Press clip:

The following article has been converted to HTML format.


SAS makes history with certifiable ADS-B display

Scandinavian flag-carrier SAS has made a little bit of history with the first flight of a certifiable automatic dependent surveillance - broadcast (ADS-B) display in a commercial airliner. The move is a significant step along the long road to free flight. ANI was on board the 14 December flight from Stockholm Arlanda as the Swedish CAA performed certification tests on what is now called the MMI5000 (as in "man machine interface). The device effectively constitutes an example of the emerging breed of cockpit displays of traffic information (CDTI), in this case complete with moving map and extensive navigation capability. The Fokker F-28 involved is also ne of the aircraft equipped with the Swedish-developed GNSS Transponder as part the North European ADS-B Network (NEAN) trial (ANI 212). That is based on use of the self-organising time-division multiple-access (STDMA) datalink invented by Hakan Lans, who was also on the flight.

The MMI5000, with hardware by Hectronic (using a Phillips colour LCD screen) and software by Carmenta, both of Sweden, replaces a cruder unit used since the NEAN flying activity began in January. In the analogue F-28 it is mounted in the centre pedestal (see illustration) and its size is consequently constrained - in glass cockpit aircraft the navigation display screen would be used. The box the AlliedSignal KNS-660 commuter FMS which was in any case being removed to have RNav functionality to it - making the financial equation for the research and development a little easier for SAS management.

Traffic and navigation functions both work well...

Although less than optimally positioned, the display is of high quality and showed good readability even on the bright winter day of the flight. The unique feature of the system is its traffic display functionality, but it is also a navigation display with limited flight management system (FMS) capability. As a result, SAS has tried as far as possible to make it resemble the FMS in its digital McDonnell Douglas MD-80 and Boeing 767 fleets. Technical pilot for flight standards and development, Lars Lindberg, says: "If we could find a standard we used it, if there wasn't one then we went to any group that was working on standards and used them." The navigation database is the standard KSSU product used by SAS.

... promising numerous benefits

Lindberg, flight officer Bengt Moberg, and F-28 fleet engineer Per Ahl, explain that the exact uses of the CDTI, ADS-B network, and datalink are numerous, but they illustrate some typical operating procedures. Entering the flight number produces a standard flight plan drawn from the database on screen which, for now, is checked against the filed paper plan on the day, In future the live plan will be uplinked to the cockpit. Pop-up menus can be used to access the airfield display, runway in use and standard instrument departure (SID) which is checked against the paper departure plate and then entered by pressing "execute". That also changes the displayed SID track from blue to yellow. Other pop-ups can be used to display waypoints, airports, beacons and so on as required, and a track deviation indicator (compared with the flight plan) can be displayed at the bottom of the screen. Lindberg notes that the STDMA datalink has the capacity to uplink the secondary radar picture and give collision avoidance functionality. SAS is nervous, however, about antagonising the TCAS vendors and is currently committed to fitting conventional TCAS fleetwide. Lindberg says: "We will use TCAS to help validate the ADS-B, and hopefully we will not get the sort of conflicts that TCAS addresses."

A major advantage of the NEAN concept is its potential for use on the ground - notably for taxying guidance in visibility and for tracking ground vehicles. A demonstration of this occurred while taxying for the CDTI certification flight when a GPS Transponder-equipped runway friction testing vehicle was observed passing the F-28 and be clearly seen on the display tracking down the centre of the runway. Position reports are updated every second now, and will be more frequent in future. Lindberg says that, in bad weather: "You can see that the runway is - even in Category III - and you can find the exit, which at somewhere like London Heathrow is one of your problems in Cat III." At Arlanda, the snow-ploughs are also transponder-equipped and, with their positions safely known, aircraft can be cleared to taxy sooner after snow-clearing than has normally been the case. In the same way, vehicle drivers should be more aware of the positions of equipped aircraft.

SAS and Lufthansa see ADS-B as key to capacity growth

The SAS team says it is hard to know where to begin in listing the potential operating benefits of ADS-B. Like other carriers, it sees a growing risk of air traffic system capacity constraining its growth. In the long term it wants ADS-B as the basis for free flight, but before then it sees it as a valuable tool in approach operations to maximise runway throughput. "I see ADS-B as a way of splitting responsibility between controllers and pilots", says Lindberg, "today they ask me if I can see the runway and the aircraft ahead and then give me a visual clearance. But I could be seeing the wrong aircraft and anyway it is hard to judge his speed, whereas with ADS-B I can be sure and should be able to get some kind of reduced separation." 'Mere are safety benefits too. "Just by having the ADS-B you have better situational awareness", says Lindberg. And he notes that it particularly helps solve the often raised issue of the loss of the "party line" effect when voice communication is replaced by datalinking. Lindberg says: "We [SAS] are spending money on this because we see the benefits of this system as being very important for us to improve safety and capacity. We are up to the limit of capacity in some areas of Europe and we are acquiring new aircraft. Most of the other carriers are doing that too. We have to create capacity to have growth in the system. This system addresses the crucial areas."

The airborne ADS-B functionality really does work. On the Stockholm flight one of the other GPS Transponder-equipped aircraft was observed on the display, complete with vector arrow showing that it was climbing. That was no surprise to the Swedish team which has seen the system working successfully for most of the last year. At Arlanda the researchers have watched aircraft climb out of Karlstad, 137nm west, as they pass about 4,000ft altitude. Lindberg says that "at normal altitude" the system has approximately the 250nm range expected from a VHF-based architecture.

NEAN work will expand next year

Early in 1997, the true performance of the 50% European Commission-funded NEAN set-up will become clearer as the ground network is completed (see map p.3), The Swedish network is already fully functional; the Danish element is complete and now being connected; and Germany is close behind, An additional station at Maastricht is to be used for Eurocontrol upper airspace trials under the PETAL 2 datalink communications trial and an STDMA station is being implemented at Brussels as a standalone project. Other stations are coming to Eurocontrol's experimental facility at Bretigny; Rome as part of the FARAWAY project; and Madrid in the SUPRA programme.

During 1997, 12 aircraft will eventually be equipped with GPS Transponders including: the two SAS F-28s; two Golden Air of Sweden Saab 340s (one is already equipped); a Maersk Helicopter of Denmark aircraft; at least one Lufthansa aircraft - either Boeing or Airbus; a German business jet sponsored by AOPA; another general aviation aircraft as part of SUPRA; two Fairchild Metros of German commuter carrier OLT of Emden; and a Danish Nord 262 flight check aircraft. The FARAWAY team hope to have three Alitalia McDonnell Douglas MD-80s equipped with at least the GPS Transponder and, hopefully, the CDTI. SAS's plans to equip a Boeing 767, primarily for the PETAL 2 work, are subject to the airline's engineering schedule and currently are in the balance. Some 30 airport vehicles are to be equipped in Sweden, Denmark and Germany. In September 1997, the one year NEAN Applications (NEAP) programme will get underway to evaluate: enhanced surveillance for ATC; pilot situational awareness; and GNSS precision navigation in all flight phases. In January, ground surveillance trials matching STDMA against Mode-S techniques are due at Atlanta Hartsfield airport.

STDMA datalinking and DGPS navigation are also put to the test

SAS and Lufthansa are focused very much on ADS-B itself, but the Swedish work is also producing valuable data regarding the overall performance of the STDMA datalink itself, and the navigation capability. SAS declares itself "pro-ADS-B" as opposed to "pro-STDMA", but it is clear that the trials have anyway overwhelmingly supported the key claims of STDMA supporters in ICAO forums and elsewhere - particularly against Mode S-proponents. Lindberg comments: "We were reluctant to do STDMA for a long time. Mode-S has benefits compared with STDMA but we think the disadvantages are more than the advantages." That comes as good news to Lockheed Martin which is still in deep discussions with the Swedish Space Corporation over the commercial exploitation of STDMA and the GNSS Transponder in aviation (ANI 2/18).

Datalink inventor addresses proprietary issues...

STDMA-inventor Hakan Lans has now taken further steps to counter one of the last remaining objections to the use of the STDMA datalink as an international standard - its proprietary nature. This issue has been repeatedly raised at ICAO and elsewhere, and Lans is determined not to let it stand in the way of STDMA compliance with ICAO's requirements. In a recent letter to ICAO and the International Maritime Organisation, Lans declares: 'The prime objective of the owners of the STDMA technology is to facilitate its widespread introduction and use for the benefits of the transport industry. A secondary goal is to get a reasonable return on investments made during the development and standardisation work." In line with this, Lans says, only "non-exclusive worldwide licences" are being granted in relation to civil aviation and maritime applications. He adds that the owners of the technology "are prepared to negotiate transfer of licences on reasonable terms and conditions to any competent and interested party in accordance with the International Telecommunication Union's code of practice" and that if negotiations should ever fail then "international or national arbitration would also be accepted".

... as dispute over Mode-S rumbles on

There is no question that the Mode-S proponents are increasingly on the defensive. In almost any forum there is less and less support for expansion in its use and, conversely, growing support for STDMA. At SAS, Lindberg remarks: "Mode-S level four was very much opposed by us and other airlines. The cost is supposedly not so expensive for the aircraft anymore but we know that we have to pay for the infrastructure!' And the European Union DGXIII's key Atlas IIA CNS/ATM Technologies document earlier this year almost universally backed STDMA against Mode-S - particularly for surveillance purposes.

Sweden prepares for DGNSS approaches in 1997

A less well appreciated feature of the NEAN infrastructure is that it effectively constitutes a highly robust regional area differential GPS system - adding to the list of alternatives to expensive wide-area augmentation systems such as EGNOS. SAS and the Swedish CAA plan during 1997 to implement four GNSS routes and also to construct a GPS non-precision approach to runway 32 at Angleholm. The procedure would replace the current complex NDB approach. Lindberg says: "It is not a good approach and it is one of the ones we want to do something about." Indeed, the airfield has already been the site of a controlled flight into terrain accident involving a Swedish commuter aircraft.

What SAS envisages initially is using the MMI5000 to navigate to a VOR/DME check point and then following a continuous curved descent through step-down points to Cat I minima with the localiser being displayed on the CDTI. A WGS-84 survey will be available, and SAS would like to use a combined GLONASS/GPS receiver "as soon as there is something good enough".

Press clip as MS WORD dokument

Return to homepage