What happened
On July 5, 2020, a PZL-110 Koliber, registration SP-ARM, was conducting a flight training mission departing from Toruń (EPTO). The crew, consisting of a flight instructor and a student pilot, had completed approximately one hour of flight time and had recently entered the Toruń control zone when they noticed uneven engine performance accompanied by intense vibrations.
Upon detecting the malfunction, the instructor took control of the aircraft and initiated an emergency landing procedure. The student pilot deployed the flaps and scanned the selected landing area for obstacles. The aircraft successfully performed a precautionary landing in a field near the village of Turz and the occupants remained without injuries. Following the landing, the crew discovered that a section of one propeller blade, approximately 15 cm in length, had detached from the tip.
The investigation
The PKBWL commissioned a detailed metallurgical expertise of the damaged propeller blade, conducted by researchers from the Faculty of Materials Engineering at the Silesian University of Technology. The analysis included visual inspections, stereoscopic microscopy, light microscopy, and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). Additionally, Vickers hardness testing was performed to evaluate the material properties.
Findings
- The investigation established that the fracture of the propeller blade had a combined fatigue and instantaneous character.
- The failure occurred due to the propagation of a fatigue crack under cyclic operational loads.
- The fracture topography indicated that the crack developed without the stresses exceeding the design limits of the propeller.
- The primary cause of the blade failure was likely a geometric notch caused by an impact with a hard, sharp object.
While the investigators could not determine exactly when the initial impact occurred, they concluded that this impact created the stress concentration point that eventually led to the structural failure of the blade tip.