What's the doctor's recommendation to help my 5 month old with a sinus infection flying in a plane?

Young for sinus inf: The perinasal sinuses don't actually begin to form in infants until about 4-5 months & then they are small pockets. Radio-graphs & ct studies would normally show fluid in these spaces until a year so use of the label at that age is speculative at best. I wouldn't expect any specific problems in a pressurized aircraft. Kids with uri's fuss the same as healthy kids at that age.