The Mount Erebus Disaster
On the 28th of November 1979, a sight-seeing flight to Antartica crashed into Mount Erebus, killing all 257 on board. The Mount Erebus Disaster, as it came to be known, is famous not just for the tragic accident, New Zealand’s worst peacetime disaster, but also because the final accident report’s conclusion was overturned within a year.
Air New Zealand flight 901 was an all-day sight-seeing trip departing Auckland at 08:00 and then landing at Christchurch at 19:00 for refuelling before returning the passengers to Auckland at 21:00, 13 hours after departure. The flight included an experienced Antarctic guide to explain the sights over the public address system. Sir Edmund Hillary had been a guide on previous flights and had been scheduled for the 28th of November flight but cancelled in favour of a speaking tour in the US. Hillary’s friend Peter Mulgrew, a New Zealand mountaineer and yachtsman, filled in for Hillary as the commentator for the flight.
The passengers were offered a champagne breakfast and three films about the Antarctic as they made their way south. The flight was due to arrive over Antarctica shortly after noon NZST.
Neither of the pilots had ever flown to Antartica before and the flight engineer had only been there once. The flight descended over McMurdo Sound for a view of Mount Erebus and McMurdo Station. These sight-seeing flights regularly descended below the minimum safe altitude of 16,000 feet so that the passengers could gain a better view and take photographs.
Air Traffic Control at McMurdo Station (Mac Centre) was aware of this and the controller advised the flight that once the flight was within radar range, about 40 miles (65 km) from the station, the flight could descend safely down to 1,500 feet using the radar controlled let-down service. The crew reported in at 43 miles from the station and asked for approval to descend further, confirming that they had clear visibility. The controller approved this and asked the flight crew to keep Mac Centre advised of their altitude. The crew reported at 13,000 feet and at 10,000 feet.
The controller asked if they still needed the radar-controlled let-down below 10,000 feet through the cloud. The crew replied that they were clear of cloud and happy to proceed visually to McMurdo Station.
However, the flight plan had been changed before the flight to fix a mistake in the earlier route. No one had informed the flight crew of the change and ATC were not aware. As a result of being on a different route, the aircraft never appeared on the controller’s radar.
The flight crew reported at 6,000 feet and reported that they were still visual and descending to 2,000 feet. They still believed they were flying west of Mount Erebus and were safely over water when they crashed into the mountain.
The DC-10 was not understood to be lost until hours later, when flight 901 failed to arrive at Christchurch. The search and rescue teams were initially searching the assumed flight path for hours. Finally at midnight, a US Navy Lockheed LC-130 Hercules spotted the wreckage on Mount Erebus. The weather was too poor for a landing but another helicopter circled the wreckage to confirm the Air New Zealand logo on the tail and that there was no sign of survivors.
The following morning, three mountaineers were lowered onto the Mount Erebus slope from a US Navy UH-1N helicopter. They confirmed that all passengers and crew had been killed in the impact. Recovery and investigation parties were taken to the site in a Royal New Zealand Air Force C-130. The mountaineers returned to the crash site where they erected polar tents and left caches of food and equipment for the parties.
A helicopter pad was established and the longer task of recovering bodies and personal belongings was begun. The site was laid out into a grid system for a detailed accounting of the wreckage. The investigations team were able to retrieve both the cockpit voice recorder and the flight data recorder with the support of mountaineer support from the Face Rescue Squad.
The final report now known as the “Chippindale Report” after chief investigator Ron Chippindale, was released in May 1980.
This final report acknowledged the change in flight plan but concluded that the principal cause of the crash was pilot error, specifically:
The decision of the Captain to continue the flight at low level toward an area of poor surface and horizon definition when the crew was not certain of their position.
The government had already decided to hold an inquiry in March, two months before Chippindale had completed his report. Despite this, they made the report public in June, leading to headlines blaming the incompetent crew for the deaths of the sight-seeing passengers. At the same time, it had become public knowledge that the flight coordinates had been altered without the crew’s knowledge. The airline countered that if the pilots had remained above the minimum safe altitude set for the flight, the plane would never have crashed.
One damning point was that the report did not stick to the official cockpit voice recorder transcript, which had been transcribed by CVR specialists with support from the NTSB. Instead, the report consistently referred to an unofficial transcript from the cockpit voice recorder, in which ambiguous and hard-to-decipher interactions were replaced by specific statements, all of which supported the conclusion of the report.
The differences included a key phrase of “Bit thick here, eh Bert?” which the report referred to as showing that they were flying in cloud, as opposed to the CVR specialists who believed that the flight crew member said “This is Cape Bird” as he recognised a landmark out the window. The audio was not clear enough to be sure and on the official transcripts it was marked as unintelligible. However, in the final report, the transcript quotes the flight engineer as saying “Bit thick here, eh Bert” as a fact, with no reference to the audio difficulties or differing interpretations.
Also, there was no one who went by the name “Bert” on the flight deck.
On the 7th of July, a Royal Commission of Inquiry began to examine every detail of the accident, which provided much new insight both into the crash and the investigation. This report is known as the Mahon Report, after Hon. Justice Peter Mahon who presided over the inquiry with the support of two barristers. He was was given a number of points to investigate, including whether any “culpable act” had directly led to the disaster.
Judge Mahon did not have an aviation background but he went to great lengths to understand the key issues of the flight, including the navigation system for the DC-10 and the process of creating a transcript from a cockpit voice recorder.
His shocking conclusion was that the airline had decided in advance that the cause of the accident must be attributed to pilot error.
The palpably false sections of evidence which I heard could not have been the result of mistake, or faulty recollection. They originated, I am compelled to say, in a pre-determined plan of deception. They were very clearly part of an attempt to conceal a series of disastrous administrative blunders and so… I am forced reluctantly to say that I had to listen to an orchestrated litany of lies.
He was less harsh about Chief Inspector Chippindale but nevertheless dismisses his findings as untenable. He also educated himself about the illusion known as “whiteout”, a circumstance which had not been investigated in the original report. The Mahon Report included in-depth explanations of all of these components so that the detailed analysis is also extremely accessible, even without aviation experience.
Although Chippindale concluded that the principal cause of the crash was the flight crew’s decision to fly beneath the minimum safe altitude, Judge Mahon showed that this was routine for these sight seeing flights and indeed, the promotional brochure showed photographs which were clearly taken from below the minimum safe altitude.
Judge Mahon concluded that the crash of Air New Zealand flight 901 was down to ten separate issues, where removing any single one would have avoided disaster.
Of these ten contributing causes, he determined that only two of them were the result of a culpable act or omission.
- There was not supplied to Captain Collins, either in the RCU briefing or on the morning of the flight, any topographical map upon which had been drawn the track along which the computer system would navigate the aircraft.
Neither Captain Collins nor any other member of his crew was told of the alteration which had been made to the computer track.
He believed that the principal cause was Air New Zealand’s decision to change the flight plan waypoint coordinates without advising the crew. This new flight plan took the aircraft directly over the mountain rather than alongside it. The crew believed that they could descend safely based on the track that they believed they were following. In addition, weather conditions most likely lead to whiteout conditions, which meant that there were no navigational references visible to the flight crew. Although they were in clear weather, they were unable to see the mountain, even when it was directly in front of them.
The dominant cause of the disaster was the act of the airline in changing the computer track of the aircraft without telling the aircrew. That blend of act and omission acquires its status as the “dominant” cause because it was the one factor which continued to operate from the time before the aircraft left New Zealand until the time when it struck the slopes of Mt. Erebus. It is clear that this dominant factor would still not have resulted in disaster had it not been for the coincidental occurrence of the whiteout phenomenon. But the conditions of visual illusion existing in Lewis Bay would have had no effect on flight TE 901 had the nav track of the aircraft not been changed, for it was only the alteration to the nav track which brought the aircraft into Lewis Bay instead of McMurdo Sound.
In my opinion therefore, the single dominant and effective cause of the disaster was the mistake made by those airline officials who programmed the aircraft to fly directly at Mt. Erebus and omitted to tell the aircrew. That mistake is directly attributable, not so much to the persons who made it, but to the incompetent administrative airline procedures which made the mistake possible.
The Mahon Report, with its emphases on detail and understanding technical aspects, changed the way we look at risk management and organisational failures. He paved the way for investigations to insist on taking on the complex issues rather than allowing an investigation to quickly settle on an easy answer and look for evidence to back it up.
The Erebus: The Loss of TE901 website is a fantastic resource that goes over the accident and both reports, along with the context in which they were written. I highly recommend taking a few hours to go over the rich collection of information and explanations that has been collected there.