The Civil Aviation Safety Authority (CASA) today issued an Airworthiness Bulletin (AWB) counseling aircraft owners about the use of unleaded avgas in aeroplane engines.
Unleaded avgas has only recently been approved for spark-ignition engines, and was developed after a campaign by the USA's Environmental Protection Agency to remove lead completely from 100LL avgas.
In September last year, US company GAMI received FAA approval via STC for its G100LL fuel to be used in spark-ignition engines, including popular models like the O-320 and O-360.
CASA's AWB 28-019 makes it clear that using unleaded avgas in aircraft engines is not as straightforward as simply substituting one fuel for another.
"CASA requires the pilot in command of an aircraft to ensure that the aircraft is not flown unless the fuel complies with the specification and grade required or approved for the purpose by CASA," the AWB states.
"The use of any fuel is dependent on that fuel being listed, by specification and grade, for a particular purpose in a manual or manuals promulgated by the aircraft and/or aircraft engine manufacturer.
"It matters not that UL avgas is simply identified as an approved fuel for certain aircraft or engines, if the fuel is not to the specification listed (e.g. ASTM D7547), then it cannot be used."
In its recommendations published in the AWB, CASA points out:
- before determining that unleaded avgas is suitable, users need to check all data sources for the aircraft and engine
- manufacturers identify a Minimum Octane Number (MON) for every engine that the fuel needs to meet or exceed
- engine manufacturers may require specific maintenance on an engine before unleaded avgas can be used
- if an engine is swapped between 100LL and unleaded avgas, maintenance may be needed before every time unleaded avgas is used
- oil additives with anti-scuffing agents may need to be used
- there may be no regular supply of unleaded avgas for some time, meaning aircraft owners need to consider the implications of swapping fuels depending on availability.
The GAMI fuel approved in September is not currently available in Australia in commercial quantities.
The full AWB can be downloaded from the CASA website.