GNSS helo approaches under study in Europe

 - September 19, 2006, 12:23 PM

No GPS-based IFR approach has been designed yet for commercial or parapublic helicopter operations in Europe. But the European helicopter industry is endeavoring to catch up with its U.S. counterpart, which has access to hundreds of GPS-guided approaches. In France, the first GPS approach dedicated to helicopter operations is scheduled to enter service next year. Eurocopter is participating in two research projects that might yield a new kind of helicopter IFR approach procedure, with vertical guidance, in four or five years.

During a recent seminar organized by the French aerospace institute, Philippe Rollet, Eurocopter’s manager of operational research, reminded the audience that current IFR procedures are unadapted to helicopters. “The only system for a precision approach in Europe is the ILS, which was designed some 50 years ago for airplanes. It requires long approaches with a limited angle of descent–usually three degrees–that penalizes rotorcraft.

“In addition, installing an ILS on the ground is complex and impossible outside airports,” he said. For example, on a hospital’s rooftop, there is certainly not enough space to install ILS antennas. Moreover, an ILS needs flat ground on a large surface because the reflection of the waves on the ground is an important factor for guidance-beam orientation.

Precision Approaches for Helicopters

Many helicopter pilots choose to fly under VFR rules to avoid IFR constraints. (In the U.S., only 10 percent of helicopter flights are IFR.) They often fly in marginal weather conditions, which threatens safety. “U.S. statistics show that 99 percent of weather-related helicopter accidents affect VFR flights,” Rollet pointed out.

Therefore, global navigation satellite systems (GNSS) such as the U.S. GPS or the future European Galileo are an attractive alternative to ILS. The FAA adopted GPS before the International Civil Aviation Organization (ICAO) released its own recommendations, Rollet noted. U.S. EMS operators use GPS-guided approaches often, and they have proved to be much safer than VFR procedures in poor weather. However, although the procedures are IFR, they are still non-precision approaches and include no vertical guidance.

Sécurité Civile (the French civil defense and emergency preparedness organization) has asked the civil aviation authorities (DGAC) to set up GPS-guided approaches at some hospitals that their helicopter crews use regularly. The first of these GPS approaches should be published in Besançon (East) by next year.

According to Rollet, the DGAC waited for ICAO to publish its recommended criteria before designing such approaches. Most civil aviation authorities routinely wait for ICAO recommendations before implementing their own rules, he added.

ICAO’s criteria have been part of the Pan-Ops for a couple of years. Approaches suited to helicopter operations would require guidance on a segmented flight path and steep angle of descent (5 to 10 degrees) at final approach. The result is the need for both horizontal and vertical guidance to create helicopter-dedicated, safe IFR procedures.

The GPS signal therefore needs to be augmented–to ensure integrity (no risk of undetected error) and to provide greater precision with no interruptions. Satellite-based augmentation systems, such as the wide area augmentation system (WAAS) in the U.S. and EGNOS (available to the industry next year) in Europe offer such augmentation and thus vertical guidance capability.

“EGNOS will enable a level of precision close to that of an ILS Category 1,” Rollet stated. This kind of approach is called approach with vertical guidance (APV). ICAO criteria exist for EGNOS and WAAS APV approaches but only for “ILS-look alike” ones, with a maximum angle of 5.7 degrees. They are thus unsuited to helicopter operations. “Adapting the collision risk model (CRM) to helicopters, ICAO will acknowledge that decision heights of less than 200 feet can be considered,” Rollet told AIN. The CRM is a tool that calculates the risk of collision with those obstacles located beneath the approach flight path.

Eurocopter’s all-weather helicopter (AWH) research program proved that EGNOS makes steep approach guidance technically possible. In 2003 an EC 155 flew experimental 6- to 15-degree glideslopes. Both hand-flown and autopilot-coupled approaches were performed successfully. In a striking video presentation, seminar attendees could see the EC 155 automatically fly to a “point in space” some 40 feet above a target drawn on the ground. Horizontal precision was within three feet.

Helicopter-friendly Procedures

After the technical demonstration, it was time to work out some new procedures that could be consistent with the existing Pan-Ops recommendations. The result was a European research project called Optimal. It was launched in 2004 to develop and validate new IFR approach procedures on airports, for both helicopters and airplanes. So far, both simulator and in-flight evaluations have been conducted.

Airbus leads the project, which includes input from Eurocontrol and navigation service providers from Germany, Italy, the Netherlands and Spain. On the helicopter side, Optimal features trajectories that do not interfere with airplane traffic. To prove the concept, the EC 155 will fly such procedures on an airport next year.

In parallel with Optimal, another European project, called Giant, was launched last year. Giant aims to develop approach and departure IFR helicopter procedures for hospitals using EGNOS. The EC 155 will fly demonstration approaches at Lausanne’s hospital in Switzerland next year. Spanish-based consultancy firm Ineco leads the project, which also includes Swiss navigation service provider Skyguide and emergency medical service operator Rega.

ICAO’s obstacle-clearance panel has recently started developing criteria for helicopter-dedicated, steep approaches (up to 10 degrees) with vertical guidance. However, Rollet does not expect those to translate to operational improvements for helicopters before 2010 or 2011. “ICAO rules will evolve all the more rapidly as operators lobby,” he concluded.