John, I'd suggest that one of the the reasons that CASA didn't take the AD route is that there has been little of no forensic investigation into the root cause(s) of engine failures in RAA aircraft either Jabiru or other makes. I'll insert the caveat here that CAMit has been conducting for some considerable time, exhaustive investigations into the root causes of jabiru failures and developing modification to address those causes they have identified. I do not include them in my criticism above .
I may well be doing RAA's techies a grave disservice by suggesting that their analysis of engine failure goes no deeper than the discovery that an engine had dropped a valve or broken a through bolt or shed a prop etc. Before people rise up from their beds shouting (again) "that's not the RAA's job" let me say I agree, in part. But if the aircraft was GA reg, the regulator would want to know what caused the valve to drop, what caused the through bolt to break etc. That way it could fullfil its role as safety regulator by issuing an AD to either inspect i.e "look for these warning signs" and/or fix the following identified faults. To support my assertion, I cannot recall any GA incident investigated and reported in the crash comic where the conclusion was that, to paraphrase: "the engine stopped and the plane crashed" It is my opinion that the RAA, as delegated sub-regulator - if you like- should be bringing pressure to bear on the engine manufacturers to conduct those forensic in depth investigations or asking big brother (CASA) to apply that pressure. Or else we should be seeking funding from government to allow RAA to develop those skills and conduct those investigations.
CASA couldn't/didn't issue and AD because they didn't/don't know what the problem(s) are. So they felt, for whatever reasons (and we don't want to re-start that bushfire on here. That's now history and unchangeable) that they had to take some form of action.
In the current case CASA seems to have had a bob each way shouting "We don't believe Jabirus have been doing as well as we think they should compared to...... um, er, AND we don't know what the problem is but we wish someone would tell us what it is, AND we think it is so serious thatis causes such immediate danger to someone (not entirely sure who, but we'll work on that one) that we're going to stop people flying with these engines unless they sign a bit of paper saying they're ok with it. AND you , or someone else , had better fix whatever it that's causing whatever it is that's worrying us AND then tell us so we can see if we agree and save face".
(Note to TP: I don't really think that's exactly what they said. I was paraphrasing and taking just a little bit of a literary license there)
Note to FT: None of what I've said above can or should be construed as me saying that CASA has acted illegally.