What happened
A pilot and two passengers departed on a local area sightseeing flight. During cruise flight at approximately 4,000 feet, the engine began to vibrate and subsequently lost all power. Oil spray was deposited onto the windshield during the event. The pilot executed an emergency landing on a sand bar. All 3 occupants were not injured.
Following the landing, it was discovered that the entire propeller, the propeller flange, and the outboard end of the engine crankshaft had detached from the engine.
The investigation
An examination of the engine revealed evidence of fatigue cracking. This cracking originated from a corrosion pit located on the inner diameter surface of the crankshaft bore. Investigators also found numerous other corrosion pits adjacent to the site of the fracture origin.
The engine manufacturer confirmed the unit was built and shipped from the factory on April 13, 1981. The engine was subject to a mandatory service bulletin (S/B) dated October 18, 1994, which required an inspection of the crankshaft's inside bore for corrosion. This S/B mandated that an initial inspection be performed within 200 hours of operation or one year from the date of the bulletin. While the operator's company manual required the Director of Maintenance to ensure compliance with all mandatory manufacturer service bulletins, no record of compliance with this specific S/B was found in the engine maintenance records.