CEN23LA025

The pilot of the aerial application helicopter completed operations for the day and stopped to refuel on the way back to the operator’s facility. After refueling and during the initial climb, the pilot reported that he was unable to maintain main rotor rpm. The pilot initiated a 180° autorotation and landed hard on a grass area near a hangar. During the landing, the right-side skid collapsed, the tail boom separated, and the helicopter came to rest upright. The helicopter sustained substantial damage to the fuselage, the tail boom, and the tail rotor system. Examination of the engine revealed that the fuel nozzle inlet screen was contaminated and partially blocked with a buildup of debris. The fuel nozzle assembly had been inspected, as part of the required 150-hour inspection interval, 25.9 hours before the accident. The director of maintenance (DOM) for the operator was interviewed for additional details on how the inspection had been performed. The DOM reported that he had cleaned the fuel nozzle, but not the fuel nozzle inlet screen. When asked specifically about the fuel nozzle inlet screen cleaning, the DOM reported that he, “has not had a chance to get to that yet.” A review of the engine maintenance records showed that the DOM had signed his initials indicating that the fuel nozzle assembly was inspected and cleaned at the required 150-hour inspection interval. The partially blocked fuel nozzle inlet screen with debris likely restricted fuel flow to the engine. The DOM’s failure to clean the entire fuel nozzle assembly, including the fuel nozzle inlet screen, likely resulted in a partial loss of engine power, an autorotation, and a hard landing. Based on the available evidence, it is likely the DOM did not clean the fuel nozzle inlet screen for undetermined reasons.

On November 2, 2022, about 1948 central daylight time, a Bell 206B helicopter, N61KH, sustained substantial damage when it was involved in an accident near Greenville, Illinois. The pilot and one passenger sustained minor injuries and one passenger sustained no injury. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 business flight. The helicopter, which had a normal and a restricted airworthiness certificate, had completed 14 CFR Part 137 aerial application work during the day near Rushville, Illinois. The two passengers onboard were loaders employed by the operator. The helicopter was returning to the operator’s facility at the Mount Vernon Airport (MVN), Mount Vernon, Illinois, and stopped at the Greenville Airport (GRE), Greenville, Illinois, to refuel. After being refueled, the helicopter departed for MVN. During the initial climb, the pilot reported he was unable to maintain main rotor rpm. The pilot initiated a 180° autorotation to land back to the airport. The helicopter landed hard on a grass area near a hangar, the right-side skid collapsed, the tail boom separated, and the helicopter came to rest upright. The three occupants were able to egress from the helicopter without further incident. During the landing, the fuel system was damaged, and a large fuel leak occurred on the grass. The helicopter sustained substantial damage to the fuselage, the tail boom, and the tail rotor system. Postaccident examination of the airframe confirmed flight control continuity, and cockpit to engine control continuity was confirmed. Examination of the engine revealed that the fuel nozzle inlet screen was contaminated and partially blocked with a buildup of debris. The fuel nozzle assembly had been inspected, as part of the required 150-hour inspection interval, 25.9 hours before the accident. The DOM for the operator, who is an airframe and powerplant mechanic with inspection authorization, was interviewed for additional details on how the inspection had been performed. The DOM reported that he had cleaned the fuel nozzle, but not the fuel nozzle inlet screen. When asked specifically about the fuel nozzle inlet screen cleaning, the DOM reported that he, “has not had a chance to get to that yet.” The DOM further reported that he had never seen the fuel nozzle inlet screen before. A review of the engine maintenance records showed that the DOM had signed his initials indicating that the fuel nozzle assembly was inspected and cleaned at the required 150-hour inspection interval. Because of the smooth coated appearance of the debris on the fuel nozzle inlet screen as well as the highly variable color of fuel observed during the airframe examination, it was decided to perform testing on the fuel samples to determine if the fuel may have been contaminated with “apple jelly” or diesel exhaust fluid (DEF). The results of the testing found no “apple jelly” or DEF contamination with the helicopter’s fuel system. The Rolls-RoyceM250-C20 Series Operation and Maintenance Manual states that the fuel nozzle assembly is required to be removed, inspected, and cleaned at 150-hour intervals. The manual further states: NOTE: Operators can find it necessary to inspect and clean the fuel nozzle more often depending on past experience or operating conditions. The National Agricultural Aviation Association published the Fly Safe Message, Avoid Engine Fuel System Contamination, on May 1, 2023. This document discusses fuel system contamination with turbine-powered aircraft used for aerial application work and states in part: Contamination of an engine fuel system could result in either a partial or a complete loss of engine power. Turbine engine components that could be adversely affected by contamination include the fuel control unit and the fuel nozzles. Due to the nature of aerial application work, operators should consider increasing the inspection frequency of turbine engine fuel system components. Always follow the maintenance manual when performing your work. Consult with the airframe, the engine, and the engine accessory manufacturers on any additional service documents regarding the topic of fuel contamination.