An inquiry into a North Sea helicopter crash that killed 16 men has found that the crash could have been avoided.
Fourteen oil workers and two crew died when a Bond Super Puma plunged into the water off the Aberdeenshire coast on April 1, 2009.
A six-week fatal accident inquiry (FAI) into the circumstances of the crash was held before Sheriff Principal Derek Pyle at Aberdeen's Town House earlier this year.
Sheriff Pyle found that the accident might have been avoided if several failures by Bond had not occurred.
He found that Bond had failed to perform a task from the aircraft maintenance manual on March 25 2009 after a metal particle was discovered on the helicopter's epicyclic chip detector.
The maintenance "would have resulted in the removal of the epicyclic module and an examination of the magnets on the separator plates", he said.
Bond also failed to ensure that communications with the manufacturer Eurocopter were done according to procedure, with the result that "misunderstandings arose between the parties" and contributed to the failure to carry out the maintenance task.
The helicopter operator also failed to identify what the metal particle was during maintenance, the report said.
The inquiry heard a witness account of how the helicopter fell from the sky ''like a torpedo'' followed separately by its detached rotor blades.
An Air Accidents Investigation Branch (AAIB) probe found that the aircraft suffered a ''catastrophic failure'' of its main rotor gearbox.
The AAIB report said that the gearbox failure caused the main rotor on the AS332-L2 model to break away and its ''tail boom'' was severed from the fuselage.
Evidence at the FAI was taken from the helicopter operator and manufacturer, as well as engineers and crash investigators.
Much of the inquiry focused on maintenance carried out on the helicopter's gearbox in the weeks and months before the tragedy.
The crash claimed the lives of captain and co-pilot Paul Burnham, 31, from Methlick in Aberdeenshire, and Richard Menzies, 24, from Droitwich Spa in Worcestershire.
Five men from Aberdeen died: Alex Dallas, 62, James Costello, 24, Stuart Wood, 27, Vernon Elrick, 41, and Brian Barkley, 30; and two workers were from Aberdeenshire: Leslie Taylor, 41, from Kintore, and Warren Mitchell, 38, from Oldmeldrum.
The other victims were Raymond Doyle, 57, from Cumbernauld; David Rae, 63, from Dumfries; Gareth Hughes, 53, from Angus; Nairn Ferrier, 40, from Dundee; James Edwards, 33, from Liverpool; Nolan Goble, 34, from Norwich; and Mihails Zuravskis, 39, from Latvia.
Many of those killed worked for KCA Deutag Drilling and were returning from BP's Miller platform at the time of the crash.
In his findings Sheriff Pyle said: "Predictably, 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. They had little choice in making that admission given the clear terms of the manual.
"On many occasions during the inquiry it was acknowledged that the primary rule throughout the industry is that everything must be done by the book - that is to say, in accordance with the maintenance manual. There can therefore be no excuse for not doing so."
But the sheriff said that while it was "certainly possible" that if Bond had carried out the maintenance task they would have removed the gearbox, "on the evidence that fact has not been proved on the balance of probabilities".
He concluded: "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."
Speaking at a news conference in Aberdeen, Chris Gordon, of Thompsons Solicitors, who represented some of the families, reiterated calls for a public inquiry and asked the Crown Office to revisit the question of whether there should be a prosecution.
He said: "Firstly it is five years since this accident happened. The inquiry has taken far too long.
"Many of the witnesses could simply not remember anything. It is an appalling state of affairs which the families all agree with."
He continued: "Another thing that arose in the course of investigating in preparation for this inquiry was the situation regarding criminal proceedings.
"About a year ago the Crown Office decided there should be no criminal charges brought.
"About six weeks before the inquiry was due to begin we heard from the Crown Office that they still had not completed their investigations.
"Therefore we are calling upon the Lord Advocate to look again at the evidence and do what the Crown did not do here, and that is consider the evidence as a whole and revisit the question as to whether or not there should be a prosecution."
Mr Gordon said: "The family members want a public inquiry because they would trust nothing else.
"If the Scottish Government and the Westminster Government looked at the way the FAI was conducted they would be astounded."
He said BP, the Civil Aviation Authority, Eurocopter and Bond had been more interested in "burying this" than fact-finding.
"Once again we reiterate our appeal that there should be a public inquiry here," he said.
Audrey Wood, who lost her son Stuart Wood in the crash, said: "On hearing the evidence at the fatal accident inquiry we were surprised and disappointed at the decision of the Crown Office not to proceed with prosecution. However, how they arrived at that decision will haunt us.
"Not only did we hear of multiple breaches of health and safety but the decision was also made without all the evidence being present and vital witness statements had not been taken.
"Safety is absolutely paramount and everything must be done by the book. There can be no excuse for not doing this. The length of wait of nearly five years has been intolerable for all the families and we, the families, feel let down by the system."
Offshore union Unite also said the Lord Advocate should re-visit evidence and bring forward a criminal prosecution of Bond after the FAI established the operator's negligence over a number of maintenance and inspection failures.
Unite Scottish Secretary Pat Rafferty said: "Our thought's today, first and foremost, are firmly with the deceased and their loved ones who have shown great courage and dignity throughout an unacceptably protracted legal process, yet seem no further forward in their pursuit of justice.
"Today's determination merely reinforces our view that the FAI legislation needs urgent reform to tackle:
* The unacceptable delays families of victims face in their pursuit of fact and justice surrounding their loved one's death
* The lack of transparency and engagement with the victims' families in the process leading to the convention of the FAI; and
* The toothless nature of determinations which cannot be legally enforced on a negligent employer.
"The Scottish Parliament has the power via the Inquiries into Deaths (Scotland) Bill to make the changes our FAI system so obviously requires. Unite therefore has no doubt that the Secretary for Justice should fast-track Patricia Ferguson's proposed reforms to advance the interests of the Scottish public and the workplace health and safety agenda.
"Unite is also bitterly disappointed the FAI findings highlight a number of maintenance and safety inspection failures on the part of Bond, failures which remain a possibility for cause of this fatal crash, yet the operator can escape any form of punishment from industry regulators or prosecution from the COPFS. This is unacceptable and should prompt a re-evaluation of the evidence by the Lord Advocate to consider prosecuting Bond and also more than justifies the growing calls for a public inquiry into offshore helicopter safety which the trade unions have been campaigning for.
"Through our Back Home Safe campaign Unite has amplified the voice of over 3,500 offshore workers who have expressed their concerns with offshore helicopter transfers to and from installations in the UK Continental Shelf (UKCS). This evidence has been delivered to the UK Transport Committee and also been debated in the Scottish Parliament with the clear message: there is a crisis in confidence among offshore workers concerning the safety of these helicopters.
"If our politicians and the UK Oil & Gas industry are serious about improving access to justice, workplace health and safety and restoring a shattered confidence in our offshore helicopter fleet, then they will back these measures.
"It's far too late for the victims of the April 2009 Super Puma crash but we must do everything we can to learn from this tragedy and limit the possibility of more fatalities happening in the future."
A statement from Bond Offshore said: "Although Sheriff Principal Pyle has indicated that spalling was, on balance, the most likely reason for the catastrophic gearbox failure which caused the accident - a view not shared by the independent Air Accidents Investigation Branch - he did not find that this was not proved beyond reasonable doubt.
"Additionally, he determined that even if we had followed the correct procedure it is by no means certain that the gearbox would have been removed, as there may not have been sufficient evidence of particles to warrant its removal."
It continued: "We are pleased the Sheriff Principal recognised that Bond engineers understood the vital importance of their role in ensuring the safety of their pilots and passengers.
"But 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 are absolutely committed to continuing to drive safety improvements across the business, and will study the Sheriff Principal's recommendations carefully, along with our industry colleagues."
It concluded: "We would like to express again our deep sorrow at the 16 lives lost in 2009. We owe it to their memories, and to the 160,000 men and women we carry every year, to continue to deliver the highest standards of safety in everything we do."