Magnetos are subject to failure at random. The security of having two will be broken if both are overhauled at four yearly intervals instead of by inspection at regular maintenance. The chances of both having similar problems is now enhanced due to CAsA interference. Well done boys and girls.
The only thing to do is mandate every aircraft has three magnetos and in the case of Chieftans who share electrical outputs from each engine, they shall have four per engine.
This will come to be known as the sure to be sure to be sure to be sure "Australian" magneto regulation. Work is still proceeding at a glacial pace to include an electronic ignition module in each engine worth about $50 in the future.
The holdup is Legal Services Branch who are still working on the paragraph pertaining to who should read the regulation as they are unsure if it is an engineering matter or something pilots should be trusted with and what the final fitted price will be. Airservices have shown interest in this aspect marking a cost benefit analysis project for taxpayer funded installation from savings made from Navaid redundancy.
Affordable safety for all.