Precision Departures and 4D RNP utilizing GNSS Augmentation Systems

Abstract

We present a concept for precision departures based on satellite navigation augmented by either a wide area or local differential GPS such as the Satellite Based Augmentation System (SBAS) and Ground Based Augmentation System (GBAS). The simplest version consists of an “inverted” precision approach in which the aircraft follows the glide path on an opposite track. As a next step, an extended capability allows for lateral area navigation combined with an angular climb out path. Both concepts are tested and evaluated using the Generic Cockpit Simulator GECO operated by the DLR Institute of Flight Guidance. These trajectories could either be encoded in the aircraft navigation database analogue to SBAS LPV approaches or broadcast by a GBAS ground station with terminal area path (TAP) functionality. Moreover, we show initial results in deriving requirements for a 4 dimensional performance based navigation concept defined as a 4D Required Navigation Performance (4D RNP). A four dimensional RNP concept needs to be seen as an extension of the current RNP X definitions and must include a required navigation performance for the vertical and the along track dimension as well as for time. The derivation of the requirements is based on the existing standards for Reduced Vertical Separation Minima (RVSM) and radar separation combined with the required probabilities concerning Target Level of Safety (TLS). An operational implementation of 4D RNP airspace would require trajectory management and continuous data connection between air traffic control and the aircraft. The along-track or longitudinal component is tightly connected to the time component by means of speed and the required time of arrival at each given waypoint. First results indicate a required vertical performance of σ=15.635 m for one standard deviation or, in other words, 102.6 feet accuracy at the 95% level. Required along track performance is dependent on sector load described by the number of aircraft N on a given route per time and the speed of the aircraft which would seek along-track or temporal RNP approval. For example, an aircraft flying at 250 kts and a load of 50 aircraft per hour on a route and an equivalent spacing of 10 nm require a controlled time of arrival within 17 seconds for 95% of the time in order to fulfill a TLS of 5x10^-9.