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The four-minute flight had not been authorized and there were no airworthiness factors that likely contributed to the Robinson R44’s crash, the Australian Transport Safety Bureau said in its final report Thursday.

The pilot, Blake Wilson, a 23-year-old New Zealand citizen, had been employed by the helicopter’s operator since April.

He had Australian and New Zealand commercial pilot licenses and had flown R44 helicopters before. But he was employed by Nautilus as a ground handler and did not have qualifications to fly at night, the report said.

“The flight was a purposeful act, but there was no evidence to explain the pilot’s intentions,� the report said.

Wilson had been due to be transferred by Nautilus on the day he died to an island 800 kilometers (500 miles) from Cairns. He had been drinking with colleagues and friends at several Cairns bars before returning to his apartment the night before his intended departure.

A toxicology report indicated he had a “significant blood-alcohol content� when he died. The report doesn't specify a level of concentration, but said he was “affected by alcohol.�

Wilson had traveled from his apartment to Cairns Airport, used as security code to enter a Nautilus hangar then flew a helicopter toward Cairns, a city of 150,000 people and a popular tourist gateway to the Great Barrier Reef.

He flew over his apartment twice, a wharf complex and along the waterfront before the crash. Security camera footage showed the helicopter pitched up before descending steeply on to the hotel roof, where most of its wreckage remained.

While pilots are required to remain at least 1,000 feet (304 meters) above the highest feature of a built-up area in Australia, Wilson’s flight never flew higher than 500 feet (152 meters).

The bureau's Chief Commissioner Angus Mitchell said Wilson had switched off the helicopter’s strobe lights which made his flight difficult to detect from the airport’s air traffic control tower.

“We do know that the pilot did take significant measures to conceal the nature of the flight,� Mitchell told reporters.

“This is quite an exceptional set of circumstances for the ATSB to be investigating,� he added.