AAIB investigation to Leonardo AW189, G-MCGT
Unexpected pitch oscillations following selection of Transition Down AFCS SAR mode, near Heads of Ayr, South Ayrshire, 30 July 2021.
Summary:
During a pre-fight brief for a SAR training flight, the co-pilot highlighted an event on a previous flight which had resulted in unexpected pitch oscillations following the selection of the Transition Down mode of the Automatic Flight Control System (AFCS). On the conclusion of the other training priorities for the flight, the crew replicated the circumstances that had triggered the pitch oscillations previously; this resulted in similar unexpected flight path oscillations in the pitch axis. The crew reported this second event 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 which also resulted in incorrect AFCS mode indications to the flight crew. To address this issue pending the correction of the AFCS software in the Phase 9 release, the helicopter manufacturer issued a Technical Information Letter detailing actions to be taken in the event of a re-occurrence and updated the FMS Pilot’s Guide for Phase 5, Phase 6 and Phase 8 software. The manufacturer has corrected the design shortcoming in the Phase 9 release of the AFCS software.
Safety action has been implemented by the operator regarding automation management and incident reporting.
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