Accident Overview
On June 1, 2022, about 1700 central daylight time, an Air Tractor AT-602 airplane, registration N5007R, sustained substantial damage during an accident near Allport, Arkansas. The pilot, who was the sole occupant, sustained minor injury. The airplane was operating as a Title 14 Code of Federal Regulations Part 137 aerial application flight.
Pilot Statement
The pilot reported that the accident occurred on his 35th flight of the day. The airplane had performed well throughout the day with no noted issues. Two flights prior, the airplane was refueled; at the time of the accident, each wing fuel tank was about half full of Jet A fuel. The hopper, with a capacity of 6,500 lb, was loaded with 3,600 lb of urea fertilizer. The pilot intended to fly to a rice field to apply fertilizer. Immediately after takeoff from a private airstrip, he heard a loud pop from the turboprop engine and observed flames from the left side of the airplane. He confirmed a loss of engine power, ensured flaps were down, and began scanning for a forced landing site. During the descent, he felt a slight recovery of power, but then the engine ceased producing power entirely. He retarded the throttle and landed on a flat field of grass, dirt, and mud. The airplane nosed over and came to rest inverted. The pilot egressed without further incident.
Examination Findings
Substantial damage occurred to the left wing, fuselage, and empennage. Airframe examination established flight control continuity. Fuel was present in the fuel lines from the fuel pump to the fuel selector, header tank, and forward to the airframe fuel filter. The airframe fuel filter assembly on the firewall was removed and found to contain foreign object debris (FOD) of unknown origin between the filter pleats and in the filter bowl. Engine examination revealed FOD contamination in the engine fuel filter and various fuel-wetted accessories. Bench testing of the fuel control unit, flow divider/dump valve, and fuel nozzles showed they performed within expected parameters. The engine exhibited rotational contact signatures on compressor turbine and power turbine components, consistent with producing power at impact, though the power output could not be determined. Propeller examination revealed no mechanical malfunctions; marks on the piston, cylinder, and blade damage indicated low blade angles with low or no power at impact. Chemical testing of FOD samples from the engine and airframe indicated a composition consistent with an unknown fertilizer-type material.
Maintenance Records
A review of the airplane’s maintenance records showed that the airframe fuel filter was last inspected and cleaned on August 12, 2021, at 1,285.5 hours Hobbs time. The accident occurred at 1,429.5 hours Hobbs time. The Air Tractor AT-602 Maintenance Manual required inspection and cleaning of the airframe fuel filter every 100 hours. Engine maintenance performed on May 23, 2022, included a successful test run, but the associated logbook entry did not show any fuel system tasks. The maintenance manual included a caution: if contamination is found in either fuel filter, investigate the cause and rectify the problem. The operator could not provide fuel or chemical loading records and reported that the other Air Tractor AT-602 they operated had no mechanical issues, with both airplanes receiving fuel from the same truck.
Related Publications
Air Tractor Service Letter #148, titled "Fuel Contamination," was published June 24, 1996. It emphasizes the importance of maintaining a clean fuel system, acquiring clean fuel, and maintaining clean storage facilities. The National Agricultural Aviation Association published a Fly Safe Message on May 1, 2023, titled "Avoid Engine Fuel System Contamination." This document notes that aerial application aircraft are subject to contamination from various sources, including unclean storage, washing, loading, refueling, maintenance, and environmental factors. It states that contamination can cause partial or complete engine power loss and that turbine engine components such as fuel control units and nozzles can be adversely affected. The message advises operators to consider increasing inspection frequency of turbine engine fuel system components and to follow maintenance manual procedures.