Performance Impact of Mountainous Topography for Cloud Break GNSS Procedure

Marc Troller, Maurizio Scaramuzza, Pascal Truffer, Heinz Wipf, and Sergio Raemi

Abstract:	Performance-based navigation allows implementing approach procedures in areas, where conventional procedures are not a feasible solution. This holds especially true for difficult topographic terrain. In case of the Meiringen Air Force base in Switzerland, which is located in a valley surrounded by mountains up to 10'000 ft, a cloud break procedure for rotary wing operations has been developed. This procedure will allow the Swiss Air Force and the local HEMS (Helicopter Emergency Medical Services) operator to fly under adverse meteorological conditions. Due to topographic constraints a required navigation performance (RNP) value of 0.3 NM is envisaged for the whole approach, starting at the initial approach fix until the end of the missed approach. One of the most critical points is the loss of GNSS navigation capability combined with a one-engine-out situation. In the first part of this analysis, the approach availability for a 30-satellites GPS constellation has been determined. A GNSS simulator has been used to assess different avionics GPS receivers envisaged for this approach. Based on the mean time between outages (MTBO) of GPS satellites, the probability of a satellite outage, and the effect thereof, has been determined. The discontinuity probability of the received GNSS signals have been considered together with other main technical error sources such as malfunction of navigation equipment and engine problems. Furthermore, statistics on meteorolo-gical conditions in the area of Meiringen have been taken into account. A failure model has been used to determine the probability of the hazardous situations for each helicopter type individually. The resulted probability has then been compared with the required target level of safety. For all helicopter types, the achieved probability values are better than the required TLS, meaning that the minimum level of safety can be maintained.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	203 - 209
Cite this article:	Troller, Marc, Scaramuzza, Maurizio, Truffer, Pascal, Wipf, Heinz, Raemi, Sergio, "Performance Impact of Mountainous Topography for Cloud Break GNSS Procedure," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 203-209.
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