I've included it being paid down.
Indexation is applied on the balance on 1 June each year. Then the tax return is done and it's determined if you have had not enough or.too much deducted from your pay, in which case you either have to stump up more or get a refund just like any tax bill. Then the required amount is taken off the loan balance. That money being deducted from wages is going somewhere else until the tax office transfer it across to the debt once a year. It's not paying down the loan throughout the year.
So the only way to get it down quicker is to make a voluntary payment before 1 June.
Study and training loan indexation rates | Australian Taxation Office (ato.gov.au)
I made a stuff up on my formula in the spreadsheet and the balance, based on 7% indexation and the repayment schedule, is $193622 with $17816 in indexation costs at the end of year 13.
At 2.5% the balance after 13 years is $93219 and the indexation costs $48369. That's still a long way off being debt free. So with the indexation being what it is, you would be better off refinancing your student debt with a bank loan and paying off a big chunk in the next week.
The good news is that when you die it gets wiped and your deceased estate doesn't have to pay it back. The taxpayers have to see it getting written off.
I'm presuming you spoke to a qualified financial advisor (not a flying school salesman) when you agreed to this massive financial commitment? They have to abide by some very strict codes of ethics so you may have some recourse there. If you just bought the package from a glossy brochure then it is a case of caveat emptor.