If playing Solo, then this achievement requires you to play as Jake.
During Chapter 4-2 Jake's Campaign, you will eventually have to shoot down a helicopter with the help of Chris and Piers. Once in this area, you will have to climb to the highest rooftop via the ladders in front of you, which is only accessable as Jake. Once you reach the rooftop, wait until the helicopter drops enemies onto the rooftops, then press A to grab onto the ropes that the enemies are climbing down. Then, climb the rope with X shooting the pilot when prompted. Despite the description, this can be done with either the Nine-Oh-Nine or the Elephant Shooter. If done correctly, this will unlock either during the cutscene, or after it. If playing in co-op, both players will receive this.