Incident Sequence
The helicopter involved in the events experienced a fuel leak and performed an uneventful precautionary landing. The leaking fuel line was replaced in field maintenance, but the replacement did not include the manufacturer's required securing clamps.
Subsequently, a second fuel leak occurred, leading to another precautionary landing. The fuel line was again replaced without the required clamps.
A third fuel leak at the same replacement line was followed by a fire after the precautionary landing.
Investigation Findings
The National Transportation Safety Board (NTSB) supervised a manufacturer's engine examination. This examination revealed vibration in rotating components at levels 15 times the allowed limits, as well as a fatigue crack in the hot section of the engine. These vibrations and cracks had not been discovered during engine maintenance and inspections conducted by company contract maintenance personnel.
A metallurgical examination of the fuel lines from each event was performed. The examination revealed fatigue propagation on the fuel lines. Additionally, the fuel lines from the second and third events lacked clamp marks, indicating that the required securing clamps had not been installed.
Probable Cause
The lack of required securing clamps on replaced fuel lines, leading to fatigue propagation, and the failure of company contract maintenance personnel to detect excessive vibration and a fatigue crack during engine inspections.