This Technical Note describes the instrument landing system (ILS) math modeling performed by the Federal Aviation Administration (FAA) Technical Center at the request of the Southwest Region. Computed data are presented showing the effects of several proposed hangar configurations on the performance of the ILS localizer for runway 18R at the Dallas-Fort Worth International Airport. The Southwest Region is concerned that reflections from the proposed hangars may degrade the localizer course beyond category II tolerances. Modeled course structure results indicate that category II localizer performance should be obtained with the existing 14/6 Type IB antenna for the proposed hangar configurations. Computed clearance orbit results indicate satisfactory linearity, course crossover, and signal clearance levels.

This Technological Note describes the instrument landing system (ILS) math modeling performed by the Federal Aviation Administration (FAA) Technical Center at the request of the Southern Region. Computed localizer data are presented showing the effects of two hangar buildings (Braniff and Comair) on the performance of an ILS localizer proposed for runway 17R at the Orlando International Airport. The Southern Region is concerned that radio frequency (RF) signal reflections from the two hangars may degrade the localizer course beyond Category II/III tolerances. Modeled course structure results indicate that Category II/III localizer performance should be obtained with the Wilcox Mark II, 14-element, dual-frequency log periodic antenna with both hangar buildings constructed at the currently proposed locations. Computed clearance orbit results indicate satisfactory linearity, course crossover, and signal clearance levels. Data are also presented showing the computed performance for a glide slope proposed for runway 17R at the Orlando International Airport. The null reference glide slope will be located 1050 feet back from runway threshold and 400 feet left offset of centerline. Glide slope modeling computed only the effect of terrain in front of the antenna system and was conducted with the GTD-2D model because of limited terrain data availability. Modeled path structure and level run plots are provided for the proposed null reference system. Modeled results indicate that the proposed site should meet Category II path structure, linearity, and symmetry tolerances. Keywords: Instrument landing; Instrument landing system math modeling; ILS Localizer; ILS Glide slope. (kt).

The Transportation Systems Center electromagnetic scattering model was used to predict the course deviation indication (CDI) at the Dallas/Fort Worth Airport in the presence of several derogating structures in the report FAA-RD-72-96 'ILS Localizer Performance Study Part 1 Dallas/Fort Worth Regional Airport and Model Validation-Syracuse Hancock Airport.' In this report the recommendation was made to use a capture effect system localizer. In the present report several additional structures, the Braniff and Delta hangar buildings, are modeled. Using the recommended capture effect localizer, it is found that these two additional structures do not add significantly to the derogation, and the category 1 and category 2 operation is still possible on the four instrumented runways tested. (Author).