Incident Overview
During a maintenance test flight, the pilot and a mechanic were conducting a climb to cruise when the incident occurred. At an altitude of 1,000 feet above ground level, the pilot reduced engine power from 2,700 rpm to 2,500 rpm. Immediately, a loud bang was heard, and the airplane began to shudder and shake violently. The pilot reduced power further and returned for an uneventful landing.
Post-Incident Examination
Inspection of the airplane revealed that one blade of the three-bladed McCauley propeller was in negative pitch and rotated freely in the hub. Further examination showed that the pitch change actuating pin for the No. 3 propeller blade had separated, with a threaded portion of the pin remaining in the hub.
Metallurgical Analysis
On May 10, 2004, the affected propeller blade and associated parts were examined at the NTSB Metallurgical Laboratory in Washington, DC. The examination determined that the ferrule hole, into which the fractured pitch change actuator pin had been inserted, had threads that did not extend into the hole as specified by the propeller manufacturer. The threads extended only about half the distance from the bottom of the hole. Fatigue cracking was found in the threads of the pin, and the fatigue crack had progressed approximately 95 percent of the way through the pin before it separated due to overstress.
Maintenance History
Records indicated that the propeller had last been overhauled on January 30, 1997, by a maintenance facility in Johnson City, New York. This overhaul occurred about 678 flight hours prior to the incident.