While cruising at FL140, the pilot in command of the Brasilia
noticed a torque drop from 84% to 74% on the right engine. Assuming
that the power lever friction was loose and had allowed the engine
to creep back from the selected power setting, he readjusted the
lever position back to 84% and reset the friction. Approximately 10
seconds later the non-flying pilot remarked that the right engine
torque had dropped to 76%. As the pilot in command again went to
readjust the torque, the engine lost power. The aircraft then yawed
significantly.
The crew then shut down the engine and feathered the propeller.
As the aircraft was flying into a 40 to 50 knot headwind, the crew
decided to return to the departure airfield.
Company maintenance investigation found that the
hydro-mechanical unit (HMU) on the right engine had malfunctioned.
The HMU was removed and forwarded to the vendor for further
investigation. A serviceable HMU was fitted to the right engine and
the aircraft returned to service.