What happened
On 22 February 2003, a Eurocopter AS332-L2, Super Puma, registered as G-JSAR, was performing a winching demonstration near the Miller Platform in the North Sea. While hovering, the crew observed the main rotor gearbox chip warning light illuminate. The pilot performed an immediate landing on the platform and shut down the engines.
Upon inspection, investigators found metal particles on the chip detector. Further examination revealed that the oil cooler drive shaft had fractured at the coupling flange on the main gearbox output drive. Additionally, the left-hand accessory module showed significant damage, including a fractured intermediate gear wheel and a fractured bearing housing lug.
The investigation
The investigation focused on the failure of the gearbox module and the drive shaft. The aircraft was equipped with a Health and Usage Monitoring System (HUMS) known as EuroARMS. Records showed that the system had generated an alert on 1 and 12 February 2003 regarding the RMSR parameter. Following this alert, the manufacturer advised the operator to continue flight operations while closely monitoring the component for an additional 50 hours.
On 21 February, just one day before the incident, the RMS parameter threshold was breached. Despite this, the decision was made to continue monitoring. The investigation also noted that the failure was linked to increased power requirements in the L2 variant of the Super Puma, which placed higher loads on the oil-cooling fan drive shaft.