Accident
On January 6, 2020, at about 1309 Pacific standard time, a Cessna 172H airplane, registration N1658F, was substantially damaged in an accident near El Monte, California. The pilot, who was the sole occupant, reported no injuries. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91. The pilot stated the purpose was to break in new engine cylinders while circling the city of El Monte at an altitude of 3,500 ft mean sea level.
During the flight, the airplane experienced a sudden severe vibration, followed by an abrupt loss of engine power and the appearance of oil on the windscreen. The pilot observed that the propeller was not rotating and noted visible damage to the engine cowling. A forced landing was initiated to the San Gabriel Valley Airport (EMT), which was accomplished without further incident.
Examination
A Federal Aviation Administration inspector examined the airplane and found that the engine mount was bent and one propeller blade had separated approximately 1 foot outboard of the blade root. The propeller was retained for further examination.
Propeller Analysis
The National Transportation Safety Board Materials Laboratory examined the propeller. The propeller exhibited a chordwise fracture across the blade approximately 12 inches outboard of the hub center. The fracture surface was relatively flat near the leading edge and transitioned to a slant-type fracture toward the trailing edge. The leading edge displayed an area of darker coloration and a smoother surface texture, visible under side lighting. Scanning electron microscope (SEM) examination revealed post-fracture impact damage on the leading edge, but further SEM analysis identified fracture features consistent with progressive crack growth (fatigue) on the darker, smoother area, originating at the leading edge.
Review of propeller logbooks showed the propeller was overhauled on December 4, 2014, and its last 100-hour inspection was completed on December 4, 2019. The total time since new or since overhaul at the time of the accident could not be determined.