After the site investigation in Antarctica was complete, Ron Chippindale and his investigators returned to New Zealand to continue their work. Chippindale's enquiries also took him to the United States and the United Kingdom from late December 1979 to early January 1980.
On 4 March 1980 the interim accident report was sent to parties whom Chippindale considered might bear 'some degree of responsibility for the accident'. At the time he refused to reveal who had been sent the interim report, advising that doing so would indicate the report's findings.
Calls for a public inquiry, which had begun shortly after the accident, continued amid the controversy over who had received Chippindale's interim report. The Attorney-General, Jim McLay, subsequently announced that there would be a Royal Commission of Inquiry. On 21 April Justice Peter Mahon was appointed to conduct the inquiry. The public hearings were subsequently set down to begin on 7 July, with a preparatory hearing on 23 June.
A number of parties protested against the planned release of Chippindale's final report in advance of these hearings. But the government went ahead with the public release of the report at midnight on 19 June.
In the days prior to the release, Chippindale advised the media that he had had difficulty finding 'the ultimate cause'. He explained that what he had said in the report was what he thought was the 'probable cause - the last thing that made the accident inevitable', but that there were other factors leading up to the accident.
These other factors, outlined in the conclusions section of Chippindale's report, included 'omissions and inaccuracies' in the route qualification briefing. Criticism was directed at Air New Zealand and the Civil Aviation Division (CAD) for these and other failures. But Chippindale ultimately concluded that the flight would have proceeded safely had the pilot not descended below the minimum safe altitudes specified by CAD and Air New Zealand.
The public hearings of the Royal Commission of Inquiry into the accident began as scheduled on 7 July 1980. Chippindale was the first of 52 witnesses examined. He was asked to expand on various aspects of his report, and was cross-examined by legal counsel. Other witnesses called during the 75 sitting days included employees of Air New Zealand, CAD, the New Zealand Meteorological Service and members of the pilots' families. In addition to hearing evidence in New Zealand Mahon travelled to the US and UK.
Mahon had been due to make his report to the Governor-General by 31 October, but he was granted four extensions to this deadline. At the conclusion of the public hearings he had 3083 pages of evidence, 284 documentary exhibits and 368 pages of closing submissions to review. His report was submitted on 16 April 1981 and released publicly on 27 April.
In the section summarising 'the cause of the disaster' Mahon argued that 'the occurrence of any accident was normally due to the existence of a variety of factors'. He asserted that in this case there were 10 factors, and the disaster would not have occurred had any one of them not been present. But he then went on to describe a single cause of the disaster. He disagreed with Chippindale's 'probable cause' that the pilot was at fault, and cleared the crew of any responsibility for the accident. Instead he laid the blame squarely on Air New Zealand.
Mahon also claimed that the airline's executives and management pilots had engaged in a conspiracy to whitewash the enquiry, accusing them of covering up evidence and misleading investigators through ‘an orchestrated litany of lies’. He ordered Air New Zealand and CAD to pay the costs incurred by the consortium representing the estates of deceased passengers, the New Zealand Airline Pilots Association, and the estates of the pilot and co-pilot. He also ordered the airline to pay $150,000 towards the government's costs.
In the months that followed Mahon's accusation of 'an orchestrated litany of lies’ was challenged by Air New Zealand in the Court of Appeal. The Court concluded that Mahon had breached natural justice by not allowing those accused to respond to the allegations and that he had acted outside his jurisdiction. His order of costs against the airline was quashed. Mahon subsequently resigned from the High Court bench.
Despite his resignation Mahon decided to appeal to the Privy Council against the Court's judgement and the government agreed to pay his costs. The Privy Council 'very reluctantly' agreed with the Court's judgements and dismissed Mahon's appeal. They also placed on record a tribute to the 'brilliant and painstaking investigative work done by the judge'.
The debate over whether pilot error or Air New Zealand was to blame for the Erebus disaster continues today. It is often stirred up by media interest or by events held on significant anniversaries of the disaster.
In 1999 the Minister of Transport, Maurice Williamson, who worked at Air New Zealand as a corporate planner at the time of the crash, tabled the Mahon report in Parliament. Williamson argued that the time for apportioning blame was over and that he was tabling it because 'of the lessons it taught'. But some involved in the accident investigation and Royal Commission of Inquiry argued that Williamson should also be tabling the judgements of the Court of Appeal and the Privy Council on the report.
On 23 October 2009 Air New Zealand CEO Rob Fyfe apologised to those affected by the tragedy for Air New Zealand's failures and for its treatment of families of the victims. But for many this apology did not go far enough. Maria Collins, the wife of Captain Jim Collins, the pilot of Flight TE901, advised the media that she still hopes to clear her husband's name.