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14 Table 3. (Continued). Category Field Level 1 Field Level 2 Incorrect Flight Planning Communication/Coordination Visual Illusion Human Errors Fatigue Pressonitis Other Wet Contaminated - Standing water Contaminated - Rubber Contaminated - Oil Contaminated - Ice Runway Surface Contaminated - Slush Conditions Contaminated - Snow Contaminated - Paint Contaminated - Other Construction Down Slope Wildlife Hazards Unstabilized - Low Approach Unstabilized - Low Speed Approach/Takeoff Long Touchdown Procedures Unstabilized - High Speed High Above Threshold Takeoff Rejected Other Aircraft Body Type Wide or Narrow Aircraft Cost 2007 dollar value Cost Human Cost 2007 dollar value Total Event Cost 2007 dollar value and world occurrences was utilized to develop the location develop risk models. However, operation conditions and models. levels of risk are different at different airports. In addition, Incorporating risk exposure information into the accident only raw distances between the final wreckage location and frequency model enhances its predictive power and provides the runway end have been used to develop current FAA RSA the basis for formulating more risk-sensitive and responsive recommendations. RSA policies. Accident frequency models need no longer rely To mitigate this difficulty, information available for differ- on simple crash rates based on just aircraft, engine, or opera- ent airports was compared by using a normalization procedure, tion type. As discussed below, factors previously ignored by to transform existing data to a standard nominal airport (Kirk- airport risk assessments and RSA regulations are accounted land et al., 2003). To normalize aircraft accident data, the "nor- for using the models developed in this study. Moreover, this mal" airport is an airport situated at the International Standard normal operations database can be used for future studies. Atmosphere (ISA) conditions, with level surrounding terrain The detailed source and sampling strategy of the NOD or obstacles and an infinitely long, hard runway. database is described in Appendix G. In addition, a small sam- Normalization was conducted for the effects of terrain on ple of the NOD being utilized in this study is included in that wreckage location using the models developed by Kirkland et al. section. A list of sampled airports is shown in Appendix H and (2003) and the effects of the local atmospheric conditions on the stratified sampling strata is presented in Appendix I. the aircraft's performance, based on standard corrections for To derive the weights to be applied to each stratum, it was aircraft distance required. Major factors that affect the runway necessary to identify the relevant traffic from Terminal Area distance required for the operation and used in the flight man- Forecasts (TAFs). Details on the calculation of TAF are pre- ual calculations are runway slope, runway elevation, and the air sented in Appendix J. temperature; however, a correction was not applied to the slope in the RSA due to missing information for the majority of the events. The RSA slope is indeed an important factor on the Normalization of Data wreckage distance and this information should be collected and The small pool of relevant data available is a fundamental made available in incident and accident investigation reports. problem to risk assessment in aviation (Caves and Gosling, Normalization procedures used in this study are presented in 1999). Most studies have used data from different airports to Appendix K.