Rockwell-Collins ventures into the commercial-aviation GPS receiver market.
Graham Warwick/CEDAR RAPIDS
Rockwell-Collins has delivered more than 100,000 global-positioning-system (GPS) receivers since flight-testing its first operational unit in 1978, but is only now developing its first commercial-aviation receiver. The company cites its busy production line for military and commercial GPS receivers as a reason for the delay; and the rapid acceptance of satellite navigation as the justification for making the move into civil aviation.
Collins Commercial Avionics launched the AVSAT line of satellite-based precision-navigation systems at the US National Business Aircraft Association convention in October 1994. The first application, Bombardier's Canadair Challenger 604 business jet, is to be certificated in October 1995.
While the AVSAT line fills a long-standing gap in the US manufacturer's range of avionics for corporate and commuter aircraft and airliners, it also introduces a new level of capability, Collins argues. The AVSAT architecture is designed to assure the absolute integrity of navigation data required to operate within the future satellite-based air-traffic-management (ATM) system, the company says.
The AVSAT line "...is based on the premise that GPS is the source of position information, not just another sensor", says Gene Schwarting, director of product management at Collins' General Aviation division. In a satellite-based ATM system, the integrity of GPS data is critical to safety, he says. As a result, the AVSAT design houses all flight-critical functions, such as position determination and approach computation, within the GPS receiver to ensure integrity.
The future-ATM concept of required navigation-performance (RNP), which will give crews the freedom to select optimum flight paths provided that aircraft are kept within "tunnels in the sky", requires GPS accuracy with high integrity, Schwarting says. RNP-1, to be introduced in mid-1997 for en route operations, requires a "normal performance" of within 1.85km (1nm) and sets a "containment limit" of 5.5km. Onboard containment monitoring is required, to ensure that the probability of the aircraft breaching the outer limit undetected is less than 10-5 en route, decreasing to 10-7 on approach.
Containment monitoring is one of the safety-critical functions, which Collins plans to embed in the AVSAT sensor. Another is position reporting for the future-ATM concept of automatic dependent surveillance (ADS). The reduced separations promised by ADS depend on accurate, high-integrity, position determination, which dictates that the function be consolidated with the GPS sensor, Schwarting argues.
SAFETY-CRITICAL GPS
The safety-critical nature of the GPS receiver within the future ATM system makes it essential that Collins has its own sensor, says technical director, satellite-navigation (satnav) programme, Wayne Savold. Collins has applied its experience in developing safety-critical avionics, including automatic-landing systems, to the design of the AVSAT family, he says.
The AVSAT family is based on a purpose-designed sensor, the Commercial Avionics GPS Engine (CAGE), which consists of a single circuit board with three five-channel GPS-receiver microchips. The choice of 15 channels enables the sensor to track 12 GPS satellites, the maximum number, which can be in view, while providing additional channels to reduce acquisition time and improve tracking during aircraft manoeuvres.
Additional channels will also allow the sensor to track at least two of the geosynchronous satellites, which make up the US Federal Aviation Administration's planned Wide Area Augmentation System (WAAS). The RNP concept requires the increased GPS integrity provided by the WAAS, Savold says, noting that receivers already in service will need "significant" modification to work with the system, which is to enter US domestic service in 1997.
The WAAS will consist of a network of 24 ground-reference stations, which will determine satellite availability and positioning errors and broadcast integrity messages and differential corrections to aircraft via Inmarsat satellites, using GPS-like signals. The FAA plans to approve GPS for sole-means en route navigation and precision approach, down to Category I minima, once the WAAS is operational.
Until the WAAS is available, the AVSAT sensor will use receiver-autonomous integrity monitoring (RAIM) and predictive RAIM - in which knowledge of the aircraft's projected track is used to determine whether the satellite geometry at the destination airport will provide the required accuracy at the planned arrival time. Other sensor features include critical-level Ada software.
The AVSAT's architecture is designed to allow for growth, Savold says. Starting with the basic GPS sensor, Collins plans to add WAAS software, RNP containment monitoring, precision-approach capability and, ultimately, a separate receiver for the Russian GLONASS satellite-navigation system. The resulting approach sensor will incorporate a VHF datalink to receive local-area differential-GPS (DGPS) corrections.
The approach sensor will use wide-area (Cat I) or local-area (Cat II/III) DGPS signals and a database of approach-path-way-points to generate guidance cues identical to those produced by the present instrument-landing system, Collins says. Ultimately, the company plans to upgrade the sensor to provide Cat III automatic-landing capability, Savold indicates.
A key element of the Collins strategy has been to provide for growth from a GPS sensor to an approach sensor within the same box achieved by adding cards, or modules. The basic 2 MCU-sized GPS sensor consists of a single module, plus the power supply, with space for three additional modules: precision-approach integrity monitor; GLONASS receiver and local-area DGPS datalink. A 3MCU version has space for a flight-management computer.
SIGNIFICANT MOVE
In a significant move for Collins, the company's general-aviation (GA) and air-transport divisions will use the same AVSAT hardware. Planning for the business-aircraft and regional-airliner sectors is more advanced and a core range of four GPS-based flight-management systems (FMS), using the GPS-4000 sensor and APR-4000 approach sensor, has been announced.
The AVSAT 6000 Series is a sophisticated FMS for long-range business jets. Functions include navigation and performance management. The 5000 Series is intended for medium and light business-jets and turboprops. Functions include navigation and avionics management. The 4000 Series is intended for regional airliners with 30 to 100 seats.
These three systems are all part of Collins' Pro Line 4 integrated-avionics line and consist of the GPS sensor, a cockpit control/display unit (CDU) and a flight- management-computer module, which plugs into the Pro Line 4 integrated-avionics processor. Differences are mainly in the level of flight-management capability and in the CDU operation. The AVSAT 5000 CDU centralises control of avionics, to save space in smaller cockpits, while the AVSAT 4000 CDU is tailored to airline operations, says satnav product manager Steve Belland.
The fourth member of the family is the AVSAT 2000 Series and this differs in that the flight-management computer is consolidated with the sensor, resulting in a slightly larger box which Collins calls a navigation processor (NMC-2000 with GPS sensor; NLC-2000 with approach sensor). This stand-alone system is designed for retrofit into existing corporate and regional aircraft, which lack an FMS, and includes a variety of CDU options.
The first AVSAT application is Canadair's new Challenger 604, which has Pro Line 4 integrated avionics with an FMS-6000 FMS. Flight tests of the GPS-4000 sensor in the Challenger 604 are scheduled to begin in April and Collins plans to start production deliveries in October to coincide with certification of the long-range business jet.
Savold says that he APR-4000 approach sensor is scheduled to become available in October 1996. This will allow use of local-area DGPS landing systems, certificated to Special Category I, which governs privately owned installations. Upgrades to give AVSAT systems Cat III automatic-landing capabilities are scheduled to become available in June 1998.
Deliveries of the NMC-2000 stand-alone navigation processor are due to begin in March 1996, with precision-approach capability (NLC-2000) becoming available a year later. Collins plans to introduce a GPS-based Series 100/200 system for smaller aircraft and helicopters, combining flight-management and precision-approach capabilities, in June 1997, Savold reveals.
AIR-TRANSPORT FAMILY
Product planning is less well advanced at Collins' Air Transport division, although its approach is to build on the GA products, says executive vice-president Dave Mineck. The aim is to produce a family of AVSAT products, which will enable airlines to add functions, as they become available within the future satellite-based ATM system.
Air transport products will be built around two basic offerings, he says, the GLU-900 GPS sensor for aircraft equipped with an FMS and the GNU-900 with embedded flight-management computer for "non-FMS" aircraft. Planned precision-approach derivatives have been dubbed the GLU-90X and GLNU-90X, respectively. These are direct equivalents of the GPS-4000/APR-4000 and NMC-2000/NLC-2000 GA systems.
Airliners, which lack FMS, make up the largest part of the air-transport fleet, Mineck says. Of some 16,000 non-FMS aircraft in service, around 12,000 are expected to remain in use for the next ten to 15 years, he estimates. Carriers, many operating six to eight different airliner types, are looking for a consistent, fleet-wide, approach to equipping their aircraft which will give them a rapid payback on the investment while allowing them to add functions as they become available, Mineck says.
The cost of fitting a GPS-based FMS will be repaid within one to two years, Collins gauges, as FMS-equipped aircraft are allowed more direct routing. GPS/FMS-based non-precision approaches to runways lacking instrument-landing systems (ILS) also offer rapid payback, Mineck says. As a result, the company expects the non-FMS retrofit market, principally that for the Boeing 737 and McDonnell Douglas DC-9, to be the first to materialise.
Collins does not offer its own air-transport FMS. Instead, it plans to embed a derivative of its general-aviation FMS-4000, with additional airline functions, in the GPS sensor. A range of CDUs will be offered. In addition, three approaches are being pursued through the company's relationship with FMS-supplier Smiths Industries, Mineck says: upgrading Smiths' FMS to operate with the stand-alone GPS sensor; integrating Smiths' software into the Collins' box; and joint development of a fully integrated GPS/FMS product.
Mineck points out that the basic AVSAT GPS sensor will allow airlines to take advantage of the FAA's WAAS. Modules could then be added to the same box for local-area DGPS and for GLONASS, if required. The approach sensor could be substituted for the existing ILS receiver, he says, noting that the AVSAT architecture has been designed to meet the flight-critical requirements of an automatic-landing system.
Collins is working closely with Daimler-Benz Aerospace (formerly Deutsche Aerospace) on development of a local-area DGPS ground-station using a 20-channel version of the CAGE receiver, says manager for advanced systems, Thomas Foster. Daimler-Benz's ground station and Collins' airborne equipment, will be tested by Boeing in a year-long GPS landing-system (GLS) evaluation programme scheduled to get under way in June. Flight tests of four competing systems in NASA's Boeing 757 are planned to develop requirements for the design and certification of a GLS, he says.
Source: Flight International