Accident Overview
On November 2, 2017, at approximately 0930 Pacific daylight time, a Cessna 172R aircraft, registration N2103T, was substantially damaged during a forced landing near Redding, California. The aircraft was operating under Title 14 Code of Federal Regulations Part 91 as an instructional flight. The flight instructor and two students on board were not injured.
Flight Sequence
The flight instructor reported that he directed the student pilot who was flying to climb the aircraft to 3,500 feet. As the airplane approached 3,100 feet, the student began leaning the mixture. Subsequently, the engine began to sputter, followed by a complete loss of power. The instructor then observed sparks emanating from the propeller area, took control of the aircraft, and turned back toward the departure airport. The instructor added that the student conducted the emergency checklist while he contacted the tower controller and maintained an airspeed of 100 knots.
Due to fire near the propeller area and the smell of smoke in the cockpit, during short final approach the instructor turned the airplane 360° in an attempt to lose altitude. However, the airplane remained too high to safely land on the runway. The instructor then executed a forced landing to a field just past the runway. During the landing, the airplane struck a fence, resulting in substantial damage to the left wing and firewall.
Engine Examination
Examination of the engine revealed that the crankshaft had separated at the propeller hub assembly, with a portion of the crankshaft remaining in the assembly. No holes were found in the engine case. Disassembly of the connecting rods showed that the No. 1 connecting rod bearing exhibited metal smearing on its face. The No. 4 connecting rod and bearing assembly had metal shavings and displayed thermal discoloration and some deformation. The other two connecting rods and bearings exhibited some thermal discoloration.
Metallurgical examination further determined that the crankshaft had fractured into two halves at the forward side of the main bearing journal. The fracture consisted of two primary mating crack faces: one circumferential crack and one spiral crack that passed through a lubrication hole to the inside of the crankshaft journal. The mating fracture surfaces of the circumferential fracture showed crack arrest marks, which had propagated from the spiral fracture, consistent with progressive crack growth. Areas outside the circumferential fracture exhibited features consistent with subsequent overstress fracture. The mating fracture surfaces of the spiral fracture also showed crack arrest marks, originating from the inside portion of the hole wall, consistent with progressive crack growth. The lubrication hole exhibited witness marks consistent with rotational wear and crack arrest marks that originated from the inside portion of the hole wall.
Maintenance Records
According to maintenance records, on March 15, 2016, the engine was signed off as overhauled, and maintenance personnel performed a final inspection with no discrepancies identified. A logbook entry made the next day indicated that the engine was overhauled to zero-time and had a previous total time of 2,754 hours. At the time of the accident, the engine had accumulated a total time of 3,907.1 hours and 1,153.7 hours since the major overhaul.