despegue,
That's not entirely correct is it? and really depends on circumstances. If I'm a pilot and a builder in my spare time, and declare income from both jobs, then in the UK at least, I'm not an employee of any particular airline. So long as they pay a company of which I am a director I can continue this relationship forever. However, in practice there's many different types of payment terms that complicate the whole thing such as agencies that put you on their own payroll.