Survivers pose for a picture in the plane's tail on November, 1972 in Mendoza, Argentina. Photo / Getty Images
Surviving a deadly plane crash would be considered by many to be a miracle.
But for the survivors of flight 571, the catastrophic crash was merely the beginning of another horror story — one that just 16 of them would make it out of alive, but only after they made an unthinkable pact.
Members of a college rugby team and their relatives on Uruguayan Air Force flight 571 were travelling from Uruguay's capital Montevideo to Santiago, Chile, for a rugby game.
Along with the 40 on board there were five crew on the chartered flight on October 13, 1972 — Friday the 13th. The plane, a twin-engine turboprop, was only four years old.
Human error caused the plane to crash into the Andes mountain range in Argentina, just shy of the border with Chile.
As heavy clouds obscured the peaks of the Andes as the plane flew overhead, the inexperienced pilot-in-command thought the plane was approaching the Chilean city of Curicó, when it was really up to 70km away.
So as the plane descended, it flew dangerously close to a mountain.
Once the flight deck realised there was a ridge directly ahead, it was too late. Pieces of the plane fell away as it hit the mountain several times on its way down.
At one point, the tail cone of the plane came off, along with the back of the fuselage, which left a gaping hole five passengers and two crew got sucked out of.
The plane eventually struck the top of a slope and slid, nose-down, at breakneck speed — about 350km/h — before crashing into a large snow bank, killing the pilots.
Amid the wreckage of the mangled plane, on a mountain glacier about 80km east of the planned flight route, 33 passengers were still somehow alive.
Five people didn't survive the first night of below-freezing conditions on the mountain in the remote Andes. A sixth person died within days.
Those who were still alive, and not critically injured or in a coma, used parts from the plane — seats, luggage, and other debris — to create shelter.
Seat cushions were used as snow shoes. One passenger used a sun visor from the pilot's cabin, wire and a bra to make goggles to prevent snow blindness. He also figured out a way to melt snow for drinking water.
They tried to write the letters "SOS" in lipstick on the roof of the crashed fuselage but didn't have enough lipstick to make the letters large enough.
The survivors had no medical supplies or appropriate clothing and were stranded on the mountain as temperatures plunged to -30C. The little food they had was fast running out.
Rescue crews from Chile, Argentina and Uruguay struggled to find the wreckage in the vast mountain range.
In a cruel twist, the survivors had found a transistor radio in the wreckage and were using it to listen to updates on the search effort.
On day 11, they heard the announcement on the radio the search for them had been called off.
Starvation soon set in. Eight bars of chocolate, a tin of mussels, three jars of jam, some nuts and dried fruit, some lollies and a bottle of wine was all the survivors had to eat.
They tried to make it last as long as possible — one man ate a single peanut over three days — but it was gone in a week.
Desperate, the survivors ate cotton and leather from the plane seats.
Survivor Nando Parrado was 22 at the time of the crash.
"At high altitude, the body's caloric needs are astronomical," he wrote in his 2006 memoir Miracle in the Andes.
"We were starving in earnest, with no hope of finding food."
Eventually, as the bodies of the dead frozen lay around them, they were forced to consider their only chance for survival.
"Our common goal was to survive — but what we lacked was food," survivor Roberto Canessa, who was 19 at the time of the crash, said in his 2016 memoir, I Had To Survive.
"We had long since run out of the meagre pickings we'd found on the plane, and there was no vegetation or animal life to be found.
"We knew the answer, but it was too terrible to contemplate. The bodies of our friends and teammates, preserved outside in the snow and ice, contained vital, life-giving protein that could help us survive. But could we do it?"
All the passengers were Catholic and held deep moral concerns about eating the dead.
And the dead weren't strangers — they were relatives and teammates and friends from school.
Mr Canessa said he prayed for guidance, worried he'd be "stealing (the) souls" of those he ate.
"We wondered whether we were going mad even to contemplate such a thing. Had we turned into brute savages? Or was this the only sane thing to do?" he said.
"Truly, we were pushing the limits of our fear."
On day nine, the survivors reluctantly decided eating the bodies of the already dead was their only chance of making it off the mountain alive.
They also mutually agreed if any of them died, the others could eat them for sustenance.
Mr Canessa, a medical student, led the way. He used broken glass from the windshield to cut off a tiny piece off one of the frozen bodies.
"I will never forget that first incision nine days after the crash," Mr Canessa said in his memoir.
"We laid the thin strips of frozen flesh aside on a piece of sheet metal. Each of us finally consumed our piece when we could bear to.
"Each of us came to our own decision in our own time. And once we had done so, it was irreversible. It was our final goodbye to innocence."
The bodies of the pilot and co-pilot were first because the survivors didn't personally know them.
It took some survivors a while to come to grips with the new source of food, and many struggled to keep it down. One woman who refused to eat eventually died on day 60 weighing just 25kg.
One night, an avalanche struck the fuselage as the survivors slept inside, killing eight. The 16 survivors were trapped in the snow-filled fuselage, buried in snow below their necks, until they got free after three days.
As the pact went, those killed in the avalanche became new sources of food.
The survivors had discussed climbing over the mountains and searching for help but their attempts failed due to the extreme cold, malnutrition and altitude sickness.
They also didn't know where exactly they were, and because the pilot had been wrong about the plane's proximity to Curicó, they thought they were closer to Chile than they were.
Two months after the crash, on December 12, Mr Parrado and Mr Canessa decided to climb west towards Chile. They had no map, supplies or climbing experience as they ventured up the mountain in difficult terrain.
On the ninth day, after they changed course and hiked down into a valley, the exhausted pair got the attention of some men on horses across a river. The men couldn't hear the survivors and tossed a pencil and paper across the river.
In a note, Mr Canessa explained they'd been in a crash and 14 injured survivors were still at the wreckage, and tossed the paper back.
Three Chilean military helicopters were dispatched and on December 22 — 72 days after the plane crash — search crews finally reached the 16 remaining survivors.
They were taken off the mountain and treated for broken bones, frostbite, altitude sickness, dehydration, malnutrition and scurvy.
A Catholic priest told the survivors they were not going to hell for eating the dead, as they had no choice, but Mr Canessa recalled agonising over what people would think of their reluctant cannibalism.
He told People magazine about the moment he revealed the truth to his mum.
"I told her, 'Mother, we had to eat our dead friends'," he said, "and she said, 'That's okay, that's okay, sweetie'."
He was also concerned about how the victims' families would react.
"But thank God, people were very receptive and very supportive and they consider what we did something we had to do," he said.
The survival of 16 through a plane crash and 72 days stranded on a mountain has since been called the Miracle of the Andes.
Mr Parrado is now a motivational speaker and works with people suffering psychological trauma and Mr Canessa is a paediatric cardiologist.
Mr Canessa gave an interview to Sputnik News in 2016, at the time Brazil was mourning the deaths of 71 members of a football team and journalists killed in a plane crash in Colombia.
"Life is a lot more fragile than is usually thought," he reflected.
"Unfortunately, such tragedies do take place. One should understand that any day might become the last one in our life. And thus hold dear every second."
The Cambridge graduate and rower is a career intelligence officer.