The Transport Accident Investigation Commission (TAIC) says a pilot who had to make an emergency landing in a Westpac rescue helicopter in 2014 should not have even been flying the aircraft.
The helicopter -- which was carrying four people, including one Christchurch Hospital-bound patient -- lost power in two engines near Springston and was forced to make an emergency landing.
No one was injured, but there was considerable risk to the aircraft's occupants -- and now TAIC says the pilot did not have the "recent experience" necessary in that helicopter model to embark on the flight.
At the time, the power loss was deemed to be a result of low fuel flow to the engines, but TAIC says there was a "substantial amount" of fuel remaining in the aircraft's tanks -- saying it was simply the pilot's "incorrect management" of the fuel supply system that was to blame.
The TAIC says the pilot should have switched on the fuel transfer pumps after starting the engines, but didn't -- and also failed to turn off a dimmer switch on his dashboard lights, which would have alerted him to his mistake.
Chief accident investigator Tim Burfoot says the pilot didn't adjust to the different procedure required to fly a BK117 model aircraft.
"He probably followed a process that was applicable to a different type of helicopter," he said.
"On one helicopter, you switch your fuel pumps on and they stay on, but actually, you switch to this type of helicopter -- which he wasn't really that experienced or current on -- and the pre-start procedure involves switching two priming pumps on, and once the engine has started they have to be switched off and another set switched on."
However, the pilot was not the only person who had made mistakes, according to the report -- with the company told it too could have helped avoid the incident.
The TAIC said the operator did not offer any procedures by which the pilot could have refreshed his understanding of how to fly a BK117, "such as additional training, supervision or a policy on the use of written checklists in such a situation".
"Pilots... may actually meet the minimum requirements of the Civil Aviation rules -- [but] actually that in itself is not enough usually to ensure that a pilot is totally experienced and comfortable flying that machine, which he may not have flown for quite some time," Mr Burfoot said.
However, Mr Burfoot says the operator has now altered its policies following the TAIC report, in response to the recommendations.
"It's a very favourable response -- they've taken the issue seriously," he said.
The commission says pilots must remain vigilant when switching aircrafts by examining cockpit checklists on procedure, and recommends that operators ensure their pilots "are appropriately experienced, trained and current on each aircraft type".