What happened
On 29 July 2011, an AS332L2 Super Puma, registration G-PUMS, was conducting a commercial passenger flight approximately 30 nautical miles east of Aberdeen Airport. While cruising at 3,000 feet within instrument meteorological conditions (IMC), the No 2 Automatic Flight Control System (AFCS) disengaged.
Following the initial failure, the crew successfully reset the No 2 system. However, shortly after this reset, the No 1 system also disengaged. Despite a subsequent attempt to reset the No 1 system, both AFCS systems disengaged almost immediately. This simultaneous loss of control systems caused the helicopter to experience a significant rightward yaw, necessitating full left yaw pedal input from the pilots to stabilize the aircraft.
Due to the inability to re-engage either AFCS channel, the crew elected to descend through the cloud layer to reach visual meteorological conditions (VMC). Once in VMC, the pilots diverted the aircraft toward Aberdeen Airport and landed safely without further incident. There were no injuries to the two crew members or the 17 passengers on board.
The investigation
The investigation focused on the technical cause of the sequential system failures. The manufacturer conducted an analysis of the two AFCS computers involved in the incident. The examination revealed independent hardware faults within the two separate computers: one unit contained a broken pin on a circuit board, while the other unit exhibited a 15 V supply voltage that was outside of the required operating range.