CASA do not investigate accidents. ATSB do as CASA may be part of the problem.
CASA may indeed be part of the problem. But long gone are the days that ATSB properly investigated CASA. From this ATSB Report: https://www.atsb.gov.au/media/577843...7_final-v2.pdf with bolding added by me.
Some operations manual parts are ‘accepted’ by CASA, while some are ‘approved’ by CASA. The operations manual part C, the training and checking manual, which contained the incorrect procedure for simulating an engine failure in a turboprop aircraft (see the section titled Engine failure simulation), was an example of a part that must be approved by CASA.
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Despite the operator’s procedure being approved by the Civil Aviation Safety Authority (CASA), reducing the power to flight idle on a turboprop aircraft is not representative of the drag associated with a real engine failure as it does not take account of the beneficial effect of auto-feather/negative torque sensing systems. Consequently, had flight idle been selected it would have created significantly more drag on the ‘failed’ engine, making it more difficult to control the aircraft and achieve the expected OEI performance. While the operator’s procedure only required use of this power setting during the initial ‘phase one’ checks (which would be expected to be completed in less than 30 seconds), it has been a contributing factor to previous asymmetric loss of control accidents (for example AO-2010-019 in the section titled Related occurrences).
The ATSB sought information from CASA regarding the circumstances under which the incorrect procedure was approved for use by the operator. Despite this request, no information was provided by CASA. Consequently, the ATSB was unable to determine whether the approval of incorrect information was an isolated human error or symptomatic of a systemic deficiency with the approval process.