No matter how level-headed, well-adjusted or frequent a flyer one is, everyone must have meditated briefly at some point on the unspeakable possibility of their plane crashing. Every flight starts with that clicheed reminder of mortality: the demonstration of life-belts, oxygen masks, and emergency exits mimed by cabin crew.

There are two classic worst scenarios that can happen on a flight, both of which have inspired a whole genre of aviation disaster movies, as well as spoof disaster movies. The first is a crash. The second is a hijack.

In 1996, Englishwomen Lizzie Anders (34) and Katie Hayes (33) both gave up successful jobs in the music industry to backpack around the world for a year.

They started in Africa, joining an Encounter Overland truck that went from Nairobi into Ethiopia. This trip took a month, after which they were eager to return to clean clothes and the break of a hotel bed in Nairobi, before flying on to India to continue their journey.

On November 24th 1996, the women boarded Ethiopian Airways Flight ET961 at Addis Ababa, for a flight to Nairobi. Twenty minutes into the flight, Katie got the creepy feeling that all was not well. A long-time nervous flyer, she was picking up on a sudden tension in the airline staff and a restrained flurry in the aisle ahead.

Just as Lizzie was reassuring her that nothing was wrong, a voice came on the tannoy. By the time the announcement was made in English, the women already knew what the message was: the plane had been hijacked and there was a bomb aboard.

What happened next is indisputably the stuff of nightmares. There were to be no negotiations with the hijackers on the runway of some unscheduled airport. Four hours after the first announcement, the tannoy crackled to life again. This second, unexpected announcement was from the captain: "We have run out of fuel in our right-hand engine and we are about to run out of fuel in our left-hand engine. Prepare for a crash landing."

Flight ET961 pitched into the Indian Ocean near Morini in the Comoros Islands. Of 172 people on board, only 45 survived the impact, to be picked up in boats by the local people. Lizzie and Katie were among them, badly injured, but alive.

A year and a half on, the co-written book of their story, Hijack! Our Story Of Survival, has just been published. "When we first came back to England, we had so much stuff in our heads and nowhere to put it," says Katie. "The book was a good receptacle. It served as a place to put our memories into, rather than keeping them all in our heads, although of course we'll never forget that day. Yes, writing the book was therapeutic."

After recovering from their injuries, which in Katie's case included broken ribs, and lungs full of aviation fuel, the women went travelling again. They had been approached by several publishers prior to leaving, all interested in their extraordinary story. Over the period of a year, they wrote the book as they backpacked through India, Laos, Thailand, Vietnam and Indonesia. "We sent chapters back to London along the way, and then made changes here and there as they suggested," says Lizzie.

Do not read Hijack! on a plane. It could well induce a panic attack in even the most blase of passengers. Although the prose is utterly basic and would not be expected to hold the attention of the reader for more than five minutes, the fact that this story is so utterly sensational keeps the pages turning.

It has to be said that there are more cliches in this book than all the tea in China: waiting for that first announcement on the tannoy, the reader is told - "We sat in silence for what seemed like an eternity, waiting to find out what was going on and hoping beyond hope that some rational and logical explanation would be forthcoming."

The chapters have alternate headings, Katie and Lizzie, which is a bit misleading. "We wrote the whole book together, but the publishers told us it would be easier to read if it was alternate chapters," explains Lizzie. This explains why there is no sense of different voices or characters in Hijack!: both women speak with the same voice.

However, there is one section in the book which they wrote separately; the description of the crash and the immediate aftermath, when they were in the water. "We had to write those bits separately," says Katie, "because although we were both in exactly the same situation, we're different people and had different perspectives on what was happening". This section is the core of the book and it is an unforgettable read. These are voices reporting from the extreme border of mortality, a rare and moving insight into the minds of those who have survived an unthinkably traumatic experience.

"If this was a Lockerbie-type bomb, we'd all be dead and we'd have known nothing about it," the Katie voice in Hijack! says. One can only imagine what the relatives of those who have been lost in plane crashes will think of this book, reliving something of what they must have endured. "Death is a very private thing," says the Katie voice, towards the end of her chapter and somehow, by the time the reader gets to this sentence, it is utterly convincing.

When Katie is under the water, she reports: "I wasn't frightened and I wasn't trying to swim anywhere. The brightness around me increased. I felt I was going somewhere else. I had completely accepted death. It did not seem like anything unknown, just something I was doing. I have always believed that you can't unlearn what you know, but this proved the exception. I now have all the same fears of death as I had before I entered the water. Perhaps the serenity is only given to you when you're about to die in order to make the journey easier. Perhaps the living have to be afraid of death in order to fight for survival effectively."

Katie and Lizzie have come back from New Zealand to promote the book. After the publicity tour, they'll be travelling again together, to North, Central and South America.

"We don't know how long we'll be away," Lizzie says serenely. "Since the crash, we don't plan more than a month ahead."

Hijack! Our Story Of Survival will be published by Andre Deutsch on May 28th, price £12.99.