This research commenced following receipt of correspondence suggesting that an increase in helicopter engine issues in northern Australia was potentially linked to a change to reduced lead content fuel in these areas. The Civil Aviation Safety Authority (CASA) advised the ATSB that, in December 2015, the colour and branding of fuel supplied to the northern region of Australia changed, from green Avgas 100/130 to blue Avgas 100LL (low lead). Although the maximum permissible lead content reduced with this change, CASA advised that the actual lead content of the supplied Avgas 100/130 fuel had already been below the maximum permitted by the Avgas 100LL standard prior to December 2015.
An analysis of safety occurrence records was conducted to identify if any significant changes to the number of reported engine failures or malfunctions had occurred following the introduction of Avgas 100LL. The analysis found that overall there had been no discernible increase in reported engine failures or malfunctions in northern Australia after the introduction of Avgas 100LL in December 2015. Specifically for helicopters with Lycoming piston engines, there was an increase in reported occurrences of engine failures or malfunctions since 2014, largely dominated by northern Australia. However, occurrence numbers are low so some year-to-year variation from chance alone is expected. Additionally, the increase did not align with the introduction of Avgas 100LL in December 2015.
Potential symptoms of the issues were reported as premature cylinder removals, and a high rate of exhaust valve and guide wear. The analysis found only one incident related to valve wear in northern Australia following the reported fuel change. However, the ATSB found a disproportionate number of engine failures or malfunctions in piston engine helicopters with unidentified failure mechanisms following the change to Avgas 100LL. Although it was not possible to eliminate the introduction of Avgas 100LL fuel as a potential factor in these engine failures, conclusive findings could not be drawn based on the available evidence.
In response to the concerns raised, the Northern Fuels Stakeholder Investigation Group was formed to investigate this issue further. Additionally, CASA has introduced airworthiness bulletin (AWB) 85-024 Issue 1, to raise awareness of an increasing incidence of premature exhaust valve and valve guide wear.