WPR25LA096

According to the pilot, who had recently purchased the airplane, he inspected the airplane’s propeller for damage before departing on a multi-leg cross country flight. During the second leg of the flight, one of the propeller blades separated about 17 inches from the hub. The pilot shut down the engine and was able to perform a forced landing on a rural road. The airplane sustained substantial damage to its airframe and engine mount from excessive vibrations caused by the propeller blade separation. The maintenance records for the airplane and propeller were incomplete, and the propeller’s maintenance and operational history could not be determined. Examination of the propeller revealed fracture features consistent with a fatigue crack that initiated from an impact pit on the blade face. The impact pit was one of several areas of damage consistent with debris impacts that were subsequently painted over and obscured with black paint. Measurement of the pit at the origin of the fatigue crack revealed it was within tolerance for a field repair; however, there was no indication any repair was performed. There was insufficient information to determine when the damage occurred or how long the fatigue crack had been present.

On February 16, 2025, at 1315 mountain standard time, a Cessna 150J, N151GW, was substantially damaged when it was involved in an accident near Minersville, Utah. The pilot was not injured. The aircraft was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, he had recently purchased the airplane. On the morning of the accident, the airplane had been parked in a dirt lot. Before departing, the pilot closely examined the propeller to ensure it had not been chipped by loose rocks in the parking area. The pilot did not observe any damage to the propeller and departed for a cross-country flight. The pilot performed the first leg of the flight and a fuel stop, both of which were uneventful. During the second leg, while in cruise flight at about 8,500 ft msl, he noted an “unusual engine vibration” followed seconds later by a loud bang. The airplane began to shake violently, and the engine cowling broke apart. The pilot shut down the engine and performed a forced landing on a dirt road. Upon exiting the airplane, the pilot saw one of the propeller blades had separated. The airplane suffered substantial damage to the engine mount and fuselage.The separated propeller blade was not located. After the airplane was recovered from the accident site, 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 had initiated on the blade face (the flat side of the blade) near the center of the chord. The fatigue crack progressed towards the blade back (the cambered side of the blade), where the final separation was due to overstress of the reduced cross-section. Examination of the fatigue crack’s origin revealed a pit that was approximately .009 inch deep and .036 inch wide. The 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 (see figure). Figure. Closeup of the fatigue crack origin with a pit that had been painted over. Crack arrest fronts can be seen emanating from the origin location. The inset image depicts the entire fracture surface, with fracture origin indicated by the red arrow. 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 from initiation to final separation. According to documentation provided by Sensenich Propeller Company, the propeller manufacturer, the propeller had been produced between October 1967 and January 1968. The airplane was manufactured in 1969. Review of the available records revealed 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 LycomingO-320-A2B engine and Sensenich M74DM propeller. These major alterations were retroactively approved in 2001 through the issuance of an FAA Field Approval. In 2010, the airplane was involved in a hard landing, which resulted in the collapse of the nose gear. The airplane underwent major repairs that were documented in maintenance record entries dated October 5, 2010. Although the maintenance record indicated an FAA Form 337 had been produced to document these repairs, it was not located in the airplane’s records, nor was it present in the airplane’s FAA airworthiness file. None of the available airplane records documented the installation of the propeller on the accident airplane, but a record made in 2023 indicated it had been installed by that time. The only documented repair performed on the propeller was during an annual inspection in November 2024. At that time, the mechanic documented they “dressed minor knicks from the leading edge.” The airplane was flown about 29 hours between the November 2024 annual inspection and the accident. The propeller repair manual states that dents or gouges on the blade face should be repaired by rounding out the damaged area with a file until the defect is completely removed, followed by polishing with abrasive cloth. The repaired area should then be inspected under magnification to ensure the bottom of the defect has been removed, that no cracks are present, and to ensure the finished repair does not exceed 0.0625 inch in depth or .375 inch chordwise. The repair manual further states “the presence of a crack indicates blade failure is imminent. The propeller must immediately be removed from service.” According to Sensenich Service Bulletin No. R-17, 90% of propeller blade failures in their products are due to improper modification, improper repairs, and poor maintenance. It states that, “[p]oor maintenance refers to the lack of maintenance by owner/operator. Damage such as leading edge nicks and cuts, face nicks and cuts or corrosion that are left unrepaired and or painted over without proper removal and re-application of a corrosion coating are considered poor maintenance.” The service bulletin recommends that the propeller should be reconditioned and inspected every 2000 flight hours. The service bulletin also warns: “DO NOT paint over corroded or damaged blades. This hides the defect and may deter needed repair and cause blade failure.”