A new Safety Alert for Operators published by the FAA warns aircraft owners/operators about the potential for uncommanded feathering when certain propeller control units (PCUs) and adapters are improperly installed, repaired or overhauled. The basic PCU in question is widely used by UTC Aerospace (Hamilton Sundstrand/Hamilton Standard) in twin-engine aircraft.

The SAfO evolved from a July 25, 2013, inadvertent feathering event that occurred shortly after takeoff on a DHC-8-100 when a beta switch was closed and lit during takeoff when a beta condition did not exist. The switch remained closed and eventually led to a propeller over-torque that commanded the propeller to feather while the engine was producing high power. Examination of the PCU involved revealed that the beta-light assembly had been installed incorrectly, deforming the switch case.

Other propellers affected by the SAfO include those on various models of the ATR 42 and 72, Embraer Brasilia, Saab 340, Casa 235, BAe ATP and Canadair CL-215T and CL-415. Affected PCUs should be removed and replaced as soon as possible, beginning with twin-engine aircraft with affected PCUs installed on both engines.