Airborne GNSS receivers: Who’s doing what?

August 16, 2017  - By
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Rockwell Collins new generation GPS-4000-100 receiver

It’s still exceptionally difficult to qualify GNSS receivers for airborne use so there are only a few existing suppliers.

They include CMC Electronics with its line of OEM and enclosure products, Rockwell Collins with a new generation of airborne receivers just entering the market, Thales in Europe continuing to offer ARINC standard and multi-mode packaged receivers, Garmin still leading the panel-mount market for business aviation, Trimble/Ashtech continuing to promote its GPS/GLONASS airborne receiver, and newer entrants including Aspen/Accord with the NexNav GNSS line, and Avidyne with a home-grown embedded receiver in its flight management systems.

It’s been a while since we reviewed the status of certified airborne receivers, and I was prompted to do so by news that Rockwell Collins has a new generation of receiver which has just received Technical Standard Order (TSO) approval from FAA.

Rockwell Collins has fielded GPS products for 20+ years, and the GPS-4000S — with SBAS capability — has been fielded for more than 8 years, so parts obsolescence may become an issue. With new constellations, and with more countries implementing Space Based Augmentation Systems (SBAS), the 10 channel + 2 SBAS design needed an update. So Rockwell Collins undertook a bold step to develop and certify a radically new architecture for airborne applications — a software defined receiver.

Some Members of the Rockwell Collins Navigation Center of Excellence, in Melbourne FL (L-R); Jeremy Kazmierczak – Senior Systems Engineer; Eyal Wilamowski – GNSS Project Engineer; De Yao – Senior Electrical Engineer; Angelo Joseph – GNSS Architect, Technical Project Manager; and Principal Systems Engineer Vikram Malhotra – Senior Systems Engineer

A multi-frequency prototype first came together during two years of intense work by a couple of individuals, led by Angelo Joseph, an ex-NovAtel Aviation Group engineer with 15 years of GNSS design experience. When this proof-of-concept receiver demonstrated the required capability, a new GNSS receiver team was put together in Melbourne, Florida, to develop a fully qualified receiver, designed and built to stringent airborne standards.

Over the next six years, hardware was proven to meet performance, environmental, electrical, safety, high-integrity and reliability standards, and software was carefully developed and tested to meet the highest aviation qualification requirements — referred to as “Level A.”

In the process, a number of patents were generated — two have so far been approved in the United States:

  • Low-cost high integrity integrated multi-sensor precision navigation system, US 9513376 B1
  • Universal channel for location tracking system, US 9702979 B1

The universal-channel technique enables the new receiver  to be configured to track any satellite navigation signal on all 14 + 4 SBAS channels (ultimately, this GNSS engine is anticipated to be able to track 100+ GNSS satellite signals), so the receiver is ready for when other constellations are approved for airborne navigation — for instance, European approval for Galileo use may be high on the list of new capabilities.

CMA-6024 GPS/SBAS/GBAS sensor

The new receiver is capable of LPV (localizer performance with vertical guidance) precision approaches to CAT I (down to ~200ft height in ~1/2 mile visibility). It features combined Required Navigation Performance (RNP) and approach capability, 10-Hz deviation output computations (20-Hz outputs), plug-and-play replacement for existing Rockwell Collins GPS receivers. It is Automatic Dependent Surveillance (ADS-B) compliant and has fast cold-start (<2 mins @ low SNR).

With production spooling up in Melbourne, Florida, it is available now for installation on business and regional aircraft.

An additional TSO application is underway to enable anticipated installations on Airbus and Boeing commercial transport aircraft. Work on the Rockwell Collins Next Generation Multi-Mode Receiver, the GLU-2100, is well advanced with an estimated availability at the end of this year.

In Europe, Thales markets the TopStar-C certified GNSS receiver solution for aircraft and helicopter navigation and approach, providing LPV, RNP and ADS-B, with Ground Based Augmentation System (GBAS) capability promised in the near future. Compliant with all these latest navigation functions, TopStar-C is available as both standard fit (installed as basic fit on a new aircraft) and for retrofit on aircraft and helicopters alike.

CMA-4124 GNSSA Precision Approach Receiver

The Thales Multi-Mode Receiver (MMR) is part of the TopFlight Line, which includes comprehensive solutions for communication, navigation and surveillance. The MMR is configured with GNSS landing system (GLS) and navigation capability, Instrument Landing System (ILS) and Microwave Landing System (MLS) receivers in one package.

ILS still provides Cat III precision landing system (effectively 700 ft visibility of the runway down to 50 ft) capability at a few key airports where severe weather can really disrupt scheduled airline operations. Nevertheless, ILS may encounters integrity problems due to FM interference and multipath reflection, which may degrade landing capabilities under low-visibility conditions — just when its most needed. MLS can provide Cat. III B (effectively 600 ft visibility of the runway down to 35 ft) landing alternative to ILS, but is fielded at very few airports.

Meanwhile, GLS is part of the international strategic plan to provide precision approach capability worldwide to an increasing number of runways. So airlines may soon have a number of precision-landing options at airports around the world — ILS, MLS or GLS — and the Thales MMR provides all three capabilities.

Garmin GTN-650 panel-mount Nav/Comm System

CMC Electronics introduced the CMA-6024 GPS Satellite Based Augmentation System and Ground Based Augmentation System (SBAS/GBAS) CAT-l/ll/lll Precision Approach Solution at the National Business Aircraft Association show in November 2016. CMC has been in the business of supplying certified GPS receivers for commercial air transport, business aviation and helicopter markets, either directly or through Honeywell and other partners for over 35 years — almost as long as GPS has been around! The CMC family of airborne receivers also has another connection with NovAtel — they were developed as a collaborative effort with NovAtel and incorporate patented Narrow Correlator signal tracking technology.

The CMA-6024 aviation GPS/SBAS/GBAS sensor has an embedded VHF Data Broadcast (VDB) receiver and an integrated GPS navigation sensor, is self-contained, and fully certified Precision Approach and navigation GBAS/GLS solution, certified to Design Assurance Level A.

Garmin GPS/Nav/Comm/Multi-Function Display.

The CMA-6024 provides a navigation solution that is fully compliant with Automatic Dependent Surveillance-Broadcast (ADS-B) and Required Navigation Performance (RNP). It comes with SBAS Localizer Performance/Localizer Performance with Vertical Guidance (LP/LPV) and GBAS Global Navigation Satellite System Landing System (GLS) GAST-C/D Precision Approach guidance for all aircraft. And it meets or exceeds the most stringent environmental requirements set out in RTCA/DO-160G, meeting additional requirements for specific aircraft, such as higher vibration levels for helicopters.

CMC’s family of GPS products includes the CMA-5024 GPS Landing System Sensor that meets the requirements for Instrument Flight Rules (IFR), civil certified GNSS, and also the CMA-4124 OEM GNSSA receiver card for embedded applications.

An SBAS/WAAS-certified, 15-channel GPS with 5-Hz outputs is embedded in the Garmin GTN-650 Nav/Comm unit, enabling GPS-guided LPV glide-path instrument approaches down to 200 ft. The system also includes VHF navigation capabilities, with a 200-channel VOR (VHF Omnidirectional Range) and ILS receiver for approaches with ILS localizer and glideslope. VOR navigation using the extensive ground VOR beacon system uses radial direction and distance to each VOR beacon within receiver range.

FreeFlight FMS/GPS

In addition, course deviation and roll steering outputs may be coupled to compatible autopilots so that IFR flight procedures may be flown automatically. And, when coupled with a flight display and compatible autopilot, the aircraft can fly fully coupled missed approaches, including heading legs as well as holds and search and rescue patterns.

In 2015, Aspen Avionics acquired Accord Technology, an Indian company which claims to have developed the first GPS WAAS airborne sensor to be authorized under US FAA TSO-C145c. These receivers are now marketed as the ‘NexNav’ product line. This receiver was apparently the first to comply with FAA AC20-165A for ADS-B GPS position source and is also sold as an OEM GPS SBAS card-level receiver authorized to TSO-204.

There are currently three NexNav receiver versions:

  • Mini (TSO-C145c SBAS Class Beta-1 only)
  • Max (TSO-C145c SBAS Class Beta -1, -2, -3) and
  • Micro-i GPS SBAS for TSO-C199 TABS for aircraft and experimental aircraft.

SBAS/GNSS (WAAS/GPS) 1201 Sensor

All NexNav GPS WAAS receivers are compatible with other SBAS systems around the world, including the European EGNOS, Japanese MSAS and Indian GAGAN.

FreeFlight also markets two GNSS sensors and a suite of aircraft avionics.

The 1203C sensor houses a high-performance 15-channel GPS engine with advanced interference protection and quick update rates, and is designed for business, regional, airline transport and heavy rotary-wing aircraft. The 1203C is certified to TSO-C145c and meets position source requirements for ADS-B and Required Navigation Performance (RNP) and other L-NAV operations. Another 1201 Sensor GNSS is specifically for General Aviation aircraft.

Bendix/King KSN 770 Flight Information Management System

Bendix/King GNSS navigation capability, like other General Aviation avionics suppliers, is often buried within a cockpit display system that serves to tune radios, and display information from weather radar, Enhanced Ground Proximity Warning System (EGPWS), XM Datalink Weather, Terrain awareness and warning System (TAWS) and Traffic Collision Avoidance System (TCAS).

Nevertheless, the KSN 770 features Wide Area Augmentation System (WAAS) and Localizer Performance with Vertical Guidance (LPV), and is specified as a “WAAS GPS enroute and approach navigation system.”

Ashtech, now a Trimble subsidiary, still lists the venerable GG12 OEM GPS/GLONASS receiver on its website, now somewhat updated to include SBAS as the GG12W.

Ashtech is careful to describe its OEM receiver as “capable of being qualified” within a TSO-ed FMS systems — presumably the approach has been to provide all the required qualification data to integrator companies, who include this receiver within the FMS as the GNSS navigation and approach receiver. The integrator then submits the Ashtech data to FAA to support their system TSO application.

Avidyne now integrates its own in-house-developed GNSS receiver into its line of cockpit mount FMS and related GNSS navigation and approach systems. And here there is another connection with Angelo Joseph — his work at Avidyne before he went to Rockwell Collins was to develop this Avidyne receiver to replace a bought-out embedded OEM GNSS receiver. The FMS has been certified using this new receiver to TSO-C146d — Stand-Alone Airborne Navigation Equipment using GPS augmented by WAAS, including Airborne Supplemental Navigation Equipment using the Global Positioning System (GPS) — Gamma 3.

Avidyne IFD540 display

There are clearly other companies who supply avionics for GA and Commercial Air Transport aircraft, but this article has attempted to capture a cross-section of GNSS offerings. Other notables include Sagem/Safran in France, Universal Avionics in Tucson, and quite possibly several others that we will no doubt hear about shortly!

As aviation agencies move towards adding the use of other constellations beyond GPS into approved, international navigation standards, there surely has to be significant change across the board for aviation as a whole as improved integrity and availability provide more options and capability. The existing avionics suppliers should be able to maintain market by offering more capability, and there might even be more opportunity for new entrants to come into the market with disruptive products, but for sure the future looks good for the industry.

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