One of the pilots was undergoing practice in engine failure emergencies at night. The helicopter was equipped with a "Nightsun" light, which was used to illuminate the ground below the aircraft. Fixed lights were also installed at the edges of the helipad. During the third practice autorotative descent, the Nightsun light was inadvertently extinguished when the aircraft was about 300 feet above the ground. It was turned on again by the time the aircraft had descended to about 100 feet, and the remainder of the descent and flare appeared to be normal. However, after touchdown the aircraft became airborne again, before touching down on the heels of the skids while moving slowly forward. The aircraft rocked forward and the main rotor severed the tail boom just forward of the tail rotor assembly. The surface of the helipad had been softened by recent rain ,allowing the heels of the skids to dig in slightly. This probably accentuated the rocking movement which led to main rotor blade contact with the tail boom. The type of manoeuvre being performed requires a high level of skill. Should a slight error of judgement occur, there is little opportunity for any corrective action to be successful.
