ATM Modernization, Commercial

The Fruits of FANS

By Brian Evans | June 1, 2001
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FANS, the Future Air Navigation System, was developed to support optimum, least-time tracks and rapid route-clearance changes for airliners flying over oceanic or remote areas, where conventional navaids and air traffic control (ATC) and communications networks were either marginal or non-existent.

In such areas, ATC dependence on unreliable HF voice communications enforced excessive "procedural" separation standards and occasional long waits. At the same time, en-route climb requests were negotiated between potentially conflicting aircraft, even though traffic was sparse over the thousands of square miles of surrounding oceanic or remote airspace.

The FANS concept was first proposed in the mid-1980s by Brian O’Keeffe of the Australian Civil Aviation Authority (now the commercialized Airservices Australia). He described an environment in which sophisticated monitoring and control technology at ATC centers would work with aircraft equipped with satellite communications, controller-pilot data links (CPDL), Global Positioning System (GPS) and inertial reference system (IRS) navigation, and automatic dependent surveillance (ADS), all of which were then in various stages of operational readiness. The concept’s primary benefit was that ATC facilities would be able to instantly and accurately track the location of each FANS-equipped aircraft by using a communications satellite link to "interrogate" the aircraft’s on-board ADS equipment. The facilities could obtain the aircraft’s position, altitude and other data without crew intervention and could, using the same satellite, exchange immediate data link messages with the pilots.

Qantas, a Pioneer

O’Keeffe’s work caused him to be dubbed the "Father of FANS." And, appropriately, it was Australia’s Qantas airline that, after the adoption of FANS by the International Civil Aviation Organization (ICAO) in the early 1990s, became the system’s pioneer. Its Boeing 747 flew the first FANS routes between Sydney and Los Angeles, followed soon after by United Airlines and Air New Zealand.

Initially, FANS coverage was limited to just a few ATC centers serving the South Pacific. The fairly costly upgrades of all the other Pacific Rim centers have taken several years to accomplish. Today, however, virtually the whole of the Pacific offers FANS service. And approximately 10 years after Qantas’ initial flights, most major trans-Pacific air carriers have become FANS equipped.

But the air carriers’ investment is not insignificant, with retrofit avionics installations in earlier-model, non-digital widebodies costing about $1 million each. Reportedly, financial managers at United Airlines, which had retrofitted FANS avionics in all of its B747s flying the Pacific, became concerned when the payback promised from improved routings and shorter flight times did not materialize across the fleet, as it had with Qantas and Air New Zealand. It turned out that the disparity resulted from the fact that the latter two airlines flew primarily across the South Pacific, which enjoyed full ATC FANS coverage from the very beginning, whereas the United airplanes flew a variety of trans-Pacific routes, only a few of which were in FANS coverage.

Today, a factory installation of a FANS avionics package in a new Boeing or Airbus airframe is reported to be less than $500,000, and most purchasers of long-range airliners take this option. The Boeing FANS-1 and Airbus FANS-A packages essentially are similar in their operating characteristics and performance–which has led to the airline industry’s common use of the collective FANS 1/A term when referring to either.

The Benefits

What benefits does FANS offer the operator? Primarily, the ability to fly least-time–and thereby least-cost–tracks to their normally very distant destinations. This usually means not following the direct, great circle route between departure and destination points, but rather tracing out a curving path to take advantage of the prevailing wind patterns.

These paths, known as "flex tracks," are calculated each day for all major trans-Pacific traffic routes by the U.S. Federal Aviation Administration’s (FAA’s) Oakland Center, which uses the most recent weather reports and forecasts available. (A similar process, called the Organized Track System [OTS], is used daily on the North Atlantic by Canadian and British route planners.)

The effect of upper winds on direct tracks is often not appreciated. But it was well illustrated some years ago when a very large, very intense low-pressure weather system was lying in the western Atlantic off New England. The wind circulation around a low is counterclockwise, and this created very strong upper winds blowing from the east over the North Atlantic and eastern Canada and from the north over the central United States. But in the mid-Atlantic, the strong winds were blowing from the south, along the normal, direct track from Europe to the Southeast U.S. On that day, airlines flying from Europe to Atlanta, Ga., and Miami, Fla., opted for a route that took them over Sault Ste Marie, Mich., many hundreds of miles west of the direct tracks. Airline planners calculated that the strong tailwinds along the longer route would get their airplanes to their destinations up to 40 minutes earlier than they would if they had attempted to battle headwinds all the way along the direct track.

On the long Pacific routes, airline crews and dispatchers can, if adverse winds are encountered on their assigned flex tracks, use the FANS Dynamic Airborne Route Planning System (DARPS) in coordination with ATC to reclear to a more efficient route. (Interestingly, this option is not available under the North Atlantic OTS, because of its shorter routes and very much higher density.)

The Bay of Bengal

More recently, FANS operators in the less crowded South Pacific have commenced tests of User Preferred Routings (UPRs), which break away from the flex track concept and allow individual routes to be based purely on each operator’s aircraft and engine type, payload, weather and other factors. Some early UPR results have surprised ATC analysts. In one case, two airlines flying identical aircraft with similar payloads between the same departure and destination points, at roughly the same time, have chosen UPRs that were 400 miles apart in the mid-Pacific.

FANS’ success in the Pacific has led to the gradual establishment of FANS routes in other parts of the world. Perhaps the one most welcome to the airlines is the route across the Bay of Bengal. Every night, the sky over these waters east of the Indian peninsula is crowded with large jets heading for Europe from Southeast Asia. In the past, HF voice communications forced many of the aircraft to fly at uneconomical altitudes for lengthy periods before getting further climb clearances. (During that time, one airline’s staff magazine carried a cartoon showing a frustrated airline crew trying to raise Calcutta on HF, while in the galley a few feet away a flight attendant was chatting over the satcom with her mother in England.)

Today, ATC centers controlling Bay of Bengal traffic have been upgraded to FANS technology, producing major improvements in traffic flow and minimal reclearance delays. But the route from landfall over India to Eastern Europe still lacks FANS capability.

The Southern Ring

One current initiative to partially close this gap is the development of the Southern Ring route across territories that were once part of the former Soviet Union. The Montreal-based FANS Stakeholders Group (FSG), an industry organization set up by the International Air Transport Association (IATA), leads this effort. The Southern Ring also involves communications providers ARINC and SITA, satcom provider Inmarsat, and other specialist groups. The FSG essentially gathers user requirements and acts as a facilitator between operators and ATC providers.

Negotiating the Southern Ring route is a complex activity, requiring close coordination of the ATC services of 10 independent nations. These include Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan, often described by ATC experts as the "stan states." Carriers hope the Southern Ring will become operational by 2002.

Pole Hopping

But the newest, and highest profile, FANS activity is unquestionably the four polar routes established over Canada and Russia, which were formally opened on March 1. On that day, a FANS-equipped Continental Airlines’ Boeing 777 flew the direct, Polar Route 2 track between Newark, N.J., and Hong Kong. On the four approved Polar routes, block time savings between the Northeast United States and Pacific Rim destinations are forecast to be two hours or more. Net cost savings is calculated to be $15,000 per hour, compared with earlier, mid-latitude routings.

Nav Canada tracked the Continental flight via satcom, although above 84� north, the communications satellites orbiting over the equator became too low on the aircraft’s southern horizon to maintain signal lock. However, two-way signals were regained once the aircraft had passed over the pole and had crossed 84� north, heading south. To fill this "polar gap," the Canadian and Russian ATC agencies likely will install unmanned HF data link stations–which are far more reliable than HF voice transmissions–along their arctic coastlines.

Nevertheless, the polar routes do not yet offer the operational flexibility achieved over the Pacific, since Russia insists that the polar tracks must be flown only along their centerlines. The country allows no deviations to take advantage of prevailing winds. At a recent ATC conference, U.S. ATC specialist Jerry Thompson pointed out that greater savings could be gained from polar operations if wind-dependent, least-time tracks and in-flight re-routes were permitted.

FANS vis-à-vis Free Flight

Is FANS the same as FAA’s Free Flight? Not exactly, although the South Pacific UPR evaluations are moving in that direction.

However, FANS was developed in the late 1980s, and its data communication protocols were based on the Airborne Communications Addressing and Reporting System (ACARS), the only data link available at the time. Yet ACARS was not, and is still not, approved by ICAO as a totally reliable ATC control medium.

Free Flight will use the Aeronautical Telecommunications Network (ATN), which is still to be internationally standardized. Operators expect that conversion from ACARS to the ATN may be costly, however, and offer somewhat questionable additional benefits.

But, eventually, there will be a worldwide convergence of Free Flight and FANS, both of which meet the broad definition of that other acronym, CNS/ATM, or communications, navigation, surveillance/air traffic management. It has been suggested that the three techniques are now similar enough to describe them all in the future as minor variants of a single, generic, ATM/CNS concept, where the capitalized CNS stresses the underlying, but essential, traffic management objective of each. Brian O’Keeffe, now retired, will be undoubtedly pleased when that day arrives.

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