How is the 30% tax calculated? Sometimes I have to pay it and sometimes I don't.
On the 11th or 12th (I forget which) of each month, you'll pay tax based on the previous month. If the tax rate is 30%, it'll just be 30% of the previous month's profits. For tax purposes, your profit/loss is worked out using everything on the income statement except loan payments/tax. So if March's income statement shows a 5 million loss, but includes 8 million of loan payments, your actual profit for March is 3 million, and on April 12 you'll pay 900k in tax.
On the 15th January, the tax is balanced for the previous year, and refunds are issued (or more tax paid if needed). So if for 1997, your income statement says you lost 15 million, paid 20 million in loan payments, and paid 10 million in taxes, that means your actual profit for the year was 15 million, your actual tax to be paid was 4.5 million, and on Jan 15 1998 you'll get a 5.5 million refund.
Plus, sometimes the bottom line is a negative but all of my flights are showing positive income.
Your flights don't include general expenses like staff salaries, staff training, loan payments, aircraft maintenance, etc, only the route-specific expenses like fuel & landing fees.
Also, I scheduled 3 new flights and assigned an airplane to it but it keeps showing no income yet. How can I tell when a route starts making money?
You should see the summary of the previous month on the route screen within a couple of days. If it's showing no data after that, something's wrong. Can you post a screenie?