ITWS and ITWS/LLWAS-NE Runway Alert Performance at Dallas-Ft. Worth and Orlando

The Integrated Terminal Weather System (ITWS) provides runway-orientated wind shear and microburst alerts in order to enhance the safety of flight operations at major U.S. airports. The alerts are reported as either losses or gains of airspeed, representing performance decreasing or performance increasing wind shears. The performance of ITWS as a stand-alone system has been thoroughly documented in previous research. During the 1994 ITWS Demonstration and Validation (DemVal) testing, the probability of detection (POD) and probability of false alarm (PFA) at Memphis (MEM) and Orlando (MCO) for all loss events were >90 and <5 percent, respectively.

The Low-Level Windshear Alert System - Network Expansion (LLWAS-NE) also generates runway alerts in the same format as ITWS. LLWAS-NE is not subject to viewing angle problems such as that experienced from single-Doppler radar. However, false alarms caused by LLWAS-NE sensor failures at some TDWR sites have reduced user confidence in the system. At those ITWS sites with an LLWAS-NE, the alerts derived from TDWR data will be integrated with LLWAS-NE alerts in order to improve the alerting performance. The ITWS integration algorithm is identical to the Terminal Doppler Weather Radar (TDWR) version with the exception of a few adaptable parameter changes. The ITWS/LLWAS-NE parameters were modified slightly to take advantage of the ITWS and TDWR algorithm performance differences. For instance, the ITWS microburst algorithm tends to underestimate the actual wind shear loss of most events, so the minimum velocity threshold to confirm a weak event was reduced slightly to account for this characteristic.

In this paper, the performance of ITWS and the ITWS/LLWAS-NE integration algorithm at the MCO and Dallas-Ft. Worth (DFW) demonstration sites will be discussed. This performance assessment is considered unique since the radar and anemometer data were combined to create the runway truth. In addition, the Dallas Love (DAL) TDWR surface scan data was incorporated every five minutes to provide an additional source of truth with a different viewing angle. The focus of the research reported in this paper is to identify the shortcomings of both systems in order to recommend modifications that will improve the integration performance. Thus, the radar data for each missed event and false alert was analyzed to ascertain the type and frequency of the failure modes. Recommendations are also made for an improved integration algorithm.