I fly frequently for business trips. When I purchase a ticket, I usually let them know that I am deaf. I haven't had any problems yet.
One time, I flew Southwest, and let a flight attendant know that I am deaf. During the flight, he approached me to ask me if I go to a city in particular. I replied, and he informed me that I have to get on a different plane after we land, because of some non official schedule problem came up. The passengers and I had to get off the plane at an airport to go to another plane. We were able to get home on time.
You have to tell at least two flight attendants that you are deaf. One flight attendant may be busy doing something else in different area of the plane. Telling two flight attendants is better than one. Also, you have an opportunity to ask them to let you know if any situation comes up. Just approach flight attendants.