You were allowed to resign means you resigned. You were not fired. You would have been fired but that is nobody's business. The fact is you resigned. The reason you were given this "opportunity" is that your former company does not want to deal with possible lawsuits dealing with your career or lack of it due to being fired.

Get over it and come up with a good explanation of why you "resigned." Don't ever admit you were fired. You should, however, examine why you were asked to leave and evaluate whether you want to stay in this career. Maybe you have poor pilot skills, maybe you don't fit in, and maybe you are just too weird. We've all flown with guys that should not be in this industry. It this is you, maybe you should try something else. If you were fired (sorry, resigned) because of some big injustice, then get on with life and get another job. Time will heal all wounds.