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OCR for page 38
38 Development of Improved Risk Models Development of Software Tool The models presented in ACRP Report 3 were improved, The approach and the improved models were integrated and new ones to address veer-offs were developed. Five sets into analysis software for risk assessment of RSA. The tool, of frequency and location models were developed, including called RSARA, is user-friendly and practical, and allows the models for LDOVs, LDVOs, LDUSs, TOORs, and TOVOs. user to consider each of the factors impacting RSA risk. These types of events constitute the great majority of aircraft The software works as a simulation tool to estimate risk for incidents that challenge the runway RSA. each operation from an annual sample of operations for an New data and new factors were incorporated into the new airport. The historical sample data include flight operations models. Two of the most important ones were the runway data, like aircraft model, runway used, and the type of oper- criticality factor and the tail/head wind component. The run- ation, as well as the weather conditions to which each of these way criticality factor was defined as the ratio between the run- operations was subjected. way distance required and the runway distance available for Within the software, the definition of RSA areas is a very the operation. The higher this value is, the smaller is the safety simple process based on Microsoft Excel spreadsheets. The margin for the operation, and it represents the relationship procedure is as easy as drawing the RSA in a plan view and between the runway and aircraft performance. defining the RSA surface type: unpaved, paved, or EMAS. The output is comprehensive, and risk estimates are pro- Development of Approach to Evaluate EMAS vided by type of incident, runway, and RSA section challenged. Risk results are provided in terms of accidents per number of EMAS has proved to be a successful alternative when the RSA operations or the expected number of years to occur an acci- area available at the runway ends is shorter than the standard. dent, and are compatible with the criteria set by the FAA. The improved deceleration capability provided by EMAS is an Histograms of risk help users identify the percentage of important consideration when performing an RSA analysis. operations subject to risk levels higher than a desired TLS. The approach presented in ACRP Report 3 did not address the possibility of using EMAS; ACRP 04-08 filled this gap. A Model and Software Validation simplified approach based on data provided by Engineered Arresting Systems Corporation (ESCO), the manufacturer of The risk models were developed and calibrated based on a EMAS, was developed and incorporated into the software. worldwide dataset of accidents and incidents. A second effort The approach used can help airport stakeholders verify the was conducted to verify and validate the models using NOD safety benefits of using EMAS beds, even when non-standard and RSA conditions for eight airports that were not used to configurations are used. create the NOD used to develop the models. The verification was a key step to demonstrate the applica- Development of Approach to Assess Impact bility of the innovative approach and models developed in this of Declared Distances research. The comparison between estimated and actual fre- quency and risk rates showed excellent agreement, despite the Statistics were used to demonstrate that the likelihood of small sample of airports used in this study. Analysis output landing and takeoff incidents may depend on the safety mar- for the eight airports and their historical records of accidents gin available for the operation relative to the runway distance and incidents helped to prove the validity of the approach and required by the aircraft. analysis software. In this project, the estimate of frequency of incidents incor- The volunteers selected to test the models provided feed- porates a runway criticality factor defined as the ratio between back to the research team that was used to improve software the runway distance required and the distance available. Al- and eliminate bugs. though the runway distance can only be calculated using the actual aircraft weight, and this information is difficult to ob- Limitations tain, other factors may be used for modeling. Some of these factors include the basic distance required for standard con- Although an intensive effort was made to develop a very ditions, the runway elevation, the air temperature, the wind, comprehensive tool, there are some limitations that users and the runway surface conditions. In this project, the land- should be aware of. Some of those limitations are related to ing distance required is estimated based on each of those fac- data availability, and some are related to the computer time tors for the specific type of aircraft. to perform an analysis. The incorporation of these factors into the frequency mod- One important limitation is that the tool is helpful for els is used to help assess the impact of the declared runway planning purposes only. Neither the models nor the software distances on risk of overruns, veer-offs, and undershoots. should be used to estimate risk during real-time operations.