More extensive footage of the accident was shown on the ABC news tonight, including a short clip taken from on-board the helicopter.
It shows the helicopter approaching the deck rapidly at a very steep angle, fast closing rate, and very high rate of descent, with coning on the main rotor disk evident suggesting very high power demand/output of the engines. The nose of the helicopter hits the helideck first, the airframe distorts causing the co-pilots door to swing open, the main wheel oleos compress fully and as the nose section bounces up off the deck the tail section pivots down causing the tail rotor to hit the safety netting resulting in immediate separation of the tail rotor pylon from the tail boom. Virtually instantaneously the cabin rotates 180 degrees to the right, the rapid rotational speed obviously due to the torque reaction applied by the engines at very high power. The helicopter appears to remain upright but spinning rapidly and pitching up as it disappears out of view prior to entering the water.
From what was shown in the video it certainly was not a normal approach by any conventional standards, although the media report described the helicopter as performing some type of tactical manouvre. For what reason they did not elaborate. In any event, having seen the footage it is a wonder that anybody survived the initial impact, let alone extraction from the aircraft whilst under water. Testament perhaps to good training and an ounce of luck.
The report went on to say that the flight data recorder was recovered and there were no indications of any systems malfunctions prior to the accident.