What happened
On 10 May 2012, an EC225 LP Super Puma, registration G-REDW, was performing a scheduled passenger flight from Aberdeen Airport to the Maersk Resilient platform. While cruising at 3,000 ft, the crew received several simultaneous warnings, including a red light and aural gong, along with indications of a pressure drop in the main gearbox oil distribution manifold. Additionally, the crew observed a loss of pressure in the standby lubrication system and a failure of the emergency lubrication system.
As the main gearbox oil temperature began to rise, the commander reduced the aircraft speed to approximately 80 KIAS and initiated a turn back toward the coast. Following standard procedures for an emergency lubrication failure, the crew activated the emergency system and began a descent. The helicopter subsequently ditched in the North Sea, approximately 20 nm east of Aberdeen. Following the impact, the crew and 12 passengers evacuated into a life raft. All occupants were eventually rescued, though 2 passengers sustained minor injuries.
The investigation
The AAIB investigation focused on the mechanical integrity of the main gearbox lubrication system. Engineers examined the gearbox, which had been drained of its fluid. The investigation identified a 36 0° circumferential crack on the bevel gear vertical shaft, specifically located near a manufacturing weld. This crack caused the drive to both the main and standby oil pumps to disengage.
Analysis of the aircraft's Health and Usage Monitoring System (HUMS) revealed that sensors monitoring the drive to the oil pumps had recorded increasing vibration levels during the hours preceding the accident flight. These vibrations were being monitored in accordance with manufacturer maintenance protocols.