WPR21LA301

The pilot reported that during the flight, the airplane suddenly started vibrating. After checking the magneto switch and looking over the instruments for any cylinder anomalies, he shut down the engine. The pilot initiated a forced landing to a field during which the right wing impacted a tree. The airplane landed hard in a muddy field, collapsing the nose landing gear. Postaccident examination of the airplane revealed a portion of the propeller blade had separated in flight. Examination of the propeller revealed that the propeller blade exhibited a fatigue crack that initiated near the trailing edge of the blade. Metal transfer from an alloy dissimilar to that of the blade’s material likely resulted from an object that impacted the blade face near the trailing edge. The red transfer marks on the blade were likely impact marks from contacting the engine cowling during the accident sequence.

On August 2, 2021, about 0930 mountain standard time, a Piper PA-28-140 airplane, N44245, was substantially damaged when it was involved in an accident near Amado, Arizona. The pilot and pilot-rated passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that while in level cruise flight, about 6,000 ft mean sea level, the airplane suddenly started vibrating. He checked the magneto switch and looked over the instruments for any cylinder anomalies and found none. He decided to shut down the engine to stop the vibrations. Soon after shutting down the engine, he said that he was committed to force land in a nearby field. He stated that, while preparing for the forced landing, he was too fast and tried to make it to the next field that was situated over the next tree line and fence. During the landing, he impacted a tree with the right wing and subsequently landed hard in a muddy field. The airplane’s nose landing gear collapsed during the landing, and the pilot and pilot-rated passenger were able to exit without injury. Examination of the accident site photos revealed that the right wing remained attached to the rear spar, separated at the main spar near the wing root and was bent upwards. The outboard right wing was buckled, and the leading edge had circular impact damage. The fuselage was buckled near the firewall and near the empennage. One of the propeller blades was separated about 5 inches outboard of the blade root. The separated propeller blade portion was not found during the investigation. The remaining propeller blade section was retained for further examination. Review of the propeller logbooks revealed that the propeller was installed on the accident airplane on March 17, 2020, with 116.1 hours of operation since overhaul. The last annual inspection was completed on April 10, 2021. At the time of the accident, the propeller had about 245 hours of operation since overhaul. Examination of the propeller blade section by the National Transportation Safety Board Materials Laboratory revealed that the propeller exhibited a fatigue crack that initiated near the trailing edge of the blade. Red transfer marks were found near the trailing edge of the blade. The fatigue crack initiated at multiple sites along the blade face surface adjacent to the trailing edge. The edge area exhibited indications of copper, as well as iron and manganese. These indicate material transfer from an alloy dissimilar to that of the blade’s material.