Just an additional note.
Because of a high degree of commonality of the propeller control mechanisms, a Propeller Control Unit failure leading to an overspeed often also meant the inability to feather the propeller.
Later propellers, such as the RR Dart 528/532 had "High Speed" intermediate stops, much limiting the degree of "fining" of the propeller, and maintaining the aircraft in a controllable situation, even if unable to feather the propeller (The earlier RR Darts did not have this feature).
Regards,
Old Smokey