Beech V35 N2059W incident near Mount Vernon, Ohio

Probable cause

The loosening of the flyweight due to the installation of an improperly hardened flyweight carrier, which resulted in the overspeed of the propeller and engine and the subsequent in-flight separation of the propeller.

NTSB analysis

The commercial pilot was conducting a personal cross-country flight. The pilot reported that, during cruise flight, he heard a sudden high-pitched whine emanating from the engine and saw that the tachometer was reading about 3,500 rpm. He was unable to bring the engine rpm within limits and diverted the airplane to the nearest airport. During the approach, he heard a "pop," and oil covered the windscreen. After landing, he found that the propeller was missing from the airplane.

A postaccident examination of the engine found metal particulates in the propeller governor. An examination of the governor revealed that a flyweight was not secured and that the flyweight carrier did not meet the factory hardness specifications. The flyweight's retaining pin hole was excessively worn, which had allowed the pin to back out and the flyweight to become loose and resulted in the overspeed of the propeller and engine and the subsequent in-flight separation of the propeller.

A review of factory records did not find any similar incidents or a history of a batch of materials not meeting factory specifications. A review of the maintenance records revealed that an overhauled propeller governor had been installed on the airplane about 16 years before the accident; however, it could not be determined if the improper flyweight carrier was installed in the propeller governor during the overhaul or at some time after the overhaul.

Text from the NTSB. Open the NTSB docket for CEN15IA365 for the full record.