Science Fair Project Encyclopedia
ETOPS (Extended-range Twin-engine Operation Performance Standards) is an acronym for an International Civil Aviation Organization (ICAO) rule permitting newer twin-engined commercial air transports to fly routes that, at some points, are further than a distance of 60 minutes flying time from an emergency or diversion airport. This definition allows twin-engined airliners—like Boeing 757, 767, 777 and Airbus A300, A320 series, A330—to fly long distance routes (especially over water, desert or remote polar areas) that were previously off-limits to twin-engined aircraft. ETOPS is sometimes read (humorously) as Engines Turn or Passengers Swim. ETOPS may be replaced by a newer system, referred to as LROPS, or Long Range Operational Performance Standards, which will affect all aircraft, not merely those with a twin-engine configuration.
The first transatlantic crossing was made in 1919, in 16 hours, by RAF pilots Alcock and Brown with a twin engined Vickers Vimy. Due to the unreliability of piston engines in those days (see internal combustion engine), long distance flight using twin engines was considered risky. A flagship of the piston era, the 4-engined Lockheed Constellation airliner, was regarded as so unreliable that it was jokingly dubbed "the most reliable 3-engined airplane flying"!
The FAA in 1953, having recognised piston engine limitations, introduced the '60-minute rule' for 2 engine aircraft. This rule states that the flight path of these types of airplanes shall not be further than 60 minutes flying time from any airport. This forced these airplanes, on certain routes, to fly a dogleg path to stay within regulations; they were totally excluded from certain routes due to lack of en-route airports. The 60-minute period is also called 60-minute diversion period. The totally excluded area is called the Exclusion Zone.
Early turbine engine experience
Turbine engines (see Jet engine) such as Pratt and Whitney JT8D series in the 1950s and 1960s demonstrated that they have much higher thrust and reliability than any then available piston engines. It was then powering the 2-engined Boeing 737 series and 3-engined Boeing 727. Because of its excellent record, the '60-minute rule' was waived for 3-engined Boeing 727 allowing it to fly transatlantic routes. This opened the way for the development of widebody intercontinental trijets such as Lockheed L-1011 Tristar and McDonnell Douglas DC-10. By then only 2-engined jets were restricted by the '60-minute rule'.
Early twin-engine high-bypass turbofan airliners
Outside the USA, other countries followed ICAO regulations, which allowed for a 90 minutes diversion time. This fact was exploited by Airbus, launching the world's first twin-engined high-bypass turbofan widebody airliner, the Airbus A300, in 1974. It was about three quarters the size of DC10s and Tristars and for an equivalent load for the same distance, is cheaper to operate. The A300 was eagerly snapped up by airlines the world over. The failure rate of this early high-bypass turbofan engine was almost as good as the JT8D and nearly 20 times better than a piston engine. This fact was not lost to Boeing, the Boeing 757 and the Boeing 767 was the response.
Early ETOPS experience
All the developments in aircraft technologies has led the FAA and the ICAO to realise that it is perfectly safe for a properly designed twin-engined airliner to conduct intercontinental transoceanic flights. The guidelines issued form the ETOPS regulations.
FAA was the first to approve ETOPS guidelines in 1985. It spelled out conditions that need to be fulfilled before the grant of 120 minutes diversion period, which is sufficient for direct transatlantic flights. Today, ETOPS forms the bulk of transatlantic flights.
The U.S. Federal Aviation Administration gave the first ETOPS rating to Trans World Airlines for Boeing 767 service between St. Louis and Frankfurt, allowing TWA to fly its aircraft up to 90 minutes away from the nearest airfield: this was later extended to 120 minutes after a federal evaluation of the airline's operating procedures.
In 1988, the FAA amended the ETOPS regulation to allow the extension to 180 minutes diversion period subject to stringent technical and operational qualifications. This made 95% of the earth's surface available to ETOPS flights. The first such flight was conducted in 1989. This set of regulations was subsequently adopted by the Joint Aviation Authorities (JAA), ICAO and other aviation regulatory bodies worldwide.
In this manner 757 series, 767 series, some Boeing 737 series, the Airbus A300-600, A310 series, A320 series and the A330 series were approved for ETOPS operations. The success of ETOPS airplanes like 767 and 777 killed the intercontinental trijets, forcing McDonnell Douglas to terminate the MD-11 programme and Boeing to scale down the production of Boeing 747.
The North Atlantic airways are the most heavily utilized oceanic routes in the world. Most are conveniently covered by ETOPS-120min rules, removing the neccesity of utilizing 180-min rules. However, many of the North Atlantic diversion airports, especially those in Iceland and Greenland, are frequently subject to adverse weather conditions making them unavailable for use. As the 180-min rules is the upper limit, the JAA has given 15% extension to the 120-min rules to deal with such contigencies, giving the ETOPS-138min thereby allowing ETOPS flights with such airports closed.
In the North Pacific, ETOPS-180 (180 minutes) is satisfied by the availability of airports in the Aleutians Islands and Midway Atoll. As the Aleutians airports are prone to adverse weather conditions and volcanic activities, Boeing subsidised construction of the Midway Atoll diversion airport to enable the 777 to fly the North Pacific routes. After a petition from Boeing and United Airlines, in 2001, the FAA allowed a 15% extension to the ETOPS-180 rules bringing them to ETOPS-207. The approval is granted only to the 777. This approval is granted only if Northern Pacific route diversion airports are closed.
However, the JAA differed because it was argued that ETOPS-180 is already the upper limit and such extension may compromise safety as the airliners are only certificated for at most, the ETOPS-180 rating. This difference remains to this day.
The regulations allows an airliner to have 120 ETOPS-120 rating on its entry into service. ETOPS-180 is only possible after 1 year of trouble-free 120-min ETOPS experience. Boeing has convinced the FAA that it could deliver an airliner with ETOPS-180 on its entry into service. This process is called Early ETOPS. Thus the Boeing 777 was the first aircraft to carry an ETOPS rating of 180-min at its introduction.
The Joint Aviation Authorities, however disagreed and the Boeing 777 was rated ETOPS-120 in Europe on its entry into service. European airlines operating the 777 must demonstrate 1 year of trouble-free 120-min ETOPS experience before obtaining 180-min ETOPS for the 777.
Private jets are exempted from ETOPS by the FAA, but are subject to the ETOPS-120 minute rule in the JAA's jurisdiction. Several commercial airline routes are still off-limits to twinjets because of ETOPS regulations. They are routes traversing the South Pacific, Southern Indian Ocean such as Perth, Australia to Johannesburg, South Africa and Antarctica such as Auckland, New Zealand to Buenos Aires, Argentina.
Approval for ETOPS
ETOPS approval is a two-step process. Firstly, the aircraft airframe and engine combination must satisfy the basic ETOPS requirements during its type certification. This is called ETOPS type approval. Such tests may include shutting down an engine and flying the remaining engine during the complete diversion time. Often such tests are performed in middle of the oceans. It must be demonstrated that during the diversion flight that the flight crew is not unduly burdened by extra workload due to the lost engine and that the probability of the remaining engine failing is extremely remote. For example, if an aircraft is rated for ETOPS-180, it means that it should be able to fly with full load and only with 1 engine for 3 hours during an emergency!
In addition to operating aircraft which are appropriately type-rated, an operator who conducts ETOPS flights must satisfy his own country's aviation regulators about his ability to conduct ETOPS flights. This is called ETOPS operational approval and involves compliance with additional special engineering and flight crew procedures on top of the normal engineering and flight procedures. Pilots and engineering staff must be specially qualified and trained for ETOPS. An airline with extensive experience operating long distance flights may be awarded ETOPS operational approval immediately, others may need to demonstrate ability through a series of ETOPS proving flights. An ETOPS operational approval rating cannot exceed the ETOPS type approval rating of an airplane.
Regulators closely watch the ETOPS performance of both type certificate holders and their affiliated airlines. Any technical incidents prejudicial to an ETOPS flight must be recorded. From the data collected globally, the reliability of the particular airframe-engine combination is measured and statistics published. The figures must be within limits of type certifications. Of course, the figures required for ETOPS-180 will always be more stringent that ETOPS-120. Unsatisfactory figures would lead to a downgrade, or worse, suspension of ETOPS capabilities either for the type certificate holder or the airline.
The following ratings are awarded under current regulations according the capability of the airline:
However, ratings for ETOPS type approval are fewer. They are:
- ETOPS-90, which keeps pre-ETOPS Airbus A300B4 legally operating under current rules
- ETOPS-180/207, which covers 95% of the earth's surface.
There are proposals (notably by Boeing and ALPA ) forwarded to FAA to extend beyond ETOPS 180/207 to ETOPS-240. The proposed changes was issued by FAA in 2004 for public comment. However JAA (now EASA) and other parties including several international organisations do not agree, and a stalemate has ensued. EASA has their own draft rules for flights beyond 180-min diversion time (LROPS-Long Range OPeration Standards), but a failure to standardize has meant that the 180/207 rating remains the maximum today. As ETOPS-180/207 practically covers all the earth's main population centres, ETOPS-240 makes little sense. Even under the current rules, an ETOPS-180/207 rated 777-300ER will comfortably fly all the main profitable 747-400 routes and great circle routes like Bangkok-New York (via the Arctics).
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details