The KC-135R that had its tail blown off was undergoing a conversion from a KC-135B to a KC-135R. The tech who did the actual maintenance (fuslage pressure check) retired early.
FedEX and UPS have problems not with fuel weight and balance, it's a problem with their cargo loading procedures.
I watched a training video done by FedEX about a DC-10 that they stood on its tail at LAX back in 1989. The problem was miscommunication between the inside loading crew and the guys working outside. The inside guys had a pallet get stuck, so they were working the problem. They had it unsecured. The outside loading guys thought they were ready for the next pallet, they placed it in the plane. When the weight of the pallet setteled it caused the aircraft to sit back a little bit. This caused the unsecured pallet to start moving aft, the resulting shift in the center of gravity put the DC-10 on its tail.
They ended up having to belly sling the DC-10 and then unload all the cargo by hand. It took them a little over 10 hours to do that, and it cost the company plenty of money to have that DC-10 sitting on the ground.