Accident Summary
On April 23, 2020, about 1600 central daylight time, a Pilatus PC-12 airplane, registration N477SS, was substantially damaged when it was involved in an accident near Mesquite, Texas. The pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 positioning flight.
Pilot Actions
Shortly after takeoff, the pilot reported to the air traffic controller that he was losing engine power. He decided to divert to Rockwall Municipal Airport and accepted vectors to that airport. Subsequently, the pilot reported that the loss of engine power had stabilized and he wanted to return to Dallas-Fort Worth International Airport. A few moments later, he reported losing engine power again and needed to go back to Rockwall. The controller informed the pilot that Mesquite Airport (HQZ) was at his 11 o'clock position and about 3 miles away. The pilot then elected to divert to HQZ.
The pilot reported that the airplane was at 4,500 feet and too close to the airport, so he planned a 360° turn to set up for a left base at HQZ. During the turn outbound, the engine lost power and the pilot was not able to reach the runway. The airplane impacted terrain in a muddy field short of the airport. The wings separated in the accident, and a small post-crash fire ensued.
Maintenance History
A review of the airplane's maintenance records revealed that maintenance was performed on the day of the accident flight to correct a reported difficulty moving the Power Control Lever (PCL) into reverse position. 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 was performed with no anomalies noted. Severe binding was observed on the beta control cable (propeller reversing cable). The cable assembly was removed from the engine, cleaned, reinstalled, and rigged in accordance with the Pilatus Aircraft Maintenance Manual and Pratt & Whitney Engine Maintenance Manual.
In a post-accident interview, the pilot reported that several days before the accident, on previous flights, the PCL was difficult to move from the idle detent into reverse (beta mode). He brought the issue to the mechanics and other pilots, who reported the discrepancy. The maintenance records reflected that there were no issues with the PCL cable; the binding was caused by binding in the beta control cable assembly. The pilot stated that the accident flight was the first flight since maintenance work on the PCL, and that before departure, he cycled the propeller 3-4 times during taxi and the PCL operated “smoothly.”
Post-Accident Examination
The engine and propeller were separated from the airframe and shipped to a Pratt & Whitney Canada facility in Bridgeport, West Virginia, for detailed examination. A first-stage compressor blade had impact damage on the leading edge, and four blades had minor leading-edge damage. A borescope inspection of the centrifugal impeller revealed a small amount of dirt/debris accumulation, but the impeller vanes were all in good condition. The power turbine module was separated from the engine. The trailing edge of all compressor turbine blades were in good condition. The combustion liner was intact with no evidence of burn through or fuel nozzle streaking. The leading edge of the first-stage PT blades and trailing edge of the second-stage PT blades were unremarkable.
The beta control cable was found mis-rigged, and the propeller blades were found in the feathered position. The beta valve plunger was 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. A wire could be inserted through both the forward and aft beta control cable clevis inspection holes, which function 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.