Shumthang

So I've been trying to search and I haven't had any successful results but I'm trying to create a "side mission" through triggers in my mission. For instance on the back end id have a blown up chopper with supply boxes and 2-3 enemies guarding it. When and if Blu For enters a trigger, something would pop up saying "A chopper has crashed go and grab supplies." Also is there a way to have this random to where every time you play the mission you may or may not have that pop up. If anyone knows, thank you in advance for the help!