What happened
The aircraft experienced a partial power loss while conducting an aerial application pass. The pilot had completed only one spraying run since refueling with a full tank of fuel and 140 gallons of chemical agent. As the engine continued to lose power, the aircraft lost altitude and was forced to make an emergency landing in the field it was treating. During the descent, the pilot attempted to dump the chemical load prior to touchdown; however, the gate valve was incorrectly set and failed to open, preventing the dump.
The impact caused the landing gear to tear away from the airframe. Despite this damage, the aircraft bounced upon contact with the ground but remained upright. No injuries were reported.
The investigation
Following the accident, the engine was removed and subjected to testing. Examination of the fuel system revealed significant contamination. Technicians found rust particles, sand grains, and fine aluminum fragments within the fuel lines. During the diagnostic process, the number six fuel nozzle became plugged sufficiently to cause a loss of power on that specific cylinder.
Findings
The primary factor contributing to this incident was mechanical failure due to foreign object damage in the fuel system. The presence of rust, sand, and aluminum debris obstructed fuel flow and engine performance. Additionally, the incorrect setting of the chemical dump gate prevented the pilot from jettisoning the load during the emergency descent.
Safety message
Regular inspection of fuel systems for contamination is critical for agricultural aircraft operators. Ensuring that all valves and gates are correctly set before flight operations can mitigate risks during emergency situations.