Communications, navigation and surveillance in European airspace will be substantially different in the next decade - but how different?

Kieran Daly/LONDON

AROUND THE WORLD, air-traffic-services (ATS) providers are coming to terms with how the advent of the future air-navigation system will affect their airspace. For dozens of nations, notably developing countries, this technological revolution gives an opportunity to attain the state of the art at the first attempt. For the developed world, however, the prizes of enhanced safety and efficiency can be achieved only if the transition process is correctly planned, and nowhere is that more true than in Europe. The continent's combination of increasingly high-density traffic and widespread instrument-flight-rules airspace makes any fundamental change a challenge indeed.

Europe's ATS planners face a mixture of issues, from those which it is generally accepted must be addressed urgently, to those for which technology may or may not offer a better way of doing things. There is no shortage of promising technology in the field of communications, navigation and surveillance; the difficulty is in knowing which techniques can be usefully applied in a foreseeable timescale. The contenders include several promising, but immature, techniques, some of which would almost certainly fade away if they are not chosen now.


Communications debate

Nevertheless, some aspects have become, or are becoming, clear. In the communications field, the heated debate over the perceived need for more VHF voice frequencies in upper airspace is effectively complete - with expensive consequences for airlines. Any doubts left were comprehensively settled when Germany announced that 1 January, 1999 would be the date for the switch to 8.33kHz channel-spacing. Germany's ATS authority, the privatised DFS, alone conducted an exhaustive study of ways around the problem, which will require the replacement of radios in hundreds, if not thousands, of aircraft. It believed that it might have been possible to push the implementation date past 2000, but it has concluded that it can delay it until only 1999. Some other countries say that even that will be difficult. In any case, the issue is likely to resurface in a different form, says the DFS, and then it will be modified by the possibility of replacing some voice communications with datalinks, such as the self-organising, time-division, multiple-access datalink (STDMA).

The DFS explains: "It is clear that, in roughly 2000, we will need to discuss it again because then we will have the problem of running out of frequencies in the lower airspace. Then we will surely have a better picture of STDMA or anything else to find a transition to this."

Traffic congestion has also had one definite consequence in the navigation field - the implementation of reduced vertical-separation minima (RVSM). While the highly positive cost/benefit ratio of RVSM - perhaps 5:1 - is widely accepted, there has been considerable heartache over the operational schedule. With great reluctance, Eurocontrol was finally persuaded by the user community to aim for a 2001 implementation date. Work is under way to devise a sound technique for monitoring the real-life altimetry performance of in-service aircraft - a critical issue if vertical separation minima are to be cut from 2,000ft (600m) to 1,000ft in upper airspace as envisaged. Although not directly related, another change is making airborne collision-avoidance systems mandatory - the traffic-alert and collision-avoidance system is the only current example - from 2000 for aircraft of more than 30 seats, and from 2005 for those with more than 19 seats.

Perhaps the next most certain development, although the details are still unclear, is the introduction of the microwave-landing system (MLS) at a handful of key European airports. The Netherlands ATS authorities are understood to have just joined BAA, the owner of London Heathrow, in deciding to install the MLS at Amsterdam Schiphol Airport. British Airways, KLM, Airbus Industrie and Avro International Aerospace have issued industry solicitations for the multi-mode receivers (MMRs) which will allow their aircraft to use the instrument-landing system (ILS), MLS or satellite-landing systems with identical cockpit instruments. Despite the repeated assertions by the UK Civil Aviation Authority that the encroachment of high-powered commercial broadcasting into the ILS band would threaten low-minima ILS use in Europe, vendors have been slow to react. It is perhaps the quintessential example of the rest of the world's difficulty in understanding Europe's unique ATS issues. A navigation veteran at one of the biggest European flag carriers declares: "It's been difficult getting people to pay attention to the problem. Boeing just didn't believe that we meant what we were saying."

Which airports will be forced into the use of the MLS, and when, remains uncertain. What is becoming accepted by airlines, however, is that the consequences of not being equipped for MLS operations, if your competitors are equipped, are not acceptable. Long-haul carriers around the world are therefore joining the search for the optimum MMR.

Airbus' vendor-selection is understood to be imminent. Its aggressive schedule has driven the activities of five contenders and that, combined with its insistence that candidates should be able to offer the MMR and differential global navigation-satellite system (DGNSS) ground-stations has generated some hasty commercial marriages. The list of competitors now consists of Sextant Avionique; Lockheed Martin; the DASA Collins joint venture; AlliedSignal with Raytheon E-Systems and Canadian Marconi; and a less intimate pairing of Honeywell with GEC-Marconi Electronic Systems.

At the same time, DASA Collins trials in Munich and Honeywell demonstrations in eastern Europe and Brussels earlier this year have shown that Category I precision approaches using local-area DGNSS are more or less available already, and that MLS use will always be a minority solution.

The strong US presence in that line-up highlights Europe's weaknesses in avionics, but in the vital area of the GNSS, Europe is rapidly catching - even outstripping - the USA. The basic US global-positioning system and Russian Glonass satellite constellations will, of course, be the basis of satellite navigation for many years to come. The augmentation systems needed to spread their use in the safety-critical sphere of commercial air transport, however, are a different story. Introduction of the US Wide Area Augmentation System is in disarray, facing a minimum of a year's delay with the prospect of a less-capable system at the end.


European progress

Meanwhile, the equivalent European Geostationary Navigation Overlay System (EGNOS), while also facing formidable challenges, has made strides. The greatest challenges facing the developers - the European Commission, Eurocontrol, and the European Space Agency - are perhaps political. Germany and the UK (the latter in particular now responsible for some of the world's most advanced GNSS development work) along with Spain, would each like to see one of the two EGNOS master control centres on their territory. One station is already earmarked for Toulouse - merely one aspect of the marked French flavour of the programme.

Comparisons with the USA are similarly unavoidable in the evolution towards so-called "free flight". Despite the concept's perceived US genesis, European progress towards a workable system is striking. The European effort is largely encapsulated in the Programme for Harmonised Air Traffic Management in Europe (PHARE). The PHARE team presented flight demonstrations of the first, en route, phase of the activity at Bournemouth in the UK in May. They emphatically impressed observers.

In the air, the programme has successfully resulted in the development of an experimental "four-dimensional" flight-management system (FMS) with an automated VHF datalink. In brief, the FMS permits the aircraft to be flown along a predetermined trajectory from take-off to touchdown within a time window of a few seconds. On the ground, the PHARE work has produced computer tools which let controllers negotiate initially non-conflicting trajectories with the aircraft by datalink. More remarkably, it has generated other tools - notably the Highly Interactive Problem Solver - which predict conflicts, for example, 30min ahead, and enable controllers to devise resolutions. This is typically done by the controller's "clicking and dragging" the displayed future trajectory with a computer mouse until the conflict disappears. The new trajectory is then datalinked directly to the FMS for active acceptance by the pilot. It sounds, and is, impressive, but equipping aircraft and control centres, even assuming that the final PHARE results in 1998 support such a move, would be a monumental task.

Even then, many free-flight advocates believe that the concept will work effectively only with the use of the automatic dependent surveillance-broadcast (ADS-B) concept. That idea, now undergoing limited trials in Europe, uses a combination of GNSS, airborne transponders and new cockpit displays to give every pilot a picture similar to that seen by the controllers. Others believe that ADS-B alone could bring most of the benefits of free flight, certainly in the en route phase. One can hardly envy the decision-makers: their judgements are crucial to the development of European air transport, and doing nothing is not an option.

Source: Flight International