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Hi-Tech Olympics
The Olympic Games in Atlanta will be the setting for an experimental air transportation system using ARNAV Systems Incorporated’s GeoNet datalink network. The Atlanta Short Haul Transportation System (ASTS) will provide transportation of goods and services during 17 days of the Olympics starting July 19. Bell 412 and Eurocopter BO 105 helicopters operated by Petroleum Helicopters of Los Angeles will help deliver overnight packages from the US Postal Service, Federal Express and United Parcel Service. The helicopters and a number of fixed wing aircraft will be managed by GeoNet, which uses a network of towers and repeaters to ensure connectivity of a 9600 baud, bit capable VHF datalink between aircraft and ground. Ground stations consist of a radio transceiver, computer workstation and large graphics display showing aircraft as icons along an airway. Aircraft will be equipped with transceivers and ARNAV multifunction displays (or handheld message terminals) showing GPS position and flightplan waypoints over a special Olympic route map. In addition to position information, the datalink will provide pilots with traffic, weather, and dispatch data, while automatically feeding position altitude and arrival/takeoff information to ground based controllers. Also, aircraft sensors will be used in the downlink of electronic pilot reports (E-PIREP) to the National Weather Service detailing ambient weather conditions. Operating within three mile temporary flight restricted (TFR) areas established around Olympic venues, and under VFR procedures, participating aircraft will receive priority dispatch handling and time critical traffic and weather information. Non equipped aircraft will require advance notice of flightplan approval. Without GPS, and the flight following capabilities that come from the transition of onboard position information via the datalink system, it is unlikely ASTS would have been possible, according to the FAA. The system is like automatic dependent surveillance (ADS), an integral feature of the future air navigation system (FANS), in that it potentially frees aircraft from the constraints of the ATC radar system. ASTS is supported by $US5m in FAA and$US5m in private funds. ARNAV is providing the equipment at cost, and avionics are being loaned to participating aircraft for the duration of the Games.
The Problem With TCAS
The Civil Aviation Safety Authority is seeking industry comment on its proposal to introduce Airborne Collision Avoidance Systems (ACAS) in Australian aircraft. The ACAS concept is not new – carriage of equipment such as Traffic Collision Avoidance Systems (TCAS) has been mandated in other parts of the world for some time. Its proposed introduction here follows a BASI recommendation last year after several reported airmiss occurrences. An ACAS is a means of alerting pilots to the proximity of other aircraft and providing warnings of potential collisions and, depending on the system, collision avoidance instructions. TCAS is the only functional ACAS system currently available. It has demonstrated its capacity to provide information that will reduce the probability of collisions in the air. In considering TCAS suitability for Australian aircraft and Australian conditions, the overseas experience can be used as a guide. But it’s interesting to hear what the international aviation community – especially pilots – have to say about TCAS. At the recent annual conference of the International Federation of Air Line Pilots Associations (IFALPA) in March, it emerged that pilots had problems accepting advice from TCAS. Manoeuvres initiated because of false or nuisance TCAS warnings have occurred, mainly due to shortcomings in system software. The association also believes that there should be Mode-S datalink between aircraft and air traffic control when a Resolution Advisory (RA) occurs. Already there is the capability for the transponders of aircraft in conflict to “talk” to each other so as the advice given to one pilot is not contradictory to the advice given to the other. Concerns were also raised about the lack of industry standards for training. According to AlliedSignal Aerospace, which has installed about 4000 TCAS sets, the previous Change 6.04A software has reduced the number of nuisance RAs. These were caused by high vertical climb rates at low level and have been dealt with by extending the trigger times. Nuisances still persist at higher altitudes, however, where the RA trigger is less delayed. Change 7.0 software is expected to be implemented by the year 2000 and is intended to be more robust in multi aircraft situations and to have a logic consistent with ICAO standards and recommended practices for ACAS. Changes are to be made to the miss distance filter (which may also avoid nuisance warnings from rapidly climbing threats) and to some features of the display and voice warnings. Operational procedures used by pilots need to be studied further, says AlliedSignal. Analysis of the record of warnings and pilot responses, using the compulsory 6.04A software has been difficult to interpret. Often no action in response to a real threat has been taken where visual contact has been established. This is renewing the debate on whether pilots must comply with RAs. Meanwhile, an evaluation of the downlinking to ATC of any TCAS RA message is planned to be carried out at Boston, Massachusetts, and oceanic in trail manoeuvres will continue to be developed. AlliedSignal reports a requirement for basic Mode S, with fixed datalink message length, may be defined in Europe by mid 1996. Extended message capability is not due until early 1999. AlliedSignal Aerospace says that it intends to release a Mode-S transponder with this capability as the Change 7.0 software comes into effect. However, at the top of IFALPA’s list of concerns is the use of ACAS for monitoring in trail separation on climb and descent. The association singles out the activities of the Informal South Pacific Air Traffic Services Coordinating Group (of which Australia is a member) highlighting the fact that, in part of the Pacific, lateral separation has already been reduced to 60nm (111km) with plans to further reduce lateral and longitudinal separation to 55nm (102km). IFALPA does not oppose the principle of in trail climb or descent, just the method presently proposed. The Civil Aviation Safety Authority stresses that ACAS is not a substitute for air traffic control, nor is it a form of pilot managed ATC. It’s also worth noting that Australian airspace differs greatly to that where TCAS is currently used and/or mandated. Unlike Europe and the US, most of Australia’s airspace does not have radar coverage, meaning Mode-S datalink messages to air traffic control of RAs are not possible in these areas. CASA is seeking the widest possible input from the public and industry, and then, following an analysis of all responses and if a decision is made to mandate ACAS, a Legislative Instrument Proposal (LIP) will be prepared in accordance with the Ministerial Direction on Rule Making. It is anticipated the LIP could be issued in late July to allow further industry comment.
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