Q: What is ETOPS?
A: ETOPS is an acronym with several different but related meanings. Originally, it meant Extended Twin-engine Operations and referred to the operation of airliners with two engines beyond distances from potential diversion airfields which were normally permited by regulations. Typically, if an engine failed, a twin-engined airliner needed to be able to fly to a diversion airport on the single remaining engine and land within 60 minutes.

The DC-9 and 737 could almost make it to many Caribbean destinations under the 60-minute rule, but not quite. Turbine (jet) engines are more reliable than piston engines, so the FAA and other agencies granted exemptions to allow these aircraft to fly up to 75 and the 85 minutes from airports.

During the development of the Boeing 767 it was recognized that the aircraft was capable of long flights which would take it over more remote stretches of water than even the Caribbean 85-minute rule would allow. That led to the development of the first ETOPS rules, which initially allowed the 767 to fly across the North Atlantic between North America and Europe. Other twin-engined aircraft were soon included and distances were extended.

With improved aircraft technology and engine reliability it was recognized that standards for operations in remote areas of the world should be applied to all airliners, not just those with two engines. The International Civial Aviation Organization (ICAO) now defines ETOPS to be Extended-range Twin-engine Operational Performance Standards while the FAA uses the simpler Extended Operations.

For additional information, see the following:

Q: What is the humorous expansion of ETOPS?
A: Engines Turn Or Passengers Swim.
Q: What does rule-time mean?
A: Rule-time is the term used for the time within which an aircraft flying under ETOPS rules must be able to get to a suitable landing airport after an engine or other failure. This is expressed as a time rather than a distance because the distance varies depending on winds, the performance of the aircraft, and other factors.

For example, airliners flying between North America and Europe are usually within 120 minutes from a suitable place to land and can operate with a 120-minute rule-time. Between California and Hawaii, airliners require a 180-minute rule time.

Q: How did someone come up with a 138 minute rule-time?
A: There are two distinct routes across the North Atlantic, one using Iceland's Keflavik airport as a key alternate, and another, more southerly route using Lajes in the Azores. West of these islands, there's a small, triangular area which is not within 120 minutes of any suitable airport. A 138 minute rule-time (120 minutes plus 15%) removes this last no-go area over the North Atlantic, and the UK's CAA approved operation under this enhanced rule for several carriers. (At the time, 180 minute ETOPS was significantly more difficult, and with no reason for it over the Atlantic many carriers neither needed nor wanted the added expense.)
Q: What is an aircraft's engine-out speed?
A: The engine-out speed of an aircraft depends on the design of the aircraft, its configuration, and other factors. Early studies leading to ETOPS were based on the Boeing 757 and used 389 kts, a typical engine-out speed for that aircraft. The Great Circle Mapper also uses this speed unless you select a different speed.

You may select a different engine-out speed by entering your own speed (between 200 and 600 knots) or by selecting typical engine-out speeds for a selection of aircraft.

Q: What are the sources for the single-engine speeds for the listed aircraft?
A: The single-engine speeds for the aircraft listed in the menu came from the following sources:
Q: What is a "no-go" area?
A: A "no-go" area is an area where an aircraft may not fly within ETOPS rules. If the aircraft is flying under a 120-minute ETOPS rule-time then a location which was more than 120 minutes single-engine flying time from any airport would be in that aircraft's no-go area.

The Great Circle Mapper's ETOPS option shades no-go areas on the map.

Q: Why are there "no-go" areas over land areas?
A: There are several reasons for this. First, data on diversion airports (or airports in general) is more difficult to obtain for some parts of the world such as Africa and much of South America.

Second, just because you're over land doesn't mean you can land a large commercial airliner there. Antarctica, for example, has few airports and is quite rugged. Air transport in Antarctica often uses military or other aircraft, often equipped with skis or other special equipment for landing on packed snow or ice. These landing facilities are not suitable for a large, widebody airliner.

Q: Why is Narsarsuaq not listed as an ETOPS alternate?
A: Narsarsuaq (BGBW/UAK) offers itself as an ETOPS alternate but the Attwooll paper cited above estimated that it would be unusable as an alternate more than 50% of the time, explained as follows: "The very high probability of outage of Narssarssuaq arises from the high minima requires for unfamiliar pilots to land at this airfield, due in turn to the difficult terrain and absence of landing aids." The remainder of the paper does not consider Narsarsuaq as an ETOPS alternate.

The airport also has a very short runway and often-poor weather.

Q: Why are so many alternates missing?
A: The ETOPS map for 60 minutes at 200 knots reveals many gaps where there are suitable airports, especially over land. Each alternate in the database adds to the time required to create ETOPS maps. At the rule-times and speeds which are usually of interest the missing airports do not make a difference so they have been omitted in order to render the maps more quickly.

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