Xv iLeGenDzZ vX & Agnt Washtub Both have written very good solutions.
i would like to add this list of the transmission times , for people who want to check them off as they go to make sure they don't miss one. use this link --->http://www.xboxachievements.com/forum/showpost.php?p=93232&a...BEST DONE WHEN GOING FOR THE "SAINT" ACHIEVEMENT AS WELL!
(as you need a certain amount of survivors in the same room as the Quest Survivors (Kindell, Cheryl, Simone, Paul etc.) for otis to call you about their Mutiny/Request)
quick tip. this is actually much easier than the 360 version, as we are now given 5 save slots to save on. so make sure to save a lot and switch save files every once and a while in case you mess up. if you follow the guide close and have the REAL MEGA BUSTER, this achievement is easy.
Finish Case 7 and get the call from otis for the beginning of case 8 then ignore the main scoops. after the case 8 "call" the only calls remaining will be about survivor request missions aka Cheryl, Kindell, Paul.
i actually followed the link "AGNT" posted above carefully time wise. keep a save file from before the bomb collector scoop (to go back and use for the saint achievement, as you should have collected all survivors at this point, plus if you load this save and dont do the main scoops, brad and jess survive and you have isabella to add to the survivor count). ( i had 52 survivors at the end game stats )
Popped for me right after otis called about Cheryl wanting to Pose for the camera.