Incident Sequence
Shortly after takeoff, the pilot informed the air traffic controller of a loss of engine power and decided to divert to a nearby airport, accepting headings toward it. The pilot then reported that the power loss had stabilized and requested to return to the departure airfield. Moments later, the pilot again reported losing engine power and needed to go back to the diversion airport. The controller advised of another airport at the pilot’s 11 o’clock position, about three miles away. The pilot chose to divert there.
At an altitude of 4,500 feet, the airplane was too close to the airport, so the pilot executed a 360° turn to set up for a left base approach. During the outbound portion of the turn, the engine lost all power, preventing the pilot from reaching the runway. The airplane impacted a field short of the airport. The wings separated from the airframe during the accident sequence, and a small postcrash fire developed.
Maintenance History
A review of the airplane’s maintenance records indicated that on the day of the accident, maintenance was performed to address reported difficulty moving the Power Control Lever (PCL) into reverse. The control cables were inspected from the pilot’s control quadrant to the engine, engine controls, and propeller governor. A static rigging check of the PCL showed no anomalies. However, severe binding was observed on the beta control cable (propeller reversing cable). The cable assembly was removed from the engine, cleaned, reinstalled, and rigged according to manufacturer guidance.
Post-Accident Examination
Examination of the engine and propeller assembly after the accident revealed the beta control cable was mis-rigged and the propeller blades were found in the feathered position. The beta valve plunger extended beyond the chamfer face of the propeller governor, consistent with a position that would shut off oil flow from the governor oil pump to the constant speed unit (CSU). A wire could be inserted through both the forward and aft beta control cable clevis inspection holes, which serve as check points for proper thread engagement. The forward beta control cable clevis adjustment nut was rotated full aft. The swaging ball end on the forward end of the beta control cable was not properly secured between the clevis rod end and the push-pull control terminal and was free to rotate within the assembly.
Analysis of Failure
Before takeoff, the beta valve was in an operational position allowing oil flow to the CSU, resulting in normal propeller control. Vibration from engine operation and beta valve return spring force most likely caused the improperly secured swaging ball to rotate (unthread) forward on the beta control cable. This lengthened the reversing cable assembly, allowing the beta valve to stroke forward and shut off oil flow to the propeller CSU. Without propeller servo oil flow to maintain control, the propeller faded to the high pitch/feather position due to normal leakage in the transfer bearing. The reported loss of power is consistent with a loss of thrust due to the beta control cable being mis-rigged during the most recent maintenance work.