The start of the story focuses on a world where the US is in real financial trouble due to depleted oil reserves. There is a lack of jobs, food and basic provisions and everyone is struggling to survive or leave the country. The central hero of the book is a passenger jet pilot who is in the process of transporting refugees to the UK, which is more-or-less living under normal conditions due to more careful management of their oil supplies. The first third of the book details the bad conditions under which the US population lives, and while it is interesting, it becomes rather irrelevant quite quickly, except as a way to fill in some character and story background.
While over the middle of the Atlantic, flying from New York to Heathrow, it becomes clear that a global nuclear war has broken out. This is where the story gets really interesting as the crew struggle to find somewhere safe to land. The mix of passengers on the plane seems somewhat unlikely, and a handy plot device to include a number of twists or aspects to the story, but this doesn't detract from the tension.
The book features quite a lot of time where the aircraft is in the air, and hence includes several scenes where the crew go through flight procedures in some detail. This is partly for the purposes of the plot, but is largely not necessary, although it appears to be technically accurate (even if it was first published in 1979). I personally found the engineering bits quite informative, but it might not be to everyone's taste.
There are a couple of plot twists near the end, where the story speeds up considerably, that I thought spoiled things slightly but for the most part this is an excellent book. The tension is incredible throughout and there are a number of incidents that are really quite touching. These mainly centre around the crews' radio contacts with other aircraft, airports and various radio operators, and feature some unique ideas that I haven't seen elsewhere in apocalpytic fiction (and I read quite a lot of it). The ending is amazing, and not what I expected at all.
In summary, an excellent book with particular interest for readers who like disaster scenarios, but with general appeal for fans of suspense/thriller stories.