In the Allied Intent Extended mod, there is a map called The Push Day. In this map, follow the left side of the course if you are on the Mec squad side or the right side if you are the Chinese. You will encounter what appears to be an apartment complex. There will be several balconies. Use your rope to rappel to the third story. When you reach the end of the rope you will always fall. If you approached this building from the Mec side it will be the first column of balconies that you need to rappel into. When you fall, press [Forward]. You will hit the first floor and can parachute inside the building. You are now impervious to bullets and artillery, while you can still shoot out and kill people. Do not walk out of the building's frame or you will have to restart everything.