On 30 March 2009, a Fairchild SA227 Metroliner III was being operated by Airwork (NZ) on a public transport air ambulance positioning flight to New Plymouth at night with the medical team on board. The visual approach at destination was rushed and unstable with the distraction of a minor propeller speed malfunction and with un-actioned GPWS/TAWS warnings caused by excessive sink and terrain closure rates. After a hard touchdown close to the beginning of the runway, directional control was lost and the aircraft left the runway to the side before continuing parallel to it for the rest of the landing roll. There was no damage to the aircraft or injury to the occupants but minor damage occurred to runway lighting fixtures.
The investigation noted the visual approach to New Plymouth which was the origin of the occurrence was not authorised under Operator procedures. It further noted that the runway excursion occurred because the PF was not in full control of the aircraft during the final approach and landing. The approach had been rushed and was interrupted first by an engine RPM anomaly and secondly by a GPWS warning caused by the rushed approach. Although the airspeed was decreasing quickly on the final approach, the PF decided not to increase power, because he had difficulty controlling the aircraft, which he attributed to the RPM anomaly. He judged it preferable to continue with the landing rather than to go-around with a possible controllability problem.
It was considered that although there had been a distracting engine speed anomaly during the approach that should not have caused unmanageable control difficulty. It was also noted that the Operator’s SOPs in force at the time for the prevention of Controlled Flight Into Terrain (CFIT) accidents was ambiguous and could have contributed to the occurrence because it allowed the pilots to continue an unstable night approach after a ground proximity warning.
During the Investigation, the Operator made a number of changes to their Operations Manuals as a result of the occurrence, including to the sections on required airport lighting, stabilised approach criteria and the required response to GPWS warnings. It also acknowledged the requirement for a more structured Crew Resource Management pilot training syllabus to be completed in respect of stabilised approaches, day and night GPWS warnings and situational awareness so that all CFIT risk indicators could be the triggers for appropriate responses. A new policy to ensure protection of Cockpit Voice Recorder (CVR) was also introduced.
The Final Report was published on 15 April 2010 and may be seen in full at SKYbrary bookshelf: Report 09-003, Fairchild SA227-AC Metroliner III ZK-NSS, runway excursion, New Plymouth Aerodrome, 31 March 2009
Safety Recommendation made to the New Zealand Director of Civil Aviation
“To address the safety issues created by the late notification of this incident (which) hampered the Commission’s investigation, because potentially valuable CVR information was not preserved. The Commission has noted recently that other serious incidents have not been notified as soon as practicable to the CAA, and in some cases the delays have affected the Commission’s decision whether to investigate. The Commission and the CAA rely on being immediately notified of serious incidents in order to be able to conduct effective investigations and to learn the lessons to prevent accidents. Late notifications prevent the Commission from meeting its statutory obligations.”