What makes someone with bipolar disorder an unsafe pilot? I've got someone wanting to learn to fly who has no bipolar diagnosis, has never been medicated, but has multiple bipolar family members and considers it possible he would be diagnosed as slightly bipolar if someone were to do an assessment. Person is generally mature and collected, has a college degree, holds a stable job in a position of responsibility, though may be considered a bit 'moody' at times. Knowing that there is a possible undiagnosed bipolar disorder, would I be unethical instructing him as a sport pilot? How about for a PPL?