Air Accidents Investigation Branch
During a pre-flight brief for a SAR training flight, the co-pilot highlighted that a previous flight on the aircraft resulted in unexpected pitch oscillations following the selection of the Transition Down mode of the Automatic Flight Control System (AFCS). After other training priorities had been completed, the crew replicated the circumstances that triggered the previous pitch oscillations. The result was similar unexpected flight oscillations in the pitch axis and the crew reported this to the operator.
The event was caused by a shortcoming in the design of the Phase 5 version of the AFCS software SAR upper modes this also resulted in the incorrect AFCS mode indications being shown to the flight crew and the conflict between airspeed and groundspeed priority on selection of the Transition Down.
Safety Action has been taken by the manufacturer and operator to address the shortcomings in the software, to brief the helicopter community and reinforce the importance of reporting issues.
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