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2 CHAPTER 1 Background Introduction On the other hand, some of the factors that lead to aircraft accidents/incidents are considered under subjective criteria. The modernization and complexity of the National Air- This research addresses a more consistent risk-based decision- space System (NAS) have increased considerably in the last four making process to analyze the separation standards at those decades, and its components require continuous improve- constrained airports. ments to increase capacity and safety. Airports are one of the main components of this complex and dynamic system. To meet higher demands for flights, airlines are operating Project Goals larger aircraft with greater seating capacity. However, the air- The main objective of this research was to develop a method- field configurations at many airports were established years ago, ology for assessing the risk of aircraft collisions associated and many existing airports were designed and constructed in with non-standard airfield separations. The methodology is the 1960s and 1970s to accommodate the smaller aircraft in use intended to provide a quantitative basis to support MOS at that time. As a consequence, some of these airports have air- requests by airport operators for airfield separations that do field separations that are not compatible with current Federal not meet FAA standards. This study is not aimed at modify- Aviation Administration (FAA) design requirements and rec- ing existing standards but rather at allowing an airport oper- ommendations. Moreover, existing airports need to increase ator to assess the level of safety when those standards cannot their capacity to meet demand. Many of these airports are con- strained by urban development and physical and environmen- be met. The methodology was developed to be simple and tal restrictions, or they do not have the necessary real estate to practical, allowing airport operators to estimate whether the accommodate the applicable separation standards. level of risk is acceptable and to compare it to the level of risk With this potential traffic growth, many airports will need to achieved when the standard separations are met. bring larger aircraft and use instrumented runways to increase their capacity; however, existing separations may not be appro- Major Challenges Associated priate for larger aircraft or for upgraded approach categories. with Airfield Separations When existing separations do not meet FAA standards, a request for modification of standards (MOS) may be required, In the coming years, it is expected that air transportation will and authorization for the operation may be granted if the MOS experience greater growth than has been observed during the fulfills the criteria described in FAA's Advisory Circular (AC) 2008 to 2011 recession period. Anticipating the higher demand 150/5300-13, Airport Design (FAA, 1989). In the context of this for flights, airlines are operating larger aircraft with greater seat- study, MOS means any change to FAA dimensional standards, ing capacity. However, it is sometimes impracticable to meet other than those for runway safety areas (RSAs), applicable to the separation standards for larger aircraft due to a number of an airport design or construction project (new, reconstruction, physical, social, economical, and environmental limitations. expansion, or upgrade). There is no acceptable method available to estimate the level So far, requests dealing with airfield separations have been of protection provided by existing airport layouts when evalu- analyzed according to non-risk-based methodologies, and the ating the operation of large aircraft in terms of the probability only available guidance is described in AC 150/5300-13 (FAA, of collision with another aircraft, vehicle, or object. Current 1989). This process can affect airport efficiency and capacity separation standards have provided an excellent level of safety, and, potentially, prevent certain aircraft from using an airfield. as evidenced by the small number of accidents associated with