The Civil Aviation Authority (CAA) says the pilot of a Van's RV-7 plane that crashed south of Dargaville, Northland in 2018 likely exceeded the plane's maximum safe air speed.
Northland Rescue Helicopter Trust operations manager Dean Voelkerling, 53, and a passenger died after crashing into a farm paddock in the Kaipara District on New Year's Day in 2018 just after midday.
A CAA investigation was launched, which was today completed and released to the public.
The chief finding was that Mr Voelkerling likely exceeded the maximum safe speed of the Van's RV-7 during a steep banking manoeuvere, which led to a situation known as "rudder flutter", and the detachment of two parts of the aircraft's tail - the vertical stabiliser and the rudder.
The report found that the pilot had initiated a series of banking manoeuvres shortly after takeoff from Whangārei.
The first banking manoevure was 70 degrees, and the CAA report said the pilot then increased the angle of bank to 130 degrees.
"The aircraft began to pitch nose-down," Aviation Safety Deputy Chief Executive Dean Winter said.
"During the resulting descent, the indicated airspeed was recorded at 244 knots [451km/h], which exceeded the aircraft 'never exceed speed' [370km/h].
"About 30 seconds after entering the high angle of bank manoeuvre, witnesses observed the aircraft break up in flight and then hit the ground about three nautical miles south-west of Te Kopuru."
Mr Winter said the accident was an important lesson to pilots about knowing the limits of their aircraft, and following them.
"Accidents can occur whenever the aircraft limitations and/or the pilot's own capabilities are exceeded," he said.
"That's why it's important to fly within those limits.
"These risks can be minimised by preparation, awareness and training."
Mr Voelkerling was an experienced pilot - he held an aeroplane private pilot licence and a helicopter airline transport licence.
He had flown about 380 hours in fixed wing aircraft and more than 4300 hours in helicopters.
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