Down to a Sunless Sea — David Graham

The six hundred passengers and crew members aboard a jumbo jetliner are left without a destination and a country when nuclear war breaks out and spreads devastation around the world.

A collapsed economy and an increasingly savage society were causing thousands to abandon America. Captain Jonah Scott was a pilot, hired to fly some lucky refugees to London. But once in the air, nuclear war broke out, and Scott became responsible for the entire human race!