A pilot who fatally crashed a helicopter on a hotel roof in a popular tourist spot was alcohol-affected, according to an official report.

Investigators on Thursday said Blake Wilson, 23, took the helicopter from a far north Queensland airport hangar for an “unnecessary and unauthorised” flight after a night of drinking.

Wilson died when the Robinson R44 helicopter struck the roof of DoubleTree by Hilton in Cairns CBD about 2am on August 12, prompting the evacuation of about 400 guests.

He was the helicopter’s sole occupant.

“There was no airworthiness factor with the helicopter that likely contributed to this accident,” Australian Transport Safety Bureau Chief Commissioner Angus Mitchell said on Thursday.

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

Witness reports confirmed that Wilson had been socialising and drinking alcohol with friends at various venues in Cairns for his work farewell party before the crash.

Wilson returned to his apartment at 11pm before driving to his employer Nautilus Aviation’s helicopter hanger about 1am.

CCTV footage showed the helicopter take off after 1.30am. It flew for less than 20 minutes before the crash.

Wilson flew the helicopter over the CBD, twice over his apartment building and along the marina before heading back towards the city centre.

The flight’s last moments caught on CCTV showed the helicopter pitch up before immediately descending steeply into the roof of the hotel.

Parts of the rotor blade were found in hotel rooms, with other debris strewn across the venue’s grounds and on the street.

Mitchell said it was fortunate no hotel guests were seriously injured. Two hotel guests were treated for smoke inhalation.

The report found Wilson did not hold the appropriate qualifications to fly the helicopter at night nor did he have any experience, given he flew at just 500 feet (152 metres) over the CBD, instead of the regulated 1000 feet.

“While it was tragic that the young man lost his life, there was significant risk to others here in the Cairns area, which is why we have put resources to find out what we can look at all the available evidence,” Mitchell said.

“It is fair to say that this is quite an exceptional set of circumstances for the ATSB to be investigating.”

-AAP