Without knowing all the details, its a bit difficult to suggest anything, but for starters:
Have the guys around the blackhawk have to go out and link up with stragglers from another mission, bring them back to the blackhawk wreck to be picked up by the convoy.
Straight out of BHD, have a technical which needs to be taken down outside of effective range. (Maybe a mortar, which makes it more plausible why they have to go out and find it, rather than just shoot it from their location)
While either of these two 'sub tasks' are being performed, have another wave of attack at the blackhawk.