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3Introduction Landing and takeoff overruns, landing undershoots, and landing and takeoff veer-offs account for most of the acci- dents that occur on or in the immediate vicinity of the run- way. Accident statistics show that, from 1959 to 2009, 55% of the worldâs jet fatal aircraft accidents occurred during landing and takeoff phases of the flight and accounted for 51% of all onboard fatalities (Boeing 2010). Although in many cases the causal factors involve some type of human error, the conditions at the airport may contribute significantly to the probability and severity of the accidents. The runway safety area (RSA) is a graded and obstacle-free rectangular-shaped area surrounding the runway that âshould be capable, under normal (dry) conditions, of supporting air- planes without causing structural damage to airplanes or injury to their occupantsâ (AC 150/5300-13 1989). The RSA improves the safety of airplanes that undershoot, overrun, or veer off the runway and has helped turn potential accidents into minor incidents. The rectangular dimensions of the RSA have changed over the years and depend on the category of aircraft using the runway. In the 1960s, in an attempt to mitigate the severity of aircraft accidents, the FAA revised the airport standards for RSA. The FAA RSA standard for most runways serving 14 CFR Part 121 air carrier operations is an area that is 500 feet wide centered on the runway and extends 1000 feet beyond each end of the runway. Because many airports were built before the 1960s, when RSA dimension standards were smaller, some airports were not complying with the new dimensions. In 1999, the FAA released Order 5200-8 and embarked upon a major effort to upgrade safety areas that do not meet the current standards. The goal is to have all possible improvements for Part 139 air- ports completed by 2015. However, it is not practical for some airports to extend their current RSA dimensions to meet the standards because they are landlocked or face insur- mountable challenges due to terrain or environmental restric- tions such as wetlands. More recently, the introduction of Engineered Material Ar- resting Systems (EMASs) has provided an alternative to achieve safety levels similar to those provided by the standards, but using only 60% of the area. Another alternative that has been used worldwide is the use of declared distances. For either of these alternatives there were no tools to help assess the true safety benefits associated with the solution selected. The study presented in ACRP Report 3 introduced a method- ology for risk assessment of RSAs that has been used to evaluate RSA alternatives by the industry. However, the methodology cannot be used to evaluate the use of EMAS, declared distances, or safety areas for veer-off incidents. Moreover, the analysis is complex and only prototype software was developed under that study. This report is organized into seven chapters. This first chap- ter provides the background and the objectives of the study, as well as the basic alternatives used by the industry to im- prove RSAs. The second chapter describes the five major types of incidents included in the analysis with major causes and contributing factors. Moreover the chapter presents the data used for the modeling process. Chapter three explains the three-part approach to model each type of incident. Also it presents the probability and location models developed in this study and incorporated in the approach. The next chapter describes the consequence approach and how it was implemented. The approach and the models developed in this study were incorporated into RSA analysis software named Runway Safety Area Risk Analysis (RSARA). Chapter 5 describes the soft- ware, and the required input and output information. Both the software and the models were validated using a sample of airports and their historical records for accidents and incidents to run the analysis and compare actual and predicted incident and accident rates. The results for validating the analysis are presented in Chapter 6. C H A P T E R 1 Background
Finally, Chapter 7 describes the major conclusions and rec- ommendations from this study. It also explains major achieve- ments and limitations. Project Goals The ultimate objective of this research was to develop a risk assessment tool that can be used to evaluate alternatives for RSA improvements, with a capability to account for the use of EMAS, declared distances, the presence of obstacles, spe- cific operations, weather, and runway conditions. New models were developed, and the capability to evalu- ate risk for veer-off events was added to the approach pre- sented in ACRP Report 3. Five sets of models were developed in this study: landing overruns, landing veer-offs, landing under- shoots, takeoff veer-offs, and takeoff overruns. Each set includes three models: incident frequency, stop/touchdown location, and consequences. The following were the specific goals that were achieved for ACRP Project 4-08: 1. Update the ACRP Report 3 accident/incident database to incorporate aircraft overrun and undershoot accidents and incidents occurring after 2006. 2. Collect data on aircraft runway veer-off accidents and in- cidents and integrate these data into the existing database. 3. Develop risk models for frequency and location for each type of incident: landing overruns (LDOR); landing under- shoots (LDUS); landing veer-offs (LDVO), takeoff overruns (TOOR), and takeoff veer-offs (TOVO). 4. Develop a practical approach to assess the impact of run- way distance available on the probability of overruns, under- shoots, and veer-offs. 5. Develop a practical approach to assess risk and the impact of using EMAS as an alternative to standard RSAs, or to use declared distances and evaluate the safety impact of reduced runway distance available. 6. Develop a practical approach to model incident conse- quences based on existing conditions and the presence of obstacles inside or in the vicinity of the RSA. 7. Develop user-friendly software that incorporates the methodology and models developed as a practical tool that airport stakeholders may use to evaluate RSA alternatives. 8. Field test the software developed. 9. Validate the new tool based on data gathered according to an airport survey plan. RSA Improvement Alternatives General Considerations To facilitate understanding the role of an RSA, it can be di- vided into three sections as a function of the types of incidents that may occur in those locations. Two of those sections are located on each runway end and include the RSA portion im- mediately before the arrival thresholds and beyond the depar- ture end of the runway. These are the sections that help mit- igate consequences of aircraft overruns and undershoots. The third RSA section is lateral to the runway and extends over the runway length on both sides of the runway. This is the area that can help mitigate the severity of aircraft veer-off incidents. For the RSA sections located laterally to the runway, im- provements can be made by removing obstacles and preparing the area according to RSA standards to increase the runway object free area (ROFA) width. In some cases this may be nec- essary to introduce the operation of larger aircraft to increase capacity; however, they may be restrained to increase the ex- isting runway separation distances to accommodate the larger airplane design group (ADG). There are four basic alternatives available to improve an RSA when it does not meet the standards: â¢ Extend the RSA laterally and longitudinally. â¢ Modify or relocate the runway to expand the RSA. â¢ Implement declared distances by reducing the available runway distances and extending the RSA section adjacent to the runway ends. â¢ Use arresting systems to obtain a level of safety similar to that provided by the standard RSA. Any combination of such alternatives is also possible, and the methodology presented in this report has the capability to analyze any such combinations. Each of these alternatives has advantages and disadvantages that are specific to each sit- uation and that need to be assessed, as described in ensuing sections of this report. It is important to note that airport operators can take addi- tional actions to mitigate the probability of aircraft overruns, undershoots, and veer-offs. Some possible alternatives may include the following: â¢ Improve skid resistance and reduce undulations of runway surface. â¢ Monitor runway friction level to determine need to close the runway (e.g., ice conditions) and time for maintenance (e.g., rubber removal). â¢ Ensure accurate weather information and runway surface conditions are available to flight crews. â¢ Improve airport capability to detect unusual weather con- ditions (e.g., wind shear). â¢ Minimize the presence of obstacles in the vicinity of RSAs. â¢ Upgrade visual and instrument landing aids to improve ac- curacy of approach path. â¢ Coordinate operational restrictions with airlines and air traf- fic control (ATC) when adverse weather conditions arise. 4
â¢ Publish RSA provision in the Aeronautical Information Pub- lication when RSAâs cannot comply with standards. Although these actions can decrease the probability of un- desirable events, it is not possible to measure the impact of these risk mitigation actions on the total airport risk of seri- ous aircraft overruns, undershoots, and veer-offs. This study introduces a risk-based methodology for quan- titative evaluation of any of the alternatives or combinations of RSA improvement alternatives identified in FAA Order 5200.8 (1999). These alternatives are described below. Extend the RSA An example of extending the RSA is shown in Figure 1. In this case, the RSA adjacent to the right runway end and the lateral area originally did not comply with the standard. This is a straightforward solution to improve an RSA and is used to extend it to the runway ends or the lateral sections. However, this alternative is not always feasible due to phys- ical, environmental, or other constraints involved with implementation. Modify or Relocate the Runway In Figure 2, the runway was relocated to the left to obtain a standard RSA of 1000 ft in length. The relocation also may involve the change of runway direction. Similar to the previous alternative, this solution may involve very high costs, particularly if changing the runway direction is necessary. In this case, a new runway must be constructed to replace the existing one. For the example shown, to keep the distance available for landing, it is necessary to extend the runway to the left. Implement Declared Distances Declared distances are a means of obtaining a standard safety area by reducing the usable runway length. When the RSA cannot be extended or the runway relocated, it may be necessary to implement declared distances to accommodate a larger RSA. Figure 3 shows an example to extend the RSA using this alternative. This is a fast and low cost alternative for the airport opera- tor; however, it may impact airport capacity, reduce payloads, and/or degrade the level of safety under specific situations, which may lead to long-term consequences to the airport. In the example provided, the runway was reduced to accommo- date a larger RSA by reducing the landing distance available. Use of Arresting Systems When a full RSA cannot be achieved, the airport may use a bed of lightweight concrete that is crushed under the wheels of a stray aircraft, causing energy from its forward motion to be absorbed, to bring the aircraft to a stop within a shorter distance. A standard EMAS bed can reduce what would nor- mally be a 1000-ft RSA to 600 ft, or even less if the land is not available, depending upon the aircraft types using the runway. Figure 4 presents an example of RSA improvement using EMAS. This is an alternative that only became available in recent years and provides a feasible solution, particularly for land- locked runways. The major disadvantages are the high initial cost, maintenance costs, the need to replace the bed when used, the need to periodically replace the bed due to natural deterioration, and it still requires some land area to be avail- able for installation. 5 Existing RSA Improved RSA Figure 1. Extending the RSA. 1000 ft Existing RSA Improved RSA Figure 2. Relocating the runway. Existing RSA Improved RSA 1000 ft Figure 3. Using declared distances.
6EMAS Bed Existing RSA Improved RSA Figure 4. Using EMAS.