OK, here how you do it.
Start the game off line. When in the tower bring up the clipboard.
Click on "options", "arena setup", "environment", "arena settings".
With that page open be sure you are on the "General" tab at the top, then double click "FlightModeFlags"
On the swing out page check the box "Lead Computer Site", click OK
Launch a plane, hit "Cntrl" and "Tab" at the same time to turn on "friendly padlock" (it will display that it is on in orange text).
When a plane is in view, hit "tab" high light it (hitting it over and over will cycle through all planes in view), and if you did it right you will see 2 green cross hairs (one for the primary gun and the second for the secondary guns), unless you only have a primary gun like from a gunners position.