If the airplane you wish to photgraph is is public space you can click
away, just as you can for cars, boats, people, etc.

I remember enough from law class to remember that is wrong with regard
to commercial photography. You can photograph "generic people" (like a
bunch of people walking down the street). However, you cannot feature
any given person without getting a release from them. The same would
apply to aircraft. However, certain people (and I assume aircraft) give
up their right to this privacy by doing things like running for public
office or appearing in movies or TV.

-Robert