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2 CHAPTER 1 Background Introduction airports have much higher tolerance to risk than others. Ide- ally the risk associated with specific airport and operation From 1995 to 2004, 71 percent of the world's jet aircraft factors should be modeled to assess the level of safety being accidents occurred during landing and takeoff and accounted provided by specific conditions of existing or planned for 41 percent of all onboard and third party fatalities (Boeing, RSA. Some intuitively important factors that would affect 2005). Landing overruns, landing undershoots, takeoff over- risk, such as various environmental and operational charac- runs, and crashes after takeoff are the major types of accidents teristics of the airport, are not considered yet. that occur during these phases of flight. Records show that In current risk assessment methods, factors that determine while most accidents occur within the boundaries of the run- safety cannot be analyzed independently; however, a rational, way strip, most fatalities occur near but off the airport area systematic identification of safety influencing factors and (Caves, 1996). their interrelationships has never been conducted. This situ- Currently, Federal Aviation Administration (FAA) stand- ation impedes the assessment of effects of safety improve- ards require runways to include a runway safety area (RSA)-- ment opportunities and, consequently, risk management. a graded and clean area surrounding the runway that "should Moreover, most airfield design rules are mainly determined be capable, under normal (dry) conditions, of supporting air- by a set of airfield reference codes, which only take into ac- planes without causing structural damage to airplanes or injury count the design aircraft approach speed and the aircraft to their occupants" (FAA, 1989). Its purpose is to improve dimensions (wingspan or tail height). The resulting protection the safety of airplanes that undershoot, overrun, or veer off the is segregated in widely differing groups that do not necessar- runway. ily reflect many of the actual risk exposure factors. The size of the RSA depends on the type and size of aircraft using the runway. RSA standard dimensions have increased Project Objectives over time. The predecessor to today's standard extended only 200 feet from the ends of the runway. Today, a standard RSA The original objective of this project was to collect histor- can be as large as 500 feet wide and extend 1,000 feet beyond ical information related to overrun and undershoot accidents each runway end. The standard dimensions have increased to and incidents to develop a comprehensive and organized address higher safety expectations of aviation users and database with editing and querying capabilities, containing accommodate current aircraft performance. critical parameters, including aircraft, airport, runway, oper- However, applying the new standards to existing airports can ation, and causal factor and consequence information that be problematic. Many runways do not meet current standards could assist the evaluation of runway safety areas. because they were constructed to an earlier standard. The prob- The research team extended the project objective to lem is compounded by the fact that the airports are increasingly include the development of risk models for overrun and un- constrained by nearby land development and other natural fea- dershoot events. The primary function of the risk models is tures, or they face costly and controversial land acquisition, or to support risk management actions for those events by in- a need for unfeasible wetlands filling projects. creasing the size of the RSA, removing obstacles, construction The runway safety area standards are prescriptive and its of arrestor beds or perhaps, where that is not possible, by the rigid nature results in "averaged" degrees of protection being introduction of procedural measures or limitations for oper- provided across broad ranges of risk levels, such that certain ations under high-risk conditions.
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3 Three sets of models were developed in this study--landing basis for creating analysis software that can be used to overruns, landing overshoots, and takeoff overruns. Each set assess risks of aircraft overruns and undershoots. is comprised of three parts: probability of occurrence, loca- tion, and consequences. The models can improve the under- Applied to any specific airport, the analysis approach for standing of overrun and undershoot risks and help airport RSA risk assessment developed in this study will allow users operators manage these risks. to determine if the risk is relatively high or low and whether Based on the information described above, the goals for there is a need for risk management action. The safety bene- this research project were extended to include: fits provided by possible mitigation measures (e.g., increased size of RSA) can be evaluated using the same approach. 1. Development of a comprehensive database for aircraft In addition, three innovative techniques were incorporated overrun and undershoot accidents and incidents; to improve the development of risk models. One major im- 2. Determination of major factors affecting the risks of such provement in the modeling of accident occurrence is the use accidents and incidents; of normal operations (i.e., nonaccident and nonincident) 3. Description of how these factors affect operations and flight data. With normal operations data (NOD), the number associated risks, to improve understanding on how these of operations that experience the factor benignly, singly, and events may occur; in combination can be calculated, so risk ratios can be gener- 4. Development of risk models for probability, location, and ated and the importance of risk factors quantified. consequences for each type of accident: landing overruns The second improvement is the use of normalization tech- (LDOR); landing undershoots (LDUS); and takeoff over- niques to convert information to a standard nominal airport. runs (TOOR); Using such normalization procedure allows comparing acci- 5. Development of a practical approach to use these models dent and NOD data for different operation conditions, thus for assessing risks on existing RSA under estimated oper- creating a larger pool of relevant information. ation conditions; Finally, the models developed were integrated in a rational 6. Development of a list of relevant factors that should be probabilistic approach for risk assessment of RSA. Based on reported for aircraft overrun and undershoot accidents so historical information for flight operations and weather con- that availability of quality data can be improved for future ditions, and considering the configuration of the RSA and studies; and presence of obstacles located close to the runway, the proba- 7. Development of prototype software to evaluate risks bility distribution for accidents involving severe consequences under specific operation conditions that may serve as the may be estimated.