FAQ: ETOPS

Q:What is ETOPS?

A:ETOPS is an acronym with several different but related meanings.Originally, it meantExtendedTwin-engineOperations and referred to the operation of airliners withtwo engines beyond distances from potential diversion airfields whichwere normally permited by regulations. Typically, if an engine failed,a twin-engined airliner needed to be able to fly to a diversion airporton the single remaining engine and land within 60 minutes.

The DC-9 and 737 could almost make it to many Caribbean destinationsunder the 60-minute rule, but not quite. Turbine (jet) engines are morereliable than piston engines, so the FAA and other agencies grantedexemptions to allow these aircraft to fly up to 75 and the 85 minutesfrom airports.

During the development of the Boeing 767 it was recognized that theaircraft was capable of long flights which would take it over moreremote stretches of water than even the Caribbean 85-minute rule wouldallow. That led to the development of the first ETOPS rules, whichinitially allowed the 767 to fly across the North Atlantic betweenNorth America and Europe. Other twin-engined aircraft were soonincluded and distances were extended.

With improved aircraft technology and engine reliability it wasrecognized that standards for operations in remote areas of the worldshould be applied to all airliners, not just those with two engines.The International Civial Aviation Organization (ICAO) now defines ETOPSto beExtended-range Twin-engine Operational Performance Standards whilethe FAA uses the simplerExtended Operations.

For additional information, see the following:

• J. Angelo DeSantis,Engines Turn or Passengers Swim: A Case Study of How ETOPS Improved Safety and Economics in Aviation, 77 Journal of Air Law and Commerce (2013)
• AC 120-42B: Extended Operations (ETOPS and Polar Operations) (FAA Advisory Circular, 13 June 2008)
• New ETOPS Regulations (FAA Information for Operators, 26 January 2007)
• The New FAA ETOPS Rule (Boeing AERO, 2nd quarter 2007)
• ETOPS, Extended Operations, and En Route Alternate Airports (Boeing presentation, 22 October 2003)
• ETOPS article at Wikipedia

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 aircraftflying under ETOPS rules must be able to get to a suitable landingairport after an engine or other failure. This is expressed as a timerather 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 areusually within 120 minutes from a suitable place to land and can operatewith a 120-minute rule-time. Between California and Hawaii, airlinersrequire 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 usingIceland'sKeflavik airport as akey alternate, and another, more southerly route usingLajes in the Azores. Westof these islands, there's asmall,triangular area which is not within 120 minutes of any suitableairport. A 138 minute rule-time (120 minutes plus15%) removes this last no-go area over the North Atlantic, and theUK's CAA approved operation under this enhanced rule for severalcarriers. (At the time, 180 minute ETOPS was significantly moredifficult, and with no reason for it over the Atlantic many carriersneither 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 theaircraft, its configuration, and other factors. Early studies leadingto ETOPS were based on theBoeing 757and used 389 kts, a typical engine-out speed for that aircraft.The Great Circle Mapper also uses this speed unless you select adifferent speed.

You may select a different engine-out speed by entering your own speed(between 200 and 600 knots) orby 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 fromthe following sources:

• Boeing 757 (389 kts): Attwooll, V.W. "The Extended Range Operation of Twin-Engined Public Trasport Aircraft,"The Journal of Navigation (1985), Volume 38, pp. 423-430, Cambridge University Press.
• Boeing 767 (415 kts): "Ocean Hops with ETOPS: Extended-Range Operation with Two-Engine Airplanes," AOPA Pilot, 5 October 1997.
• Boeing 777 (410 kts): estimated based on 757 speed.
• Boeing 737-700/800 (397 kts): derived from Bechtel, Brad (Boeing Commercial Airplanes). "ETOPS, Extended Operations, and En Route Alternate Airports," FAA/AAAE Basic Airport Safety & Operations Specialists School, p. 11, 22 October 2003.
• Airbus A330 (402 kts): estimated from private communication
• Gulfstream IV and V (370 kts): estimated from private e-mail
• Bombardier Challenger (343 kts): private e-mail
• ATR 42-500 and 72-500 (215 kts): estimated fromATR: Experience the Innovation

Q:What is a "no-go" area?

A:A "no-go" area is an area where an aircraft may not fly within ETOPSrules. If the aircraft is flying under a 120-minute ETOPSrule-time then a location which was more than120 minutes single-engine flying time from any airport would be inthat 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 ofthe world such as Africa and much of South America.

Second, just because you're over land doesn't mean you can land a largecommercial airliner there. Antarctica, for example, has few airportsand is quite rugged. Air transport in Antarctica often uses militaryor other aircraft, often equipped with skis or other special equipmentfor landing on packed snow or ice. These landing facilities are notsuitable 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 aboveestimated that it would be unusable as an alternate more than 50% ofthe time, explained as follows: "The very high probability of outageof Narssarssuaq arises from the high minima required for unfamiliarpilots to land at this airfield, due in turn to the difficult terrainand absence of landing aids." The remainder of the paper does notconsider Narsarsuaq as an ETOPS alternate.

The airport also has a short(6004 ft /1830 m)runway and often-poor weather.

Q:Why are so many alternates missing?

A:The ETOPS map for60 minutes at 200 knotsreveals many gaps where there are suitable airports, especially over land.Each alternate in the database adds to the time required to create ETOPSmaps. At the rule-times and speeds which are usually of interest themissing airports do not make a difference so they have been omitted inorder to render the maps more quickly.

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