Have you ever asked yourself, during a transatlantic flight for example, why the twin-engined ‘plane you are in does not fly directly to your destination by flying the shortest distance possible.
Well, it's just to meet the safety standards imposed by the International Civil Aviation Organization (ICAO) since 1985. In terms of long-haul flights over uninhabited zones, such as oceans or deserts, twin-engined jets must in fact be able to reach an airport in the event of failure of one of their engines in an allotted time. So, each type of aircraft has its own specific certification called ETOPS (Extended-range Twin-engine Operation Performance Standards).
The number following this norm actually corresponds to the maximum allowed distance, in minutes, from an emergency landing airstrip or runway. The Boeing 787, for example, which has just been certified by the U.S. Federal Aviation Administration ETOPS-330, can fly 330 minutes (five and a half hours) from a diversion airport that it must be capable of attaining under power of a single functioning engine.
With the ETOPS rules reference speed, for a Boeing 767, being 389 knots (720 km/h or 450 miles/h), the Dreamliner, therefore, can fly nearly 4,000 kilometres (2,480 miles) distance away from an airport capable of receiving it in an emergancy.
At present, the ETOPS standard only takes into account twin-engined aircraft, but could soon be replaced by the LROPS standard (Long Range Operational Performance Standards). This new certification will then apply to all types of aircraft.