I wasn't able to save that one until I...The one in Chapter 5 I couldn't even save.
The second one I did by first rocket launcher the flying dude from far, and then throw an emp nade from somewhat closer and rush in for the slaughter. Saving civilians sucks. Those fucking enemies tend to shoot civs RIGHT AWAY when they see you.
1./Threw a red phosphorus grenade at the GRAD.
2./Ninja-killed the guy on the ledge.
3./Approached the two holding the hostage from behind (I hit them with a couple of rocket launchers afterward).
I wound up needing to repeat that rescue attempt more than any other in order to figure it out.