A fatal accident inquiry is to be held into a helicopter crash which claimed four lives in 2013.
George Allison, 57, from Winchester; Sarah Darnley, 45, from Elgin; Duncan Munro, 46, from Bishop Auckland; and Gary McCrossan, 59, from Inverness, died and 14 others were rescued when the Super Puma aircraft crashed two miles from Sumburgh Airport on Shetland.
The helicopter was transferring oil workers at the time.
Evidence has been considered by the Crown Office and it said the investigation has now "reached a significant stage".
A date and venue for the fatal accident inquiry (FAI) are yet to be announced.
A statement from the Crown Office said: "The investigation into the helicopter crash off Sumburgh in Shetland in August 2013 that resulted in the loss of four lives has reached a significant stage.
"Crown counsel have instructed that a fatal accident inquiry be held into the deaths of Duncan Munro, Sarah Darnley, Gary McCrossan and George Allison, who were passengers being transported from North Sea oil and gas platforms to the mainland.
"In coming to this decision, Crown counsel have considered the available evidence, the recommendations of the COPFS (Crown Office and Procurator Fiscal Service) helicopter incidents investigation team, and expert opinion.
"The investigation by the police, with officers working closely with the COPFS helicopter team, has been complex and challenging. COPFS will now work closely with the Scottish Courts and Tribunals Service to make suitable arrangements for holding the inquiry.
"COPFS will continue to keep the relatives of the deceased informed of significant developments."
Shetland MSP Tavish Scott has made repeated calls for an inquiry to be held into the crash.
He said: "I am very pleased that the uncertainty is now over. It has taken too long for a FAI to be confirmed.
"Families who lost love ones have had to live under this cloud for too many years. But at least now the inquiry can find out what happened and why.
"The families of the bereaved deserve answers and that will now finally happen.
"On the wider point about the length of time since the helicopter crash and the loss of life, I want the Government to consider reforms to the process to speed this up.
"This has simply taken too long."