Event Description
During the takeoff climb, at an altitude between 400 and 500 feet above the runway, the outer 14 inches of one propeller blade separated from the rest of the blade. The certified flight instructor (CFI) retained control of the airplane and executed a landing on a parallel taxiway without further incident. The propeller had accumulated 236 total hours of operation at the time of the event.
Investigation Findings
A metallurgical examination was conducted on the fractured propeller blade. The examination revealed that approximately 60 percent of the fracture surface exhibited features characteristic of fatigue cracking. The fatigue crack originated from the flat face of the blade arm, near the trailing edge. The microstructure of the blade material was reported as normal, with one exception: the grain flow pattern followed the surface of a scallop region rather than the surface of the blade itself.
Further analysis identified the presence of chromium within the scalloped region of the fracture surface, while chromium was absent on the fatigued surface. This disparity indicated that the chromic anodized solution had penetrated the indication during the anodizing process, prior to the application of paint to the blade.