Sunfish.
Many older aircraft have been lost on firebombing activities with metal fatigue later being found as the cause. The names Electra and C-130 come to mind.
Just exactly what do you think the role of regulators/investigators is after an accident where there's a possibility of a systemic fault that just might affect other aircraft? Do nothing? It only took a little while for the all-clear to be given for the helicopter fleet of similar aircraft to fly. A small and prudent precaution I would have thought.
Bash CASA and ATSB when they deserve it by all means but please leave things like post-accident precautions to the professionals.