There have been quite a few queries regarding the tax arrangements for contact pilots.
Very briefly my understanding of the situation is that under self deeming the tax office may conduct an audit on you personally at any time to check the accuracy of your accounts. This audit is conducted with reference to your particular set of circumstances and is not necessarily formula driven. In other words just because you self deem yourself as non resident for tax purposes on the hearsay of others does not necessarily make it so.
Some things to note before declaring yourself non resident for tax purposes are,
1. Your overall situation will be taken into account. Does your family reside in Australia? Do you maintain a house (residence) in Australia? Do you maintain bank accounts, drivers licences etc?
2. Do you intend to return to Australia? Do you maintain a superannuation account? If your contract is for a fixed period with no clause for renewal then you may be considered as only temporarily non resident and liable for tax. Where is your salary deposited? Is there a reciprocal tax agreement with Japan?
3. Length of time outside the country by itself is irrelevant for ascertaining non residency. It is only a guide to tax liability after deeming for non residency, ie. just because you may spend 183 days outside the country doesn't make you non resident.
4. Finally just because you deem yourself non resident doesn't mean the tax department agrees with you. If you do this and then return to the country say in one or three years and the tax department does an audit you may well find yourself with a tax bill and penalties.