A SUPER Puma helicopter ditched in the sea near Shetland after the pilots were alerted to failure of the main gearbox lubrication system.

A new report on what happened to the CHC- operated EC225, which was finally salvaged yesterday, said an initial visual examination identified a crack on a gear shaft.

The Air Accidents Investigations Branch (AAIB) said the same "bevel gear vertical shaft" failed when another EC225 was forced to carry out an emergency landing in the North Sea in May.

The AAIB said the European Aviation Safety Agency and Eurocopter, the helicopter manufacturer, are "urgently reviewing the effectiveness and scope" of an Airworthiness Directive, a notification to owners and operators of certified aircraft that a known safety deficiency exists and must be corrected.

All 19 people were rescued when the CHC-operated helicopter was forced to ditch while flying from Aberdeen to the West Phoenix drilling rig on Monday.

In April 2009, 16 people died when a Super Puma – operated by Bond – plunged into the sea after its gearbox failed en route to Aberdeen. The disaster happened six weeks after another of the helicopters ditched with 18 men on board.

CHC and two other offshore helicopter companies, Bond and Bristow, have suspended their use of the Super Puma EC225.