What happened
On 10 May 2012, an EC225 LP Super Puma, registration G-REDW, was performing a commercial passenger flight from Aberdeen Airport to the Maersk Resilient platform in the North Sea. While cruising at 3,000 ft, the flight crew observed indications of low oil pressure in both the main and standby lubrication systems of the main gearbox (MGB).
In response, the crew activated the MGB emergency lubrication system. However, approximately 32 seconds later, a warning illuminated indicating that the emergency system itself had failed. Faced with this indication, the crew performed a controlled ditching into the sea. All 12 passengers and 2 crew members evacuated into a life raft and were rescued, though 2 passengers sustained minor injuries.
The investigation
The AAIB investigation focused on the failure of the MGB lubrication system and the subsequent false warning. Investigators established that a failure of the bevel gear vertical shaft within the MGB had interrupted the drive to the oil pumps, causing the initial loss of pressure.
Testing of the emergency lubrication system components, including the P2.4 valve, the bleed air heat-exender, and the Hydrosafe 620 pump, showed they were all functioning according to specifications. Analysis of the MGB sump revealed that the system had successfully delivered Hydrosafe 620, as evidenced by the presence of glycol throughout the gearbox casing. Furthermore, the amount of fluid remaining in the Hydrosafe 620 reservoir was consistent with normal operation during the 7.5 minutes between system activation and the loss of electrical power after ditching.
Findings
- The primary cause of the initial pressure loss was the failure of the bevel gear vertical shaft in the MGB.
- The emergency lubrication system was operating effectively and successfully lubricating the gearbox until the aircraft ditched.
- The monitoring system provided a false indication of system failure.
- The investigation concluded that the bleed air pressure sensor could trigger a low-pressure warning even when operating within its specified tolerance, as the measured pressure was near the lower limit of the allowable range.
Safety action
- Safety Recommendation 2012-034: It is recommended that the European Aviation Safety Agency requires Eurocopter to review the design of the EC225 LP Super Puma main gearbox emergency lubrication system to ensure the crew receives an accurate status indication when the system is activated.