ETOPS

(Extended Range Operation with Two-Engine Airplanes). An airplane flight operation during which a portion of the flight is conducted beyond 60 minutes from an adequate airport for turbine-engine-powered airplanes with two engines, and beyond 180 minutes for turbine-engine-powered passenger-carrying airplanes with more than two engines. This distance is determined using an approved one-engine inoperative cruise speed under standard atmospheric conditions in still air.
At first, the acronym ETOPS was used to describe only aircraft with two engines. Since its inception, the ETOPS regulations have been expanded to include any two, three or four-engine aircraft carrying passengers for hire over an area in which airports are not accessible per the FAA's regulations, hence the acronym change from "extended twin operations" to just "extended operations."
Beginning in 1936, a pilot or operator had to prove that there were suitable landing fields at least every 100 miles along their route. When CFR Part 121.161 was established in 1953, aircraft operators had to ensure a landing area within 60 minutes of their route. With three and four-engine aircraft, the rules continued to change to keep operators flying efficiently while maintaining a safety net for aircraft should an engine fail.
The first ETOPS approval was given to TWA in 1985, the same year the FAA began allowing twin-engine aircraft an extension to a 120-minute diversion period. It was then extended even further to the 180-minute maximum in 1988.
Today, an ETOPS rule of 240 minutes is approved in certain circumstances for three and four-engine jets. Boeing was the first to obtain ETOPS-240 certification for its Boeing 777 aircraft.
For any airplane to successfully fly under ETOPS rules, it must be certified and approved by the FAA first. The approval process for ETOPS is outlined in advisory circular 120-42B.
Carriers using twin-engine aircraft can apply for ETOPS certification in any of the following categories, according to AC-120-42B:

75-minute ETOPS

90-minute ETOPS

120-minute ETOPS

138-minute ETOPS

180-minute ETOPS

207-minute ETOPS

240-minute ETOPS (for a specific geographical area)

240+minute ETOPS (based on specific city pairs)