Extended Range Twin Engine Operations - ETOPS
ETOPS is not as recent as many would think with first flights taking place in 1919 with the crossing of the Atlantic by a twin engined Vickers Vimy. Up till today these kind of flights are common practice and are executed many times a day by numerous of operators and aircraft. A flight plan that is based upon ETOPS regulations is divided into different segments and has certain entry, exit and critical points. Although ETOPS has major advantages it still features some minor disadvantages that should be taken into account by the operator when commencing ETOPS certificated flight.

ETOPS History
ETOPS is the term created by the International Civil Aviation Organization (ICAO) which describes the operation of twin engined aircraft on a route that contains a point further than one hour flying time from an adequate diversion airport. This means that an aircraft should be able to land safely within one hour at the approved one engine inoperative cruising speed (figure 1.1).

The original rules were set-up as early as 1936 and were applied to all types of aircraft regardless of the number of engines. This meant that all operations were restricted to operate within an area that could guarantee a maximum distance of 100 nautical miles (nm) from an adequate airport. In these days, 100 nm was about 60 minutes flying time for most twin engine aircraft with one engine inoperative. These rules formed the basis for the regulations as we know them today. Today's twin engine aircraft have reliability and safety features that are far beyond of those aircraft operating in the early days which were much less reliable and technically advanced. The development of modern twin jet aircraft therefore required the adjustment of present ETOPS rules in order to accommodate the unique capabilities of these aircraft. Especially North Atlantic routes could be flown much more economically under 120-minute ETOPS rules than it would under 60-minutes maximum diversion time operations.

Figure 1.1 General ETOPS
Overall, a 60 minute diversion time would require indirect routings thus an increase in fuel burn and operating costs. Thereby, these routes would mean the use of en-route alternates which have limited airport facilities and services and are subject to weather limitations that change frequently. However, North Atlantic operations flown under 120-minute rule would permit operators to use the minimum cost routings and enable the use of alternates that are properly equipped in order to service and support an aircraft that has diverted.
Practical ETOPS
In order to illustrate just how restrictive the 60-minute ETOPS rule can be for a large twin engined aircraft, the shortest route between London Heathrow (LHR) and New York, John F. Kennedy (JFK) could be considered, under both 60-minute as 120-minute rules (figure 1.2). As can be seen from the graph the 60-minute rule results in a longer flight time and an increase of fuel burn. It is obvious that the extra fuel burn-off could be translated into an equivalent payload range gain and it is easy to understand why it motivates airlines to operate under ETOPS. Additionally, ETOPS provides the possibility for twin engined aircraft to operate routes which were previously denied to them under the 60-minutes rule. Eventually this means that a smaller twin could be used on routes between two city pairs where passenger numbers are not economically viable for large aircraft to operate them. The following images illustrate the range of a typical twin engined aircraft flying at 400 kts under different ETOPS diversion times (click here). From this, it is clear what actually drives airlines to operate their twin under ETOPS and what motivates aircraft manufacturers to anticipate on this.

Figure 1.2 London to New York under both 60 and 120 minute ETOPS rules

ETOPS Route Segments
Not only does the operator or aircraft it operates have to satisfy certain requirements, so does the way in which a flight is planned and a certain route is flown. Before commencing flight, a flight plan has to be build and filed which describes the route of flight in detail. In case of an ETOPS approved flight plan, certain route segments and ETOPS points along the flight path should be determined. An ETOPS flight requires the determination of the ETOPS Entry Point (EEP), ETOPS Exit Point (EXP), ETOPS Critical Points (CP) and Points of Equal Time (PET).

  • The EEP is located at one hour flying time from the last adequate airport prior to entering the ETOPS segment at the selected one-engine-out diversion speed schedule on the aircraft's outbound route. This point actually marks the beginning of the ETOPS segment.
  • The EXP marks the end of the ETOPS segment and is marked by a point where the aircraft leaves the area exceeding 60 minutes flying time at the approved one engine inoperative speed from a suitable aerodrome for the last time on that particular route.
  • The CP marks a point on the aircraft's flight path that is critical in terms of fuel. Usually the CP is the last PET within the ETOPS segment.
The PET's are points along the route, which are located at the same flying time from two suitable diversion airports. In general, these points are calculated either by a computerized flight planning system or graphically on a navigation chart.

ETOPS Advantages & Disadvantages
Although ETOPS has many advantages for both operators as passengers it comes under certain preconditions. First of all, flying under ETOPS means that there are additional Flight Operations costs which are part of the required ETOPS crew training programs. Thereby, crews require route clearance before being allowed to operate as ETOPS crew. Secondly, additional costs have to be made in order to support and maintain required levels of airframe and propulsion reliability and the more restrictive dispatch requirements of the ETOPS MEL. Eventually, there is always the risk for an operator to lose its ETOPS approval. Authorities and manufacturers keep a close eye on aircraft reliability under ETOPS conditions. This means that every problem or malfunction should be reported to the authorities and the manufacturer. If they conclude that the operator has not kept itself at the required level of reliability which is stated by ETOPS regulations, ETOPS approval could be withdrawn.
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Certified ETOPS aircraft

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