A fractured rigid fuel injector line from a Textron Lycoming IO540-C4B5 reciprocating piston engine was received by the Australian Transport Safety Bureau from the Civil Aviation Safety Authority (CASA), with a request to determine the mechanism of failure and the likely contributing factors. It was reported that the line had fractured during engine operation, spraying pressurised aviation gasoline into the engine compartment. The released gasoline did not catch fire.
The line had fractured in a single location, adjacent to the union at the injector (cylinder) end. Metallurgical examination determined that the fracture was the end result of high-cycle fatigue crack growth; cracking having initiated at one of a number of large corrosion pits on the lines external surface.
Analytical techniques identified the line as a UNS S30400 austenitic stainless steel; a material susceptible to pitting corrosion attack in the presence of chlorides. Chloride compounds were detected within the corrosion pits and were attributed to the salt-laden air associated with the coastal environment in which the engine/aircraft had been operating.
Safety action initiated as a result of the investigation findings included CASA revising airworthiness directives AD/LYC/90 and AD/CON/60; related to the maintenance of fuel injection supply lines on Textron Lycoming and Teledyne Continental aircraft engines respectively. Additionally, CASA published an information article in their periodical Flight Safety Australia, providing a summary of the event and investigation findings, together with advice and guidelines for maintenance personnel when installing and maintaining fuel injector lines.