In 1936, airline flights were not allowed to fly along any route (over water or land) unless suitable airports were available at no more than 100-mile intervals. This limitation eventually evolved into Federal Aviation Regulation 121.161, which prohibits operating an airline flight along any route that is more than one hour (in still air at normal cruising speed with one engine inoperative) from a suitable airport unless the airplane has at least four piston engines or three turbine engines.
As a result, airline traffic across the world's oceans consisted only of three- and four-engine aircraft. This changed, however, a few years after the wide-body, twin-engine Boeing 767 entered service in 1978. Boeing argued that its new-generation twin could operate on extended-range routes (more than one hour from an en route alternate airport) with as much reliability and safety as older-generation airplanes with more engines.
The FAA agreed but required that the high-tech twins comply with additional airworthiness requirements. These include providing a third source of AC electrical power that would be available for the duration of a flight in the event of an en route generator or engine failure. This is accomplished by providing an auxiliary power unit (APU) that could be started and operated at altitude.
Additional requirements include enhanced avionics cooling, improved fire suppression and containment for cargo compartments, ice protection sufficient for prolonged operation at the lower single-engine cruise altitudes, and other refinements to assure a high probability of safe continuation in the event of an engine shutdown or the failure of a major system.
A given airframe/engine combination is approved, however, only after the worldwide fleet of such aircraft demonstrates an acceptable level of reliability.
There currently are three levels of extended range operation with two-engine airplanes (ETOPS). These allow an approved carrier to operate on routes that are 75, 120, or 180 minutes from an en route alternate (at single-engine cruise speed in no-wind conditions). The approval given to a specific airline involves many factors, the most important of which are the aircraft/engine combinations to be used, the airline's experience with that aircraft, and its in-flight engine shutdown rate (IFSD). An acceptable rate is one engine shutdown (or failure) every 20,000 hours of operation, with a trend toward an IFSD rate of one in 50,000. ETOPS approval, however, can be either rescinded or restricted if the carrier does not continue to demonstrate the required reliability.
El Al Israel Airlines became the first to take advantage of the 120-minute exemption by operating nonstop flights in 1986 between Montreal and Tel Aviv. Following closely were Air Canada and TWA. No one anticipated then that the vast majority of airline traffic connecting the New World with the old would eventually consist of twin-engine airplanes.
Although North Atlantic flights can be scheduled using the 120-minute rule, flights from North America to Hawaii and across the Pacific require using the 180-minute rule.
The most significant difference between ETOPS and conventional transoceanic flights has more to do with planning than execution. There are two basic requirements that must be satisfied before departure. The first is that the aircraft conform to a stringent minimum-equipment list. The second is that a route is selected such that the aircraft will not be more than 120 minutes, for example, from an en route alternate based on engine-out cruising speed under no-wind conditions.
For a Boeing 767 heading across the North Atlantic, for example, the flight must be planned so that the aircraft is always within 830 nautical miles (based on a single-engine cruise speed of 415 knots) of a suitable en route (or "rim") alternate.
Twenty-four rim alternates are shown on the accompanying North Atlantic Planning Chart. The idea is to select as rim alternates those airports that meet the alternate requirements listed in the table and are nearest the desired track.
In the example shown on the chart, the captain and the dispatcher agree to use Stephenville (Newfoundland), Santa Maria (Azores), Dublin (Ireland), and Sondre Stromfjord (Greenland) as rim alternates for the planned flight. Using these points as the centers of circles, the crew then plots an 830-nm arc about each of the four alternates.
After these arcs are drawn, the crew can see at a glance where they may and may not plan to fly. Because the route must be within at least one of the arcs at any given time during the ETOPS portion of flight, the crew must plan to avoid the large no-fly zone, which is outside all of the arcs. In other words, the crew may file a flight plan for Track Victor or Whiskey and must avoid X-ray, Yankee, and Zulu.
Keflavik, Iceland, was omitted in this example to show its importance as a rim alternate. Large no-fly zones can result when the forecast for Keflavik precludes its use as an en route alternate. If it were available in this example, it would reduce the size of the no-fly zone by considerably more than 50 percent. Using Gander (Newfoundland), Shannon (Ireland), and Lajes (Azores) — instead of Stephenville, Dublin, and Santa Maria — would eliminate the no-fly zone entirely.
When critical rim alternates are available (which is most of the time), an ETOPS crew ordinarily can fly across the North Atlantic without having to go out of its way at all. Otherwise, the additional distance involved seldom is in excess of 100 to 200 miles.
A crew using the 180-minute rule, however, would rarely, if ever, encounter a no-fly zone when operating across the North Atlantic.
Although an airline might file for North Atlantic Track Victor or Whiskey (in this case), it would not be unusual for Gander Oceanic Control to issue a clearance for a different track, one that penetrates the no-fly zone. An ETOPS crew may not accept such a clearance and must negotiate with Gander for an acceptable track before beginning the oceanic portion of their flight.
Once the flight begins oceanic tracking, however, all bets are off. A crew may divert to any alternate that it considers most suitable and one that is not necessarily closest in terms of flight time.
As an extreme example, assume that a flight is within the arc defined by the rim alternate of Kuujjuaq (Ft. Chimo) in northeastern Quebec at a time when the need for an en route diversion develops. Kuujjuaq's longest runway is only 6,000 feet long, might be occupied during arrival by large animals, and could be contaminated with ice and/or snow in the winter. Consider that a Boeing 767, for example, must be flown at a higher-than-normal airspeed and less than full-flap deployment during an engine-out approach, both of which increase its required landing distance. Furthermore, Kuujjuaq reportedly does not have facilities to accommodate a widebody jetliner. Clearly, Kuujjuaq is a "paper" alternate that helps to provide a needed rim alternate in a pinch. The only reason a captain might opt to divert there would be in case of a time-critical event such as a major fuel leak. In other circumstances, the captain would be justified in opting for a more distant alternate, even if it is more than 120 minutes away.
It is interesting to note that an engine failure is one of the least likely causes of an en route diversion. The most common reason is passenger incapacitation caused by symptoms of a cardiac arrest. (This causes one to wonder what medical facilities are available at Kuujjuaq.)
The initial problem created by an engine failure while on an oceanic track has little to do with aircraft performance and management of the emergency. Instead, the most serious concern is traffic, especially now that aircraft are separated vertically by only 1,000 feet as a result of the new reduced vertical separation minimums (RVSM).
An ETOPS twin (and most other aircraft) begins to descend from high-altitude cruise as soon as an engine fails. To avoid traffic below, the aircraft must be immediately turned 90 degrees to the track (while keeping a careful eye on the TCAS display). Because North Atlantic tracks are only 60 nm apart, the descending aircraft should be turned parallel to the track system when 30 miles off course. The aircraft is turned toward the selected rim alternate only when it is below the track system.
If a diversion becomes necessary with both engines operating, descending usually is the safest course of action until below most of the traffic. If desired, the crew can return to a higher altitude once clear of the track system.
In any event, the appropriate oceanic control facility should be advised as soon as possible about the diversion and the desired or required altitude.
Once the aircraft is en route to a rim alternate and is stabilized in single-engine cruise, new considerations might develop. Icing and turbulence, for example, are more prevalent at lower altitudes over the North Atlantic. And then there is the notion of cruising for two or more hours in a widebody jetliner on only one engine, an uncomfortable concept for some (especially passengers). Fuel, however, should normally not be a problem. Except for the possibility of a fuel leak, it is difficult to imagine a scenario where an aircraft fueled for a transatlantic flight would not have sufficient fuel to divert to a rim alternate on one engine (even at a relatively low altitude).
Those operating extended-range flights under Part 91 of the regulations are not subject to ETOPS limitations and requirements. In fact, Part 91 flights may be planned and executed without reference to en route alternates, as inadvisable as that might be. Nor is it likely that the FAA will ever impose ETOPS-type limitations on Part 91 operators. This is because — according to current criteria — the reliability of various airframe/engine combinations can only be evaluated after 250,000 hours of in-service experience. Business jets require several years to amass such a record because they do not have the utilization rates of jetliners (typically 3,000 hours per year per aircraft).
It is worth noting, however, that the Gulfstream V and the Bombardier Global Express have been designed with ETOPS reliability and capability even though not required. Perhaps this was done because the manufacturers of these aircraft have heard rumblings from across the Atlantic. The European Joint Aviation Authorities (JAA) is considering applying ETOPS standards and requirements to twin-engine business jets operating as charter flights. Consequently, some fear that this eventually will be applied to noncommercial operations (as unlikely as this might be).
The new Boeing Business Jet (the BBJ) will be ready in any event. This Boeing 737 hybrid will be certified as an ETOPS aircraft as soon as it enters service in much the same way that the Boeing 777 was certificated when it was introduced in 1995.
ETOPS has proved that twin-engine, extended-range airline flights are safe and reliable. Pilots recognize, however, that there have been rare instances of total power loss in twin-engine jetliners (as well as in three- and four-engine aircraft). Some claim that it is only a matter of time before one of them makes a splash, which has led to another meaning for ETOPS: Engines turn or people swim.
Forecast minimums for ETOPS
There are minimum forecast requirements for ETOPS en route alternate airports. The following forecasts must be in effect prior to departure for the period commencing one hour before the earliest time of landing (as the result of an en route diversion) and ending one hour after the latest time of landing at the en route alternate airport in question. Also, the forecast crosswind component, including gusts, for the anticipated landing runway shall not exceed the maximum permitted for landing.
Airport with a single precision approach
- Ceiling of 600 feet and visibility of 2 miles, or
- Ceiling of 400 feet and visibility of 1 mile above the lowest authorized landing minimums; whichever is higher.
Airport with two or more separate precision approach-equipped runways
- Ceiling of 400 feet and visibility of 1 mile, or
- Ceiling of 200 feet and visibility of 1/2 mile above the lowest authorized landing minimums; whichever is higher.
Airport with only nonprecision approaches
- Ceiling of 800 feet and visibility of 2 miles, or
- Ceiling of 400 feet and visibility of 1 mile above the lowest authorized landing minimums; whichever is higher.
Lower-than-standard weather minimums
Exceptions to the above may be approved by the FAA for certain operators on a case-by-case basis when both the aircraft and the airport in question are certified for Category II and III operations.
