Accident Overview
On April 28, 2020, at approximately 1752 Pacific daylight time, a Cessna 177, registration N3386T, was substantially damaged during a forced landing near Lodi, California. The pilot, a student pilot, was operating the aircraft under Title 14 Code of Federal Regulations Part 91 as a personal flight and sustained minor injuries.
Pilot Report
Approximately 15 minutes after takeoff, while at an altitude of 1,400 feet, the engine began to run rough and produced metallic noises. Oil appeared on the windscreen, followed by a total loss of engine power. The pilot attempted to restart the engine without success and initiated a forced landing to a nearby field. The aircraft touched down hard and came to rest upright.
Engine Examination
Post-accident examination revealed that the engine remained attached to the airframe with all accessories intact. A hole was observed in the crankcase above cylinders No. 4 and No. 3. No loose oil lines were found except the oil pressure line, which was separated from the crankcase consistent with impact damage.
The No. 4 cylinder exhibited extensive damage to the piston skirt area and cylinder wall. The No. 4 connecting rod remained attached to the crankshaft, but the web was separated from just outboard of the crankshaft to about 1 inch inboard from the piston pin. The separation near the piston pin was flat with no apparent mechanical damage, while the separation near the crankshaft showed extensive mechanical damage. The middle portion of the connecting rod web was found in the oil sump and exhibited mechanical damage.
Fracture Analysis
The fracture surface on the piston pin side of the connecting rod was relatively flat and oriented perpendicular to the rod's longitudinal direction. Most of this surface exhibited crack arrest marks indicative of progressive crack growth consistent with fatigue. The remaining surface showed a rougher texture consistent with overstress fracture. The fatigue crack covered approximately 95% of the rod flange-to-flange cross section, measuring about 1.086 inches.
No ratchet marks were observed, suggesting a single initiation site located at the inside corner of a flange edge. River patterns and crack arrest marks emanated from this feature. The outer flange surface showed smoothing and deformation over the side of the inner flange surface.
Maintenance History
The engine was overhauled on November 10, 1986, and had accumulated 887.86 hours at the time of the accident. Review of the engine logbook revealed no maintenance entries regarding the No. 4 connecting rod.