Operation was pull out of hole and lay down 4 joints of 2 7/8” DP which was used for fishing BHA. While pull out the 2nd joint of 2 7/8” DP, Rig crew started to breakout the DP by using Power tong, after the connection was open, the tong Jaws jammed to DP tool joint ,So the crew tried to released it by turning tong forth and back, and due to dynamic movement of the connection, the thread between drill pipe and the cross over was unscrewed, after the tong came out from the joint, and while the crew were moving the joint to the v door side, the connection between the crossover and the joint completely opened and the 2 7/8 DP slid from V-door to cat walk and then to the ground.