While taking off from Big Bay, a beach north of Milford Sound, the aircraft's propeller was severely damaged by stones thrown up during the take-off run.
Despite being aware of the potential for damage when landing on strips such as Big Bay, the Civil Aviation Authority said the pilot did not conduct an inspection of the aircraft after return to Queenstown, not even a quick "walk-around" which would have revealed the damage.
"The pilot then flew to Milford Sound to pick up a group of tourists and it was at this stage that he noticed the damage to the propeller and phoned head office to inform them of the damage.
"He also attempted to minimise the damage by filing down the propeller – a maintenance task only appropriately qualified aircraft engineers can perform."
Despite not hearing back about the airworthiness of the propeller, the pilot decided to fly back to Queenstown with six passengers onboard.
"Upon landing, the aircraft was immediately grounded in the interests of safety by the company's owner."
Charges were laid in 2010, but the prosecution remained on hold for close to a decade, as the former pilot was living overseas.
His association with the tourism operator ended shortly after the incident and the company is now under new ownership and management.
CAA deputy chief executive David Harrison said the conviction highlights the importance of aircraft damage being assessed by appropriately qualified engineers, not by pilots taking a punt.
"Taking a 'she'll be right' attitude just doesn't cut it when there's damage to critical aircraft components such as propellers," Harrison said.
"Pilots and engineers each have hugely important roles to play in keeping aviation safe, but there are clear lines about the sort of work that needs to be carried out by qualified aircraft engineers.
"In this case we're lucky that there weren't more serious consequences given the seriousness of the damage to the prop."
