Technology suppliers make it possible to fly aircraft closer together. Concept art Thales
As navigation systems from technology suppliers such as Thales develop, it becomes possible to fly aircraft closer together.

How Next-Gen Navigation Systems Will Improve ATM

A primer on navigation systems—from sextant ports to the next generation of systems—that will make air traffic more resilient and safe.

Air traffic management is under pressure in the U.S., Europe and elsewhere as demand for flights increases, and airlines attempt to squeeze more aircraft into the same available airspace.

The technologies to help achieve this are evolving. Today’s cockpit contains an array of navigation and flight-planning tools that would have seemed the province of science fiction a few decades ago. In fact, seismic shifts in navigation took place in the 1990s, when the introduction of the Future Air Navigation System (FANS)—involving a transition from inertial navigation to satellite navigation using GPS satellites—increased airspace capacity in the oceanic regions by more than 400%. This system also greatly improved communications capability.

“There is a combination of technologies that have allowed us to develop, from post-World War II systems and equipment to our current ability to see air traffic, communicate with air traffic and be able to navigate precisely,” explains Mary McMillan, vice president of aviation safety and operational services at Inmarsat. McMillan, a 30-year veteran of the aviation industry, recorded more than 12,000 hr. flight time as a United Airlines pilot in aircraft ranging from the Boeing 747 and 767 to the Airbus 320. She also was a standards captain and flight operations duty manager at United.

McMillan wryly notes that on transatlantic flights early in her career there was the option to navigate using a sextant via a “sextant port” in the cockpit. “If necessary, we could open it up and put out a sextant and take a Sun shot or a star shot,” she says. “But we relied much more heavily on inertial navigation systems, which were in themselves a development from ballistic missile technology used in the Second World War.” Now as technology develops further, undreamed-of levels of navigation and flight-planning efficiency are becoming possible, she says.

Inmarsat

Capt. Mary McMillan, Inmarsat vice president of aviation safety and operational services.

Airspace is monitored using primary and secondary radar systems. Pilots also use the GPS or GNSS (global navigation satellite system) to monitor position. The GNSS receiver processes signals from satellite constellations to accurately determine aircraft position, altitude and velocity. According to Thales, which supplies navigation systems to Airbus, “consistent [GNSS] accuracy, availability and reliability are essential to safely accomplish ever more demanding missions,” says Tristan Grivel, Thales vice president for avionics marketing and product policy.

Satellite technology is changing with several GNSS core constellations that will be available in 2020, including the EU Galileo system and China’s BDS. Merging the capabilities of these systems will enhance navigation capabilities, says Grivel. “They will provide added operational capabilities, gaining from the capability to mix constellations, or comparing each other for better integrity,” he notes.

Traditional technologies such as radar still do the bulk of the work in determining an aircraft’s position when it is over land. Primary radar detects and measures the approximate position of aircraft using reflected radio signals. Secondary radar, which relies on targets being equipped with a transponder, also requests identity and altitude. All commercial aircraft are equipped with these transponders, which automatically transmit a four-digit code when they receive a radio signal sent by radar. The code gives the airplane’s identity, or “call sign.” Radar stations go on to establish speed and direction by monitoring successive transmissions. This flight data is then relayed to air traffic controllers.

When an aircraft is out over the sea, radar coverage begins to fade. Air crew keep in touch with air traffic control and other aircraft using high-frequency radio. Pilots rely on satellite systems such as GPS, radio and inertial navigation systems—a navigation aid that uses a computer and a series of sensors—to calculate the position, orientation and velocity of the aircraft. Flight management systems feature navigation databases and waypoints, backed up with radio navigation to plan and negotiate the flightpath. For example, Thales says its latest high-performance inertial navigation systems certified for civil use have a drift of less than 2 nm per hr.

Satellite monitoring of flights for navigation is helping to optimize available airspace, known as performance-based air traffic management. Grivel says: the transition to it “will require the highest performance of navigation systems to secure accuracy and integrity of aircraft positioning at all times and under all conditions.” From a technological point of view, such accuracy requires both greater precision from individual sensors on the aircraft as well as the consolidation of data produced by those sensors, including optical, inertial, pressure and temperature systems. 

“It also requires increased use of GNSS receivers and multiconstellation signals to provide the greatest level of positioning accuracy,” adds Grivel.

In fact, having proved its worth over the oceans, experts say the next step is for satellite-navigation technology to be used much more widely over land to increase capacity and reduce flight times, delays and fuel burn, which should lower CO2 emissions.

Inmarsat is working with the European Space Agency (ESA) on a program known as IRIS, to enable what it calls 4D trajectory management of aircraft via satellite—4D because it pinpoints where an aircraft is in latitude, longitude, altitude and time. The result should provide very precise tracking of flights over continental Europe and more efficient management of air traffic, benefiting airlines economically and reducing the impact of aviation on the environment.

Thales

As navigation systems from technology suppliers such as Thales develop, it becomes possible to fly aircraft closer together.

When the FANS system was developed, thanks to the use of advanced satellite navigation technologies, it was possible to reduce separation standards for aircraft over the oceans to 25 mi. and 2,000 ft. from 100 mi. and 4,000 ft., greatly boosting route capacity, says McMillan. Now the airline industry is hoping to achieve greater efficiencies and improvements to flight planning through the use of secure data links and the analysis of the latest, real-time information on the route, traffic and weather patterns. 

“In the early days, satellite communications were primarily a safety utility,” McMillan says. “Then airlines realized they could benefit from more efficient routing and take advantage of reduced separation standards,” allowing more flights within a given airspace on the North Atlantic tracks. “But when they reached the continental shelf they transitioned to ground-based navigation,” she says.

With the advent of improved satellite tracking and two-way secure communications with aircraft, there is now the possibility to provide navigation, communications, weather information, aircraft surveillance and even telemedicine via satellite if passengers or crewmembers become ill en route over land. “The way I think about it is that this is a step change comparable to when we first put VHF radio on aircraft,” McMillan says.

The Inmarsat program supports the Single European Skies ATM Research (SESAR) plan for next-generation air traffic management, which is aiming to optimize airspace and enhance safety and cybersecurity while reducing flight times, delays and CO2 emissions. 

There is a lot of pressure on VHF radio links that are near capacity in Europe, and IRIS could help relieve that, says Inmarsat.

As SESAR comes to fruition, thanks to the introduction of technologies such as IRIS, pilots and air traffic controllers should enjoy an increased ability to calculate shortest available routes, cruise at optimum altitudes and use continuous climb and descent paths—enabling them to save fuel. Communications links will move from voice communications to data links, such as text messages, via the Inmarsat system, which the company says could help to boost both operational efficiency and safety.

In short, aircraft are becoming more connected. As we look to eke more capacity out of the crowded skies above Europe and the U.S., satellite navigation technologies are set to play an important role.

“We can make use of real-time data on the weather, real-time data on wind, and real-time data on what other aircraft are doing in the vicinity,” McMillan says. It may be possible to slow aircraft for portions of the journey without causing them to arrive later, for example. The need to place the aircraft in a holding stack above an airport that is very busy, such as London Heathrow, might be obviated by more efficient navigation. Air traffic controllers will be able to deconflict flights with higher degrees of efficiency and accuracy, freeing up airspace.

But the increased use of data and satellite links for aircraft navigation and communications carries an increased cybersecurity risk. “You occasionally hear an alarmist story about the possibility of hacking the aircraft from seat 23A. We know that that is not the case in reality. But our current family of satellites supporting aviation is digital and internet-protocol-based, so we are very aware of cybersecurity,” says McMillan. “With IRIS, we are essentially creating a virtual private network that allows only authenticated users to operate the system and exchange information. We can guarantee safety and security,” she says.

Air traffic management must change to accommodate demand for air travel, and to do so new navigation and communications technologies will come to the fore, McMillan says. “The air traffic control system should become much more resilient. There are fewer unknowns—you shouldn’t have to guess about what kind of weather and wind you are going to encounter on a flight, or volcanic ash or icing,” she says.

Pilots will have more information, to everyone’s advantage. “The flight should enjoy a level of certainty in regard to its duration, convenience and comfort—before the pilot even taxis out of the gate,” she says.

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