Wikipedia
ETOPS is an aviation acronym for Extended Operations. The term used to signify Extended Range Operation with Two-Engine Airplanes but the meaning was changed by the US Federal Aviation Administration (FAA) when regulations were broadened to include aircraft with more than two engines. It refers to the standards and recommended practices (SARPS) issued by ICAO for aircraft (such as the Airbus A300, A310, A320, A330 and A350, the Boeing 737, 757, 767, 777, 787, the Embraer E-Jets, and the ATR 72) to fly long-distance routes that had been off-limits to twin-engined aircraft, and subsequently to extended range operations of four-engined aircraft (such as the Boeing 747-8 Intercontinental).
In aviation vernacular, the colloquial backronym is "Engines Turn Or Passengers Swim", referring to the inevitable emergency water landing of a twin engine aircraft after a double engine failure over water outside gliding range of land. But ETOPS operation has no direct correlation to water or distance over water. It refers to flight times between diversion airports, regardless as to whether such fields are separated by water or land.
There are different levels of ETOPS certification, each allowing aircraft to fly on routes that are a certain amount of single-engine flying time away from the nearest suitable airport. For example, if an aircraft is certified for 180 minutes, it is permitted to fly any route not more than 180 minutes single-engine flying time to the nearest suitable airport.
According to the FAA in the Federal Register, "This final rule applies to air carrier (part 121), commuter, and on-demand (part 135) turbine powered multi-engine airplanes used in extended-range operations. However, all-cargo operations in airplanes with more than two engines of both part 121 and part 135 are exempted from the majority of this rule. Today's rule [January 16, 2007] establishes regulations governing the design, operation and maintenance of certain airplanes operated on flights that fly long distances from an adequate airport. This final rule codifies current FAA policy, industry best practices and recommendations, as well as international standards designed to ensure long-range flights will continue to operate safely." Prior to 2007, FAA defined ETOPS as "Extended Range Operations with two-engine airplanes" and applied to twins only. International Civil Aviation Organization (ICAO) Standard and Recommended Practice (SARP) applies only to twins and defines ETOPS as "Extended-range Twin-engine Operational Performance Standards".
ETOPS applies to twins on routes with diversion time more than 60 minutes at one engine inoperative speed. For rules that also cover more than two engines, as in the case of the FAA, ETOPS applies on routes with diversion time more than 180 minutes for airplanes with more than two engines.
Until the mid-1980s, the term EROPS (extended range operations) was used before being superseded by ETOPS usage. In 1997, when Boeing proposed to extend ETOPS authority for twins to beyond 180 minutes, Airbus proposed to replace ETOPS by a newer system, referred to as Long Range Operational Performance Standards (LROPS), which would affect all civil airliners, not just those with a twin-engine configuration with more than 180 minutes ETOPS. According to the FAA in 2007, "Several commenters … recommended use of the acronym "LROPS"—meaning 'Long Range Operations'—for three- and four-engine ETOPS, to avoid confusion, particularly for those operations beyond 180-minutes diversion time. The FAA has decided to use the single term, 'extended operations,' or ETOPS, for all affected operations regardless of the number of engines on the airplane."
Government-owned aircraft (including military) do not have to adhere to ETOPS regulations.