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.