A FAULTY gearbox ‘possibly’ caused a helicopter crash killing 16 people aboard, an inquiry has heard.

When the Super Puma aircraft came down in the North Sea off the Aberdeenshire coast on April 1, 2009, it killed 14 oil workers and two crew members.

After carrying out a six-week probe into the fatal accident, Aberdeen’s Sheriff Principal Derek Pyle, concluded that it might have been avoided if it were not for several failures by its operator, Bond Offshore Helicopters.

The relatives of the 16 men have now called for a criminal investigation to be opened into the tragic incident.

An Air Accidents Investigation Branch (AAIB) probe found that the aircraft suffered a ‘catastrophic failure’ of its main rotor gearbox causing the main rotor to break away and its ‘tail boom’ to break away from the fuselage.

Sheriff Pyle said Bond had failed to replace part of the gearbox just a week before the crash, a task specified in the aircraft maintenance manual, because of a failure in communication with the manufacturer.

He said: “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.

Mark James,a scaffolder from Middlesbrough, was one of 18 men who escaped with their lives when a Super Puma helicopter plunged into the North Sea just six weeks before the fatal incident.

A statement from Bond Offshore said: “Lessons needed to be learned, lessons have been learned and lessons continue to be learned. We are absolutely committed to driving safety improvements across the business and will study the Sheriff Principal’s recommendations carefully, along with our industry colleagues.”