There might be questions about what did and did not happen to Air New Zealand Flight TE901 on November 29, 1979, but one thing is abundantly clear: The crash was 100% avoidable.

Pilots Jim Collins and Greg Cassin were experienced but had not flown into Antarctica before that trip. They received their first copy of the flight’s itinerary on November 9, a plan that had been established and approved by the New Zealand Department of Transport Civil Aviation Division in 1977. It was a detailed flight plan that consisted of flying directly from Cape Hallett to the McMurdo beacon on Antarctica.

But here’s where things get a little odd: The flight plan as approved and as received by pilots during the few years of the sightseeing flights’ history had the pilots instructed to take the plane almost directly above the summit of Mount Erebus, a 12,448-foot (3794-metre) peak.

Update to the flight plan

The printout given to Collins and Cassin on Nov. 9, taken from Air New Zealand’s ground control system, instructed then to fly a more southerly route down the middle of McMurdo Sound, putting Mount Erebus about 27 miles (43.5 kilometres) to the east of the flight.

This was the path used previously by other pilots and crew when embarking on the sightseeing trips; no one was consciously aware that the flight plan and the ground control system printout were divergent, according to a report on the crash published in 1984.

When the coordinates were compared by Captain Leslie Simpson, who piloted a similar flight from New Zealand to Antarctica on Nov. 14, 1979, Simpson was surprised by the disparity and mentioned the difference to Air New Zealand’s Navigation department, which triggered an update to the flight plan reinforcing the McMurdo coordinates with the navigational beacon.

The flight crew was never notified of this change. According to the same report from 1984, the flight plan given the morning of the Mount Erebus crash included the path directly over the mountain’s peak the flight was below 13,000 feet (3962 metres) in altitude.

The data entry operator keyed a 4 instead of a 6 into the machine

According to a website dedicated to the disaster and the investigation into the crash, the original flight plan was over Mount Erebus but trips “were able to operate away from the planned nav track in brilliant weather conditions ensuring good surface and horizon definition.

Then, some 18 months after Antarctic flights began, 14 months prior to the accident, the airline computerized its method of storing and producing flight plans. At this time, an error was made; the data entry operator keyed a 4 instead of a 6 into the machine, and this error had never been noticed as such.

The effect of this erroneous keystroke was to shift the route nearly 30 miles (48 kilometres) to the west, so that it ran down McMurdo Sound. One of the reasons that no one saw this as an error was that it seemed a logical change to make; shifting the route away from an active volcano and down over the flat sea ice of McMurdo Sound actually produced a better, safer result.

A sightseeing flight at low altitude

After all, if the point of the trip was to give tourists a good view and pretty scenery, why not fly through a 40-mile-wide (64 kilometre) Sound and provide a glimpse of the mountain in profile, instead of having them look down onto a peak which can’t be all that visually impressive from above?

But there’s another glitch in all the day’s proceedings. Anyone who’s driven in snow is familiar with whiteout conditions, in which it’s nearly impossible to determine what’s a road, a ditch or an empty field. Such conditions are disorienting and make it hard to find any point of concentration on which to focus and establish a horizon.

The transcript of the flight’s final few minutes indicates no severe weather conditions or any other obstacles that might’ve indicated the pilots were in distress or otherwise aware of any problems. It’s a chilling read as Peter Mulgrew—a friend and expedition companion for Sir Edmund Hillary—on the flight as a tour guide, tells the passengers the flight is about to descend.

“This is Peter Mulgrew speaking again folks,” he said. “I still can’t see very much at the moment. Keep you informed soon as I see something that gives me a clue as to where we are. We’re going down in altitude now and it won’t be long before we get quite a good view.”

One member of the crew asks where the flight is in relation to Mount Erebus; another says the mountain is “left, about 20 or 25 miles.” (Remember, they were unaware their flight plan had changed.) “That looks like the edge of Ross Island there,” someone identified in the transcript as MU says. “I don’t like this,” responds someone identified as F/E (first officer).

Suddenly, at 12:49 p.m., the navigation system begins sounding alarms.

F/E: “Five hundred feet” – GPWS: “Pull up!” – F/E: “Four hundred feet.” – GPWS: “Whoop, whoop pull up. Whoop whoop pull up” – CA: “Go-around power please.” – GPWS: “Whoop whoop pull” (Sound of impact)

Endless world of white

Alwyn Gordon Vette was a pilot in New Zealand for decades before he was involved in the investigation of the Mount Erebus crash. His research suggested the pilots weren’t flying in poor conditions but rather had become slightly disoriented due to an endless world of white in front of them which made it practically impossible to notice the mountain directly in front of them.

Found among the wreckage of the downed plane were cameras, the film from some of which was processed and provided evidence of clear flying conditions the day of the crash. Based on these photos and his own research, Vette determined the pilots were in the middle of whiteout conditions, not because of active snowfall but because the horizon and landscape blurred together.

“Vette’s theory of sector whiteout, where visibility is affected in just one direction, is now an accepted factor in arctic flying,” Air and Space Magazine noted in an article about Vette’s death, at the age of 82, in August 2015. Vette received the New Zealand Order of Merit in 2007 for his work not only in this investigation but his actions in 1978 when he heard a distress call while piloting an Air New Zealand flight.

Vette picked up a signal from the pilot of a small Cessna who had gotten lost on his way to Norfolk, an island in the Pacific Ocean. Vette helped locate the plane and guide it to safety just as the pilot, Jay Prochnow, was running out of fuel.

The same set of gloves to put food in your mouth

After the crash, recovery crews, led by New Zealand police, spent two continuous, nonstop weeks on the scene, an isolate stretch of glacier that was difficult to get to and a harsh environment in which to work. The crew had to share a single bowl for washing, meaning the water often turned black—there wasn’t much water for the crew for the first few days and nothing went to waste.

Also, the workers had to use the same pair of gloves for recovery as they did when eating, meaning their hands would smell like the grease from charred remains while trying to eat.

Bob Mitchell led the recovery attempt and told the UK Telegraph newspaper about that during in 2015 when a documentary on the crash was released.

“There is no easy way to deal with a body,” he said. “You have to pick it up, put a label on it, and you have to handle it. You can’t airbrush it. And some of those bodies were very difficult to get to.”

Stuart Leighton, 22 at the time of crash and a member of Mitchell’s team, told the newspaper that the gloves they wore “were baked with the fatty human remains, the soot, the whatever, and you ended up having to use the same set of gloves to put food in your mouth.”

Mitchell, who feared the investigation and reclaiming of bodies from such a grotesque scene would traumatize him, admits “The smell of kerosene, jet fuel, takes me straight back to Erebus. It’s not that I get flashbacks, but I immediately remember.”

And to make matters even more challenging, the workers sometimes had to rebury remains under thin layers of snow and ice to keep the body parts from being consumed by skua gulls, a predatory bird native to Antarctica, who kept swooping down onto the crash scene and wouldn’t be deterred by noise, flame or any other measures.

Wreckage largely in place today

Despite controversy into the crash’s cause, the recovery work is considered a success, as the vast majority of the victims—213 of 257 or 82.9%– were identified and their remains reclaimed.

The wreckage of the flight remains largely in place near Mount Erebus and, when conditions are right, it can be seen from the air as the snow recedes and uncovers what’s left of New Zealand’s deadliest peacetime disaster.