For over a decade, Rega has pursued its vision of all-weather air rescue. Our avowed aim is to further reduce the number of missions that cannot proceed due to poor weather conditions and to help even more people in distress. Key to this are the instrument flight rules (IFR), which permit cockpit crews to navigate predefined flight paths, saved in the on-board computer, through fog and cloud on autopilot. Rega has steadily progressed towards its ambitious goal: today, helicopter crews make use of the instrument flight rule over 700 times a year when, for instance, flying a seriously injured winter sports athlete safely from the mountains to a central hospital below the fog cover during high fog.

Efforts are bearing fruit

What today is part of the daily routine for Rega’s rescue crews took many years to achieve: intensive training of cockpit crews, measurement flights, proofs of risk, flight path designs, our own weather stations for up-to-date flying weather data as well as expensive and extensive simulator training sessions were all crucial. The creation of the “Low Flight Network” (LFN) has been pivotal: the Switzerland-wide network of satellite-aided instrument flight routes that enables helicopters to safely navigate between Rega bases, airports and hospitals even in poor visibility is the brainchild of Rega and was developed in partnership with the air force and the Federal Office of Civil Aviation (FOCA). Since the political decision to classify it as a “critical national aviation infrastructure” in mid-2021, this network ought to come under the auspices of Federal Government. Since progress in this regard has ground to a halt, Rega is working on continuing the project.
 

RNP-AR rules can be designed with greater precision, along narrower routes, because they place higher demands on navigational precision, the helicopter’s technical equipment and the crew’s training. Thanks to advanced avionics, the regulator’s approval (AR = Authorisation Required) and rigorous operating procedures, RNP-AR rules can use smaller buffer tolerances while affording the same level of safety. 

A combination of modern satellite navigation, inertial navigation systems and autopilot allows highly precise guidance along the planned route, even when there are tight turning radii and steep descent profiles which preclude conventional RNP rules.

This means approach and departure routes can be adapted to accommodate difficult terrain, enabling safe approaches in narrow valleys. Furthermore, the decision point can be closer to the hospital: the closer this point is to the hospital, the lower the cloud cover can be without preventing Rega’s crews from coming in to land at the hospital.

The invisible road network in the clouds

The LFN routes connect different regions in Switzerland, similarly to a network of motorways. “Approaches and departures” on this network take place at Rega bases, airports and hospitals. “Departures” undertaken so far, such as from the Inselspital University Hospital in Berne or the University Hospital in Zurich, were developed according to the LPV Point-in-Space procedure. These approach methods involve satellite-aided, vertical and horizontal course guidance to a specified point before the landing site where the pilot decides either to land under visual flight conditions or to follow the pre-defined alternative route on autopilot. The routes designed according to this concept require a lot of space and distance from obstacles. Furthermore, there can be no turns in the approach flight, for example to adapt the route to the topography.

New challenges in the Alpine valleys

The “departures” from central hospitals are all in the lowland area of Switzerland, where the flat topography allows the wide approach routes to be designed at sufficient distance from the terrain. In the Alpine valleys, however, this is not so. In areas such as Engadin, Davos or the Bernese Oberland, the topog-raphy around the hospitals precludes the use of conventional IFR approach procedures. As far as Rega was concerned, the solution to this problem had long been evident: what was needed was an even more accurate IFR procedure, of the kind already occasionally employed in fixed-wing aviation. RNP-AR (Required Navigation Performance Authorisation Required) permits extremely accurate route guidance, fully tailored to the terrain, and enables “narrower” routes to be developed with tighter turning radii and steeper descent profiles. This means Rega can navigate according to instrument flight rules even in the challenging topography of Alpine valleys, where obstacles have to be circumnavigated and the decision point should be as close as possible to, and as low as possible over the hospital: much like a narrow mountain pass road in challenging terrain where is no room for a wide motorway.

Ultra-precise navigation

These “tight” air corridors place the highest demands on the navigational precision of the helicopter and its navigation and autopilot systems. This is not so dissimilar to self-driving cars: a wide, straight motorway places fewer demands on navigational precision and autopilot than if the vehicle has to autonomously navigate a tight pass with a narrow road and hairpin bends. The challenge of putting this idea into practice has shades of the famous “chicken & egg” scenario: since no helicopters were yet authorised for an RNP-AR rule anywhere in the world, no RNP-AR rule could be approved. And without a rule, no helicopters could be certified.

Rega takes the initiative

Rega, however, was not going to settle for that: having some time ago set itself the goal of using this new rule, it brought together around one table the various parties whose input is essential in establishing the criteria for certification. The ARIOS (Advanced Rotorcraft IFR Operations in Switzerland) project involved Rega, along with FOCA and the European Union Aviation Safety Agency EASA, rule designers, helicopter manufacturers and other experts, joining forces to develop the criteria for RNP-AR helicopter rules. In recent years, Rega has conducted numerous measurement flights, drawn up risk calculations and designed and tested a new instrument flight route for Interlaken hospital and the regional airport in Samedan. On the back of these, the list of criteria has been adapted and confirmed based on the measurement and test flights. Finally, Rega was able to submit to FOCA the evidence needed to approve the rule at Interlaken hospital.

Interlaken becomes the first RNP-AR route

The Interlaken region was the obvious choice as the first place to deploy RNP-AR. Rega’s Widerswil base, which is just a few minutes’ flying time from Interlaken hospital, undertakes more missions than any other mountain base. In the challenging topography around Interlaken, with its narrow valleys and high peaks, the rule’s precision really comes into its own. FOCA reviewed the documents and, last July, authorised the rule. The foundations are thus now in place for the Low Flight Network to be further expanded and, in particular, for hospitals in the Alpine valleys to be added to it.
 

The new RNP-AR rule means that obstacles such as power cables or mountain peaks can be safely circumnavigated, and precise approach routes minimise the risks to Crews and patients. Yet even this rule has its limits: extremely bad weather conditions such as ice, dense fog at ground level or strong winds can still make it impossible to fly missions. Nonetheless, the RNP-AR rule is a major milestone towards making Rega’s vision a reality. A vision which is just that: a goal towards which we are moving ever closer while acknowledging that, whilst one can pursue a vision, one can never fully achieve it. We are passionate about continually developing the technologies involved in helping even more people in distress – safely and reliably, in even the toughest conditions.