The only time we see the airport is when Michael and David pick up Hank, then when Michael is on his way to Portland in 122. I would think that, since most airports are outside city limits, that it would be about a half hour away, max. Also, I would think that Justin and Brian would use the regular airport...that is, unless Brian bought a jet. Then they would use a jetport, which is sometimes attached to a major airport, or not far from one. Air traffic is strictly controlled, especially since 9/11. Only crop-dusters are outside of regular airports, as far as I know.