What is ETOPS?
ETOPS is the certification that allows a twin engine aircraft to fly a route that takes it a long way from any suitable diversion airport. The number attached to it, such as ETOPS 180, is how many minutes the aircraft may be from one on a single engine.
ETOPS explained
The rule exists because two engines used to mean staying near land. Before ETOPS, twin engine aircraft were kept within sixty minutes of a diversion airport, which made most ocean crossings the preserve of three and four engine aircraft. That is why the Boeing 747 and the McDonnell Douglas DC-10 once dominated long haul flying.
Certification is granted to a specific combination of airframe, engine and airline, not to an aircraft type in general. The carrier must demonstrate maintenance procedures, engine reliability records and crew training to the standard the rating demands. Two airlines flying the same aircraft can hold different ratings.
The numbers have climbed steadily. ETOPS 120 and 180 opened the Atlantic to twins in the 1980s and 1990s. ETOPS 330 and beyond now allow aircraft such as the Boeing 787 and Airbus A350 to fly almost any route on the planet, including the southern Pacific, which is why four engine aircraft have all but disappeared from passenger service.
For passengers the effect is entirely about which routes exist and what you fly on them. The reason a modern transatlantic or transpacific business class cabin is usually on a 787 or A350 rather than a 747 is ETOPS. It is also why thin long haul routes to smaller cities became viable at all, since a twin can fill an aircraft that a quad could not.
More on etops
Extended range Twin engine Operational Performance Standards. Pilots often joke that it means Engines Turn Or Passengers Swim, which is not the official expansion but does describe the concern the rule addresses.
That the aircraft is certified to fly up to 180 minutes from a suitable diversion airport on a single engine. Higher ratings such as ETOPS 330 allow correspondingly remote routings.
The certification is granted only after an airline demonstrates engine reliability, maintenance procedures and crew training to a defined standard, and it applies to a specific airframe, engine and operator combination rather than to a type in general.
Because ETOPS ratings rose high enough that twins can fly almost any route. Two engines burn considerably less fuel than four, so once the regulatory barrier lifted the economics decided the outcome.
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