Grumman G164 accident near Sedgwick, Arkansas, June 20, 2021

The NTSB's narrative final · quoted from the NTSB record

The pilot was conducting an agricultural flight when the airplane had a sudden total loss of engine power. The pilot stated that the sound of the engine went from normal to silent, with no indication of an engine issue before the loss of engine power. The airplane impacted a levee and nosed over in a flooded rice field during the forced landing. The airplane’s empennage, aft fuselage, and engine mounts were substantially damaged during the forced landing. A postaccident engine examination and disassembly revealed the torque sensor assembly front spur gear was disengaged from the splined shouldered shaft on which it was installed. Additionally, the self-locking nut that secured the front spur gear to the shaft had backed off which allowed the front spur gear to disengage from the shaft. The examination and testing were unable to determine if the front spur gear self-locking nut was improperly torqued at installation or if it became loose during operation due a loss of retention. However, had the self-locking nut not been seated properly at installation, the disengagement of the front spur gear would likely have occurred well before the accident (2,541.5 hours since the overhauled torque sensor was installed on the engine). Additionally, no anomalies were found with the self-locking nut to suggest why it would have lost retention during operation. The engine-driven fuel pump and fuel control unit (FCU) are driven through a series of gears in the accessory gearbox, including the front spur gear, and any failure in the gear train that drives the fuel pump and FCU would prevent the fuel pump from delivering fuel to the FCU to sustain engine operation, resulting in an uncommanded engine shutdown.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.