Sequence of Events
The pilots of two helicopters conducted multiple flights to fishing locations without incident. On the return trip from Pipon Island to Mossman late in the afternoon, progress was slower than expected due to prevailing weather. The pilots diverted to Cooktown to refuel, landing about 10 minutes before last light.
As both pilots were only qualified to fly during daylight hours in VFR conditions, there was insufficient time to conduct the flight to Mossman within regulatory requirements and with an appropriate level of risk. Despite this, they departed Cooktown just after last light for the nominally 45-minute flight.
Decision-Making
The decisions by both pilots to depart after last light are not analysed in depth. In simple terms, they were motivated to reach the intended destination and either did not perceive the high level of risk, or had a high tolerance of risk. Both pilots had reportedly completed other flights in low visibility conditions, including landing on a beach when required. This may have provided a level of confidence in their ability to fly at night, which would be misplaced if based on daylight experience.
Flight Conditions
As the flights progressed down the coast, natural light was reducing. By 1919 (local end of nautical twilight), at low level over water and without moonlight or significant artificial lighting, the horizon would technically not be visible. Other factors adversely affecting visibility southward were high terrain to the west and potentially cloud and/or rain.
By the time YLY passed Cape Tribulation, the pilot was operating in dark night conditions with little to no terrestrial lighting. When the passenger expressed concerns about variations in the helicopter’s height relative to the water, there was no apparent consideration of landing. Landing in an unfamiliar area in darkness and windy conditions was likely not a favorable option. YLY was over halfway to the destination, and turning back to Cooktown was unlikely viewed as realistic. The pilot may have been influenced by the progress of the more experienced lead pilot.
Loss of Control
It is not clear how the pilot of YLY was maintaining control. Without an artificial horizon instrument and the training to use it, the pilot relied on external reference to a natural horizon or surface features. As the horizon became less distinct, the pilot presumably maintained visual reference to the coastline and water surface. The pilot dimmed the instrument panel lights to reduce internal glare, which was apparently necessary to assist with external reference.
Although the lead pilot's method to maintain height was to use the altimeter, it was difficult for the pilot of YLY to monitor instruments with dimmed lighting while scanning surrounding features. This was made more difficult by windy conditions and inherent helicopter instability.
Collision
Shortly after passing Cape Tribulation, the helicopter collided with water in a right skid-low attitude. Given the passenger account that the helicopter was operating normally and the accident occurred without warning, the pilot was probably unaware of the proximity of the water and/or was losing control. In dark night conditions, the pilot could have encountered an area of cloud and/or rain not evident in the weather radar image.
ATSB Findings
The ATSB found that the pilot of YLY, who was only qualified to operate in day-VFR conditions, departed on a night flight and continued towards the destination in deteriorating visibility until inadvertently allowing the helicopter to descend into water.
It is concerning that some day-VFR helicopter pilots continue to operate illegally and unsafely by flying at night. Although pilots have done this with mixed outcomes, as the two pilots involved experienced, the risks are extremely high. This was demonstrated on 24 April 2011, when an R44 registered VH-RUR collided with the sea while on approach at reduced airspeed to a landing site, flown after last light by a pilot.