Flight Performance Investigations of Enhanced Rotorcraft Operations in Mountainous Areas � Towards a More Ambitious RNP Performance

Abstract

The implementation of performance-based navigation allows advanced flight operations in areas without conventional navigation aids. Especially helicopter operations, which usually have been conducted under Visual Meteorological Conditions (VMC), may now operate more independently of the weather situation under Instrument Flight Rules (IFR). Nevertheless, at common helicopter IFR flight altitudes, icing conditions are a major threat. Therefore, helicopter operators have a signi¬ficant interest to fly at the lowest possible altitude. High navigation accuracy and reliability is imperative for such flight operations, this holds true especially in mountai¬nous areas. In the frame of the Swiss-wide implementation program to promote GNSS procedures and performance based navigation applications (CHIPS), a low-level flight net-work for helicopter operations is being implemented in Switzerland. The newly developed routes are still designed at relatively high altitudes and lowering them closer to the ground is definitively envisaged. For such operations, the RNP 0.3 navigation specification would however not suffice. A more ambitious performance would be in demand. The highest risk in low-level flight operations is the proximity to the terrain. Loss of navigation for instance due to an RF-interference event or even because of an insufficient satellite coverage may immediately lead to a hazardous situation. In order to analyze the performance of helicopter operations, 11 Agusta DaVinci helicopters have been equipped with a recording unit to obtain on-board GPS, EGNOS, FMS and flight plan information. As additional data recording measure, a geodetic receiver may be installed on-board the helicopter to record GPS and GLONASS dual-frequency data. These recordings allow the determination of the true flight path. Data is recorded in daily operations whenever possible. More than two dozens of flights have been analyzed so far. In addition, a dedicated high dynamic test routing has been developed using straight segments and RF legs featuring extremely narrow radii which are beyond the limitations of the current ICAO criteria. Furthermore, an approach procedure with RNP 0.1 performance including RF legs has been used. The resulting total system error usually remained below 0.02 NM. With few exceptions, all dedicated operations have been flown without issues. In summary, the investigation shows that a more ambi-tious RNP navigation accuracy requirement than 0.3 NM is feasible for advanced rotorcraft operations. Such performance-based navigation applications would allow safe flight operations at a lower flight altitude. For HEMS organizations, this would allow a significant increase of the efficiency and a more robust rescue service resulting in human life savings.