What happened
The aircraft sustained damage following an emergency landing in a rural area approximately 31 miles northeast of Watertown, South Dakota. The incident occurred during the final cleanup swath run of the day's agricultural spraying operation. Prior to the accident flight, roughly 25 minutes before takeoff, the pilot landed to reload the chemical hopper.
During this stop, the aircraft owner asked if the pilot required additional fuel. The pilot declined the offer, stating that he had between 10 and 12 gallons remaining in the tanks. He considered this amount sufficient to complete the spraying operation for the day. Throughout the day, the pilot had made several landings specifically to refill the hopper rather than refuel.
Upon takeoff after these stops, the engine initially provided full power, registering 2775 RPM. However, after completing several swath runs, the pilot observed a reduction in performance, noting that the engine would only reach 2500 RPM during pull-ups. During the pull-up on the final cleanup run, the engine failed to respond when full throttle was applied. Power could not be restored, causing the aircraft to stall and fall to the ground.
At the time of the accident, recorded at 19:51 CDT, the temperature was 77 degrees Fahrenheit and the dew point was 64 degrees. Meteorological data indicated that these conditions were conducive to carburetor icing.
The investigation
Investigation into the mechanical state of the aircraft focused on the engine's performance degradation during the flight. The pilot reported that while the engine provided full power at takeoff, it progressively lost ability to maintain RPM during high-power phases like pull-ups. The final failure occurred when the engine did not respond to full throttle application.
Findings
The primary factors leading to the accident were fuel exhaustion and carburetor icing. The pilot's decision to forgo refueling, relying on a marginal fuel supply of 10 to 12 gallons, left insufficient reserves to complete the operation. Additionally, the atmospheric conditions at the time created a high probability for carburetor ice formation, which likely contributed to the loss of engine power.
Safety message
Pilots conducting agricultural operations should ensure adequate fuel reserves are available throughout the day. Refueling stops should be prioritized over hopper refills when fuel levels drop low. Furthermore, pilots must remain vigilant for signs of carburetor ice, especially in conditions with high humidity and moderate temperatures.