Fog and disorientation contributed to a microlight crash last year that killed two West Coast men.
But the Civil Aviation Authority (CAA) concluded that if Civil Aviation Rules had been adhered to, the accident would not have happened.
Roger Smith, 58, and workmate Cole Ashby, 25, were both killed when Smith's microlight crashed near Westport on January 30, 2013.
The pair were reported missing the next morning and at about 9.30am the partially-buried wreckage was found by a member of the public on Carters Beach.
Ashby's body was found within the wreck but Smith's was about 1.5km east along the beach.
A CAA investigation found no mechanical defects that could have contributed to the accident.
There were no medical conditions likely to contribute and neither man had alcohol or drugs present in their blood.
At about 8pm on January 30, Smith and Ashby went to Westport Airport to take a flight, with the intention of looking for deer.
Piecing together CCTV footage, eyewitness accounts and photos the CAA concluded the accident happened at about 9.20pm, about 20 minutes after sunset.
A dense fog formed at about 9pm and by 9.30 visibility at the airport was reported to be 300 metres.
Smith did not have a current microlight pilot certificate at the time of the accident and was about a year overdue for a biennial flight review.
He was not certified to fly at night or in weather conditions that required a pilot to fly primarily using the instruments.
The CAA investigation report noted that once a pilot had lost visual reference, such as during dense fog, spatial disorientation could quickly lead to loss of control.
This was likely to be the cause of the accident.
The CAA investigation concluded that Smith took off when visibility was already low and continued to fly despite conditions worsening.
In 2007 Smith had come to the attention of the CAA when it was alleged he flew at a low level in the vicinity of Westport Airport.
- The Press