Analog Track Angle Error Displays Improve Simulated GPS Approach Performance

Abstract

Pilots flying non-precision instrument approaches traditionally rely on a course deviation indicator (CDI) analog display of cross track error (XTE) information. The new generation of GPS based area navigation (RNAV) receivers can also compute accurate track angle error (TAE). Does display of supplementary TAE information improve intercept and tracking performance? Six pilots each flew 20 approaches in a light twin simulator to evaluate 3 different TAE/XTE display formats, in comparison to a conventional receiver CDI display and a more centrally located Horizontal Situation Indicator (HSI). Statistically significant performance improvements were seen in several phases of the approach when using the supplementary TAE information. Analog was preferred over numeric format. However, the advantage was offset by the need to widen the pilot's instrument scan to include the receiver display. Pilots found TAE helpful in establishing intercepts and the appropriate wind correction angle. Findings support the recent FAA TSO-C129 requirement that XTE be presented in the pilot's primary field of view, and the recommendation that avionics manufacturers include supplementary analog TAE display capability.