Accident Summary
On February 16, 2025, at 1315 mountain standard time, a Cessna 150J, registration N151GW, was substantially damaged during a forced landing near Minersville, Utah. The pilot, the sole occupant, was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Report
According to the pilot, he had recently purchased the airplane. On the morning of the accident, the airplane was parked in a dirt lot. Before departure, the pilot closely examined the propeller for any damage from loose rocks but observed none. He then departed for a cross-country flight. The first leg and a fuel stop were uneventful. During the second leg, while cruising at about 8,500 ft msl, the pilot noted an unusual engine vibration followed seconds later by a loud bang. The airplane shook violently, and the engine cowling broke apart. The pilot shut down the engine and performed a forced landing on a dirt road. After exiting, he saw that one propeller blade had separated. The separated blade was not located.
Examination Findings
The propeller was removed and sent to the NTSB Materials Laboratory. Examination revealed the propeller had fractured about 17 inches from the hub. The fracture features were consistent with a fatigue crack that initiated on the blade face (flat side) near the center of the chord. The fatigue crack progressed toward the blade back (cambered side), where final separation occurred due to overstress of the reduced cross-section. At the origin of the fatigue crack, a pit approximately .009 inch deep and .036 inch wide was found. Features of the origin pit were consistent with a gouge caused by particle impact. The pit had been obscured by a layer of black paint. No paint was found within the fatigue crack. Removal of the paint revealed several more pits on the blade face. It could not be determined how long the fatigue crack had been present or how many flight hours it took to progress.
Propeller History and Maintenance
Documentation from Sensenich Propeller Company indicated the propeller (model M74DM) was produced between October 1967 and January 1968. The airplane was manufactured in 1969. Review of records showed the airplane was originally equipped with a Continental O-200 engine and a McCauley 1A101 propeller. At an unknown date, the original engine and propeller were replaced with a Lycoming O-320-A2B engine and the Sensenich propeller. These major alterations were retroactively approved in 2001. In 2010, the airplane was involved in a hard landing that collapsed the nose gear; major repairs were documented in October 2010 maintenance records. The records referenced an FAA Form 337 for those repairs, but it was not found. No available records documented the installation of the propeller on the accident airplane, though a 2023 record indicated it was installed by then. The only documented propeller repair was during a November 2024 annual inspection, when a mechanic dressed minor nicks from the leading edge. The airplane flew about 29 hours between that inspection and the accident.
The propeller repair manual specifies that dents or gouges on the blade face should be repaired by rounding out the damaged area with a file, then polishing, and inspecting under magnification to ensure no cracks remain and the repair depth does not exceed 0.0625 inch. It warns that a crack indicates imminent blade failure and the propeller must be immediately removed from service.
Sensenich Service Bulletin No. R-17 states that 90% of propeller blade failures are due to improper modification, improper repairs, and poor maintenance. It notes that damage left unrepaired or painted over without proper removal of corrosion coating constitutes poor maintenance. The bulletin recommends reconditioning and inspection every 2000 flight hours and warns against painting over corroded or damaged blades, as it hides defects.
Damage Assessment
The airplane sustained substantial damage to the engine mount and fuselage. The separated propeller blade was not recovered.