What happened
On 3 March 2006, a Eurocopter AS332L2 Super Puma, registration G-CHCG, was performing a commercial air transport flight between the Beryl ‘B’ oil platform and Aberdeen Airport. While flying at approximately 3,000 feet, the aircraft encountered light hail and was subsequently struck by lightning. The crew reported a loud bang and a visible flash, though no immediate vibration or obvious external damage was noted.
Following the strike, the aircraft's electronic flight instrumentation screens momentarily went blank, and the navigation system experienced a power interruption. As the helicopter approached Aberdeen and the crew lowered the landing gear, the aircraft experienced a sudden hydraulic system failure. The hydraulic pressure gauge fluctuated before dropping to zero, and the flight controls became noticeably stiffer. Despite the loss of the No 1 hydraulic system, the crew managed to land the aircraft safely at Aberdeen Airport.
The investigation
AAIB investigators examined the aircraft and discovered significant lightning damage to both the main and tail rotor blades. The investigation revealed that the external damage was typical for such an event; however, a much more critical issue was found within the main rotor hydraulic actuators.
Upon dismantling the actuators, engineers found internal metal erosion and damage to the seals. Specifically, the external portion of one piston showed erosion that had likely caused the hydraulic leak. Furthermore, the investigation uncovered evidence of electrical tracking and damage that suggested the internal components may have been impacted by a previous lightning strike occurring three days prior, which had gone undetected during routine post-strike inspections.
Findings
- The lightning strike was likely a triggered event, induced by the aircraft's presence near convective activity.
- The primary cause of the hydraulic failure was a leak in the No 1 system caused by damage to the hydraulic actuator seals.
- Internal damage to the actuators was not visible during external inspections.
- The aircraft had previously sustained a lightning strike that resulted in unobserved internal damage to the hydraulic components.