The Norway helicopter crash, which claimed 13 lives, was caused by technical failure and not human error, according to investigators.
Eleven passengers and two crew members were killed after the Super Puma aircraft came down near the city of Bergen on Friday.
British oil worker Iain Stuart, from Laurencekirk in Aberdeenshire, was among those who died in the crash.
Norway's Accident Investigation Board said on Tuesday that its probe and visual evidence - including video of the helicopter's rotor propelling into the sea moments before it crashed - indicated sudden mechanical failure, the Associated Press (AP) reported.
The board did not elaborate, saying a full investigation would take time.
The Super Puma was travelling from the North Sea Gullfaks B oil field, around 74 miles (120 kilometres) off the Norwegian coast when it crashed en route to Flesland Airport.
The aircraft shattered into pieces when it smashed into the rocky shoreline of Turoey, a tiny island outside Bergen, western Norway.
The 10 other passengers who died were Norwegian, while helicopter operator CHC lost two pilots, a Norwegian and an Italian.
Police have identified the victims, but have not released all their names in accordance with the wishes of some of the families.
The tragedy led to the Civil Aviation Authority (CAA) grounding all UK commercial passenger flights using the Airbus EC225LP - or Super Puma - model.
It also sparked calls for the aircraft type to be permanently removed from service, with an online petition so far collecting more than 21,000 signatures.
A team from the UK's Air Accidents Investigation Branch (AAIB) is assisting with the crash investigation.
Following the latest announcement by Norwegian investigators, unions have called for flights by the same model of helicopter involved in the crash to remain grounded until the cause of the incident has been established.
The Offshore Coordinating Group (OCG), an umbrella body of unions representing North Sea oil workers, also said workers should not be forced to fly in the helicopter type.
OCG chair Tommy Campbell said: "The Offshore Coordinating Group stands shoulder to shoulder with the Norwegian trade unions in their demand that the Puma 225 helicopter must be grounded until proof of the cause of Friday's tragic crash has been presented by the Accident Investigation Board.
"Workers in both the Norwegian and UK sectors must have genuine guarantees from regulators before flights in this aircraft can be considered. Statements from manufacturers and operators will not suffice.
"Until such guarantees are forthcoming, workers must not be forced to fly in the Puma 225. We therefore welcome the statement from Step Change in Safety to the effect that workers choosing not to fly must be treated sympathetically.
"The OCG and its member unions will vigorously defend any worker threatened with disciplinary action for refusing to fly".
Helicopter manufacturer Airbus Helicopters said it welcomes the announcement made by the Accident Investigation Board Norway (AIBN).
In a statement on its website, it said: "The investigation will now solely be focused on potential root causes of a technical failure, such as design, production, and/or maintenance.
"Airbus Helicopters continues to provide its full support to the AIBN investigation."
Mr Stuart's family have said they are devastated by his death.
A statement released by relatives of the 41-year-old at the weekend said: "Iain was a loving husband and devoted father to his two children and as a family we are heartbroken. He was a caring son, brother, uncle and friend to many."