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Mahon, Peter Thomas

by Grant Morris


An experienced lawyer and judge, Justice Peter Mahon is best known for his report on the 1979 Erebus air crash, which killed 257 people. Mahon concluded that Air New Zealand’s inadequate safety processes led directly to the crash. He accused the airline of covering up its mistakes with ‘an orchestrated litany of lies’. This controversial finding was fiercely refuted by Air New Zealand.

Early life and Second World War

Peter Thomas Mahon was born in Christchurch on 1 November 1923, the son of Agnes Helen Tankard and her husband, sales manager Cecil Owen Mahon. Peter Mahon was raised a Roman Catholic, attending St Mary’s Primary School and St Bede’s College in Christchurch. His family was not wealthy, but he won an academic scholarship which covered his tuition at St Bede’s. A top scholar, he enrolled in law at Canterbury University College in 1940. 

Mahon enlisted in the Second New Zealand Expeditionary Force after completing two years of his studies. He served in Italy, an experience which provided insights into human suffering and enabled him to lead and interact with people from varied backgrounds; such insights are invaluable to a legal professional, especially a judge. Mahon actually completed some of his legal studies while on active service. He ended the war as a Second Lieutenant, subsequently serving in Japan in Jayforce, part of the British Commonwealth Occupation Force.

Building a legal career

Mahon returned to Christchurch, graduated with a Bachelor of Laws, and was admitted to the bar in 1947. Mahon had clerked at Raymond, Stringer, Hamilton and Donnelly before he enlisted, and he now joined the firm as a lawyer. Sir Arthur Donnelly, one of the partners, continued to serve as a mentor and role model for Mahon. This was Mahon’s most important professional relationship.

In 1954 Mahon served as junior prosecution counsel to Crown Solicitor Alan Brown in the notorious Parker–Hulme murder trial. Brown became ill during the case, providing Mahon with the opportunity to play a key role. Both Pauline Parker and Juliet Hulme were convicted. Three years later, aged 34, Mahon became a Crown Solicitor, and he was soon a well-known and respected advocate in the Christchurch courts. He had the opportunity to conduct three appeals before the Privy Council. In recognition of his leading role at the Bar, he was appointed a Queen’s Counsel in 1971.

While Mahon enjoyed the role of courtroom lawyer, both in prosecution and defence, he accepted an offer of a temporary Supreme Court judgeship in late 1971 and a permanent judgeship in October 1972. This involved a move from Christchurch to Auckland. While Mahon was considered an able and articulate judge, he expressed some frustrations in the role and appeared to have some regrets in leaving the Bar for the Bench. In particular, Mahon disagreed with the strain of judicial activism seen in the judgments of Court of Appeal judge Sir Owen Woodhouse. This rivalry reached its climax in Woodhouse’s 1981 judgment criticising Mahon’s Erebus report.

Private life and relationships

Mahon married Margarita Carol Smith on 17 April 1952 at All Saints’ Anglican Church, Dunedin. Both husband and wife were intelligent and cultured individuals with shared interests. This made for a successful marriage and provided Mahon with invaluable support during the Erebus saga. The couple had three children: Janet, Sam and Tim. Sam Mahon became a well-known artist and outspoken conservationist, who wrote an insightful, poetic biography of his father in 2008. This followed Peter Mahon’s own book, Dear Sam (1985), which includes personal letters to his family.

Mahon was devoted to the law but also found time for outside activities, such as golf, hunting and following horse-racing. His other interests suggest a less conventional man. He loved poetry, and the Erebus report and his two books demonstrate his attention to detail in writing. He also had a keen interest in ornithology and clearly enjoyed being outdoors. He could be described as a ‘Renaissance Man’, especially in comparison to many of his male peers of the post-war era. This was helped by his patrician bearing and eloquence.


On 28 November 1979, Air New Zealand’s sightseeing flight TE901 flew directly into Mt Erebus in Antarctica, instantly killing the 237 passengers and 20 crew. The tragedy stunned the nation and many New Zealanders had connections to those who had died. Chief Inspector of Air Accidents Ron Chippindale investigated the crash and his report, released to the public in June 1980, found that it had been caused by pilot error. Robert Muldoon’s National government established a royal commission of inquiry, with Mahon as sole commissioner, on 21 April 1980. It was unusual to appoint only one commissioner, and Mahon was soon under extraordinary pressure in terms of both workload and public focus.

The hearings lasted several months, with Mahon hearing testimony from 52 witnesses and studying 284 documentary exhibits. He also travelled to Antarctica and the United States as part of the investigation. During the hearings, Mahon formed the view that Air New Zealand ground crew were primarily responsible for the crash because they had changed the flight coordinates without notifying the pilots. Management were most directly responsible, he believed, because their ‘incompetent administrative … procedures … made the mistake possible.’1 The error was exacerbated by whiteout conditions during which the mountain was indistinguishable from clouds. He also surmised that Air New Zealand witnesses, including senior management, were presenting false evidence to the commission in an attempt to avoid liability.

Mahon’s report was released to the public on 27 April 1981. He contradicted Chippindale’s finding that pilot error had been the primary cause of the crash, and concluded that Air New Zealand witnesses had engaged in ‘an orchestrated litany of lies’. This memorable line has become one of the most famous in New Zealand’s history, aided by the carefully chosen words and use of iambic pentameter. The report’s conclusions caused huge controversy and sparked a furious backlash from both the airline and Prime Minister Muldoon. Air New Zealand argued that in making the perjury finding, Mahon had breached natural justice and acted ultra vires (beyond his jurisdiction as commissioner).

Air New Zealand pursued legal action which resulted in a judicial review of Mahon’s findings in the Court of Appeal. In December 1981 the court found that Mahon had breached natural justice by not allowing those accused to respond to his allegations, and that he had acted beyond his jurisdiction in his findings of perjury. The court also cancelled Mahon’s order of costs against Air New Zealand, but did not challenge his findings relating to the cause of the accident. Justices Woodhouse and Duncan McMullin delivered particularly critical judgments. Mahon resigned as a judge, citing loss of confidence from his peers. He appealed the court’s decision to the Privy Council, an expensive, time-consuming, stressful and ultimately unsuccessful process. Mahon’s finding regarding the cause of the accident remained but, in his view, his reputation had been impugned. The saga divided the New Zealand legal profession and played out in full public view.

The aftermath

In the aftermath of the Erebus report and his subsequent resignation from the Bench, Mahon pursued scholarly and literary activities. He was initially unsuccessful in securing an academic post, possibly due to the Erebus report fallout. Mahon was eventually appointed to an academic post in the University of Auckland’s law school. Sam Mahon subsequently donated a bust he had made of his father to the law school library. Mahon published his personal perspective on the Erebus report saga, Verdict on Erebus, in 1984. The book was a best-seller and cemented his reputation as a man of principle speaking truth to power. In keeping with his penchant for being involved in high-profile events, Mahon headed the royal commission of inquiry into the 1984 Queen Street riot.

Peter Mahon died of heart failure in Auckland on 11 August 1986, aged 62. He had been suffering poor health for several years, and the stress of the Erebus report may have contributed to his relatively early death. He had built up some momentum as an author, and death ended what could have been a successful literary career.

Mahon is an excellent example of a member of New Zealand’s elite challenging that elite. He angered the leaders of New Zealand’s national airline, the prime minister, and many in the senior judiciary. This obviously damaged his professional career but also made him a national hero for many New Zealanders. Others, however, including many in the legal profession, rejected this assessment and considered that Mahon had overstepped his authority. He remains a controversial figure who will always be remembered for the Erebus report; it overshadows his other achievements but guarantees him an important place in New Zealand’s legal history.

  1. Report of the Royal Commission to Inquire into the Crash on Mount Erebus, Antarctica of a DC10 Aircraft Operated by Air New Zealand Limited. Wellington, 1981, p. 159. Back

Links and sources


    Mahon, Peter. Dear Sam. Auckland, 1985.

    Mahon, Peter. Verdict on Erebus. Auckland, 1984.

    Mahon, Sam. My father’s shadow: a portrait of Justice Peter Mahon. Dunedin, 2008.

    Report of the Royal Commission to inquire into The Crash on Mount Erebus, Antarctica of a DC10 Aircraft operated by Air New Zealand Limited. Wellington,  1981.

    Erebus: the aftermath. TVNZ documentary, 1987.

How to cite this page:

Grant Morris. 'Mahon, Peter Thomas', Dictionary of New Zealand Biography, first published in 2019. Te Ara - the Encyclopedia of New Zealand, (accessed 20 June 2024)