Analysis of aircraft lateral path tracking accuracy and its implications for separation standards

Application of Area Navigation (RNAV) and Required Navigation Performance (RNP) to aircraft separation continues to be a point of difficulty which frequently centers on defining statistical models for Performance-Based Navigation (PBN). Given that questions of the statistics associated with position estimation error are fairly well known, and that path definition error is near zero in modern RNP avionics, this paper will focus on path steering error, which has not been studied using operational data. We propose analysis methods that can be applied to analyzing large volumes of recorded, in-service data to answer the questions of statistical modeling for the path following behavior of these systems. Preliminary analysis results derived from partner airlines' RNAV and RNP equipped aircraft flying in revenue service are presented. Answers to key questions related to the Flight Management System's (FMS) Path Steering Error (PSE, also known as Flight Technical Error, or FTE) will be presented. This paper will characterize any variations that might exist in the distributions due to flight phase (climb, level or descent), flight path characteristics (turning or straight) and piloting mode, e.g., flight director or autopilot coupled with Lateral Navigation (LNAV). Results are presented as sample statistics, cumulative distributions, and Q-Q plots.