Partial power loss involving a Piper PA-31T, VH-DXI, Point Cook, Victoria, on 12 March 1993

When the pilot attempted to reduce propeller RPM from 2000 to 1900 the right propeller wound down to between 1100 and 1200 and the right torque exceeded maximum limits. The pilot shut down the engine and feathered the propeller when he was unable to regain control. A successful single engine landing was carried out.

The right engine beta light wiring was found to be routed close to the engine exhaust stack. Radiant heat from the exhaust stack had melted the insulation and had allowed the wires to contact and create an electrical short circuit. This had activated the propeller lock valve which effectively caused the propeller to operate at fixed pitch.

It could not be determined whether the burned wiring installation was installed in accordance with the manufacturers original design. A modification has now been incorporated to introduce fire sleeved wiring and a heat deflector baffle.