How does one make a prop-based helicopter fly in the distance?

I’d like to make prop-based helicopter fly overhead, put simply. Far outside the skybox. Therefore I have a couple of questions before I endeavor on hours of trial and error;

  1. Would an object in a skybox outside the main skybox be visible from the main skybox, or would I have to expand my current skybox?
  2. How would I make a prop-based helicopter fly overhead? I know I can use doors, but I’d like the chopper to fly in a curved path. Would I use trains? If so; how? (I never got the train stuff in Hammer to work)
    Any help I can get on this is thoroughly appreciated and I will have statues of whoever helps me made in bronze.

For the flying helicopter, use this and just adjust to suit your needs:

Thank you, that’s very much helpful. I’ll post results later.

[editline]16th January 2012[/editline]

Well it doesn’t work because only NPC’s have target path corners

How about using path_track combined with func_tracktrain?

Read up on the Valve Developer Wiki pages, they’re very helpful.

You can have it fly outside the skybox by using a 3D skybox. There’s several tutorials on how to use them.