The aircraft was tasked to carry out a marine pilot pick-up from a departing
tanker. The flight was conducted by two pilots operating under night visual flight
rules. Conditions were a moonless night with no defined horizon, no outside
lighting other than from the ship, and a surface wind that was light and variable.
The ship was steaming in a northerly direction at 12.5 kts.
The flight proceeded normally until the aircraft was established on final approach
to the helideck. As the aircraft descended through 500 ft the rate of descent had
increased to about 1,000 ft/min. Although the pilot in command increased main
rotor pitch, the aircraft's rate of descent continued to increase until just prior to
impact with the water. Both occupants were rescued approximately 1 h after they
evacuated the helicopter.
The report concludes that the standard approach technique used by the pilots,
coupled with the prevailing weather conditions, caused the aircraft to enter a high
rate of descent shortly after the aircraft started its normal final approach to the
deck. The high rate of descent was probably the result of entry to the incipient
stage of Vortex-ring state'. A lack of visual cues and inadequate management of
cockpit resources prevented the crew from recognising the abnormal situation
until the aircraft was well into the descent. Recovery action was commenced too
late to prevent impact with the water.