The Civil Aviation Authority is warning pilots to ensure they fly within an aircraft's limitations, to avoid the type of "structural failure and in-flight breakup," that occurred during a flight that killed two men south of Dargaville.

The home-built Van RV-7 light aircraft crashed into farmland near Te Kopuru, on January 1, 2018.

Experienced pilot Dean Voelkerling, 53, operations manager at the Northland Emergency Services Trust and a Northland Rescue Helicopter pilot, and his passenger Paul Fabien Rawiri, 45, of Leamington, died in the crash when the light aircraft plunged into farmland about 12.20pm.

The CAA Safety Investigation Report released today said that the amateur built, single engine aircraft, registered ZK-DVS, was on a private flight from Whangārei towards Dargaville.

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Aviation Safety Deputy Chief Executive Dean Winter said the key learning from this tragic accident is to understand the performance and handling characteristics of the aircraft and the risks associated with operating close to the aircraft limitations.

"Accidents can occur whenever the aircraft limitations and/or the pilot's own capabilities are exceeded and that's why it's important to fly within those limits," Winter said.

"These risks can be minimised by preparation, awareness and training."

Part of the light plane that crashed near Te Kopuru in January 2018 that killed two men, sparking a safety warning from the Civil Aviation Authority.
Part of the light plane that crashed near Te Kopuru in January 2018 that killed two men, sparking a safety warning from the Civil Aviation Authority.

Voelkerling held an aeroplane private pilot licence and a helicopter airline transport pilot licence. He had flown about 380 hours on fixed wing aircraft and had gained most of his flying experience on helicopters where he had more than 4300 hours.

The report said the aircraft left Whangārei aerodrome at 12pm, on January 1, 2018, and 17 minutes later the aircraft entered a high angle of bank (AoB) manoeuvre, achieving 70 degrees AoB.

"Five seconds later the AoB increased to 130 degrees and the aircraft began to pitch nose-down. During the resulting descent, the indicated airspeed was recorded at 244 knots, which exceeded the aircraft 'never exceed speed'. Winter said.

''About 30 seconds after entering the high AoB manoeuvre, witnesses observed the aircraft break up in flight and then hit the ground about three nautical miles south-west of Te Kopuru."

The report found that in-flight breakup occurred as a result of "rudder flutter", as the aircraft airspeed exceeded the design limitations. The rudder flutter resulted in the separation of both the rudder and the vertical stabiliser.

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The investigation analysed the human, equipment and environmental factors that may have caused, or contributed, towards the accident.

The safety investigation identified the following contextual factors.

• The aircraft entered a high-speed descent from an unusual altitude.

• The pilot did not recover the aircraft from the unusual altitude or subsequent highspeed descent, which resulted in structural failure and in-flight breakup.

• In-flight breakup occurred as a result of rudder flutter, as the aircraft airspeed exceeded the design limitations.