The AAIB has today published a Joint Report on the accidents involving Eurocopter EC225 LP Super Puma G-REDW on 10 May 2012 and G-CHCN on 22 October 2012.
On 10 May 2012, an EC225 LP Super Puma, G-REDW, ditched in the North Sea approximately 32 nm east of Aberdeen and on 22 October 2012 an EC225 LP Super Puma, G-CHCN, ditched in the North Sea approximately 32 nm southwest of Sumburgh, Shetland Islands.
In both of these incidents, the Air Accidents Investigation Branch ("AAIB") deployed teams to Aberdeen to commence an investigation and, as a result of the similarity of the circumstances that led to both of the incidents, the Chief Inspector of the AAIB ordered that both investigations be combined into a single report.
The crews of both G-REDW and G-CHCN experienced a loss of main rotor gearbox oil pressure, which required activation of the ‘emergency lubrication system’. The emergency lubrication system uses a mixture of glycol and water to provide 30 minutes of alternative cooling and lubrication to allow the aircraft to continue to fly.
Both helicopters should have been able to make it to the nearest airport within this 30 minute window, however shortly after each helicopter activated the emergency lubrication system, a warning illuminated indicating that the emergency lubrication system had failed. As a result, the helicopter crews needed to ditch their helicopters immediately in the North Sea.
Both ditchings were successful and the crew and passengers evacuated into the helicopter’s life rafts before being rescued. There were no serious injuries.
The finding and recommendations
The AAIB report found that the loss of oil pressure on both helicopters was caused by a failure of the bevel gear vertical shaft in the main rotor gearbox, which drives the oil pumps. These shafts failed as result of a circumferential fatigue crack in the area where the two parts of the shaft are welded together.
The report further found that, while the emergency lubrication system operated in both cases, the system warning light illuminated as a result of an incompatibility between the helicopter wiring and the pressure switches. This meant the warning light would always illuminate after the crew activated the emergency lubrication system, regardless of whether the emergency lubrication system was functioning correctly or not.
The AAIB have made several recommendations, and called for new research into fatigue of the kind of metal alloys used in helicopter gear shafts. This coincides with the CAA’s pledge to seek to ensure funding for research in relation to other aspects of helicopter safety.
The AAIB’s recommendations also included new cockpit checklists for all helicopters, as well as changes to how offshore helicopter life rafts should be installed and moored.
Click here for a full copy of the report.