A Study of Time-To-Fly Estimates for RUC and ITWS Winds

Automated air traffic decision support tools must compute the time it takes an aircraft to fly along a path. The estimation of Time-To-Fly (TTF) requires accurate knowledge of the wind. Two proposed sources of wind data for the Center-TRACON Automation System (CTAS) developed by NASA are the Rapid Update Cycle (RUC) and the Integrated Terminal Weather System (ITWS). The ITWS winds are generated by refining RUC forecast winds with recent wind measurements. TTF is computed using a path integral through the wind fields along nominal flight paths in the terminal area. This study examines the difference in TTF estimates between RUC and ITWS winds.

We chose to use data archived from the ITWS Dallas/Ft. Worth prototype ITWS and the operational RUC. We performed the comparison for 11 days: seven days known to have a large shear in the vertical and four consecutive days with more benign weather. The days with large shear are expected to provide larger differences in TTF estimates between the ITWS and RUC winds than those provided on an average weather day.

There are often substantial differences between RUC TTF and ITWS TTF estimates due to the difference in accuracy, resolution, and timeliness. Because ITWS winds: (1) use Doppler data and aircraft reports to refine the RUC wind estimates, and (2) have been shown to be more accurate in estimating winds at a point, the hypothesis is that the differences between the ITWS and RUC TTF estimates correspond to the accuracy improvement using ITWS.