The German tax system is extremely complicated and subject to permanent "fine-tuning" as seems fit by the government. Even most Germans are using an accountant (Steuerberater) for there returns. A foreigner will have no choice, there is no way of wading through all the bits and pieces of the law (Einkommensteuergesetz = EStG).
It is not possible to determine the exact amount of tax you may have to pay by just looking at the income. There are several different tax classes, each reflect different circumstances (unmarried, married, married with two income per household, kids, houseowner etc....). Beside this, a considerable amount of the due tax can be deducted again partially or in full if job related (office, car, commuting costs, overtime allowances....)
The employer has to deduct the tax at source. Every month your total annual income will have to be "guessed" and taxes are deducted accordingly.
And no, flightcrew are not artists, students or any individuals considered to fall into the low-tax paying community.
Don't listen to any tax adviser / return filing software, they are not tailored for flightcrew.
And the tax is not the only part of all the deductions you will have to pay.....