The biggest change in the commercial-avionics industry since the move to digital technology isnow under way.
Graham Warwick/ATLANTA
FANS, CNS/ATM, Free Flight: the names change, but the story remains the same. Aviation is moving away from the reliance on ground-based systems which has marked its first century and into a era of satellite-based communication and navigation; from ground radars to passive surveillance; and from air-traffic control to airspace management.
The future air-navigation system (FANS) has become the more-accurately, but less-elegantly, termed communication, navigation, surveillance/air-traffic management (CNS/ATM) system. In the USA it has become the concept of "Free Flight" - the ability of aircraft operators to choose their own direct routes, speeds and altitudes, with controllers intervening only to ensure safe separation.
Whatever the name, the impact on the avionics industry of these changes is enormous. More capability is being transferred from the ground to the aircraft at a time when airlines are increasingly cost-conscious. Almost every avionics discipline is affected, as integration holds the key to realising the promised economic and operational benefits.
Datalink communications
For airlines operating over the South Pacific, the FANS became a reality in 1995. By the end of 1995, some 40 Boeing 747-400s belonging to Air New Zealand, Qantas and United Airlines had been fitted with Honeywell's FANS-1 package. This introduces automatic dependent surveillance (ADS) and controller-pilot datalink communications via satellite. The airlines involved are projecting major savings as a result of the flexible routeing made possible by reduced separations and dynamic route planning.
Boeing's FANS-1 upgrade is intended as an interim solution. Airbus has its FANS-A equivalent, which is scheduled to become available in mid-1997, and McDonnell Douglas is studying similar upgrades. Despite its interim nature, FANS-1 acceptance is spreading.
The FANS-1 package uses existing equipment. The flight-management system (FMS) is upgraded and the existing ACARS airline-datalink unit is used to send position reports and to exchange datalink messages via the aircraft's satellite-communications (satcom) terminal. This necessitated the development of an interim message protocol, called ARINC 622, which enables digital data to be converted into characters for transmission over the teletype-style ACARS datalink.
Many now consider the ARINC 622 to be a threat to the planned aeronautical telecommunications network (ATN) - the communications system intended to connect the elements of the future CNS/ATM system. The ARINC 622 is a threat because it is available and the ATN is not - nor will it be before 1998 at the earliest - and because the "character-oriented" ARINC 622 is not compatible with the "bit-oriented" (ie digital) ATN.
Airlines are pushing for the ATN to be ready for introduction on the North Atlantic by the end of 1998. Eleven US carriers have formed the ATN Systems consortium and joined forces with the US Federal Aviation Administration to fund development of an ATN "router", the communications processor which will connect the aircraft and the ground via VHF, satcom, HF and Mode S datalinks.
ATN Systems plans to seek router proposals in mid-February, and to have a production unit in service by August 1998. American and United, meanwhile, plan demonstrations using Collins DLM-900 datalink-management units modified to handle ATN-compatible messages. United, using a Boeing 767-300ER scheduled to be flown at the end of February, will demonstrate automatic ADS position-reporting via satcom, using ATN protocols, on transatlantic flights. American, also using a 767, will demonstrate an ATN-compatible VHF datalink, with flights scheduled to begin in April.
The ATN router is planned to become part of a communications-management unit (CMU), a follow-on to today's ACARS management-units. Collins' DLM-900 is intended to evolve into a CMU. Certification of the system, initially as an ACARS management-unit, is scheduled for April, on a UPS Airlines 767 freighter.
Airlines are hoping that the eventual CMU will overcome the problem of incompatibility between the ARINC 622 and the ATN, as even those that support ATN acknowledge the possibility that the ARINC 622 may have to be used on the North Atlantic, to provide an interim capability for reduced separations and flexible routeing.
In a move which acknowledges the role of the ARINC 622 in the transition to CNS/ATM, Boeing has elected to use a development of Honeywell's FANS-1 FMS in its 757 and 767. This will give both aircraft a FANS capability using the ARINC 622, initially at least.
The FANS promises to give new life to an old technology - HF radio, once thought to have been superseded by satcom. HF datalink (HFDL) is being evaluated as a back-up to satcom - and as an alternative in aircraft not equipped with satcom. AlliedSignal Aerospace and Collins now offer HFDL radios, and datalink upgrades to existing HF radios.
The benefits of datalinks are not restricted to airlines and, at the 1996 Summer Olympic Games in Atlanta, Georgia, the FAA plans to demonstrate a low-airspace management system involving helicopters equipped for GPS-based ADS position-reporting using a VHF-datalink network supplied the Arnav Systems.
Global navigation
While US political and military control of the GPS continues to trouble international users, the system is firmly established as the basis of a global navigation-satellite system. While the US general-aviation industry has led its application and acceptance, 1995 witnessed US airlines taking major steps towards the routine use of GPS.
American Airlines' December 1995 order for more than 500 Honeywell/Trimble HT9100 GPS-based navigation-management systems, for retrofit to 340 Boeing 727s and McDonnell Douglas MD-80s and DC-10s, was the most significant in a series of breakthroughs made during the year. Now, United Airlines, among others, is planning an FMS/GPS retrofit programme.
Reasons vary between airlines. American says that the USA's intention to decommission the Omega/VLF ground-station network, starting in 1997, is driving its decision to begin installing FMS/GPS systems in the third quarter of 1996. United cites the USA's move towards a free-flight air-traffic system as its principal reason for upgrading to FMS/GPS.
In 1995, US-based Sun Country Airlines gained approval to use GPS as the sole means of navigation in oceanic and remote airspace. The charter carrier's fleet of 727s are equipped with Trimble TNL-8100 GPS-navigation systems. The same system was certificated in an Evergreen International Airlines' Boeing 747-100 freighter, marking the first time that GPS has replaced the inertial-navigation system in a 747.
During the year, US regional SkyWest Airlines installed Universal Avionics Systems' UNS-1M GPS-navigation systems in its Embraer EMB-120s, gaining certification for autopilot-coupled non-precision approaches. Puerto Rico-based American Eagle regional Executive Airlines began installing UNS-1Ms in its ATR 42/72s, after a six-month evaluation which showed that GPS allowed more direct routeing on its Caribbean network - and reduced its reliance on surface navigation-aids susceptible to hurricane damage.
Illustrating the close coupling between communication and navigation in the future air-traffic system, USAir Express launched Magellan Systems' CNS-12, a combined GPS-navigation and datalink-communication unit. The USAir regional subsidiaries will begin installing the $10,000-class CNS-12 in some 100 Bombardier de Havilland Dash 8 and Dornier 328 turboprops early in 1996, providing access to the ACARS airline-datalink and, initially, sole-means GPS navigation and non-precision approach capability.
Collins estimates that the market to retrofit so-called "classic" (non-FMS) airliners at between 6,000 and 8,000 aircraft. The company is aiming to meet the demand for both new-build and retrofit installations with its Avsat family of satellite-based avionics, which is built around a new GPS receiver. Collins' first system, the Avsat 6000, was certificated on the Bombardier Canadair Challenger 604 business jet in 1995.
The company's first air-transport customer is Fokker, which plans to install the Avsat 900 FMS/GPS as standard on the Fokker 70 and 100 twinjets from 1997 - the Netherlands' manufacturer's present financial difficulties permitting.
Collins' Avsat product line includes a GPS sensor and several levels of flight-management-system (FMS) capability. The family provides a growth path to a GPS precision-approach sensor, initially Category I but ultimately Cat II. Other manufacturers are following a similar path. Honeywell has extended its alliance with GPS-sensor supplier Canadian Marconi to include development of a differential-GPS sensor, initially with Cat I capability.
Honeywell aligned with Trimble in 1995 to pursue the retrofit market, and the American Airlines deal was the team's first success. The HT9100 is a development of the established TNL-8100 GPS-navigation system and will be manufactured by Trimble. The system will provide performance similar to Honeywell's FANS-1 FMS in the Boeing 747-400 and will be certificated initially for sole-means GPS navigation and non-precision approach.
So far, Russia's equivalent to the GPS, the Glonass, has not emerged as a major rival or even as a useful adjunct to the US system, although the 24-satellite constellation was completed in late 1995. Only one US company, 3S Navigation, has seriously pursued the development of Glonass receivers. Its latest product is the GNSS-200, a combined GPS/Glonass receiver, which 3S says is attracting some interest.
Head-up guidance
A head-up display (HUD) is an increasingly common sight in airliner cockpits, as airlines seek to minimise the disruption caused by weather. Alaska Airlines has been demonstrating since 1992, first on its Boeing 727s and now its 737s, that manual Cat IIIa landings can be performed routinely using Flight Dynamics' HGS head-up guidance system.
During 1995, Alaska was joined by Ryan International Airlines, which has HGS-equipped 727s, and Southwest Airlines, which began installing systems in 236 737s in service and on order. Alaska regional subsidiary Horizon Airlines gained Cat IIIa approval for its HGS-equipped Dash 8s - the first Cat IIIa regional-turboprop operations.
Bombardier has gained Cat IIIa approval for the HGS-equipped Canadair Regional Jet and certification is pending for Horizon's Dornier 328s, while HGS qualification is under way on the Saab 2000 and Dassault Falcon 2000. By early 1996, Flight Dynamics had orders and options for more than 500 systems, worth more than $100 million.
At Cat II/III-approved airports, the HGS allows landings in runway visual ranges (RVRs) down to 215m (700ft) and take-offs in RVRs down to 90m. Flight Dynamics expects to gain approval in 1996, on the HGS-equipped 737-300, for landings in RVRs down to 90m. Horizon, meanwhile, has begun exploiting the system's ability to enable landings in reduced visibility at Cat I-approved airports.
Sextant Avionique received Cat IIIb certification of its HFDS head-up flight-display system on the 737-300 in 1995, and French launch customer Aeropostale planned to have ten aircraft equipped by January 1996. The system allows landings with an RVR of 125m and take-offs with a 75m RVR. The HFDS is already approved on the Airbus A320 and A330, and in use with Air Inter. Sextant is working with Alitalia to certificate the system on the McDonnell Douglas MD-82.
Business-aircraft operators also are becoming increasingly interested in HUDs, and the ability to land in reduced visibility. The most popular general-aviation HUD, Flight Visions' FV-2000, does not, yet, provide any reduction in landing minima, but is seen as a safety enhancement. The company says that its HUD improves situational awareness on the approach, while the latest version, with velocity-vector cue, provides for safer and more accurate approaches.
By early 1996, supplemental type-certificates had been obtained for the FV-2000 on the Canadair Challenger 601-3A, Cessna Citation II, Dassault Falcon 50, Gulfstream IV, Learjet 55 and Sikorsky S-76. Aftermarket approvals are pending on the Citation III, Falcon 20 and 900, Gulfstream II and III, and Raytheon Hawker 800.
Business-jet manufacturers, meanwhile, are pursuing reduced landing minima, particularly on long-range aircraft, as a means of assuring that an operator will be able to land at the planned destination. Sextant's HFDS has been selected for the Bombardier Global Express, and Honeywell and GEC-Marconi Avionics have teamed to develop the HUD-2020, initially for the Gulfstream IV and V. Cat II certification is planned for the third quarter of 1996, on the GIV, with GV approval following in 1997.
Gulfstream's ultimate goal is to achieve Cat IIIa capability, possibly as early as December this year, by combining the HUD with a forward-looking infra-red (FLIR) sensor to produce an enhanced-vision system (EVS). Honeywell plans to flight-test a FLIR sensor in its HUD-equipped Citation testbed during 1996.
While EVS development has slowed in the face of lukewarm airline interest, technology work continues. The goal is to provide a Cat III landing capability at Cat I-approved airports by supplying the pilot with an enhanced image of the runway, from a FLIR sensor or millimetre-wave (MMW) radar, projected on to the HUD.
A major test of the EVS concept is expected to get under way in March, with flight-testing of the US Air Force's C-135 Speckled Trout testbed equipped with the autonomous landing-guidance (ALG) system developed by a industry team lead by Lear Astronics. The ALG consists of a Sextant HUD, FLIR Systems dual-band FLIR sensor and Lear Astronics MMW radar.
Flight-testing of a United Airlines 727, equipped with the same system, is expected to begin about a month later. United is interested in the EVS as lower-cost alternative to installing Cat III automatic-landing systems in 727s, which it plans to keep in service past the year 2000. ALG team-member Northwest Airlines is now less interested in upgrading its Boeing 747s, but continues to study the cost benefit of an EVS on the McDonnell Douglas DC-10 and other aircraft.
Multi-mode landing
The International Civil Aviation Organisation's (ICAO) 1995 decision to allow continued use of the instrument-landing system (ILS), development of the microwave-landing system (MLS) where required, and introduction of the GPS landing-system (GLS) where feasible, has breathed life into development of a multi-mode receiver (MMR) which may allow airlines to make an orderly transition from today's ILS to tomorrow's likely standard, the GLS.
This transition strategy takes the pressure off development of the GLS, the timescale for which many observers still consider optimistic. The ICAO decision means that the ILS will remain in service until it can be replaced by the GLS, with countries being permitted to install the MLS where the ILS will become untenable before the GLS is available. The strategy means that some airlines will be operating into airports with different landing systems. This is generating the need for an MMR, whether an ILS/GLS, ILS/MLS, or ILS/MLS/GLS receiver.
Use of the GPS as a landing aid is already growing. General aviation has led the way in using the GPS for non-precision approaches. At several US hospitals, for example, emergency-medical-service helicopters, equipped with approach-certificated GPS receivers from AlliedSignal Aerospace, Arnav Systems or Garmin International, can now operate in reduced visibility.
Airlines are exploiting the capability of the GPS for non-precision approaches, particularly to airports where siting problems prevent the use of an ILS. In 1995, Boeing and Smiths Industries demonstrated unaided GPS approaches to a 300ft decision height at Juneau, Alaska. The aircraft, an Alaskan Airlines 737-400, had dual modified Smiths flight-management computers and a single Honeywell GPS receiver.
Two distinct avenues to Cat I precision-approach capability using the GPS are being pursued. In the USA, the intention is to achieve Cat I standard using the wide-area augmentation system (WAAS), which will improve GPS integrity, availability and, eventually, accuracy. Wilcox Electric was awarded a $475 million contract in 1995 to implement the WAAS, with the system to be available by early 1998 and capable of providing Cat I by 2000.
In the near term, and for many countries outside the USA, the likely route to Cat I GLS is through local-area augmentation using differential GPS (DGPS). Several manufacturers are developing airborne receivers and ground stations meeting the US Special Category I (SCAT I) specification. This uses a VHF datalink to transmit DGPS error-corrections to incoming aircraft. Certification of several SCAT I installations, in the USA and elsewhere, is expected during 1996.
The feasibility of Cat II/III GLS continues to be evaluated. In 1995, the FAA completed flight tests to determine the feasibility of Cat IIIb automatic landings using different DGPS technologies. Both trials, by E-Systems and Wilcox, demonstrated the accuracies required for Cat III. Also in 1995, Boeing conducted its own Cat III GLS automatic-landing trial, using NASA's 757 and prototype equipment supplied by three teams: Collins/Daimler-Benz Aerospace (DASA), Honeywell/Pelorus and Litton/ Wilcox. An Interstate Electronics/Airport Systems International team also participated in the Boeing trial, which demonstrated Cat III accuracies. Analysis of both trials continues, along with further simulation work, as the industry works towards a standard for Cat II/III GLS.
Internationally, interest in the GLS is increasing. Trials are under way at Munich Airport, in Germany, to collect DGPS data from aircraft flying ILS approaches, for direct comparison. Collins/DASA equipment is being used. Swiss regional Crossair plans SCAT 1 GLS trials at Lugano, Switzerland, for comparison with earlier MLS tests. These will use a Saab 2000 fitted with an Interstate FMS/GPS, and an Airport Systems DGPS ground station.
Airbus Industrie is being aggressive in its pursuit of Cat I DGPS capability, and has conducted demonstrations, including automatic landings, as far afield as China and South Africa. The trials, using an Airbus A340, have involved both Honeywell and Litton GPS receivers and Sextant and Thomson/Wilcox DGPS ground-stations. Airbus plans to certificate a Cat I DGPS capability on its aircraft by the end of 1997.
The European manufacturer is the first to seek industry proposals for an MMR, which it plans to certificate by the end of 1997 and which will consist of an FM-immune ILS and Cat I GLS, initially, with MLS available only as an option. British Airways and KLM, meanwhile, are the first airlines to seek an MMR, in their case a unit combining an ILS and an MLS.
Even in the USA, interest in the MMR is emerging as airlines tackle the issue of how ultimately to transition from the ILS to the GLS. Already Collins has announced plans to develop the GLU-900 MMR, which will have the ILS and GLS as standard, with the MLS as an option. The unit will provide Cat IIIb capability and is scheduled to be available by late 1997/early 1998.
International TCAS
With the US air-transport fleet now fully equipped with the traffic-alert and collision-avoidance system (TCAS), attention has switched to the international arena. Some 6,000 aircraft are already fitted with the TCAS 2, and estimates suggest that at least another 6,000 aircraft worldwide will be equipped with the system.
So far, only Australia has announced a deadline for TCAS installation - the year 2000 - but Europe's Eurocontrol has recommended that TCAS 2 be mandatory by January 2000, on all aircraft with 30 or more seats, and by January 2005 on all aircraft with 19 or more seats. China, India, Japan and Russia are all considering TCAS and several Asia-Pacific airlines are already moving to install the system.
The International Civil Aviation Organisation has adopted the US TCAS 2 specification as the international standard for what it calls the airborne collision-avoidance system (ACAS). The present ACAS specification is based on the current standard of the TCAS 2, Version 6.04, but this will be updated to the latest software iteration, Change 7, after US testing is completed at the end on 1996.
Change 7 is intended to remove anomalies still present in TCAS 6.04, eliminating conflict-resolution advisories when aircraft are passing, in opposite directions, at similar altitudes, but with adequate separation, for example. The update also further reduces false alarms and improves the aural and visual cues provided to the pilot. The new software is scheduled to be available early in 1997.
While Version 6.04 was made mandatory in the USA, causing problems for suppliers and airlines in meeting the deadline for its implementation, Change 7 will not be mandated. Change 7 is regarded as a transition to the planned GPS-based TCAS 4, which the USA intends to introduce beginning late in the year 2000.
The TCAS 4 will use differential GPS to determine aircraft positions, and will incorporate the automatic dependent surveillance - broadcast (ADS-B). The system is based on the so-far-unused "long-squitter" capability of the Mode S transponder. While the TCAS 2 uses the Mode S "sort squitter" - which is simply a broadcast of aircraft identity - the TCAS 4 will use the transponder's ability to transmit longer messages, including information such as GPS position.
Consideration is being given to including the GPS squitter in ACAS/TCAS 2, to provide an ADS-B passive-surveillance capability ahead of the availability of the TCAS 4. Suppliers suggest that the software "hooks" for the ADS-B will be included in the Change 7 update to the TCAS 2.
Change 7 will require existing Mode S transponders to be upgraded. At the same time, Eurocontrol is calling for the installation of a more advanced Mode S in all European aircraft by January 1999. Suitable transponders, which would enable aircraft to downlink position and intent to improve air-traffic control, are scheduled to be available by the end of 1996.
Use of the Mode S extended-message capability, however, will require development of an airborne datalink-processor (ADLP), the characteristics of which are still being defined. Collins is already conducting flight trials of the ADS-B, using a test system consisting of a modified TCAS 2 Mode S transponder, prototype ADLP and a GPS receiver.
In these trials, aircraft position reports are being broadcast via Mode S transponder, received by modified TCAS 2 units on the ground and displayed on a controller's workstation. Concurrently, DGPS error-corrections are being broadcast by TCAS 2 ground units, received by the Mode S transponder and passed via the ADLP to the GPS receiver.
AlliedSignal, meanwhile, plans to have a production ADLP available in late 1996/early 1997 which includes Mode S extended-message capability and compatibility with the TCAS 2 Change 7. The company also plans to make kits available to upgrade existing Mode S transponders to the full capability.
Flexible displays
The changes under way threaten to overtake the technology available in today's cockpits, principally in the ability to display information to the pilot. The result is an accelerating shift towards liquid-crystal displays (LCDs), which have powerful graphics capabilities, as well as being easier to maintain than either today's cathode-ray tubes (CRTs) or yesterday's electromechanical instruments.
LCDs have become viable because of advances in the optical properties of the displays which make them readable in sunlight and off axis - cross-cockpit viewability is essential in airliners. These improvements have made it possible to take advantage of the LCD's lower weight, volume and power consumption when compared with CRT displays used in electronic flight-instrument systems.
Boeing was the first to introduce LCD flight displays, on the 777. The same Honeywell 200 x 200mm displays have been selected for the next-generation 737-600/-700/-800, and the 737/777 common display-system may ultimately be introduced on both the 757 and 767. These displays form a key part of Honeywell's VIA 2000 integrated-avionics system, which has been selected for the McDonnell Douglas MD-95. The displays, meanwhile, will be used in an upgraded MD-90 cockpit.
The VIA 2000 is a derivative of the aircraft information-management system developed by Honeywell for the 777. Compared with a conventional "federated" avionics system, which has a separate line-replaceable unit for each function, the VIA 2000 combines functions in a modular cabinet, reducing weight and volume.
LCDs are also at the heart of Collins' latest integrated-avionics system for business and regional aircraft, the Pro Line 21. This was launched in 1995 on Raytheon Aircraft's new Premier I light business-jet and features 200 x 250mm LCDs. The size of these "adaptive" flight displays allows new formats to be developed.
All the information required to fly the aircraft can be presented on a single display, including engine instruments, TCAS and radar. Four Pro Line 21 displays can provide the same functionality as the six CRTs installed in the 747-400.
Collins and Honeywell are demonstrating the advanced capabilities of their displays, including the ability to present complex graphics such as flight manuals, approach charts, airport maps and external video. When combined with a cursor controller, these displays provide a means to manipulate graphical information.
LCDs can also emulate existing electromechanical and electronic instruments, where commonality is an issue. This is a key feature of Sextant Avionique's avionics suite for the Dash 8-400. Sextant was selected in 1995, over Collins and Honeywell, as avionics integrator for the stretched Dash 8. The key requirement was to maintain training commonality with other members of the regional-turboprop family.
Sextant's system for the Dash 8-400 features five 150 x 200mm LCDs linked to two integrated modular-avionics cabinets. The functionality will be unchanged from earlier Dash 8s, but the number of parts will be reduced significantly, improving maintainability. Bombardier says that the Sextant system will be lighter by 50-100kg, and occupy 100litres less volume, than the equipment now in the Dash 8.
Another new entrant riding the LCD "wave" is Arnav Systems, which is providing the display suites for two new general-aviation aircraft - the Cirrus Design SR-20 piston-single and the single-turboprop Israviation ST-50. Arnav's ICDS 2000 integrated cockpit-display system is based on 200 x 150mm LCDs. The full system consists of four LCDs - two primary-flight displays, a multi-function display with GPS-based moving map and an engine-instrument/caution-advisory system.
LCDs have the potential to replace conventional instruments in new aircraft and in upgrades. In 1995, both BFGoodrich Aerospace and Meggitt Avionics introduced 75mm (3ATI) standby attitude-indicators with solid-state inertial sensors and flat-panel displays, to replace conventional electromechanical instruments, which offer increased reliability and the ability to present formats other than an attitude indicator.
Parker-Hannifin's Gull Electronics System division, meanwhile, is developing a second-generation flat-panel integrated instrument-display system (IIDS) to replace the conventional engine instruments in the Sikorsky S-76. A similar IIDS is being developed for the Canadair CL-415 and other manufacturers are producing systems for the Agusta A.109 (Ametek), Bell 430 (Rogerson Kratos) and McDonnell Douglas Explorer (Canadian Marconi).
Upgrades are growing in importance, as airlines find it increasingly difficult to maintain out-of-production instruments - and it is increasingly apparent that analogue cockpits will not provide the functionality required to operate within the future airspace-management system. AlliedSignal, which is developing an LCD-based avionics suite for Russia's Beriev Be-200 twinjet amphibian, is pursuing the retrofit market with a 125mm (5ATI) LCD designed to replace standard electromechanical flight displays. Collins has also launched a "drop-in" LCD replacement for its 5ATI instruments, claiming four times the reliability, at half the cost, with the ability to display radar, TCAS and GPS information.
Source: Flight International
