UNION leaders say families of the 16 men who died in a North Sea helicopter crash will be upset by a decision not to pursue criminal proceedings.

All 14 passengers and two crew lost their lives after the Super Puma plunged into the sea off the Aberdeenshire coast while returning from the BP Miller platform on April 1, 2009.

Eight of the victims came from the north-east of Scotland, seven from the rest of the UK, and one from Latvia.

Yesterday, the Crown Office said there was insufficient evidence for a prosecution. A fatal accident inquiry is planned for October.

A report into the crash found the aircraft suffered a catastrophic failure of its main rotor gearbox.

The Air Accidents Investigation Branch (AAIB) said the failure caused the helicopter's main rotor to break away from the aircraft and its tail boom to become severed from the fuselage.

Problems with the Super Puma resulted in the ban of their use over British seas in October last year.

It came after an EC225 that came down in the sea while flying workers from Aberdeen to the West Phoenix drilling rig had gearbox and emergency lubrication problems similar to those that caused another Super Puma to make an emergency landing months earlier.

An investigation by the AAIB found the two accidents were the result of gearbox failure and new advice on checks for the EC225 Super Puma model were issued as a result.

Jake Molloy, offshore organiser for the Rail, Maritime and Transport Workers (RMT) union, believed a fatal accident inquiry would go some way to answer doubts over what happened.

He said: "There is going to be upset for some families, possibly outrage there is no prosecution. But given what I have learned since April 1, 2009, it would have been difficult to substantiate a prosecution to some extent.

"The helicopter operator and manufacturer were complying with all regulatory requirements at that time. That's why a fatal accident inquiry is probably required to alleviate the lingering doubts and questions that will exist in the minds of a lot of people out there."

The tragedy happened about six weeks after another Super Puma with 18 on board ditched as it approached a production platform owned by BP. Everyone survived that accident.

A Crown Office spokesman said: "Having carefully considered all the circumstances of this incident, Crown Counsel have decided that there is insufficient evidence for a prosecution and as result no criminal proceedings are instructed."

He added that a fatal accident inquiry will take place in Aberdeen in October, saying: "The deaths of all 16 men who lost their lives in the tragedy are to be the subject of an inquiry in terms of the Fatal Accidents and Sudden Deaths Inquiry (Scotland) Act 1976."