An inquiry into the deaths of 16 men in a North Sea helicopter crash has concluded that the accident could have been prevented.
All on board died when the Bond Super Puma came down in 2009.
Relatives have called for a criminal inquiry, but the Crown Office defended its decision not to prosecute.
Sheriff Principal Derek Pyle said the precautions which might have avoided the deaths included following agreed procedures and communications.
He said the operators had considered replacing part of the gearbox just a week before the crash but did not do so because of a failure of communication with the manufacturer.
Sheriff Pyle said: "During the course of the inquiry there was much discussion about the circumstances which led Bond not to follow the clear terms of the maintenance.
"Bond readily acknowledged that they ought to have done so.
"The essential fact is that everyone in the company well knew that maintenance must be done by the book.
"On one occasion, that fundamental rule was broken. It resulted in the failure to detect a significant fault in the helicopter's gearbox, which possibly - but only possibly - resulted in the crash."
The Air Accidents Investigation Branch (AAIB) pinpointed a catastrophic failure of the gearbox in its examination of the crash.
Sheriff Pyle acknowledged that the exact cause of the gearbox failure which led to the crash could not be fully determined.
He concluded that on the balance of probabilities the spalling - the fracturing of metal - in the gearbox was the probable cause of the accident.
Lawyer Tom Marshall, for the families, said he was pleased the sheriff principal had accepted that the crash could have been prevented if Bond had followed the maintenance manual.
He said there was a need for a wider public inquiry, and that the families wanted to meet the Lord Advocate to discuss the earlier decision not to pursue criminal prosecutions.
Audrey Wood, whose son Stuart died, said: "Safety is absolutely paramount, and everything must be done by the book.
"We, the families, feel let down by the system. We just wanted answers.
"We will never have closure, this will go on and on for us."
Helicopter operator Bond said: "We have always accepted that we made mistakes through honest confusion over telephone calls and emails.
"Lessons needed to be learned, lessons have been learned and lessons continue to be learned.
"We would like to express again our deep sorrow at the 16 lives lost.
"Bond Offshore hopes that Sheriff Principal Pyle's determination brings a degree of closure to the families, friends and dependents of those who died in the tragedy of 2009."
Tommy Campbell, from the Unite union, said it was a "travesty of justice" that there had not been a criminal prosecution.
He also called for the decision to be reconsidered, and added: "These failings have cost lives."
A Crown Office spokesman said Crown Counsel had "fully assessed" the evidence before deciding there was not enough evidence for a prosecution.
"For a criminal prosecution to have taken place, the Crown would have to prove its case beyond reasonable doubt. The Sheriff Principal makes clear that a reasonable doubt remained over the technical cause of the crash.
"The evidence presented during the FAI has not altered the insufficiency of evidence, therefore the decision not to hold criminal proceedings remains the correct one.
"We will be offering to meet relatives again to discuss the Sheriff Principal's judgement."
A six-week hearing into the crash was held in Aberdeen earlier this year.
It heard evidence from the helicopter operator Bond Offshore Helicopters and manufacturer Eurocopter, as well as crash investigators.
Senior AAIB operations investigator Timothy Atkinson told the fatal accident inquiry that the gearbox failure meant there was nothing the crew could do - and the crash was "not survivable".
Eight of the victims came from the north east of Scotland, seven from the rest of the UK, and one from Latvia.
The two crew who died were Capt Paul Burnham, 31, of Methlick, Aberdeenshire, and co-pilot Richard Menzies, 24, of Droitwich Spa, who worked for Bond Offshore Helicopters.
The KCA Deutag employees killed were Brian Barkley, 30, of Aberdeen; Vernon Elrick, 41, of Aberdeen; Leslie Taylor, 41, of Kintore, Aberdeenshire; Nairn Ferrier, 40, of Dundee; Gareth Hughes, 53, of Angus; David Rae, 63, of Dumfries; Raymond Doyle, 57, of Cumbernauld; James John Edwards, 33, of Liverpool; Nolan Goble, 34, of Norwich, and Mihails Zuravskis, 39, of Latvia.
The other victims were James Costello, 24, of Aberdeen, who was contracted to Production Services Network (PSN); Alex Dallas, 62, of Aberdeen, who worked for Sparrows Offshore Services; Warren Mitchell, 38, of Oldmeldrum, Aberdeenshire, who worked for Weatherford UK; and Stuart Wood, 27, of Aberdeen, who worked for Expro North Sea Ltd.