I absolutely concur with Globalstream's post #19, EXCEPT for some of what he advises at point 2. Because it is PNG, you could be placing yourself at risk by making any threats or delivering ultimatums. Also, although the law may require a company to remain financially solvent to hold an AOC, much of what passes for law in PNG is never enforced.
Better to send a polite email to the CEO asking for a specific date when he will pay you any arrears. If it is ignored (quite probable) or if any promise he makes proves to be false, step on an aeroplane and leave the country. Preferably when you are due out on leave and with a ticket that they paid for, but not if that means staying beyond the 30 days (or more?) that you have already worked for free. If that means parking their aircraft in POM on a layover stop, so be it. You would not be the first and you won't be the last.
In the case of such a clear breach of employment contract by the employer no resignation notice period applies. In a 'safe' country, having given the ultimatum of requiring salary in arrears to be paid, you could give a day's notice in writing and despite this, would have a fair chance of legal action to recover monies owing. In the case of PNG - and only when safely out of the country - you could send a follow-up resignation letter stating the reasons why you are not returning. Not that it will do any good other than give you some small satisfaction.
These guys are not going to give you a job reference anyway, so don't worry about upsetting them.
You are unlikely to be successful with legal action. Save the lawyers' fees and spend the money on a nice holiday instead.