The crash on March 5, 2006, killed Wanaka-based pilot Keith McKenzie (29), of Canada, and his passenger, American tourist Jonathan Stein (61), who were taking a private sightseeing flight in a Robinson R22 owned by Wanaka Helicopters. It crashed on Homestead Peak, near the Matukituki Valley, causing a large tussock fire.
The New Zealand Civil Aviation Authority (NZCAA) report into the crash said an in-flight break-up of the helicopter had occurred at least half a nautical mile before the impact point. However, its investigation was unable to conclusively establish what had caused the left cabin door, which was struck by the main rotor blade, to detach.
Retiring Queenstown coroner Alan Macalister said the crash was the result of the passenger door detaching and damaging the rotor, causing irreversible loss of control, and the most likely reason for the door detachment was the lack of a cotter pin securing the lower hinge.
The potential hazard arising from the absence of a cotter pin in the lower hinges of R22 doors had been identified in 1994 when the manufacturer introduced Revision H, which required all new helicopters and those overhauled after that date to be fitted with a lower door hinge that made provision for a cotter pin.
In late 1994, the UK CAA issued an airworthiness directive that required all UK registered R22 helicopters to be fitted with Revision H-compliant hinges by January 31, 1995, following an incident in a UK-registered R22. This was not reported to other national regulatory authorities.
The manufacturer also referred to the use of upper and lower cotter pins in the 2000 Pilot Operating Handbook and the 2004 Illustrated Parts Catalogue, but the significance was "largely unrecognised by the industry in New Zealand".
In April 2010, four years after the Homestead Peak accident, the manufacturer issued a service bulletin requiring pins in both hinges.
Following an initial adjournment of the inquest in January, pending the receipt of the accident report, the matter was set down for a hearing then adjourned again on August 30 this year by Mr Macalister to enable further inquiries to be made.
Mr Macalister had raised questions over why the cotter pin safety risk in the R22 was identified by the helicopter's manufacturer and a leading aviation authority nearly 12 years before the accident but did not come to the attention of the NZCAA.
The NZCAA aircraft certification manager responded to Mr Macalister's questions and said aviation authorities did not monitor airworthiness directives issued by every other country and it would be "impracticable" to do so. The United States was the "State of Design" for R22s, making it responsible for transmitting any information found necessary for the aircraft's continuing airworthiness and safe operation.
The information issued by the UK CAA about the problems with R22 lower door hinges had "not been promulgated as mandatory continuing airworthiness information by the US Federal Aviation Administration (FAA)", so New Zealand had not been notified of the safety issues before the Homestead Peak accident.
In March 2008, as a result of what was learned from the accident, the NZCAA issued an airworthiness directive requiring cotter pins in both door hinges and regular inspection. The FAA was notified of the directive, but did not issue any subsequent notification of its own to address the issue with its world fleet of aircraft, the NZCAA said.
In his finding released this week, Mr Macalister said the NZCAA had advised it issued about 300 airworthiness directives each year in relation to small aircraft, with all but 5% or less resulting in State of Design-issued airworthiness directives. The few which were not actioned could generally be explained by the probability that the environmental or operational conditions underlying the issue of the directives were not seen by the State of Design as having worldwide application.
The wide compliance in New Zealand with the NZCAA's airworthiness directive suggested that would have also been the case had the process been initiated by an FAA airworthiness directive given in response to the 1994 UK CAA airworthiness directive, Mr Macalister said.
Because the NZCAA believed there was no evidence the case pointed to risks in relation to other aircraft or passengers, Mr Macalister made no further recommendations.
