Oil Sheen on Windshield Precedes Propeller Detachment During Approach (N73100)

Incident Summary

An airline transport pilot reported that approximately 10 minutes after departure, while the aircraft was in level cruise flight, a light sheen of oil began to form on the windshield. The pilot elected to return to the departure airport. As the aircraft neared the airport, within two miles, difficulty seeing through the windshield due to heavy oil accumulation was noted. While on approach, the propeller RPM increased for about 20 seconds, after which the propeller detached from the engine. The pilot was able to glide the airplane to the runway and land without further incident.

Investigation Findings

A postincident investigation revealed that the engine had been rebuilt/zero-timed by Teledyne Continental Motors. The engine had accumulated 9.0 hours of operation and had been installed 3 days before the incident. A Safety Board metallurgist examined the fractured crankshaft flange. Initial visual examination showed that about one-half of the fracture was on a flat plane and contained crack arrest positions, features indicative of fatigue cracking. The metallurgist added that the primary fatigue initiation appeared to be from a very large number of individual initiation sites in the center of the fatigue region.