Accident Overview
On June 7, 2020, at approximately 15:00 local time, a Tecnam P92 ECHO ultralight aircraft, registered SP-SAWS, experienced a catastrophic propeller blade separation during a private flight from Elbląg to Katowice Muchowiec. The aircraft was at an altitude of about 2,200 ft near Łódź when the pilot felt a sudden jolt, heard a bang, and the engine stopped. The pilot executed an emergency landing on a meadow. During the flare, to avoid a ditch, the pilot pulled the control column, causing the aircraft to climb to about 4 meters, stall, and drop to the ground. The pilot and the sole passenger were uninjured. After exiting, the pilot noticed one propeller blade was missing. A local resident found the blade later that day in the village of Wiązyń Dolny.
Aircraft and Crew Information
The aircraft was a Tecnam P92 ECHO, an ultralight, operated privately. The 45-year-old pilot held an ultralight pilot certificate (UACP) issued on October 26, 2018, with a total flight time of 220 hours, all on the same type. His medical certificate was valid until April 3, 2021. The aircraft was fitted with a KASPAR propeller, initially installed on a Rotax 912 UL engine on April 4, 2018. In January 2019, the engine was replaced with a Rotax 912S, and the same propeller was used despite a warranty note recommending a three-blade propeller for the 912S. The pilot had previously reported vibrations at around 5,000 RPM, which were traced to an unbalanced propeller. The manufacturer rebalanced the propeller on June 15, 2018, adding three weights. The aircraft had accumulated 22 flight hours with the unbalanced propeller and a total of 152 hours on the propeller at the time of the accident. Maintenance was performed regularly by a licensed mechanic, with the last 100-hour inspection on January 2, 2020.
Accident Sequence
On the day of the accident, the aircraft departed Elbląg at 12:30. Approximately 2.5 hours into the flight, while cruising near Łódź, the propeller blade separated. The engine stopped immediately. The pilot identified a suitable meadow for an emergency landing. During the approach, he saw a ditch crossing his intended touchdown point. To clear it, he pulled back on the control column, causing the aircraft to climb momentarily before stalling and falling from about 4 meters. The impact damaged the front landing gear, engine frame, and propeller spinner. The pilot and passenger exited without injury.
Investigation Findings
The Polish State Commission for Aircraft Accident Investigation (PKBWL) examined the aircraft and the recovered propeller blade. The blade had separated at the last thread of its attachment shank. Microscopic analysis revealed a fatigue fracture surface with circumferential cracks. Similar cracks were found on the other blade's attachment, indicating a common issue. The fracture was initiated at the thread root, likely due to over-tightening of the retaining nut or manufacturing defects. The propeller had been previously unbalanced, and the manufacturer had added balancing weights. The metallurgical examination showed a martensitic structure without inherent material defects. The investigation concluded that the fatigue crack propagated over time, leading to the in-flight separation.
Conclusion
The accident was caused by a fatigue fracture of the propeller blade attachment, originating at the last thread. This failure was probably due to improper tightening of the retaining nut or other factors related to the propeller manufacturing process.