OK here goes! I will add this to the Mission Builder FAQ section later today:
I. IMPORTANT THINGS TO REMEMBER
1)There can be only 1 ALT PATH per mission.
2)It mainly is applied to the PLAYER, but you can be crafty and make it work for AI. (see II)
3)YOU MUST HAVE AN ACTIVE AWACS AIRCRAFT IN THE MISSION FOR ALT PATH TO WORK
4)The trigger for the ALT PATH can be anything, but I have found that AREA EVENTS do not seem to work.
If an AREA EVENT is used to set a FLAG, and the FLAG used to trigger the event, it works fine.
II. HOW TO DO IT
1)Place your flight as you normally would. Lay out all the WP's for the 'normal' tasking. This is ALL the Player will see on the Mission Map.
2)Click the ALT PATH ICON (curved arrow). Now start placing the WP's for the ALT PATH. The first will
appear as a disembodied point not connected to previous ones. For BEST results, make sure you include a
WP with no action, i.e. if the ALT PATH is to bomb a target, don't make the first ALT PATH waypoint the
BOMB TARGET action.
3)Continue placing ALT PATH WPs. The player will NOT see the original WPs in the NAV system any more, so
be sure you cover INGRESS, ACTION and EGRESS.
4)Set your ALT PATH trigger. As above, FLAGs work best, but other events will also do it. The AREA EVENT
is the only one I have had problems with.
5)MAKE SURE YOU HAVE AN ACTIVE AWACS AIRCRAFT
II. MAKING AN ALT PATH FOR AN AI FLIGHT
1)Follow the steps above, using the PLAYER aircraft.
2)After the ALT PATH is set, change the PLAYER aircraft to an AI aircraft using the right click menu.
3)Be sure you ADD a new aircraft to be the PLAYER, or change an existing one to be a HUMAN, BRIEFING GROUP A.
The AI aircraft will now respond to the ALT Path trigger.
4)The logic for AI response to ALT PATH is a little different..they will respond after hitting their next WP, so for AI aircraft, you should put WP's pretty close together so that when ALT PATH is triggered, there isnt a great time lag between the trigger and the action.
5)If you are making an ALT PATH for a RED flight, you should use a RED AWACS (e.g. A-50). Using an E-2C or E-3 and making it ENEMY doesn't SEEM to work in all cases.