Operators of a North Sea helicopter had been planning to replace its main rotor gearbox a week before the unit suffered a 'catastrophic failure' leading to a crash which killed all 16 aboard - including Norfolk man Nolan Goble (pictured) - an air accident report said.

A magnetic particle had been found in the gearbox of the Eurocopter Super Puma, a final report by the Air Accidents Investigation Branch said.

This had led the operator to initiate a plan to remove the main rotor gearbox and replace it with a unit from another helicopter, the AAIB said.

But the discovery of the particle was not recognised as an indication of the degradation of another part of the gearbox which failed as a result of a fatigue crack.

As the helicopter was flying at 2,000ft to Aberdeen from the Miller Platform in the North Sea on the afternoon of April 1 2009, the main rotor separated from the fuselage and the aircraft crashed into the sea.

All 14 offshore workers and the two crewmen died.

In the final report the AAIB listed 17 recommendations that it had made during its investigation.

Relatives of some of the men killed in a North Sea helicopter crash have already received a �15m compensation package.

The flight was operated by Bond Offshore Helicopters. 34-year-old Mr Goble lived in Norwich but was born in Wells, where he grew up with three brothers, including former Norwich City player Paul Goble.