An Air New Zealand De Havilland Canada Q300 descended more than 2,500 ft below its planned flight path on approach to Timaru in June 2023, reaching roughly 1,000 ft below the minimum safe altitude before the captain corrected course and landed safely with 33 passengers and three crew aboard.

The Transport Accident Investigation Commission (TAIC) has concluded the event was not an isolated flight-crew lapse. Chief investigator of accidents Louise Cook said investigators identified six similar events on Q300 aircraft, plus another two after the inquiry opened.

"It wasn't the case that the crew had a bad night," Cook said.

The aircraft was operating from Wellington to Timaru when it deviated from its programmed flight path. TAIC found the way the aircraft's systems were configured forced pilots to remember to reverse a manual step partway through descent — a workaround that increased the likelihood of human error. Both pilots missed the deviation because they were fixated on visually identifying the runway lights, degrading their instrument monitoring.

Cook said TAIC's view was that the appropriate response would have been a go-around, allowing the crew to recheck everything before starting the descent again. While the event looked like a simple crew error, she said the error type was already known to both the operator and the regulator, and the defences in place should have stopped it becoming a serious incident.

The inquiry identified contributing factors across four areas: crew training, the safety culture within Air New Zealand, the Q300 autopilot design, and regulatory oversight by the Civil Aviation Authority (CAA).

On oversight, Cook said regulators needed to scale their surveillance to match an operator's changing risk profile. "The commission identified that in 2019 Air New Zealand went through some pretty major changes, particularly around the merger of its regional carriers and then there was also Covid-19," she said. "Those factors introduced new significant risks and that should have triggered close scrutiny by the Civil Aviation Authority."

TAIC also found the regulatory relationship was too close in nature, which likely "impeded the regulator's ability to impartially oversee" Air New Zealand's safety management system.

Of nine safety issues identified, seven have been addressed. "Air New Zealand and the CAA have taken on board the commission's findings and made important changes to training, procedures, safety culture work, and how the CAA structures its oversight," Cook said. "We're satisfied those actions address seven of the nine safety issues we identified, so we haven't needed to recommend further action there."

The two open recommendations concern the flight management system and the cockpit voice recorder. TAIC recommended Air New Zealand work with De Havilland Canada on an FMS design that calculates a smooth descent profile through transition and removes the manual workaround. It also recommended the CAA push for a change to international rules so that all transport aircraft required to carry a cockpit voice recorder meet modern recording requirements.

Air New Zealand chief safety and risk officer Nathan McGraw said the airline opened its own investigation after the incident and strengthened procedures, training, monitoring and safety culture before TAIC completed its inquiry. "When something doesn't go as it should, our job is to understand why and learn from it," he said, adding that work is underway with De Havilland Canada on a technical solution for the descent profile. "We're very confident in the training, systems and safety culture we have in place today."

A CAA spokesperson said the authority accepted the cockpit voice recorder recommendation and plans to raise it through the appropriate International Civil Aviation Organization forum. "Since then, CAA has strengthened how it brings together safety intelligence, monitoring, certification and regulatory decision-making, with a more coordinated and risk-based approach to oversight," the spokesperson said.

New Zealand Air Line Pilots' Association president Andrew McKeen, a 787 pilot, said the findings reinforced that safety is a shared system responsibility: operators must identify emerging risks, regulators must retain the capability and independence to oversee them, and pilots must maintain disciplined monitoring and recovery decision-making. He said the report showed how safety depends on recognising and acting on precursor events before an individual error becomes a more serious one.

The outstanding items now rest with De Havilland Canada's FMS redesign work and the CAA's push at ICAO level on recorder standards, with both actions still open as of the report's release.