Runway Protection Zones (RPZs) Risk Assessment Tool Users’ Guide (2016)

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48 Runway Protection Zones (RPZs) Risk Assessment Tool Users’ Guide Two roadways pass through the Runway 2 RPZs. Bravo Road has a speed limit of 30 mph and intersects with the RPZ for a distance of 0.24 miles. The AADT of Bravo is 6,323, which is the highest for all roadways intersecting with airport RPZs. The population density of the road is calculated to be 1 × 10–04 persons per square foot. Charlie Road has a speed limit of 30 mph and an AADT of 845. It intersects with the RPZ for a distance of 0.05 miles. The population density of this section of Charlie Road is calculated to be 1.1 × 10–05 persons per square foot. Two railway segments also intersect the Runway 2 RPZs. A straight, 0.35-mile segment of railway with an assumed average speed of 55 miles per hour is in the RPZs, as is an adjoining, curved segment with a length of 0.11 miles and an assumed speed limit of 35 miles per hour. The population densities for these railway segments are calculated to be 1.0 × 10–06 and 4.0 × 10–06 persons per square foot, respectively. As depicted in Figure 6.6, part of a storage container yard is within the RPZ. This area was assigned a population density of 2.5 × 10–04 persons per square foot. Although the storage con- tainer yard is the farthest from the runway, it is spread around the extended runway centerline and encompasses a relatively large area. 6.5 Interpretation of RPZ_RAT Results Once a successful analysis has been completed, the RPZ_RAT generates two types of outputs: a graphical representation of crash likelihood contours and a Microsoft Excel file. The Excel file includes several sheets: an airport data sheet summarizing some of the inputs; a summary sheet presenting the summary of results for all the RPZs analyzed; and separate sheet for each RPZ presenting the detailed analysis results. RPZ Crash Likelihood Contours The RPZ_RAT generates crash likelihood contours depicted in blue shades graduating in scale from lighter to darker representing increasing crash likelihood. The contours are generated within a grid overlaid on the RPZ configuration. The size of individual grids selected for the case study analysis was 100 square feet. This was determined to provide a desirable degree of preci- sion for the analysis while still allowing the model to run smoothly. The crash likelihood contours are depicted in a color range of ten shades of blue. Each of the ten shades represents a crash likelihood increase in ranked increments of 10% or deciles of the full range of computed values for all the airport RPZs. Each darker shade indicates a correspond- ing increase in crash likelihood. The darkest shaded contour represents the area associated with the top 10% of crash likelihood values of the airport. The same color range and values apply across all the RPZs at the airport. Crash likelihood is expressed in scientific notation in the RPZ_RAT output tables. Scientific notation is a mathematical convention for expressing very large or very small numbers. For example, scientific notation could be used to express the number 5,000,000,000 as 5e9, where the 9 indicates the order of magnitude above zero. Scientific notation can also be used to express a very small figure such as 0.000000005 as 5e-9, where -9 indicates the placement of the number to the right of the decimal point. Because crashes are rare occurrences, crash likelihood values are typically very small and expressed by the RPZ_RAT in scientific notation. The contours indicate that crash likelihood tends to increase with proximity to the extended runway centerline and the runway endpoint. This tendency is generally observable in the RPZs for Runways 6, 20, and 24 where the contour shading is darkest near the base and center of the associated RPZ while lightening as distance from the runway ends and the extended runway þÿRunway Protection Zones (RPZs) Risk Assessment Tool Users  Guide Copyright National Academy of Sciences. All rights reserved.

Case Study Airport 49 centerline increases. Crash likelihood contours for each RPZ are depicted in Figure 6.7. Where RPZs overlap, such as the southern corner of Runway 6 RPZ, the crash likelihood is affected from likely accidents on both runways. It is evident from the figure that the darker shades are dominant and cover a larger area in Runway 24 RPZ than, for example, compared with Runway 20 RPZ. This suggests that accidents are more likely to occur in Runway 24 RPZ than Runway 20 RPZ. This could be explained by the distribution of the operations on the runways. As was shown in Table 6.5, 71% of airport arriv- als land on Runway 24, giving rise to the possibility of a landing undershoot in this RPZ. Also, 61% of airport departures take off from Runway 6 where they may crash in a takeoff overrun or a takeoff overshoot in Runway 24 RPZ. The RPZ configuration for Runway 2 with a displaced landing threshold results in crash like- lihood contours that extend farther and exhibit more variability than the RPZs for the other runway ends. Two sets of overlapping contours were produced, with the first indicating accident likelihood concentrating at the base of the approach RPZ, 200 feet south of the displaced thresh- old. The other set of contours begins at the physical end of the runway and accounts for crash likelihood in both the approach and departure RPZs. From the runway end, the contours then indicate declining degrees of crash likelihood, narrowing along the extended runway centerline before terminating at the southern boundary of the RPZ. Microsoft Excel Output File In addition to the graphic depiction of crash likelihood contours, the RPZ_RAT generates an Excel file with detailed data. The first table in the summary sheet of the Excel file presents the Figure 6.7. RPZ crash likelihood contours at case study airport. þÿRunway Protection Zones (RPZs) Risk Assessment Tool Users  Guide Copyright National Academy of Sciences. All rights reserved.

50 Runway Protection Zones (RPZs) Risk Assessment Tool Users’ Guide Figure 6.8. Average likelihood of accidents from RPZ_RAT output summary sheet. expected accidents in every 10 million movements—essentially the average from the accident likelihood models. The output data for expected accidents is depicted in Figure 6.8. The table pro- vides separate estimates for every type of accident—landing overruns (LDOR), landing under- shoots (LDUS), takeoff overruns (TOOR), and takeoff overshoots (TOOS). The graphs below the table illustrate the number of expected accidents from each runway for each type of accident. On average, landings on Runways 2 and 20 are more likely to undershoot the runway than landings on Runways 6 and 24. This outcome depends on various factors (e.g., runway usage in adverse weather conditions, the type of operation, and the aircraft type that land on the runways). As was presented in Table 6.4, most landings on Runways 2 and 20 are GA operations (657 out of 879 for Runway 2, and 535 out of 634 for Runway 20). Recognizing that many GA operations at the airport are smaller aircraft types with piston engines, higher average likelihoods of LDUS in Runways 2 and 20 RPZs are perceivable. Not every accident affects the RPZs. In fact, many overruns and undershoots are contained within 200 feet from the runway before the RPZs begin. The likelihood that an aircraft that has gone off the runway impacts the RPZ (which are the findings from the location models) is presented in the second table in the summary sheet of the output file and is depicted in Figure 6.9. The like- lihoods could be viewed as the percentage of excursions that, if they occur, affect the RPZs. Figure 6.9. Likelihoods of accidents impacting RPZs from RPZ_RAT output summary sheet. þÿRunway Protection Zones (RPZs) Risk Assessment Tool Users  Guide Copyright National Academy of Sciences. All rights reserved.

Case Study Airport 51 The software tool has returned the highest values of LDOR and TOOR for Runway 2 RPZ. This is anticipated because the displacement of the runway threshold has shifted the approach RPZ to the north and has removed the 200-ft separation between the physical end of the runway and the beginning of the RPZ (Figure 6.6). As a result, in an overrun, the aircraft impacts the RPZ as soon as it leaves the end of the runway. Also, the displacement of the threshold increased the land area in RPZ 2, which also contributes to the higher likelihoods. The RPZs of Runways 24 and 6 have the same dimensions and are both located 200 feet away from the runway ends. As a result, the likelihoods of accidents impacting the RPZs are the same (the slight difference in LDOR values is the result of approximating RPZ boundaries with square cells and rounding decimals). The third table generated in the summary sheet presents the annual RPZ crash likelihoods as shown in Figure 6.10. The RPZ crash likelihood combines the likelihoods from all accident types (Figure 6.8) with the likelihoods of the accidents impacting the RPZ (Figure 6.9) and factors in the number of operations in a year that may crash in the RPZ. The Runway 24 RPZ is presented with the highest crash likelihood among airport RPZs. This validates the findings from the likelihood contours in that a larger area of the RPZ was colored in darker shades when compared with other RPZs. This is mainly because 90% of the airport operations either land on Runway 24 or Runway 6 where the aircraft may undershoot or over- run and crash into the RPZ. Also, 61% of airport operations that take off from Runway 6 may overrun or overshoot into Runway 24 RPZ (Table 6.5). As shown in Figure 6.10, the crash likelihoods in Runways 6 and 2 RPZs are very similar over the study year. The number of movements that may crash in Runway 6 is much larger than that for Runway 2; however, the landing threshold displacement of Runway 2 substantially increases the likelihood of a LDOR and TOOR affecting the Runway 2 RPZ, as shown in Figure 6.9. These factors have balanced, resulting in similar annual RPZ crash likelihoods. Figure 6.10. RPZ crash likelihoods from RPZ_RAT output summary sheet. þÿRunway Protection Zones (RPZs) Risk Assessment Tool Users  Guide Copyright National Academy of Sciences. All rights reserved.

52 Runway Protection Zones (RPZs) Risk Assessment Tool Users’ Guide Figure 6.11. RPZ risks from RPZ_RAT output summary sheet. Runway 20 RPZ has the lowest crash likelihood in the given year as shown in Figure 6.10. This is despite having the highest average likelihood of accident for LDOR, LDUS, and TOOR among other RPZs as was shown in Figure 6.8. The RPZ is subject to the lowest number of movements that may crash in the RPZ among other RPZs. It is also the smallest RPZ of the airport. The RPZ_RAT also presents the expected average number of years between accidents in the RPZs using the annual crash likelihoods and the expected movement growth of 0.2 percent. The fourth table in the summary sheet of output presents the RPZ risk. The RPZ risk is the combination of the likelihood of an accident in the land uses of the RPZ and the consequences of the accident. The worst credible outcome associated with the airport accidents to the people on the ground is fatality. The consequence models described in the project report assess the likelihood of fatality for RPZ risk assessments. To arrive at RPZ risks, the risk for every land use is obtained and summed. As shown in Figure 6.11, Runway 2 RPZ is found to yield the highest risk by far. This is, in part, due to the relatively intense developments within the Runway 2 RPZ. Given the land uses within the RPZ and their population densities, the number of people pres- ent inside this RPZ is almost 13 times that of the other RPZs combined. Another reason is the relative proximity of the developments to the runway end and around the extended runway cen- terline. The mix of aircraft types that operate on the runway also contributes to the higher risk. Runway 24 RPZ risk is assessed as the second in the airport and about 75% higher than the Runway 20 RPZ. The annual crash likelihood in Runway 24 RPZ is about 6 times higher than Runway 20 RPZ, and the area of the land uses within Runway 24 RPZ is 7 times higher than Runway 20 RPZ. However, movements on average are much more likely to be involved in all types of events in Runway 20 RPZ (Figure 6.8). Also, the location of Highway Yankee passing across the RPZ close to the runway end and its relatively high AADT account for much of the difference between the overall risks of the two RPZs. Runway 6 RPZ has the least RPZ risk at the airport. Even though the RPZ was ranked the second in annual RPZ crash likelihood and was identified with nine land uses inside the RPZ, the land uses were tucked away in a corner at the end of the RPZ. The area occupied by the land uses was also relatively small, all contributing to the lowest overall risk. þÿRunway Protection Zones (RPZs) Risk Assessment Tool Users  Guide Copyright National Academy of Sciences. All rights reserved.