Flight Evaluation of Center-TRACON Automation System Trajectory
Prediction Process

David H. Williams and Steven M. Green


ABSTRACT

Two flight experiments (Phase I in October 1992 and Phase II in
September 1994) were conducted to evaluate the accuracy of the
Center-TRACON Automation System (CTAS) trajectory prediction process.
The Transport Systems Research Vehicle (TSRV) Boeing 737 based at
Langley Research Center flew 57 arrival trajectories that included
cruise and descent segments; at the same time, descent clearance
advisories from CTAS were followed. Actual trajectories of the airplane
were compared with the trajectories predicted by the CTAS trajectory
synthesis algorithms and airplane Flight Management System (FMS).
Trajectory prediction accuracy was evaluated over several levels of
cockpit automation that ranged from a conventional cockpit to
performance-based FMS vertical navigation (VNAV). Error sources and
their magnitudes were identified and measured from the flight data. The
major source of error during these tests was found to be the predicted
winds aloft used by CTAS. The most significant effect related to flight
guidance was the cross-track and turn-overshoot errors associated with
conventional VOR guidance. FMS lateral navigation (LNAV) guidance
significantly reduced both the cross-track and turn-overshoot error.
Pilot procedures and VNAV guidance were found to significantly reduce
the vertical profile errors associated with atmospheric and airplane
performance model errors.