What happened
While climbing at 16,000 feet, the pilot of a Cessna aircraft observed oil droplets forming on the windscreen. Following this observation, the pilot contacted air traffic control, declared an emergency, and initiated a standard rate, 180-degree turn to return to the airport.
As the turn was being completed, an audible bang and a physical shudder were felt by the pilot, after which the windscreen became covered in oil. The pilot noted a possible pitch-up motion during the event but immediately stabilized the aircraft at a best glide speed of 90 knots. Using GPS to retrace the ground track, the pilot returned to the airport, where the aircraft landed uneventfully.
The investigation
An examination of the aircraft revealed minor damage to the front of the cowling. Investigators found that the engine's crankshaft had fractured aft of the flange, and both the propeller and spinner were missing from the engine. Several months after the incident, the separated propeller assembly and crankshaft were recovered.
Detailed inspection of the engine determined that the crankshaft had fractured through at a point aft of the propeller flange. The fracture originated from a fatigue crack that began at the aft relief radius of the propeller flange.