The Taic said it could not determine the cause of the collision but could not rule out that the 52-year-old pilot reverted to "previously reported behaviour and misjudged his approach".
In August 2013, other pilots expressed "concern" to THL's chief pilot that the pilot misjudged his separation from another helicopter on a photographic flight and made an "unnecessarily fast" landing approach, the report said.
The chief pilot briefed him on "general flying standards" but did not formally record the concerns or actions taken.
The pilot was observed by the chief pilot on a flight crew competency check on August 22, 2013.
The pilot had passed the check but the chief pilot "remained concerned that the pilot, like some other pilots at the time, had let his standards slip and was displaying a degree of complacency".
The pilot then flew a "snow experience" flight with the chief pilot in a second Squirrel. The chief pilot found "no fault", so considered the previous issues rectified.
The briefing and monitoring were not recorded in the pilot's personnel file.
On the day of the crash, two Squirrels left for the Lochnagar Saddle at 2.49pm, each with six Chinese passengers.
The more experienced pilot, flying the second helicopter, changed the landing site due to better snow conditions further north, took the lead, and landed on the Tyndall Glacier.
The second pilot approached to the right, where blowing snow made the parked helicopter "barely visible".
He initiated a "go-around" manoeuvre, passing closely in front of the parked helicopter, eliciting a rebuke from the senior pilot that was not responded to.
"It could not be determined whether the senior pilot's rebuke adversely affected the pilot's concentration or spatial judgement on the following approach," the report said.
About 3.08pm, the airborne helicopter hit the parked helicopter from behind.
It climbed slightly and spun rapidly before tipping forward.
It hit heavily on the left before rolling to the right, coming to rest about 70m in front of the parked helicopter.
Unable to contact the Queenstown base, the senior pilot activated his emergency locator transmitter and the first rescue helicopter arrived at 3.55pm.
The pilot sustained a severe brain injury and some minor fractures, and spent 39 days in hospital. He had a "lengthy period" of post-traumatic amnesia during which he was unable to recall the accident and had limited recall of the two months prior.
All six passengers were injured. Three required hospital treatment and two stayed in hospital for two nights. The Taic ruled out helicopter performance and other environmental factors as causes.
There was no evidence suggesting the pilot had a medical condition that contributed, but that possibility could not be excluded.
No alcohol or illicit drugs were found in his system.
The commission also found THL's standard of record-keeping for the pilot's training and performance monitoring did not meet "generally accepted best practice".
Totally Tourism Ltd managing director Mark Quickfall told the Otago Daily Times the company accepted the report and supported the Taic's key lessons.
"[We] have taken those on board and reviewed our standard operating procedures and made sure we have those covered."
Quickfall said the injured pilot could no longer fly after the accident but, following rehabilitation, he was employed in a "non-flying role" within the company until he relocated to Nelson.
Key lessons
• Transport operators should keep formal records of concerns about operational staff and how they are dealt with.
• Pilots should inform flight-following organisations of any changes to operating areas or destinations.
• The "widespread practice" of allowing passengers to leave and return to a helicopter parked on snow while the rotors are turning is "hazardous".
• Civil Aviation Authority director recommended to advise helicopter operators who conduct snow landings to address the hazard of passenger disembarkation and embarkation during snow landings while rotors are turning in safety management systems.
