It is not decided yet, only a proposal, but it does sound severe: only single-occupant flights, thus no more training flights, not over cities, not over crowds, &c.
The 4-cylinder has a rather poor reputation; without having really sought it out, I have often wondered if the quality of build/components is sufficiently stable. But of the 6-cylinder I hear nothing but good, there’s a couple at my homefield. They do take a fair deal of maintenance though, for example adjusting the valves every 50 hours or even more frequently.
Does Australia have a real experimental airworthiness category, or A.D. process for certified aircraft? If I were being (potentially) affected by this, I would want as step one to understand the explicit legal basis and limits for the proposed action. Why would the operating limits for an already Experimental aircraft require further limitation, and what is the authority of the CAA to revise the operating limits of an existing Experimental aircraft because its engine was originally produced by a given manufacturer?
It would effect more microlights than experimental aircraft
Perhaps (and hopefully!) meaning “affect” rather than “effect” ?
But still I am confused: 120 hp is quite a lot on the typical 450 kg microlight. Even high profile microlights like the VL3 can make do very well with a 100 HP 912ULS. I am unsure about the typical application of this 120 HP 6-cylinder Jabiru, it must depend very much on local regulations, but it seems to me more of a low-end alternative to an O320 than as a high-end alternative for a 912(S). Which would make the proposed change, if approved and if approved internationally, more relevant to experimentals than to microlights.