The Super Puma which ditched in the North Sea on Monday, last week was brought to shore at Peterhead.
The helicopter was placed upon support vessel Olympic Zeus and taken to Peterhead Harbour in the early hours of Wednesday morning.
The aircraft was then transported to Aberdeen where members from the Air Accident Investigation Branch (AAIB) examined why the helicopter ditched.
After the gearbox was drained, an initial visual examination identified a 360 degree circumferential crack on the gear vertical shaft, in the area of the wield that joins two sections of the shaft. This meant that the main and standby oil pumps were no longer being driven.
The digital Voice and Data Recorder and other items have since been removed from the aircraft and transported to Farnborough for further analysis.
The crew of the helicopter carried out a controlled ditching following indications of a failure of the main gearbox system.
The aircraft was on a scheduled flight from Aberdeen Airport to the West Phoenix drilling rig.
Whilst in flight at around 3,000 ft, the crew reported that captions on the Vehicle Management System illuminated and the main gearbox oil pressure indicated zero.
As a result, the crew carried out the ‘Emergency Landing - Power ON’ checklist and successfully ditched the helicopter in the sea, close to a ship.
The 17 passengers and two crew members evacuated the helicopter and boarded two life crafts before being rescued and transported to the ship. There were no reported injuries.
A detailed engineering investigation of the helicopter is continuing with the full assistance of the helicopter manufacturer and operator.