In theory it is possible to book a flight if you have a white card or a police note, but only for flights inside Greece and only if the white card/ police note is still valid. Also there are some flight companies who might not accept a white card or a police note. So please ALWAYS check before you book a flight, if the flight company will except the identification document you want to use. Otherwise it might happen, that you will not be allowed to fly and you will lose all the money you paid for the tickets. For flights outside of Greece, there are different requirements and you are not allowed to travel with a white card or a police note. As an asylum seeker you are not allowed to leave the country by law.