Here is a classic. Two new 25 ton RTUs being installed. A local crane/rigging company did the lift. First unit was lifted using two long cable slings on the four lower lift points. The top of each was looped through. Should have used four individual slings. As it was lifted, the compressor ends being heavier caused the sling cable to slip in the upper ring, and flip inverted. That move caused the lifted RTU to hit the second one still on the truck, wiping out the condenser coil and bending the frame. It took a second crane to stabilize the mess. New RTUs at the crane co. expense.