slotted shear nut exhibited abrasion. Additionally, circular abrasion on the back of the crankshaft idler gear was consistent with the fasteners contacting the gear during engine operation.
The idler shaft recess in the crankcase showed deformation and abrasion. The idler gear shaft contained a bushing that matched the specifications of Lycoming Engine's Service Instruction No. 1197A, Repair of Idler Gear Shaft Recesses, dated March 29, 1974. The bushing was fractured in two sections and deformed.
Maintenance References
According to Lycoming Engine's Service Instruction No. 1310A, Lockwire for Idler Shafts, dated February 25, 1977, the required capscrew torque is 200 inch-pounds and the slotted shear nut torque is 150 inch-pounds. The instruction also requires both fasteners to be lockwired.
Missing Records
The pilot's flight logs and airplane maintenance records were not made available during the investigation. Additionally, the pilot did not submit the Pilot/Operator Aircraft Accident/Incident Report Form despite multiple requests.