What happened
On May 5, 2019, a Schweizer G-164B airplane, registration N3630D, was involved in an accident near Sutter, California, while operating as an aerial application flight. After completing 17 takeoffs earlier that day, the pilot departed a gravel runway carrying approximately 2,500 lbs of fertilizer and 45 gallons of Jet-A fuel.
Upon reaching a cruise altitude of approximately 500 feet above ground level, the engine speed suddenly reduced to idle power without any input from the pilot. The pilot attempted to restore power by advancing the throttle but was unsuccessful. To prepare for an emergency, the pilot jettisoned the fertilizer load and initiated a forced landing toward a nearby road. The aircraft struck a group of prune trees short of the road, resulting in substantial damage to the wings and fuselage. The pilot was not injured.
The investigation
An examination of the Pratt & Whitney PT6A-34AG turboprop engine by the NTSB revealed that the fuel control unit (FCU) interconnect rod had disconnected from the FCU actuating lever. The hardware normally used to secure this connection—including a bolt, nut, spacer, and cotter pin—was not recovered from the scene. Additionally, investigators found that the reversing cam had fractured due to overstress.
Maintenance records indicated that the engine had been installed in N3630D in 2014, with the FCU receiving repairs in May 2017 and March 2019. The operator's director of maintenance noted that a mechanic might have disconnected the interconnect rod during the most recent service to provide easier access to the FCU. Laboratory analysis of the reversing cam showed no evidence of fatigue, and the interconnect rod itself showed no signs of corrosion or mechanical damage.