Accident Overview
On November 2, 2022, at approximately 1948 central daylight time, a Bell 206B helicopter, registration N61KH, sustained substantial damage when it struck the ground near Greenville, Illinois. The helicopter was operating as a Title 14 Code of Federal Regulations Part 91 business flight. The pilot and one passenger sustained minor injuries; one passenger was not injured.
Accident Sequence
The helicopter had completed aerial application work under Part 137 near Rushville, Illinois earlier that day. Two loaders employed by the operator were on board. The flight was returning to Mount Vernon Airport (MVN) in Mount Vernon, Illinois, but stopped at Greenville Airport (GRE) to refuel. After refueling, the helicopter departed for MVN. During the initial climb, the pilot reported being unable to maintain main rotor rpm. He initiated a 180-degree autorotation to land back at the airport. The helicopter landed hard on grass near a hangar. The right skid collapsed, the tail boom separated, and the helicopter came to rest upright. The three occupants egressed without further incident. During the landing, fuel system damage caused a large fuel leak on the grass. Substantial damage occurred to the fuselage, tail boom, and tail rotor system.
Postaccident Examination
Examination of the airframe confirmed flight control continuity and cockpit-to-engine control continuity. The engine fuel nozzle inlet screen was found to be contaminated and partially blocked with debris. The fuel nozzle assembly had been inspected 25.9 flight hours before the accident as part of the required 150-hour inspection interval.
Maintenance Findings
The operator's Director of Maintenance (DOM), an airframe and powerplant mechanic with inspection authorization, was interviewed. He reported that he had cleaned the fuel nozzle but not the fuel nozzle inlet screen. When asked specifically about cleaning the inlet screen, the DOM stated that he "has not had a chance to get to that yet" and had never seen the screen before. A review of engine maintenance records showed the DOM had signed his initials indicating that the fuel nozzle assembly was inspected and cleaned at the required interval.
Fuel Testing
Due to the smooth, coated appearance of the debris on the screen and variable fuel color during examination, samples were tested for "apple jelly" or diesel exhaust fluid (DEF) contamination. The results found no such contamination.
Manual and Industry Information
The Rolls-Royce M250-C20 Series Operation and Maintenance Manual requires removal, inspection, and cleaning of the fuel nozzle assembly at 150-hour intervals, with a note that more frequent cleaning may be necessary based on operating conditions. The National Agricultural Aviation Association published a Fly Safe Message on May 1, 2023, titled "Avoid Engine Fuel System Contamination," which discusses fuel contamination in turbine-powered agricultural aircraft. It notes that contamination could result in partial or complete loss of engine power and that turbine engine components such as the fuel control unit and fuel nozzles can be adversely affected. The message recommends considering increased inspection frequency for turbine fuel system components in agricultural operations and following maintenance manual procedures.