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Aviation History
1996
1996 - 0310.PDF
DEFENCE "We never forget you have a choice!' ...as SAS examines datalinking options more than one slot. The system is now capable of handling 9,000 32-byte messages/min and has a 25kHz bandwidth. Nilsson says that, not only is die concept superior to the carrier-sense multiple-access datalink envisaged for commu nications, but it can also replace the Mode-S datalink for surveillance (and for traffic alert and collision avoidance, for that matter), and it is capable of handling differential GNSS data for precision-approach guidance or for surface-sur veillance purposes. He explains: "STDMA/GNSS is a toolbox and, from that, you can build almost any applica tion. I think that that message is starting to mat ter in the airline industry. So, the question is: what are the datalink options? I would say that no-one disagrees that STDMA is a very, very, good option. Then people start to look at the other options, but this is the only one of the future technologies that works." He concedes that, for example, Mode-S also works (for sur veillance at least), but he comments: "The ques tion then is 'can VHF STDMA do the same thing?' and the answer is yes." RACE AGAINST TIME Nilsson accepts that he is, to some extent, in a race against time, but comments: "If the focus had been on STDMA, then there could proba bly be systems out there working already." In fact there are, but not in the air-transport world. As with the GNSS, air transport may be the most demanding customer for the technol ogy, but it will ultimately be among the most numerically insignificant. STDMA technolo gy is already in limited use in the maritime- and surface-transport communities. Further more, helicopter operators in Malaysia and Scandinavia are pursuing it as a way of passing operational data and bringing surveillance into offshore operations (Flight International, 12-18 April, 1995). In me air-transport world, STDMA activity is about to be stepped up substantially. By now, a Scandinavian Airlines System (SAS) Fokker F28 should be flying in revenue service with Swed- avia's "GNSS/STDMA transponder" fitted, to gether with a dedicated cockpit-screen for ADS-B use. The SAS programme is one ele ment of the most extensive aviation-STDMA evaluation to date — the North European ADS- B Network (NEAN). The programme is 50% funded by the European Commission (EC) and falls under the ATM item in the EC's Trans- European Transport Network project. The work programme is to demonstrate the benefits of ADS-B systems to the user, to develop and validate the technology for ATM and to estab lish a cost database. Eventually, as many as 15 aircraft are due to be involved, but, in the short term, they will include at least two SAS F28s, one now equipped and one to be ready later this month; a Golden Air of Sweden Saab 340; a Lufthansa Airbus type and, possibly, a Boeing 737. Lufthansa is a keen supporter of ADS-B as a possible part of future ATM. Talks are under way with a Danish commuter carrier as well. The current ground stations are at Stockholm Arlanda, Stockholm Bromma, Norrkoping, Jon- koping, Gothenburg and Malmo Stump in Swe den; Braunschweig, Bonn, Bremen, Berlin and Frankfurt in Germany; and Copenhagen, Aal- borg and Billund in Denmark. Most of the Swedish and Danish stations, plus Braun schweig, are already operating. Eventually, it is intended to have ten to 15 airborne units and 20- 2 5 ground stations under die NEAN effort. The Swedish, Danish and German civil-aviation audiorities are the main partners — together with the airlines — plus the UK Civil Aviation Authority for certification and validation work. If the STDMA concept is to enter service, and particularly if ADS-B is to become reality, a great deal of work will be required to hone the appropriate displays and controls in the air and on the ground. Nilsson notes: "There will be a lot of issues on die human-machine interface [HMI] to determine exact ly how the ATM worksta tion should be and how to address the HMI in the cockpit." At SAS, F2 8 chief tech nical pilot Lars Lindberg is chairman of a project group looking at new navi gation aids, and he is specif ically responsible for the NEAN input. SAS is incor porating its NEAN activity into a wider programme, looking at GPS navigation and differential GPS (DGPS) approaches — using the STDMA datalink to pass the differential cor rections. That comes about because the GNSS/ STDMA transponder includes a GPS naviga tion function, and the cockpit processor has a limited flight-management-system capability. Lindberg explains: "The primary target is to demonstrate ADS-B capability, but also to use some of the navigation information from the system." In the second phase of SAS' pro gramme, there will be greater concentration on the navigation function, using the GPS data and, in the third phase, the airline will use DGPS to conduct approaches to certain Scandinavian air ports where the only options now are non-direc tional-beacon-aided approaches or other non-precision procedures. F28 AIRBORNE EQUIPMENT The F28's airborne equipment consists firstly of the GNSS/STDMA transponder, which incorporates the GPS; a communications ele ment with STDMA processing; and a VHF transceiver. The GPS receiver is an off-the- shelf unit which is incorporated into the transponder, but production transponders would not necessarily have the GPS integrated inside. Mounted in the cockpit centre-pedestal of the thoroughly analogue F28, is the "MMI" — a colour screen with a 486 processor and integral database. The initial transponders are scheduled to be replaced with updated units which will comply with draft ICAO standards and recommended procedures. At SAS, the programme could have radical consequences for operating procedures. Lind berg says: "We have been following this and other things for several years, and it is our view diat ADS-B could be a crucial part of the CNS/ATM environment." He adds: "In Scan dinavia, we have quite a few airports with a pre cision approach at one end and not at the other. We know that controlled flight into terrain is a big issue and a big problem — so we are very interested in this." The datalink debate has a long way to go yet, but there is no doubt that Johnny Nilsson and his colleagues at Swedavia have changed the agenda. J <j - . — 0943z ATC UPLINK l/i STATUS - _ REJECTED AT - -_ .CLEARED ROUTE CLEARANCE : [_ 1 . "H RESPONSE 0r-J: • " F=% UNABLE VflK TlflT ' STir CEF ,T|- :'v«»« REF ",- ARR AlL : """* vfc~- ,»_, <fc T— - T- "H FiX LESS K3LD MJ es-; 3G> Datalinking is crucial to the FANS 38 FLIGHT INTERNATIONAL 7 - 13 February 1996
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