TAIC finds systemic issues behind Air NZ Q300 unsafe descent
By Andrew Curran.
New Zealand’s Transport Accident Investigation Commission (TAIC) has identified systemic safety issues behind an Air New Zealand DHC-8-Q300 that descended below the minimum safe altitude while approaching Timaru (TIU) at night in June 2023.
The aircraft, ZK-NEM (msn 630), carrying 33 passengers and three crew, descended around 2,500 feet below its programmed flight path and reached a recorded altitude of 1,156 feet, approximately 1,022 feet above ground level. The minimum safe altitude in the area was 2,000 feet.
The captain eventually identified the deviation, levelled the aircraft and climbed back to the correct approach profile before landing safely. There were no injuries.
TAIC found the immediate cause was an incorrect autopilot mode. During a routine altimeter check, the captain selected a different descent mode to provide a smoother transition but subsequently did not switch the system back to the mode required to follow the programmed approach.
Both pilots were also focused on visually identifying Timaru’s runway lights, reducing the effectiveness of their instrument monitoring. Neither pilot detected the unexpectedly rapid descent until the aircraft had already passed below the minimum safe altitude.
However, TAIC found the incident was not an isolated crew error. Its investigation identified six earlier Q300 events in which crews inadvertently remained in an incorrect descent mode or failed to adequately monitor the aircraft’s flight path, resulting in the aircraft descending below the approach profile. Two further events occurred after the investigation began.
Vertical profile of ZK-NEM on descent into Timaru. Graphic: TAIC.
Systemic issues identified across Q300 operations
The Commission found the DHC-8-Q300’s flight management system contributed to the risk because it requires pilots to manually change between descent modes and then remember to reverse that change during the approach. TAIC concluded that this workaround was vulnerable to pilot error.
The crew had also not set the altitude alerter to provide a warning before reaching the minimum safe altitude. Air New Zealand’s own investigation found this was routine across the Q300 fleet because pilots expected to return to the normal descent mode almost immediately.
Air New Zealand operates 23 DHC-8-Q300s across its domestic network.
TAIC also identified shortcomings in crew resource management and training. It found Air New Zealand’s training programme did not adequately address the risks associated with Q300 pilots joining the airline with comparatively less multi-crew experience.
The Commission linked some of the wider issues to the 2019 integration of Air Nelson and Mount Cook into Air New Zealand. Four years after the integration, TAIC found the Q300 fleet’s safety culture had not fully aligned with Air New Zealand’s broader expectations around risk management.
Air New Zealand's Chief Safety & Risk Officer, Nathan McGraw, told Aero South Pacific that safety and a strong safety culture are fundamental at the airline.
"When something doesn’t go as it should, our job is to understand why and learn from it," he said. “We began our own investigation immediately in June 2023 and strengthened our procedures, training, monitoring and safety culture, well before the TAIC inquiry was complete. TAIC has recognised that work."
The investigation also examined the role of the Civil Aviation Authority (CAA), concluding that its oversight of Air New Zealand had not kept pace with changes to the airline and its risk profile.
TAIC said the CAA’s relationship with Air New Zealand had also become too close, potentially making it more difficult for the regulator to maintain sufficient independence in its oversight.
Map of ZK-NEM's flight path into Timaru. Image: Google Earth/TAIC.
Safety improvements and outstanding issues
However, significant safety changes have since been introduced. Air New Zealand changed its altitude alerter policy shortly after the incident, introduced verbal cross-checking of mode changes and revised its ground-proximity warning procedures.
The airline has also strengthened its DHC-8-Q300 training covering go-around decision-making, high-workload situations, crew resource management and deviation calls. It has introduced a cultural reset programme for Q300 pilots and increased safety monitoring.
The CAA has meanwhile moved towards more risk-based and intelligence-led oversight, with changes to its monitoring, certification and occurrence-triage processes. Procedures for reporting incidents to TAIC have also been strengthened.
TAIC says these measures address seven of the nine safety issues identified during its investigation.
Two issues remain open. TAIC has recommended that Air New Zealand continue working with De Havilland Canada and Universal Avionics on a technical solution that would allow the Q300’s flight management system to calculate a smooth descent through the transition without requiring the manual workaround.
"The final report makes one recommendation to Air New Zealand, which we've accepted and progressed," added McGraw." Independent investigations, regular audits, and being open about what we can do better are all essential parts of a safe aviation system. We’re very confident in the training, systems and safety culture we have in place today."
TAIC has also recommended that the CAA work through the International Civil Aviation Organization to promote longer cockpit voice recorder recording requirements. New Zealand regulations currently require two hours of recording, creating a risk that important evidence from an incident could be overwritten.
Aside from the unresolved technical and cockpit voice recorder issues, TAIC acknowledges that Air New Zealand and the CAA have implemented substantial changes.
You can read the full findings of TAIC's investigation here.
Photo: AI-Generated.
Contact the writer: andrew@aerosouthpacific.com