Helo satnav approaches tested

 - December 28, 2007, 5:51 AM

Last year in Toulouse, France, Eurocopter completed two series of tests that demonstrated the feasibility of satellite-navigation precision approaches for helicopters. Europe, which lags behind the U.S. in creating satnav nonprecision approaches for helicopters, has almost completed some research toward addressing that imbalance. The purpose of the approaches is to incorporate helicopter traffic into airports without interfering with existing airplane traffic. The tests in Toulouse were part of a European research program dubbed Optimal.

The European manufacturer used an EC 155 Dauphin dedicated to system demonstration. During the testing, the rotorcraft flew 13.5 hours in 58 sorties.
“We tried steep approaches–six and nine degrees–toward Toulouse Airport’s final approach and takeoff [FATO] helicopter area,” Philippe Rollet, Eurocopter’s research manager for operations, told AIN. Eurocopter selected Toulouse for the trials because it features one of the few experimental ground-based augmentation systems (GBAS, the international designation of the U.S. LAAS) in Europe, therefore allowing tests of both GBAS and the so-far-experimental EGNOS satellite-based augmentation system (Europe’s WAAS equivalent).

For each runway direction, the OEM tested three procedures. Two were direct approaches, tested for development purposes. They were not far enough from airplane trajectories to be considered independent.

The third test approach was designed under the point-in-space concept. IFR guidance was supplied to a nearby bridge, and from there the crew had to fly VFR to the FATO area. This approach was truly independent from surrounding airplane traffic.

One benefit of the point-in-space approach is noise reduction. “Flying steeper descents, the helicopter is higher above populated areas,” Rollet explained. The second reduction comes from the main rotor, which is less noisy in such regimes.
Rollet deemed the satellite-based system “ideal for helicopters” because it provides almost the equivalent of a Category I ILS without any ground equipment. The ground-based system can so far provide the same level of performance. “However, it is interesting to test it because in the future it might reach Category Three,” Rollet said. It might eventually replace the ILS.

The EC 155’s autopilot was necessary for the steep approaches in Toulouse. Without an autopilot providing airspeed hold, it is difficult to fly steep approaches with the required low speed. The EC 155 commonly flew nine-degree-slope approaches with a descent rate of 800 fpm and a groundspeed of 50 knots.

The Optimal program is scheduled to end in October, after which Eurocopter plans more trials in Donauwörth, Germany, with an EC 145. In addition, German research agency DLR will use an EC 135 to test continuous descent and time-referenced approaches in Bremen.

Before helicopters can use satnav precision approaches in Europe, all EGNOS satellites have to enter service, which is pegged for 2010. In addition, air traffic management rules must implement parallel approaches between helicopters and airplanes. Finally, EGNOS receivers have to be certified for rotorcraft.