Accident Overview
On July 19, 2021, at approximately 1410 central daylight time, a Grumman G-164B agricultural airplane, registration N8422K, was substantially damaged in an accident near Amana, Iowa. The pilot, who was the sole occupant, was not injured. The airplane was being operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight.
Sequence of Events
The airplane operator reported that the engine lost power shortly after departure from runway 26 at the Amana Airport (C11). The accident takeoff was the sixth takeoff of the day, following engine start at about 0630. Prior to takeoff, the airplane was loaded with 420 gallons of fungicide and 110 gallons of fuel. The pretakeoff engine indications were normal. The airplane accelerated normally, lifted off at an airspeed of approximately 65 mph, and then accelerated in ground effect to about 78 mph when the engine lost power. The airplane subsequently settled into a cornfield approximately 300 ft from the end of the runway, nosed over, and came to rest inverted. The fuselage and wings sustained substantial damage.
Postaccident Examination
During a postaccident examination, all three propeller blades were found bent aft and opposite the direction of rotation. The blades were twisted toward low pitch, and chordwise/rotational scoring was visible predominantly on the cambered side of the blades. The propeller examination revealed no visible preimpact discrepancies that would have prevented normal propeller operation.
Engine Examination
The engine was a Honeywell model TPE331-6-252M turbo-propeller engine. It is a single-shaft engine with a two-stage centrifugal compressor, an annular combustion chamber, and a three-stage axial turbine that drives the compressor and the reduction/accessory gearbox. An attempted engine run at the manufacturer’s facility indicated low torque, suggestive of a discontinuity in the drive system. Subsequent disassembly confirmed that the aft end of the torsion shaft was found free and resting against the splined end of the main shaft. Further examination revealed burnt fibrous material throughout the engine. No pre-impact damage was found that would have precluded normal operation.
Propeller Governor and Fuel Control Unit Examination
The propeller governor and fuel control unit were tested at the manufacturer’s facility. Except for slight deviations attributed to possible field adjustments, both the governor and fuel control unit operated within the manufacturer’s specifications. No anomalies were detected that would have prevented normal operation.