camera tracking and camera switching

Ok so i know this is probably a really stupid question, how do i get a camera to track an object within the game then switch to the camera one within the first person prefab?.

This is fairly simple. Create a new camera, add the Smooth Follow script to it, set the target to your player.

Disable the FPS cam.

Then, using a script, activate the camera you want to use. I use this a lot:

firstPersonCam = Screen.lockCursor;
thirdPersonCam = !Screen.lockCursor;

Of course you would have defined both of the cameras in your vars at the top of the script and then set them in the inspector.

var firstPersonCam : GameObject;
var thirdPersonCam : GameObject;

Related to "When should this happen", you could create a triggerbox that executes this code when your airplane flies into it.

Hope this helps!