Mr Harrison’s answer is quite correct. Some years ago, the world’s aviation authorities had to decide whether flying all the way across an ocean on an aircraft with just two engines was safe. The answer was two-fold: implausibly high engine reliability has become the standard so engine failures are truly rare, but in the rare instances when one does fail, you need to be within a reasonable distance of someplace to go on the one remaining engine.
Small aircraft can fly across the Atlantic Ocean, even on a single engine, but the prudent pilot does so by hopscotching along a “great circle” route that provides dozens of safe havens in case of mechanical or weather trouble. This route, which includes larger airports at Halifax, Goose Bay and Gander in Canada, Thule in Greenland, and Keflavik, Iceland, has been popular since World War II.
It’s nice to have somewhere to go when you need it, and planning paid off for an Air Transat crew flying an Airbus A330 that encountered a fuel problem. On August 24, 2001, as they were headed from Toronto to Lisbon, they observed a problem they first attributed to a simple fuel imbalance, but which actually was the first indication of a fuel leak. Their attempts to rebalance their tanks resulted in more fuel being lost.
However, their assessment of the fuel remaining told them they should divert to Lajes Air Base in the Azores, which they did. Good thing, too — they lost one engine 135 miles out, and the other somewhere between 65 and 85 miles out. Some first-rate flying resulted in their making a successful gliding landing at Lajes, after almost 20 minutes of power-off descent and maneuverin