Accident Overview
Approximately five minutes after departing on a Part 135 air taxi cross-country flight, the helicopter experienced a loss of engine power while in cruise flight. The commercial pilot executed a forced landing at an off-airport site characterized by tall vegetation and soft terrain. The helicopter came to rest upright, and the two rear-seat passengers egressed unassisted. Moments later, the helicopter was consumed by fire.
Wreckage and Environmental Conditions
The wreckage path was oriented on a magnetic heading of 225 degrees. Wind at the time was reported from 020 degrees at 12 knots.
Engine Examination
On-site examination revealed that the fuel line to fuel nozzle "B" nut could be turned by hand and was not secured with lock wire, as required. All other fittings and nuts on the engine were found to be secure. A subsequent teardown examination of the engine found no preimpact anomalies.
Maintenance History
Review of maintenance records showed that a 50-hour fuel nozzle inspection had been performed the evening prior to the accident flight. This inspection involved removal, disassembly, cleaning, inspection, reassembly, and reinstallation of the fuel nozzle. An interview with maintenance personnel confirmed that the fuel nozzle installation procedures specified in the engine manufacturer's maintenance manual had not been followed.
Operational Testing
Investigators conducted operational tests on an engine of the same make and model to determine the effect of a loose fuel nozzle "B" nut. The tests demonstrated that a loose nut could cause a substantial loss of power, potentially resulting in a flameout. Further testing indicated that conditions would have been conducive to an in-flight fire.
Fire Origin
Investigators could not determine whether the fire originated in flight or during the ground impact.
Conclusion
The loss of engine power was attributed to the loose fuel nozzle "B" nut, which lacked lock wire due to maintenance personnel not following the manufacturer's procedures. The subsequent fire consumed the helicopter.