engine, as were the blades. In reconstructing the wreckage, the investigators discovered that the right propeller had separated during flight and severed the fuselage. During manufacture, propeller pistons, which control the pitch of the propellers, are coated through a process called nitriding, which hardens them and increases their resistance to surface wear. They are supposed to be inspected to ensure that the process is completed, but investigators could not determine why N73130's propeller was not nitrided and did not fail inspections. During the life of the engine, the piston had been slowly wearing away. During the flight, the piston finally failed, causing the propeller to speed beyond its limits. The stress caused the propeller to fail one to two seconds later. When the propeller failed, the blades were hurled through the cabin, severing control cables and compromising the plane's structural integrity. The investigators determined that the crash was caused solely by the propeller defect and subsequent failure. References External links A detailed explanation of the propeller failure Photo of N73130 Aviation accidents and incidents in the United States in 1967 1967 in Ohio Airliner accidents and incidents in Ohio Lake Central Airlines accidents and incidents Airliner accidents and incidents caused by in-flight structural failure Accidents and incidents involving the Convair CV-240 family Transportation in Wyandot County, Ohio March 1967 events in the United States