Fairly self-explanatory achievement - and one that you'll get on your way to completing the campaign mode... There are 3 beacons in total, and each requires the activation of 3 AU's beforehand.
Trigger each of the 3 AU's, then locate the dropzone for the beacon, call in the helicopter to drop the beacon, and defend the beacon for the next couple of minutes until it's full charged. Rinse and repeat for the other two beacons in this area of the city!
Check the
Light Bringer solution for more info...