@strokerman:
There are 2 possibilities:
* either your aircraft does not have weapon or ammo: check in the equip menu of your aircraft
* or the UFO is too far from your base, and your interceptor doesn't have enough to reach UFO: wait that it comes closer
Or you set up an 'air patrol' as i did for a long time.
For that (v2.2.) go to your interceptors in the base and click on the start-button. The game switches back to global scale and near the base you have an icon for your interceptor.
This interceptor you can direct where you like it to patrol on the may - as long as it is in range. Therefor simply click on the destination. The interceptor will move there an stay as long as its fuel last.
I used to have 6 or 8 interceptors per base and placed 3 of them in a triangle around my base. This was the only way to ensure that I got my heavily armed and armored Stilettos in combat range to most UFOs.
But ensure, that your interceptors patrol in just half of your rage of radar - as it'll loose track on the UFO if that retreat. In addition to that, I had one time an UFO shooting down my interceptor beyond the range of my radar as my interceptor lost the track.
cu