If you join as a cadet you’ll be into a service company which means that much of your living expenses can be deducted against income, so when you do start earning you’ll be paying little or no tax for some time to come, but be very careful to document everything that you spend and get receipts for everything. How long this will last going forward will likely depend on the country that you’ll be based in. In many countries this type of service company will not pass the test of false self employment, the real irony is that the revenue go after you not the employer, yet it is the employer who gets the real saving through not having to pay NI (national insurance contributions) which unlike the employee NI have no upper limit and are levied at around 13.2% in the UK, put into perspective that means a pilot earning a £100k over any period in a service company is allowing the true employer (if proved) to evade/avoid £13200 in NI contributions.
There is a similar example in the UK courts this week involving a BBC TV presenter who had a service company claiming she was self employed but the courts found in favour of HMRC that in reality she was employed by the BBC and they (HMRC) are chasing her for £400K in taxes, interest and penalties
Seek professional advice before you sign up to a limited company scheme as a service provider and secondly ask if you have any choice in the matter, ie is direct employment an option to self employed, if you are told it must be a self employed service provider then you have your answer, you aren’t really self employed because the ‘true’ employer is dictating the terms of your contract.......
Of course there are an increasing number of airlines playing this game to a greater or less degree, if you join Norwegian you wont be employed by them but by OSM who provide pilot services to the airline, the difference is that you are 100% an employee of OSM and pay tax and and NI the same as you would if you were employed by Norwegian directly, for most that means you can sleep at night not worrying about a dawn raid by the tax authorities