Embedded Avionics

En Route: Evolving Navigation Systems

By by Robert W. Moorman | October 1, 2014
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The transition to satellite-based navigation has escalated in recent years, reflecting the move toward full implementation of the U.S. Next Generation Air Transportation System (NextGen), and other systems like it worldwide. But experts are convinced traditional ground-based navigational aids (navaids) will remain on the market as a necessary backup.

“The state of the art of navigation is in a transformation period from traditional ground-based navigation aids developed many years ago to an RNP-based world,” says Bill Stone, senior business development manager for Garmin International.

The science of navigation is moving from high-frequency Omnidirectional Range (VOR)-based route structure to Performance-Based Navigation (PBN). Routes and procedures are replacing VORs and providing pilots with improved accuracy, availability, integrity and continuity through the use of satellite-aided PBN.

“In the past, [Global Navigation Satellite System] GNSS was considered by many to be yet another navigation sensor,” says Mike McDowell, principal marketing manager for Rockwell Collins. “But the future will rely on PBN. And GNSS is a key contributor to PBN.” GNSS is an all-encompassing ICAO term for the global collection of satellite navigation systems.

As technology evolves, so do the uses for satellite-based navigation. “As we move into PBN, we enter the fourth dimension of navigation, specifically controlling arrival times,” says Dan Reida, vice president of sales, marketing and support for Universal Avionics. “It comes down to trying to fit more aircraft into a given environment. If you can time the arrival of aircraft, you can increase capacity. That is what is next.”

RNP, which began in the business aircraft world and is now being adopted by commercial airlines, is a method of navigation for any requested flight path within the coverage of ground- or space-based navigation aids. So far, the FAA has published 7,000 PBN procedures throughout the National Airspace System (NAS).

Required Navigation Performance (RNAV), a type of PBN, yields several benefits: reduction of flight time, fuel and carbon emissions; dependence on vectoring; changes in altitude, speed and ATC communications; and a more efficient use of airspace.

With higher-end business and commercial aircraft comes a blend of traditional inertial and space-based navigation with Global Positioning System (GPS)/Automatic Dependent Surveillance Broadcast (ADS-B) Out and Wide Area Augmentation System (WAAS), according to Stone.

Another advance worth noting is the use of GPS navigation for airport approaches, or Ground-Based Augmentation System (G-BAS).

At present, the FAA and industry partners are conducting trials at various airports for G-BAS, also referred to as the Local Area Augmentation System (LAAS). G-BAS takes satellite navigation and couples it with error corrections from ground-based monitoring stations to produce a more accurate position that can accurately guide an aircraft below Category 1 decision height (200 feet or 61 meters).

G-BAS and new related procedures provide significant safety and economic value in areas such as displacing the threshold of a runway to mitigate wake vortex separation constraints. Furthermore, the money- and fuel-saving technology can help separate the aircraft more effectively.

The Future Air Navigation System (FANS), a means of direct communication between the pilot and air traffic control through data link communications, is another evolutionary element of satellite-based navigation. Along with navigation and surveillance, data link communications is part of the trinity of managing aircraft, both in the air and on the ground.

“If you can get away from voice transmissions toward digital communications it will be a massive game changer,” says Capt. Sean Cassidy, first vice president and national safety coordinator for the Air Line Pilots Association, International, referring specifically to the benefit of the Controller Pilot Data Link Communications (CPDLC) aspect of the Data Communication program, part of NextGen.

Data Comm is scheduled to roll out in 2015 in the tower domain and between 2018 and 2022 for the enroute environment.

Old & New

For years civil navigation has relied on traditional ground-based navaids, such as VOR, Distance Measuring Equipment (DME), Instrument Landing Systems (ILS) and Non Directional Beacons (NDB).

Upgrading older aircraft from ground-based to space-based navigation is a “slow migration,” says Todd Donovan, vice president of Air Traffic Management (ATM) Strategy at Thales. “We don’t see a situation where legacy ground-based systems will be replaced totally by satellite-based systems.”

Satellite-based navigation is quickly becoming the future of navigation, but legacy navaids are likely to be retained to backup the system in case of a catastrophic situation, such as a solar flare.

The FAA is working to adopt the Minimum Operating Network (MON) program aimed to reduce the number of ground-based navaids for enroute navigation and approach control. The remaining ground stations would ensure aircraft could, with the help of ATC, land safely. The FAA would retain a sufficient number of VORs and Distance Measuring Equipment (DMEs) as backup.

Navigating the U.S. Air Transportation System (ATS) is based on three basic principals: pilots and controllers talk to each other through communications devices; Air Traffic Control (ATC) monitors aircraft through surveillance technology; and the pilot navigates using onboard navigation technology. This three-legged approach is set up to maintain a safe ATS, any one leg can be taken away and the system will still stand.

The challenge for regulatory authorities and users is that GPS will one day be used for navigation and surveillance when the U.S. ATS moves to ADS-B. “Which means you have the potential to lose not one but two of these means,” says Donovan. “There is a need to maintain a backup system.”

By Jan.1, 2020, the FAA will require ADS-B equipment for aircraft flying in classes A, B, C and certain E class airspace, at or above 10,000 feet, as well as around busy airports. Moreover, timing is a huge reason to maintain a backup system. “It extends beyond aviation,” says Stone. “As a society, we have become highly dependent upon GPS, not only for navigation but the crucial element of timing.”

Cell phones, networks, power grids and stock trading are synchronized to the GPS timing signal. “If GPS is denied in a broad area, there are far greater concerns than just loss of aircraft navigation,” says Stone.

Using legacy ground-based navaids as a backup is only an interim solution. At some point, next generation GPS will provide operational capabilities that can’t be duplicated by the ground-based navaids. This will create the need for a more capable long-term backup navigation system.

The FAA’s Alternative Positioning Navigation and Time (APNT) program are considering ideas such as: enhancing the existing DME network; using wide-area multilateration techniques that rely on existing navigation system 1090 MHz transmissions; or a pseudo-satellite (pseudolite) network leveraging the FAA’s DME and ADS-B Ground Based Transceiver (GBT) networks.

The Radio Technical Commission of Aeronautics (RTCA) — a technical organization that develops minimum performance standards for avionics — is working on standards for next-generation GPS systems.

“We’re headed toward the completion of a second generation of GPS avionics standards that will embrace the new GPS L5 frequency as well as foreign satellite navigation systems, like Galileo, that are part of the GNSS,” says Christopher Hegarty, co-chair of the Radio Technical Commission for Aeronautics’ (RTCA) Special Committee 159, the GPS Committee.

Work on the minimum standards for next generation GPS avionics is proceeding slowly, Hegarty said, because there are only a handful of satellites transmitting L5 so far. Seven of the 31 operational satellites are equipped with the L5 signal. It is likely the constellation won’t have a sufficient number of L5-capable satellites to provide a useful operational capability for civil aviation until 2020, says Hegarty.

The first GPS satellite was launched in 1978. At the time, each GPS satellite broadcast only one civilian signal and two military signals. The GPS Modernization Program is adding the capability to broadcast three new civilian signals (including L6) and two new military signals to each satellite.

“The manufacturers aren’t in a big rush to create standards until the space component of GPS can support it,” says Hegarty who is also the director of CNS Engineering and spectrum for MITRE Corporation.

Navaid Enhancements

Avionics manufacturers continue to enhance existing or offer new navigation-related products.

“The key developments we have today are centered around PBN and GNSS, as well as the introduction of multi-frequency and multi-constellation GNSS system,” says McDowell.

Rockwell Collins’ next-generation Multi-Mode Receiver (MMR) will add multi-frequency and multi-constellation capabilities to the GNSS as well as add growth to CAT II and CAT III capability for the GLS, to support the ATM initiatives associated with NextGen and Europe’s Single European Sky ATM Research (SESAR).

The MMR combines the ILS and GNSS sensor into one box. Subsequently, Rockwell Collins developed and integrated the GPS landing system (GLS) into the MMR. The MMR is the centerpiece of the navigation system, particularly in the air transport market. The company is also involved in improving other navigation sensors, such as its low range radio altimeter. The company also added FANS capability to its Flight Management System (FMS).

Universal Avionics is developing a GPS receiver that should include support for GBAS/LAAS, Galileo, L5 and Russia’s Glonass satellite navigation system, among others.

Honeywell recently released two improvements to its Laseref VI IRU. The GG1320 Ring Laser Gyro (RLG) has been updated and certified in the Laseref VI to extend its performance. In addition, Laseref VI’s hybrid function has been updated to make it fully compliant to the ADS-B mandate, said Stevan Siijepcevic, vice president, navigation marketing and product management, Honeywell Aerospace.

The Laseref VI can also serve as the ADS-B navigation source in aircraft in which the inertial/GPS hybrid function serves as the primary navigation source allowing additional availability in the GPS-denied environments.

In 2015, Honeywell will expand the Laseref VI family by introducing a high-performance special missions version for the military, a mid-grade “Super AHRS” (Attitude Heading Reference System) version, and a helicopter version, which was initially developed for Airbus Helicopters light rotorcraft, such as the EC145 T2 and EC645 T2 family.

In another navigation-related development, ACSS, an L-3 and Thales company, received Technical Standard Order (TSO) Authorization for its NXT-600 Mode S Transponder. The NXT-600 meets the requirements for the ADS-B mandates taking effect in some regions of the world, beginning this year.

Avidyne, a provider of integrated avionics and safety systems for general aviation aircraft, received Technical Standard Order (TSO) approval this summer from the FAA for the installation of the panel mounted IFD40 FMS/GPS/NAV/COM system. Which, along with its AXP340 Mode S Transponder, provides a certified 1090 MHz ADS-B Out solution, said Tom Harper, director of marketing at Avidyne. The system provides a number of navigation-related enhancements, including a powerful FMS navigator with menu-driven airway flight plan entry.

Creating or enhancing existing navigation products is only one component of the navigation market.

Thales, which has a broad portfolio of navigation related products, is a major subcontractor to Exelis for the FAA’s Surveillance and Broadcast Services contract. It supplies more than 1,200 advanced 1090ES and UAT radios as well as multi-sensor tracker software used to support the Traffic Information Services-Broadcast (TIS-B) service. Thales’ technology supports the “service provision” of ADS-B, TIS-B, Flight Information Services-Broadcast (FIS-B) and Automatic Dependent Surveillance-Re-broadcast (ADS-R).

As for growth opportunities, manufacturers of avionics and ground-based systems say they are marketing their products to those countries and regions whose satellite-based navigation programs are maturing, such as the United States and Europe. They’re also beefing up sales efforts to high growth regions, such as South America, the Middle East and Asia.

One market focus for Universal Navigation is FANS, which provides a means for direct data link communication between the pilot and ATC through data link technology. “We are targeting customers that fly the North Atlantic,” says Reida.

The North Atlantic air tracks have new regulatory requirements for optimum altitude and flight paths across the ocean. Authorities are restricting use of North Atlantic flight paths to aircraft with FANS capability. The FANS-equipped aircraft obtains permission from ATC through data link to use the optimum flight path. Communications via satellite data link also allow the ATC to track the aircraft.

Avionics manufacturers are seeing a trend by government agencies to outsource navigation-related services. “Standards bodies and [Air Navigation Service Providers] ANSPs are moving toward specifying performance of communication, navigation and surveillance in terms of required levels necessary to implement specific operational capabilities in certain segments of airspace,” says Thales’ Donovan. “It naturally follows for these agencies to move to performance-based contracting to ensure the capabilities put into service match those required for the operational concept.”

The shift allows ANSPs to focus on operations and gives vendors the flexibility to adopt solutions to meet the requirements, and a way to increase revenue. “Some agencies want to go a step further and purchase a service where they have one contractor to hold accountable for delivering the required [Communications, Navigation and Surveillance] CNS performance level,” says Donovan.

Thales and other manufacturers of navigation-related products are exploring this concept, which is likely to be embraced worldwide.

Robert Moormanis a freelance writer specializing in various facets of the fixed and rotor wing air transportation business. With nearly 30 years of experience, he runs a freelance writing business, RWM Associates. His writing clients include several of the leading aviation magazines targeting the civil and military markets. He can be reached at [email protected].

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