What happened
Two separate serious incidents involving a Bell 206L-3, registration JA6114, occurred during flight testing in Japan. The first incident took place on July 15, 2004, near Kinugawa field in Tochigi Prefecture. While the pilot was performing an autorotation test, the engine suddenly stopped at an altitude of approximately 2,800 feet. The crew noticed a drop in turbine outlet temperature, and despite attempts to increase power, the engine failed to respond, forcing an emergency landing at the Kinugawa field. No injuries or aircraft damage were reported.
The second incident occurred on September 20, 2004, during a follow-up test flight intended to investigate the first event. While performing repeated autorotation tests over the Utsunomiya aerodrome runway, the engine experienced a similar sudden stoppage at about 1,000 feet. The pilot reported a flameout and executed an emergency landing on the aerodrome runway. Again, there were no injuries and no damage to the aircraft.
The investigation
The investigation, conducted by the Aircraft and Railway Accidents Investigation Commission, involved extensive testing of the engine and its fuel control components. Investigators performed bench tests on the engine, fuel control accessories, and the Gas Producer Fuel Control (GPFC) unit. Representatives from Canada and the United as well as the United States participated in the technical review.
To determine if the fuel control unit was at fault, the GPFC was replaced with a unit from a different source for a test flight. However, the flameout recurred during this flight, suggesting the issue was not a defect in that specific component. Extensive teardown inspections of the fuel pump, fuel nozzles, and combustion liners were also conducted, but no mechanical abnormalities were found.
Findings
Technical analysis revealed that in both instances, the engine stoppage was characterized by a rapid decrease in N1, N2, and turbine outlet temperature indications. The investigators concluded that the engine stoppages were caused by insufficient fuel being supplied to the engine during the autorotation maneuvers. While the investigation established that the fuel supply was inadequate, the specific reason why the necessary amount of fuel was not reaching the engine could not be determined.