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46 events. Whenever possible, these factors were incorporated in A sample of NOD for the runway must be representative of the the modeling approach. traffic occurring in the airport during at least one year so that it covers different meteorological conditions for the airport. Normal Operations Database In addition, depending on judgment by the analyst, there may be multiple crash scenarios and these will require modeling for Another achievement in this research is the availability of each of these situations. a normal operations database for U.S. flight operations. The To facilitate these computations, software that incor- NOD sample comprising 242,420 flights is a representative porates models developed in this study was developed. sample of 95.8 percent of flights in the United States and cov- The software allows one to enter existing RSA conditions ers the great majority of airport types, geographical regions, and a sample NOD for each type of operation that may and operational and meteorological parameters. The devel- challenge the RSA to run the analysis for an existing opment of this database was crucial in quantifying and char- obstacle. Appendix O describes the prototype software de- acterizing accident risk factors, as well as the development of veloped for this project and shows some screens, and accident frequency models. In addition, the NOD provides an input and output parameters. assessment of flight risk exposure and may be used for future studies on airport and runway safety. Model Limitations Development of Risk Models for RSA Modeling aviation risks always has been a challenge. Acci- Each set of models includes one model for frequency and dent and incident reports often lack quantitative information two models for location: one developed from raw distance for causal factors of overrun and undershoot accidents. The data and one based on normalized distance data. A rational large quantity of causal factors and the scarceness of reliable approach was developed to model severe consequences and data limits the accuracy of models developed. Modeling con- serves for any of the model sets. sequences still depend on some judgment from the analyst. In These models incorporate several risk factors identified for this study it was not possible to make more solid recommen- each type of accident. These include a range of meteorologi- dations on how to treat the obstacle/aircraft interaction and cal conditions, operational parameters, and existing features how much energy is required to cause severe consequences and obstacles present in the RSA and its surroundings. In during the impact. addition the approach allows consideration of multiple risk Most likely, airport operators may need expert help to factors in a single model that accounts for their joint influ- make correct use of the models developed in this study, but ences on accident likelihood. Consequently, the models they should be able to use them effectively with the help of a developed have substantially improved predictive power, risk assessment professional. The modeling approach on its with enhanced sensitivity and specificity, versus existing reg- own is not enough to allow anyone to perform a risk analysis ulations based on a small number of risk factors. for RSAs. The assessment of risk associated with overrun and undershoot events has to be placed in some context, a process Integrated Practical Approach to be followed by airport operators that will support their risk management decision making. This study also brings a new rational and probabilistic ap- A review of existing databases has shown that deviation proach to integrate the frequency and location models for data for air operations are generally sparse, particularly for evaluation of the likelihood of an accident with severe conse- reporting of relevant details on incidents (more detailed data quences. The approach accounts for the variability and risk generally are available for accidents). Collection of NOD was exposure relative to various factors and provides a proba- a challenge, particularly to counteract the impossibility of bilistic assessment of risks. accessing the flight operation quality assurance (FOQA) data- The output of the risk assessment is a probability distribu- base from the airlines. tion of risks for an existing RSA subject to specific meteoro- The models and approach developed in this study can be logical and operation conditions. As a result, it is possible to helpful for airport planning and safety management RSA evaluate quantitatively the overall risk of accidents for a par- improvement actions. However, under no circumstances ticular runway and associated RSA. should the models developed in this research be used to as- sess real-time operational risks. There are several factors not Prototype Software accounted for in the models and their accuracy is not ap- Running a risk assessment for a specific RSA using the ap- propriate for decision making during actual operations or proach developed in this study requires extensive calculations. emergency situations.