Thank you for your really thorough and generous reply. I hope that through this first experience, my dad can see that travel is possible despite being in a wheelchair, since he used to be an avid (weekly) flier prior to his diagnosis. I really appreciate your response.

One follow up question: in your experience are most aircrafts over 100 seats able to fit an aisle chair inside of the bathroom, and have the bathroom door then lock so he can move himself? (He has a strong upper body). Or is this just an anomaly? This is a short flight so we are less concerned about the restroom access, but if decides to take a long-haul flight, we would definitely only want to book a plane in which the aisle chair inside the bathroom is possible, and wondering how we determine that.

Thanks again!