The Future of Global Navigation

 - December 29, 2009, 5:17 AM

For years the world’s aviation authorities have been preparing for the transition to a re-imagined operating environment where an array of new technologies–placed on the ground, in space and in the cockpit–can be applied to the daunting task of funneling thousands more airplanes from departure to destination each day without encountering the choke points that inevitably would arise from using a global navigation infrastructure developed when DC-4s and Super Constellations ruled the skies.

The FAA and Eurocontrol predict a doubling of air traffic in the U.S. and Europe in the next 15 years, this in spite of the brief hiccup triggered by the current economic slowdown. To cope with such a dramatic rise in flight movements, planners in the U.S. have begun crafting the Next Generation Air Transportation System, more commonly referred to as NextGen. In Europe a parallel effort is called Sesar, for Single European Sky ATM Research Program. Both of these initiatives seek to use 21st-century technology to move airplanes as efficiently and safely as possible while minimizing the environmental impact of packing ever more flights into already crowded airspace.

Today, delays in the U.S. are estimated to cost users $9 billion a year, according to the government. “And that’s only going to grow as we move into the future,” said Vicki Cox, the FAA’s senior vice president of NextGen operations and planning. “Some estimates say that by 2025 delays could cost $22 billion a year.” What’s urgently needed, say experts, is a way to maximize efficiency and safety by leveraging the technologies that already exist–but which so far have been adopted by few operators–while also creating entirely new ones.

The good news: the FAA has laid out for the next decade and beyond a rough road map that offers a fairly clear picture of the technologies that will matter most in the NextGen era. The bad news: the roadmap can be redrawn at any time (if, for example, a better technology comes along to supersede one already in use). What’s more, some end users will be skeptical about equipping their aircraft with new technology unless they absolutely must. Equipage incentives will help move NextGen and Sesar along, as will development programs by avionics makers and infrastructure designers, without whom future nav cannot emerge much less flourish.

One of the key components of NextGen is a satellite-based technology called automatic dependent surveillance-broadcast (ADS-B). ADS-B offers broader coverage and is more precise than surveillance radar. It allows for greater capacity by separating airplanes more efficiently. The technology is already in use at the UPS hub in Louisville, Ky., where airplanes have been equipped with onboard avionics from Aviation Communications and Surveillance Systems, a Phoenix company that has positioned itself at the forefront of ADS-B technology development.

ADS-B is also being installed in Miami and Philadelphia to supplement coverage along the East Coast. By 2013 ADS-B coverage will blanket the entire U.S. above 1,800 feet agl, giving controllers a better overall air traffic picture and eventually providing pilots of properly equipped aircraft detailed information about other ADS-B-capable targets. In the Gulf of Mexico, where radar coverage is unavailable, ADS-B is being installed to allow thousands of helicopters to operate more safely among oil rigs.

Some NextGen benefits are already being realized. Today aircraft fly satnav-based Rnav procedures, including Rnav Waas/LPV approaches, which use onboard avionics to allow pilots to navigate more precise paths to lower minimums than are available flying nonprecision procedures. Required navigation performance (RNP) builds on Rnav by letting pilots benefit from even more precise navigation, including curved pathways and more closely spaced approaches. Special AR (approval required) RNP procedures can be tailored  for a specific runway.

Weather also plays a role in reducing air traffic capacity, accounting for 70 percent of all flight delays, according to the FAA. Data communications and network-enabled weather will allow better coordination to resolve critical weather issues using a shared, common picture. Combining advanced traffic-flow management tools with readily accessible weather information can reduce delays and increase capacity. Controllers and pilots will have access to the same weather information, further aiding in tactical and strategic decision-making.

On the ground, ASDE-X technology provides conflict alerts to controllers if an airplane, for example, rolls through a hold line. In the future, surface management systems in the cockpit will give pilots a bird’s-eye view of all runways, taxiways, ramp areas and ground targets, including vehicles such as baggage carts and fuel trucks. Just as important as the technology in the cockpit will be infrastructure improvements at airports, such as runway status lights (a currently available technology) that tell the pilot whether the runway is clear.

A Flight into the Future
The previous generation of navigation technology restricted aircraft to the equivalent of a one-lane highway for a given route. NextGen adds more lanes to help smooth the flow of traffic and eliminate bottlenecks that can spawn airport delays. To better understand how the NextGen puzzle pieces will fit together to change the way pilots fly, it’s useful first to look at how a flight is conducted with the current ATC structure.

Let’s say we’re taking a team of pharmaceutical company executives from Teterboro, N.J., to Van Nuys, Calif., in a Gulfstream V. We start out by getting the current ATIS and talking to clearance delivery, ground control and finally the TEB tower for instruction on how to taxi, take off and navigate. After takeoff a Tracon controller steers us through maneuvers that require us to climb thousands of feet while we travel about 100 ground miles from the airport. Once we reach FL230, a center controller directs us to climb to our final cruising altitude at FL410.

All across the country, our Gulfstream follows other airplanes like cars on an interstate highway. As with cars, the route is dictated by what’s on the ground–even though we’re flying on what are called airways or jet routes. The airplane must pass over radar fixes–generally not the most efficient path. And every time we cross an airspace boundary, we must switch frequencies to a new controller, and then to another–more than 25 times cross-country.

Let’s say weather along our route forces us farther north for a while. We’re not really sure how far the controller is going to send us out of our way or what sort of ripple effect the weather is having on other flights. When it’s time to descend, the controller steps us down several thousand feet at a time and moves us around to align with other traffic on the way to the runway at Van Nuys, perhaps giving us a single turn in a holding pattern for spacing before handing us over to the tower for landing clearance.

Now let’s look at the same flight flown in a Gulfstream G700 (a fictional future model). The improvements are noticeable as soon as we start to taxi. The surface management map on the cockpit MFD shows us a datalink routing to the departure runway, a picture of all other airplanes on the ground and an assigned number indicating where we are in the departure queue. We don’t spend much time talking to TEB controllers, but instead click menu buttons that simply say “Accept” to enter the various routings into the FMS, which controllers have sent to the airplane via text message.

After takeoff, a pre-loaded RNP departure routing quickly gets us out of the busy lower-level airspace to FL410, saving us time and fuel and rattling fewer windows on the ground. Once en route, Rnav, RNP and ADS-B allow us to fly closer to other airplanes and on a direct route that accounts for wind, weather and traffic. The weather over the Midwest that caused our previous flight to divert more than 100 miles is easily circumnavigated thanks to collaborative planning tools that accounted for the conditions before we ever left the ground using an FAA system called Swim (system-wide information management).    

There are fewer radio handoffs thanks to increased use of controller-pilot datalink messaging. Instead of a gradual step-down from cruise altitude, we fly a single continuous descent to the numbers calculated by the FMS. The more precise arrival cuts time, fuel, noise and emissions and makes holding patterns a relic. As we line up for the destination runway, our place in line has been planned hundreds of miles in advance.

Like how that all sounds? It’s the utopian vision; but it’s hard to say what the reality will be. Traditionally, flying has been based on the “first come, first served” philosophy, which means–in theory, at least–that in a mixed operation a Cessna 172 on approach has priority over a following Airbus A380. True, it doesn’t usually happen that way, but that’s the general idea. Now, the FAA’s NextGen Task Force has proposed introducing a new concept: “best equipped, best served.”

The FAA will almost certainly adopt such an approach, slowly and selectively at first, but we can expect that eventually it will become an ICAO-endorsed worldwide rule, invoked wherever traffic densities warrant it.

In fact, the FAA adopted a form of the concept in 2005 when it mandated reduced vertical separation minimums (RVSM). If you wanted to fly above 29,000, you invested in the necessary equipment. If you didn’t, you didn’t. So at some point in the future, the admission fee for entry into what the task force called “Metroplex” airspace–for example New York or Los Angeles–will be the cost of equipage to do so.

The idea makes sense. With the forecast doubling of aircraft movements by 2025, the future air traffic management system will demand carriage of “performance-based” equipment, such as RNP, ADS-B, digital coms and other advanced technologies to handle the volume in high-density airspace.

What does “best equipped” mean? So far, it hasn’t been defined officially, but we can intuitively guess that newer business jets and airliners will meet the highest standards, followed by their older cousins, along with midsize corporate jets, commuters and the like, and with smaller GA airplanes likely to be the least well equipped. One possible yardstick that could be applied to the best-served model would be ICAO’s proposed required total system performance (RTSP) concept, which will set international capability standards in communications, navigation and surveillance systems.  

The End of Mandates?
The task force’s report appears to signal the end of equipage mandates, which have normally been the FAA’s preferred way of moving ahead. Still, mandating anything that could be applicable to the still distant (and somewhat amorphous) NextGen operating environment is a tough call. Consequently, to determine how best to bridge the gap between today’s environment and that of NextGen, the FAA took the unprecedented step of asking the user community, via the task force, for input, recognizing that users could have a much clearer understanding of their needs than FAA planners.

As it turned out, the task force saw greatly expanded use of non-mandated RNP and Rnav procedures as probably the major benefit of NextGen, both from operational and economic aspects. Interestingly, there appeared to be little task force enthusiasm for the FAA-mandated ADS-B plan, the final rule for which is currently planned for March 10 and calls for user community compliance for ADS-B out by Jan. 1, 2020.

However, while industry observers expect the rule to be issued unchanged, some anticipate a future slackening of the general aviation equipage mandate. This is based on Eurocontrol’s ADS-B mandate due to come into force on Jan. 1, 2015, which excludes all aircraft below 12,500 pounds that cruise at less than 250 knots. Other regulatory authorities are expected to adopt Eurocontrol’s rules, and the FAA might feel pressure to follow along in the interests of international standardization.

The other problem with mandates lies in their necessarily long implementation lead times versus the extremely rapid pace of technology development. Clearly, anything built today to comply with a 2020 mandate will be approaching obsolescence by the time that date arrives. This could particularly affect ADS-B out, a technology that does little more for pilots than a standard transponder–although, reportedly, it provides better position accuracy to controllers, but not enough to be able to reduce separation standards.

By 2020, however, ADS-B in, which provides inestimable value to pilots in providing them with the position of other aircraft, will likely cost no more, and by then perhaps even less, than the out units. Similarly, general aviation universal access transceiver ADS-B units could possibly be superseded at some point in the future due to their slow data rates in receiving weather information–a key NextGen goal.

The End of Radar, Too?
It is generally accepted that today’s secondary surveillance radar (SSR), based on technology developed during World War II, is nearing the end of its technology lifespan. Its replacement is expected to be multilateration, or MLat, which is less expensive, more accurate and less operationally constrained. Some observers argue that MLat, using basic transponder data, can provide essentially the same data to ARTCCs as the FAA’s ADS-B ground station network across the NAS, and that the data, when converted to ADS-B formats, could be uplinked to ADS-B in users in the same way as ADS-B out messages are currently. MLat is also ADS-B compatible by design, and its flexibility allows it to accurately triangulate on transponder, ADS-B, military IFF and other aircraft transmissions.  

Yet while MLat is still, by radar standards, in its development infancy, it is already seeing wide acceptance as an alternative to SSR in Canada, Europe, Asia, Australia, New Zealand and South Africa. Consequently, it is likely SSRs gradually will be replaced worldwide by transponder/ADS-B-compatible MLat.

The ILS Replacement Question
ILS, designed in the 1940s and progressively improved in the decades since, has proved to be one of aviation’s most enduring precision landing systems. What’s more, there is at present no system that can replace the ILS in its Category II and Category III roles, which are essential to corporate and airline operators worldwide. For this reason, ILS seems likely to continue in operation worldwide well beyond 2020, although the numbers of Category I installation will probably decline earlier than that, albeit at a measured pace.

Eventually Category II and III ILS is likely to be replaced either by the GPS ground-based augmentation systems (GBAS)–known in the U.S. as the local area augmentation systems (Laas)–or by an onboard hybrid GBAS/IRS/FMS avionics package. Or perhaps both. But neither development is close to certification: at a recent ATC conference, industry and FAA officials, speaking off the record, told AIN that these techniques would see certification no sooner than 2015.

Category I ILS is expected to be replaced sooner and, interestingly, by either of two different GPS applications. One of these is a lower-performance version of GBAS/Laas mentioned above, while the other uses the space-based augmentation system (SBAS), aka Waas. The difference between GBAS/Laas and SBAS/Waas is rather subtle. GBAS/Laas uses several airport-based GPS monitor receivers, which pass their raw data to a computer that calculates the local GPS errors and then transmits appropriate accuracy corrections over a VHF link to approaching aircraft, where they are applied to the onboard GPS receiver. SBAS/Waas uses a nationwide monitor network whose raw data signals go to two regional master stations, where the corrections are beamed up to two geostationary satellites in a 23,000-mile-high orbit, and from which they are retransmitted down directly to user GPS receivers on the GPS frequency, removing the need for costly airport area monitoring networks.

GBAS was developed during the time when it was believed Waas would be unable to meet Category I criteria, but this is no longer the case, and both systems now support 200-foot Category I equivalent operation. Indeed, technical experts report that Waas now meets most Category II accuracy and integrity standards, save for the required two-second time to alarm in the case of failure–although they suggest that this problem can be overcome with a future Waas conversion to dual-frequency operation. They also point out that Category I equivalent SBAS/Waas is expected to spread rapidly as foreign Waas-type coverage–from Europe’s Egnos, Russia’s Glonass, India’s Gagan, China’s Compass and Japan’s MSAS–becomes widespread internationally between now and 2015.

4-D Trajectory Operations
In theory 4-D capability (where the fourth dimension is the time element) is available today. It was successfully simulated in Eurocontrol trials several years ago. One result was that controllers could handle much more traffic than was the case with conventional flows, and fewer en route conflicts arose. Concept advocates point out that to work most efficiently, 4-D trajectories should be gate-to-gate, or chock-to-chock, continuums that include taxiing out and in. Preceded in the NAS by high-accuracy GNSS-based required time of arrival (RTA) procedures for continuous descent approaches (CDA), 4-D trajectory flight plans supported by advanced versions of the FAA’s computer-based user request evaluation tool (URET) should be in wide use in North America and Europe by the early 2020s.

It’s probably a safe bet that NextGen will become a reality only after hitting some stumbling blocks. Some of them could be quite major, causing certain elements of the concept to be delayed or even shelved. What is certain is that new technologies will be needed to accommodate an expected two-fold increase in air traffic. Even if only a portion of NextGen technologies are implemented, we should be well on our way to meeting this 21st-century challenge.    

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