L ying on the draughty floor of the aeroplane, there was no way to warm myself. But the cold was not my only concern. There was also a throbbing pain in my head. Carefully, I reached up to touch the crown of my head. Clots of dried blood were matted in my hair, and three bloody wounds formed a jagged triangle about 4in above my right ear. I felt rough ridges of broken bone beneath the congealed blood, and when I pressed down lightly I felt a spongy sense of give. My stomach heaved as I realised what this meant - I was pressing shattered pieces of my skull against the surface of my brain. Just as I was about to panic, I saw those brown eyes above me, and at last I recognised the face of my friend Roberto Canessa.

"What happened?" I asked. "Where are we?" "You have been unconscious for three days," he said, with no emotion in his voice. "We had given up on you."

I remembered the flight through Planchon pass, where we travelled in cloud cover so heavy that visibility was nearly zero and the pilots were forced to fly on instruments. Severe turbulence was tossing the plane around, and at one point we hit an air pocket that forced the plane to drop several hundred feet. This rapid descent dropped us below the clouds, and that was probably the moment when the pilots saw the black ridge rising dead ahead. They gunned the Fairchild F-227's engines in a desperate effort to climb. This effort managed to raise the plane's nose a few degrees but their actions were too late to lift the plane completely over the mountain. The Fairchild's belly slammed into the ridge, and the damage was catastrophic. First, the wings broke away. A split second later, the fuselage fractured along a line directly above my head, and the tail section fell away. Everyone sitting behind me was lost - the plane's navigator, the flight steward and the three lads playing cards.

The forces of the collision were huge. The Fairchild's nose was crumpled like a paper cup. In the passenger cabin, seats were ripped loose from the floor of the fuselage and hurled forward along with the people sitting in them, and dashed against the cockpit bulkhead. Several passengers were crushed instantly as the rows of seats closed on them like the folds of an accordion, then tumbled into a mangled heap that filled the front of the fuselage.

As more and more passengers were pulled from the wreckage, the "doctors" were amazed to see that most of the survivors had suffered only minor injuries. Canessa and Zerbino cleaned and bandaged their wounds. My sister Susy was lying beside my mother's dead body. She was conscious but incoherent, with blood streaming over her face. Roberto wiped the blood from Susy's eyes and saw that it was coming from a superficial scalp wound, but he suspected, correctly, that she had suffered much more serious internal injuries.

In those early days we all believed that rescue was our only chance of survival, and we clung to that hope with an almost religious zeal. I never stopped praying for the arrival of our rescuers, or for the intercession of God, but at the same time the cold-blooded voice that had urged me to save my tears was always whispering in the back of my mind: "No one will find us. We will die here. We must make a plan. We must save ourselves."

We knew we were high in the Andes, but the snowy slopes above us rose up even higher, so that I had to tilt my head back on my shoulders to see their summits. The ridges formed a ragged semicircle that ringed the crash site like the walls of a monstrous amphitheatre, with the wreckage of the Fairchild lying at centre stage.

In the days after Susy died, my love for my father [who remained at home] was the only thing that kept me sane. In my desperation, I raged silently at the great peaks that loomed above the crash site, trapping me in this evil place. After Susy's death, 27 survivors remained. The damage to my head was one of the worst injuries suffered in the accident, but the shattered fragments of my skull were beginning to knit themselves together.

We were dressed only in light summer clothing - some of us were wearing blazers or sports jackets, but most of us were in shirtsleeves. We had no warm coats, no blankets, nothing to protect us. High-altitude cold is an aggressive and malevolent thing. It burns you and slashes you, it invades every cell of your body. The draughty fuselage shielded us from the winds that would have killed us, but still, the air inside the plane was viciously frigid. I would lie in the dark for hours, my body shivering so hard that the muscles of my neck and shoulders were constantly in spasm.

The cold was always our greatest agony, but at first the greatest threat we faced was thirst. At altitude, the human body dehydrates five times faster than it does at sea level. There was no lack of water in the mountains - we were sitting on a snow-packed glacier, surrounded by millions of tonnes of it. Our problem was making the snow drinkable.

One sunny morning, Fito noticed that the sun was melting the thin crust of ice that formed every night on the snow. An idea came to him. He rummaged through a pile of wreckage and found, beneath the torn upholstery of a battered seat, a small rectangular sheet of thin aluminium. He turned up the corners of the aluminium sheet to form a shallow basin, and pinched one of the corners to form a spout. Then he filled the basin with snow and set it in the sunshine. In no time water was trickling steadily from the spout. Fito collected the water in a bottle and when the others saw how well his contraption worked, they gathered more of the aluminium sheets and fashioned them in the same way.

In the early days, hunger was not a great concern for us. The cold and the mental shock we had endured, along with the depression and fear we all were feeling, acted to curb our appetites. And since we were convinced that rescuers would find us soon, we were content to get by on the meagre rations we had. But rescue did not come. Deep down, I always knew we would have to save ourselves.

Again and again, I came to the same conclusion: unless we wanted to eat the clothes we were wearing, there was nothing here but aluminium, plastic, ice and rock. But, of course, there was food on the mountain - meat, plenty of it, and in easy reach. One afternoon, as we were lying in the fuselage, my gaze fell on the slowly healing leg wound of a boy lying near me. The centre of the wound was moist and raw, and there was a crust of dried blood at the edges. I could not stop looking at that crust, and as I smelled the faint blood-scent in the air, I felt my appetite rising. Then I looked up and met the gaze of other boys who had also been staring at the wound. In shame, we read each other's thoughts and quickly glanced away.

But for me, something had happened that I couldn't deny: I had looked at human flesh and instinctively recognised it as food. "We are going to starve here," I said. "I don't think the rescuers will find us in time."
"You don't know that," Carlitos answered.
"I know it and you know it," I replied, "but I will not die here. I will make it home."
"Are you still thinking about climbing out of here?" he asked.
"Nando, you are too weak."
"I am weak because I haven't eaten."
"There is no food here," he said.
"There is," I answered. "You know what I mean."
"Fuck, Nando," Carlitos whispered.
"There is plenty of food here," I said, "but you must think of it only as meat. Our friends don't need their bodies any more."
Carlitos sat silently for a moment before speaking. "God help us," he said softly. "I have been thinking the very same thing."

For a moment, no one moved, then we all reached forward, joined hands, and pledged that if any of us died here, the rest would have permission to use our bodies for food. After the pledge, Roberto rose and rummaged in the fuselage until he found some shards of glass, then he led three assistants out to the graves. When they came back, they had small pieces of flesh in their hands. Gustavo offered me a piece and I took it. It was greyish white, as hard as wood and very cold. I reminded myself that this was no longer part of a human being; this person's soul had left his body. Still, I found myself slow to lift the meat to my lips. I avoided meeting anyone's gaze, but out of the corners of my eyes I saw the others around me. Some were sitting like me with the meat in their hands, summoning the strength to eat. Others were working their jaws grimly. Finally, I found my courage and slipped the flesh into my mouth. It had no taste. I chewed, once or twice, then forced myself to swallow. I felt no guilt or shame. I was doing what I had to do to survive.

Death was drawing closer; its stink was growing stronger all around me. We had been trapped on the glacier now for 60 days. The crash site was an awful place, soaked in urine, smelling of death, littered with ragged bits of human bone and gristle, but to me it suddenly felt safe and warm and familiar. I wanted to stay there. How badly I wanted to stay.

"Nando," said Roberto, "it's time to go."
I glanced at the graves once again, then turned to Carlitos.
"If you run out of food," I said, "I want you to use my mother and Susy."
Carlitos was speechless for a moment, then he nodded. "Only as a last resort," he said softly. Roberto called again. "Nando?"
"I'm ready," I said.

We waved one last time and then began to climb. We did not know that the Fairchild's altimeter was wrong; the crash site wasn't at 7,000ft, as we thought, but close to 12,000. Nor did we know that the mountain we were about to challenge was one of the highest in the Andes, soaring to the height of nearly 17,000ft, with slopes so steep and difficult they would test a team of expert climbers. The three of us were climbing in street clothes, with only the crude tools we could fashion out of materials salvaged from the plane. Our bodies were ravaged from months of exhaustion, starvation and exposure. If we had known anything about climbing, we'd have seen we were already doomed. Luckily, we knew nothing: our ignorance provided our only chance.

The incline of the mountain grew steadily sharper, and soon we reached slopes that were too steep and windblown to hold deep drifts of snow. The mountain fell away so steeply behind me now that when I looked down on Tintin and Roberto, I saw only their heads and shoulders outlined against the empty sky. Turning to look behind me was like pirouetting on the ledge of a skyscraper. "Do you still think we can make it by nightfall?" asked Roberto. He was looking at the summit. I shrugged. "We should look for a place to set up camp."

Huddled together in the sleeping bag, we kept ourselves from freezing, but still we suffered terribly. In the morning we placed our frozen shoes in the sun and rested in the bag until they thawed. Then, after eating and packing our things, we began to climb. How we continued to climb, I cannot say. I was shivering uncontrollably from cold and fatigue. My body was on the verge of complete collapse. Roberto was sullen that night as we lay in the sleeping bag.

We will die if we keep climbing," he said. "The mountain is too high."
"What can we do but climb?" I asked.

It was an agonising process, inching up the mountain, and the hours passed slowly. Sometime in late morning I spotted blue sky above a ridgeline and worked my way towards it. After so many false summits, I had learned to keep my hopes in check, but this time, as I climbed over the ridge's edge, the slope fell away flat and I found myself standing on a gloomy hump of rock and wind-scoured snow. It dawned on me slowly that there was no more mountain above me. I had reached the top.

Roberto surveyed for a few minutes, shaking his head. "Well, we are finished," he said flatly.
"There must be a way through the mountains," I said. "Look down. There is a valley at the base of this mountain. Do you see it?"
Roberto frowned. "It's too far," he said. "We'll never make it. We don't have enough food." "We could send Tintin back," I said. "With his food and ours, we could last 20 days."

As we ate together that night, Roberto spoke to Tintin. Tintin nodded in acceptance, with relief shining in his eyes. In the morning, we embraced him and then sent him back down the mountain. Then it was just the two of us.

Roberto stood beside me. I saw the fear in his eyes, but I also saw the courage and I instantly forgave him all the weeks of arrogance and bull-headedness. "We may be walking to our deaths," I said, "but I would rather walk to meet my death than wait for it to come to me."
Roberto nodded. "You and I are friends, Nando," he said. "We have been through so much. Now let's go die together."

We walked to the western lip of the summit, eased ourselves over the edge, and began to make our way down. As we slipped off the summit, I realised immediately that descending the mountain would be even more terrifying than the ascent. Each step was treacherous - rocks that looked firmly fixed to the mountain would break away under our feet and we would have to scramble for something solid to hold on to.

"Let's keep going until the sun sets," I said. Roberto shook his head. "I need to rest. We must be smart about this, or we will burn ourselves out." We spread the sleeping bag on a flat, dry rock, climbed in and rested for the night.

The next morning was December 15, the fourth day of our journey. I roused Roberto as the sun rose and we set off down the slope. When we reached the bottom of the mountain, sometime near noon, we found ourselves standing at the entrance to the valley that we hoped would be our pathway to civilisation.

It was difficult and painful progress, and we had to be careful about every single step - we both knew that in this wilderness a broken ankle would be a death sentence. I wondered what I'd do if one of us was injured. Would I leave Roberto? Would he leave me?

At some point on the afternoon of December 18, I heard a sound in the distance ahead - a muffled wash of white noise that grew louder; I soon recognised it as the roar of rushing water. "This is the birth of a river," I said to Roberto. "It will lead us out of here."

We had left so many dangers behind; we were no longer at risk of freezing to death, or of dying in a fall. It was a matter of simple endurance now, and of luck and time. We were walking ourselves to death, hoping that we would stumble upon help before we used up the life left in us. Another day passed.

The next was December 20, the ninth of our trek. Roberto was very weak. Darkness was beginning to fall now, and a chill was rising. "I'm going to find some firewood," I said, but when I had walked only a few yards across the meadow, I heard Roberto shout. "Nando, I see a man!" Roberto was pointing at the slope on the far side of the river gorge. I squinted into the evening shadows. "I swear I saw something," he said.
"It's dark over there," I replied. "Maybe it was the shadow of a rock."

I took Roberto's arm and helped him back up the hill to our campsite, when we heard, above the roar of the river, the unmistakable sound of a human voice. We whirled around, and this time I saw him too - a rider on horseback. He was shouting to us, but the noise of the river drowned out what he said. Then he turned his horse and disappeared into the shadows. "Did you hear him?" shouted Roberto. "What did he say?"
"I only heard one word," I answered. "I heard him say 'Manana' ['I'll be back tomorrow']."
"We are saved," Roberto said.

· This is an edited excerpt from Miracle in the Andes, by Nando Parrado, published by Orion Books.