While practicing autorotations during a military night training exercise a Huey Cobra screwed up the landing and landed on the tail rotor. The landing was so hard that it broke off the tail boom. However, the chopper fortunately remained upright on its skids, sliding down the runway doing 360s. As the Cobra slid past the tower, trailing a brilliant shower of sparks, this was the radio exchange that took place... Tower: "Sir, do you need any assistance?" Cobra: "I don't know Tower, we ain't done crashin' yet."