If a 777 lost one of its two engines, the plane has a computer that automatically adjusts the aircraft's controls to compensate for unbalanced thrust. Pilots flying other airliners may have to manually adjust the plane to compensate. How reliable are those engines?
"We've never seen an issue where a twin-engine plane has lost one engine during a transoceanic flight and can't make it somewhere with the other engine," says Snyder. "And engines almost never fail. With high reliability, airlines are free to look at economics and say, 'Why would we have aircraft with four engines when we can have one that performs the same mission with two and save us money?'"