Aspen was 9 months on our first plane trip and got super sick. Germs and airports and newborns don't mix.
I agree with Joy about the illness factor. A baby does not have an efficient immune system until 6 weeks of age which is why when you take your little one in for a 2 week checkup they will often put them in a special waiting area. The flu, which is prevalent at this time of the year can be lethal to a newborn (and of course anyone in the general public).
http://www.mayoclinic.com/health/air-travel-with-infant/HQ00197
Heres a good website that talks about taking infants on plane rides.
Oh, and another thing--- one of the problems of taking a newborn on a plane is the air and germs. The air on an airplane is recycled as you're flying. So you're breathing in the same air over and over. If someone has an airborne illness you and baby could get it.
I believe it is safe but I haven't really researched this. Many people feed their babies so that their ears "pop". I just don't know how young their babies are when they do this. I know that people who adopt newborns across country usually fly home with them, so I can only assume it is safe.