During a night flight and upon entering the cruise phase, shortly after take-off, at approximately 700 ft above sea level, the pilot-in-command thought that he had carried out an action to engage the autopilot ‘ALT’ (altitude hold) upper mode. He did not check the result of his action and did not detect that the ALT mode was not actually engaged. While turning, the helicopter gradually lost altitude at a vertical speed of about -700 ft/min.
The aural and visual warnings of the two radio altimeters, set to 500 ft and 300 ft, were not noticed by the pilot or the hoist operator who were focused on managing the radio communications and locating the vessel. The pilot did not notice that during the descent, the helicopter’s speed exceeded the maximum never-exceed speed (VNE).
A few metres above the water surface, one of the passengers reported to the crew his feeling that they were flying very low. At about the same time, the pilot detected the low height indicated by the radio altimeter and regained control of the path.
The flight continued without any other incident with the setting down of the two passengers by hoist.