In 1983 the Judicial Committee of the Privy Council held that Mahon had made serious mistakes of law through acting in excess of his jurisdiction and in breach of natural justice by going on to make findings of a conspiracy by Air New Zealand to cover up the errors of the ground staff. This conclusion was reached on the point of law that those accused of the conspiracy had not been given an opportunity to contest it in Mr Justice Mahon's inquiry: his conclusions that documents had been suppressed, and that witnesses had lied, were not set aside as an appellate court is not permitted to investigate findings of fact.