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 in the North Sea. While cruising at 3,000 ft, approximately 34 nm east of Aberdeen, the flight crew received indications of low pressure in both the main and standby oil lubrication systems of the main gearbox (MGB).
In response to the loss of oil pressure, the crew activated the MGB emergency lubrication system. Shortly after activation, a warning appeared indicating that the emergency system itself had failed. Following this secondary indication, the crew performed a controlled ditching into the sea. All 12 passengers and 2 crew members evacuated into a life raft and were successfully rescued, though 2 passengers sustained minor injuries.
The investigation
The AAIB investigation focused on the failure of the bevel gear vertical shaft within the MGB and the subsequent behavior of the emergency lubrication system. Investigators examined the MGB, finding that while the shaft had failed, the emergency lubrication system had actually functioned as intended.
Analysis of the Hydrosafe 62 and the MGB sump revealed that the system had successfully delivered the required lubricant. The investigation also examined the printed circuit board (PCB) responsible for monitoring the system, the bleed air heat-exchanger, and the pressure sensors. Testing of the electrical wiring and the P2.4 valve showed no abnormalities. However, the investigation highlighted that the bleed air pressure sensor was operating at a level that could potentially trigger a low-pressure warning even when the system was functioning within its design specifications.
Findings
- The primary mechanical failure was the failure of the bevel gear vertical shaft in the MGB.
- The emergency lubrication system operated correctly from activation until the aircraft ditched.
- The monitoring system provided a false warning of system failure.
- The bleed air pressure sensor was measured at 0.68 bar (relative), which, when combined with pressure losses across the heat-exchanger, could trigger the MGB EMLUB caption despite the system being operational.
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 to ensure the main gearbox emergency lubrication system provides the crew with an accurate status indication.