What happens to a child who has fluid in his ears when he flies on a plane?

I have plans to fly to florida. My son is going halfway with me and meeting his grandma during out layover. This is about a 2 hour flight. The problem is that he had an ear infection a few weeks ago and his docotr said the infection was gone but there was still fluid and to come back in a month to recehck. I've made him an appointment and I will not put him on a plane if the doctor sais no but I'm just wondering what are the ddangers of flying with fluid in your ears? He's 2 by the way.