Grumman G164 N3630D accident near Sutter, California

Probable cause

A loss of engine power due to the in-flight separation of the fuel control unit interconnect rod for reasons that could not be determined due to lack of available evidence.

NTSB analysis

Shortly after the pilot transitioned from climb to cruise flight, the engine power suddenly decreased to idle power without any control inputs from the pilot. He attempted to cycle the throttle to restore power but was unsuccessful. The pilot jettisoned the fertilizer payload he was carrying and initiated a forced landing to a nearby dirt road. The airplane impacted the ground short of the road and collided with trees before it came to rest, substantially damaging the wings and fuselage. The engine continued to run at idle power after the airplane came to rest.

Examination of the airplane found that an interconnect linkage between the fuel control unit (FCU) and propeller governor had separated from its mount and the bolt, nut, spacer and cotter pin normally used to secure the FCU interconnect rod to the FCU actuating lever were missing. Additionally, the cam designed to adjust the FCU and propeller governor conditions simultaneously through cockpit control inputs had fractured. This fracture was the result of overstress and likely occurred after the interconnect linkage separated.

Based on the design of the FCU, it is likely that the loss of power occurred when the FCU interconnect linkage disconnected in flight, which caused the FCU to revert to its idle power condition. The engine examination revealed no further anomalies, and the pilot reported that the engine continued to function on idle power after the airplane came to rest. As maintenance records indicated that the FCU intermediate linkage had recently been removed, it is likely that maintenance personnel disconnected the interconnect rod for easier access to the FCU. However, as the securing hardware was not recovered, the actual circumstances that led to the separation of the bolt, nut, and washer from the FCU could not be determined.

Text from the NTSB. Open the NTSB docket for WPR19LA137 for the full record.