FLIGHT INTERNATIONAL 7-13 FEBRUARY 1996 (all pictures are not included)
Talk this way
planners have been tempted to press ahead with A Swedish-laed technology could their introduction. Throughout all this, there has provide a key element of the Future always been the niggling knowledge that the
STDMA datalink appeared to offer a robust, all-Air Navigation System.
encompassing, alternative. At least three issues have kept it in the background, however: its Kieran Daly/LONDON aviation application was less mature, it was poorly understood and its primary champion - Sweden - THE GLOBAL-NAVIGATINON satellite-system-was a relatively small player in a FANS world synchronised, self-organising, time-division, dominated by the USA, and France. multiple-access (STDMA) data-ink really needs a much better name. It is one thing for the dedicated SWEDISH FANS DEDICATION souls serving on the International Civil Aviation This not for want of effort by the Swedish civil-Organisation's (ICAO) technical committees to aviation authority. The director of international cope with this sort of linguistic horror, but there is projects of its Swedavia arm, Johnny Nilsson, has now good reason to think that a much wider become one of the most enduring fixtures at the aviation community will have to incorporate host of conferences and commit-tees where FANS "STDMA" into its vocabulary. Indeed, it may issues are thrashed out. Voluminous test-data become one of the most important technical under one arm, lap-top computer under the other, elements of the Future r Navigation System Nilsson has briefed, and rebriefed, anyone who will (FANS). listen. His reception has varied from bafflement to In the rarefied world of the FANS planners, respect, but, above all, there has been a reluctance datalinks are the number one technical concern. to come to terms with the implications of what he Datalinking pervades the entire philosophy behind is saying. the FANS and, even now, new applications for it That may be about to change. Not only has the are emerging: as a replacement for voice frustratingly slow pace of FANS implementation communications; to pass position reports ii let the Swedish technology catch up, but renewed satellites; to convey intentions; to enable satellite-interest in another FANS concept - automatic aided approaches; and to assist with air-port dependent surveillance-broadcast (ADS-B) - has surface-surveillance, The list goes on, but one focused new attention on STDMA work. ADS-B major potential result is a proliferation of types of could fundamentally transform ATM - and it is datalink, each with its own infrastructural and accordingly controversial, particularly when linked avionics requirements. with so-called "free-flight" concepts. In some The problem has been recognised for some rime, circles, however, it is seen as perhaps the only way but there is a desperate need for the FANS and, to win substantial ATM efficiency-gains in the type since many of these datalinks are technically of high-density airspace, where it is proving reasonably mature, air-traffic-management (ATM)
difficult-to-extract benefits from the FANS - comments: ”The question then is 'can VHF
notably Europe. Crucially, the STDMA datalink is STDMA do the same thing?' and the answer is well suited to the ADS-B application. yes."
ADS-B-proponents, with Swedavia prominent
among them, envisage an ATM system in which
the positions and intentions of aircraft in the air
and on the ground are constantly broadcast - by
datalink - to each other and to air-traffic control.
Everyone in the system has real-time access to precisely the same data, via similar displays, with a … as SAS examines datalinkig options
consequently vast improvement in situational
awareness. Tle STDMA datalink is a prime RACE AGAINST TIME
candidate for the resulting robust, time-critical, Nilsson accepts that he is, to some extent, in a race communication requirement. Nilsson, against time, but comments: ”If the focus had been understandably, is pleased to see the progress being on STDMA, then there could probably be systems made, declaring: ”I think that the message is out there working already." In fact there are, but starting to come across: it is very, very difficult to not in the air-transport world. As with the GNSS, have situational awareness throughout all phases of air transport may be the most demanding customer flight without STDMA [datalinking]. I also think for the technology, but it will ultimately he among that there is now a fairly mature understanding that the most numerically insignificant. STDMA the datalink issue is one of the most critical ones technology is already in limited use in the for these new technologies. But most people in maritime and surface-transport communities. aviation have been so used to thinking of a Furthermore, helicopter operators in Malaysia and dedicated system for each special type of Scandinavia are pursuing it as a way of passing application that they have not really thought about operational data and bringing surveillance into a system where you can get a multitude of offshore operations (Flight International, 12 -18
applications." April, 1995).
An important quality of the STDMA datalink for In the air-transport world, STDMA activity is aviation users is that its use of global-navigation-about to be stepped up substantially. By now, a satellite systems (GNSS) - primarily the global-Scandinavian Airlines System (SAS) Fokker F28 positioning system (GPS) for now - ensures should he flying in revenue service with extremely precise (sub-second) co-ordination Swedavia's ”GNSS/STDMA transponder” fitted,
between the communicating stations. The together with a dedicated cockpit-screen for ADS-principle of the STDMA datalink is that access is B use. The SAS programme is one element of the divided into discrete time-slots each equating to most extensive aviation-STDMA evaluation to date one message of up to 32 bytes at 9,600 bits/s (a - the North European ADSB Network (NEAN). basic ADS message for example). Longer The programme is 50% funded by the European messages, such as text, use more than one slot. Commission (EC) and falls under the ATM item in The system is now capable of handling 9,000 32-the EC’s Trans-European Transport Network
byte messages/min and has a 25kHz bandwidth. project. The work programme is to demonstrate the Nilsson says that, not only is the concept superior benefits of ADS-B systems to the user, to develop to the carrier-sense multiple-access datalink and validate the technology for ATM and to envisaged for communications, but it can also establish a cost database. Eventually, as many as replace the Mode-S data for surveillance (and for 15 aircraft are due to be involved, but, in the short traffic alert and collision avoidance, for that term, they will include at least two SAS F28s, one matter), and it is capable of handling differential now equipped and one to be ready later this month; GNSS data for precision-approach guidance or for a Golden Air of Sweden Saab 340; a Lufthansa surface-surveillance purposes. Airbus type and, possibly, a Boeing 737. Lufthansa He explains: "STDMA/GNSS is a toolbox and, is a keen supporter of ADS-B as a possible part of from that you can build almost any application. I future ATM. Talks are under way with a Danish think that that message is starting to matter in the commuter carrier as well.
airline industry. So, the question is: what are the The current ground stations are at Stockholm datalink options? I would say that no-one Arlanda, Stockholm Bromma, Norrköping, disagrees that STDMA is a very, very, good option. Jönköping, Gothenburg and Malmö Sturup in Then people start to look at the other options, but Sweden; Braunschweig, Bonn, Biemen, Berlin and this is the only one of the future technologies that Frankfurt in Germany; and Copenhagen, Aalborg works. ”He concedes that, for example, Mode-S and Billund in Denmark. Most of the Swedish and also works (for surveillance at least), but he Danish stations, plus Braunschweig, are already
operating. Eventually, it is intended to have ten to environment.” He adds: "In Scandinavia, we have 15 airborne units and 20-25 ground stations under quite a few airports with a precision approach at
the NEAN effort. The Swedish, Danish and one end and not at the other. We know that
German civil-aviation authorities are the main controlled flight into terrain is a big issue and a big
partners - together with the airlines - plus the UK problem - so we are very interested in this." The
datalink debate has a long way to go yet, but there Civil Aviation Authority for certification and
is no doubt that Johnny Nilsson and his colleagues validation work. If the STDMA concept is to enter
at Swedavia have changed the agenda. 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 the human-machine interface [HMI] to determine exactly how the ATM
workstation should be and how to address the HMI in the cockpit."
At SAS, F28 chief technical pilot Lars Lindberg is chairman of a project group looking at new navigation aids, and he is specifically responsible for the NEAN input. SAS is incorporating its NEAN activity into a wider programme, looking at GPS navigation and differential GPS (DGPS) approaches using the STDMA datalink to pass the differential corrections. That comes about because the GNSS/STDMA transpon er includes a CPS navigation 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' programme, 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 airports where the only options now are non-directional-beacon-aided approaches or other non-precision
F28 AIRBORNE EQUIPMENT
The F28s airborne equipment consists firstly of the GNSS/STDMA transponder, which incorporates the GPS; a communications element 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 "AWI" - 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. Lindberg says: "We have been following this and other things for several years, and it is our view that ADS-B could be a crucial part of the CNS/ATM