An ATSB report released today compares the rate of engine failures in light general aviation and recreational aircraft, focusing specifically on Jabiru engines.
Aircraft powered by Jabiru engines have been on limited operations since December 2014 over what the Civil Aviation Safety Authority (CASA) deemed a "high and increasing" rate of failures.
The report covers all engine failures in aircraft with a maximum take-off weight of 800 kg or less that occured between 2009 and 2014, and indicated that 40.4% – or 130 out of 322 – involved Jabiru engines.
Although the report covers all engine manufacturers, it focuses specifically on four that account for 94% of the failures over the six-year period: Jabiru, Rotax (27% - 87 failures), Lycoming (18% - 58 failures) and Teledyne Continental (8.7% - 28 failures).
According to the ATSB, no single component accounted for more than two incidents in the report period for Lycoming, Rotax and Continental, whereas 47% of Jabiru engine failures were attributed to the 3/8" through-bolts fracturing.
There were also 13 reported fractures in Jabiru engine valves.
The report notes that Jabiru Aircraft released two service bulletins to deal with the through-bolts, the second of which was an increase in diameter from 3/8" to 7/16", which required the engine to be sent back to Bundaberg.
In-house studies targeted the solid lifters as a root cause of the valve issues, prompting a change to hydraulic lifters.
Jabiru responded to the ATSB in February 2015, stating that "Production records show that 272 production engines have been released in to service with the 7/16" diameter through bolts. There have been no reported through bolt failures with these engines. [However] failures continued to occur in engines that are in service with the hydraulic lifters and 3/8" diameter bolts."
That performance seems to have not impressed the ATSB, which remarks in the report, "the lack of reported failures in 7/16 inch through-bolts may be related to the small proportion of the fleet that have thicker through-bolts and that most of these engines have relatively low time-in-service."
The ATSB has recommended that Jabiru takes further safety action to encourage all owners of Jabiru-engined aeroplanes that have not adopted the 7/16" through-bolts, or any alternative to the 3/8" parts, do so immediately, and that CASA continues to monitor the failure rate until they are satisfied of the engine's reliability.