WPR18LA039

Two student pilots and the flight instructor were conducting a cross-country instructional flight. The instructor reported that he told the student who was flying to climb to 3,500 ft above ground level (agl). As the airplane approached 3,100 ft agl, the student began leaning the mixture. Subsequently, the engine began to sputter, followed by a loss of all power. The instructor then saw sparks near the propeller area, took the flight controls, and turned back toward the departure airport. During short final, due to fire near the propeller area and the smell of smoke in the cockpit, the instructor turned the airplane 360° to try to lose altitude; however, the airplane was still too high to safely land on the runway. Subsequently, he conducted a forced landing to a field just past the runway, during which the airplane struck a fence, which resulted in substantial damage to the wing and firewall. Examination of the engine revealed that the crankshaft had separated at the propeller hub assembly and that a portion of it remained in the assembly. No holes were found in the engine case. Metallurgical examination revealed that the crankshaft had fractured into two halves at the main bearing journal’s forward side. The fracture consisted of two primary mating crack faces, one of which was circumferential and the other of which was a spiral through a lubrication hole to the inside of the crankshaft journal. The lubrication hole exhibited crack arrest marks that originated from the inside portion of the hole wall. The mating fracture surfaces of the circumferential and spiral fractures exhibited crack arrest marks consistent with progressive crack growth due to fatigue. The areas outside of the circumferential fracture exhibited features consistent with subsequent overstress fracture. Maintenance records revealed that at the time of the accident the engine had accumulated a total time of 3,907.1 hours and 1,153.7 hours since major overhaul. Based on the evidence, it is likely that the crankshaft fractured due to a fatigue crack that had initiated at a lubrication hole on the main bearing journal and then progressed in an outward spiral direction toward the inside surface of the crankshaft journal. The fatigue crack then progressed circumferentially until the crankshaft fractured into two halves due to overstress, which resulted in a subsequent total loss of engine power and off-airport landing.

On November 2, 2017, about 0930 Pacific daylight time, a Cessna 172R airplane, N2103T, was substantially damaged when it was involved in an accident near Redding, California. The flight instructor and two students were not injured. The airplane was being operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor reported that he told the student pilot who was flying to climb the airplane to 3,500 ft. As it approached 3,100 ft, the student began leaning the mixture. Subsequently, the engine began to sputter, followed by a loss of all power. The instructor then saw sparks emanating from the propeller area, took the flight controls, 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 100 knots. Due to fire near the propeller area and the smell of smoke in the cockpit, during short final, the instructor turned the airplane 360° to try to lose altitude; however, the airplane was still too high to safely land on the runway. Subsequently, he conducted a forced landing to a field just past the runway, during which the airplane struck a fence, which resulted in substantial damage to the left wing and firewall. 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. After the connecting rods were disassembled, examination revealed that the No. 1 connecting rod bearing exhibited metal smearing on its face. The No. 4 connecting rod and bearing assembly had metal shavings on it and exhibited thermal discoloration and some deformation. The other two connecting rods and bearings exhibited some thermal discoloration. Metallurgical examination further revealed that the crankshaft had fractured into two halves at the main bearing journal’s forward side. The fracture consisted of two primary mating crack faces, one of which was a circumferential crack and the other of which was a spiral through a lubrication hole to the inside of the crankshaft journal. The mating fracture surfaces of the circumferential fracture exhibited crack arrest marks, which had propagated from the spiral facture, consistent with progressive crack growth. The areas outside of the circumferential fracture exhibited features consistent with subsequent overstress fracture. The mating fracture surfaces of the spiral fracture also exhibited crack arrest marks, which originated 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 revealed that On March 15, 2016, the engine was signed off as overhauled and maintenance personnel performed a final inspection of the engine with nodiscrepancies identified. According to a logbook entry made the next day, 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.