What happened
During the initial takeoff climb phase, the aircraft reached an altitude of approximately 300 feet above ground level when a significant mechanical failure occurred. Specifically, nine and one-quarter inches of the propeller blade on the right engine separated from the assembly. The loss of this component necessitated an immediate emergency response, leading to a forced landing in a nearby field. During the descent and subsequent touchdown, the right wing of the aircraft made contact with a tree, resulting in structural damage.
The investigation
Following the accident, a detailed metallurgical examination was conducted on the separated propeller blade to determine the root cause of the failure. The analysis focused on the fracture surface to identify the mechanism that led to the separation. Investigators looked for signs of material defects, manufacturing errors, or operational overloads that might have contributed to the event.
Findings
The metallurgical examination revealed that the failure was caused by progressive fatigue. Analysis of the fractured surface indicated that approximately 75% of the area showed evidence of fatigue cracking. This damage originated from two small, shallow pits located on the cambered surface leading edge of the blade. These initial stress concentrators allowed cracks to propagate over time until the remaining cross-section could no longer support the operational loads, leading to sudden separation.
Safety message
This incident highlights the critical importance of regular inspection for fatigue damage in propeller systems. Early detection of small surface imperfections or pits can prevent catastrophic failures during flight operations.