packages (Long et al. 1999, Stamatopoulos et al. 2003, EUROCONTROL 2001) that perform both capacity and delay analyses and, in the instance of the last two references, include models of aprons and aircraft stands. After some necessary enhancements and an adequate amount of testing in a variety of airport environments, packages of this type may provide airport planners within a few years with an easy-to-use and very fast set of tools for the study of a host of airside issues.
4.1.2. Airside Simulations. General-purpose simulation models of airside operations first became viable in the early 1980s and have been vested with increasingly sophisticated features since then. Three models currently dominate this field internationally: SIMMOD, The Airport Machine, and the Total Airport and Airspace Modeler (TAAM). A report by Odoni et al. (1997) contains detailed reviews (somewhat out-of-date by now) of these and several other airport and airspace simulation models and assesses the strengths and weaknesses of each. At their current state of development (and in the hands of expert users), they can be powerful tools in studying detailed airside design issues, such as figuring out the best way to remove an airside bottleneck or estimating the amount by which the capacity of an airport is reduced due to the crossing of active runways by taxiing aircraft. Unfortunately, these models are frequently misused in practice, at great cost to the client organization. This happens when they are applied to the study of “macroscopic” issues that can have only approximate answers because of the uncertainty inherent in the input data. An example is a question that often confronts airport operators: When will airside delays reach a level that will require a major expansion of an airport’s capacity (e.g., through the construction of a new runway)? Questions of this type, often requiring a look far into the future, are best answered through the approximate analytical models surveyed earlier, which permit easy exploration of a large number of alternative scenarios and hypotheses. Detailed simulation models, by contrast, cannot cope well with the massive uncertainty involved because they require inputs that are difficult to produce (e.g., a detailed schedule of aircraft movements at the airport for a typical day 10 or 15 years hence) and lack credibility under the circumstances.
4.1.3. Optimizing Airside Operations. The airside models discussed so far are descriptive in nature. Their objective is to help users understand and predict the operational characteristics of the various airside facilities under different operating scenarios. A considerable amount of OR work with an optimization focus also exists, much of it concerned with the effective use of runway systems. The capacity of a runway is largely determined by the separation requirements specified by the providers of ATM services (e.g., the FAA in the United States). For any pair of consecutive runway operations these requirements depend on the type of aircraft involved. For example, in the United States, when an arriving “heavy” (H) aircraft—defined as one with a maximum takeoff weight (MTOW) greater than 255,000 lbs—is immediately followed by an arriving “small” (S) aircraft (MTOW < 41,000 lbs), the required separation between them, at the instant when H is about to touch down on the runway, is 6 nautical miles (∼10.9 km). This is because “heavy” aircraft (wide-body jets) may generate severe wake turbulence, which may be hazardous to other aircraft behind it. By contrast, when an aircraft of type Sis followed by one of type H, the required separation is 2.5 nautical miles (∼4.5 km). Note that given a number n of aircraft, all waiting to land on a runway, the problem of determining the sequence of landings, such that the time when the last aircraft lands is minimized, is a Hamiltonian path problem with n points. However, this is only a static version of a problem which in truth is a dynamic one: Over time the pool of aircraft available to land changes, as some aircraft reach the runway while new aircraft join the arrivals queue. Moreover, minimizing the “latest landing time” (or maximizing “throughput”) should not necessarily be the objective of optimal sequencing. Many alternative objective functions, such as minimizing the average waiting time per passenger, are just as reasonable. A further complication is that the very idea of “sequencing” runs counter to the traditional adherence of ATM systems to a first-come, first-served (FCFS) discipline. Deviations from FCFS raise concerns among some airside users about the
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แพคเกจ (ลอง et al. ปี 1999, Stamatopoulos et al. 2003, EUROCONTROL 2001) ที่ทำการวิเคราะห์ความจุและความล่าช้า และ ในอินสแตนซ์ของการอ้างอิงที่สองล่าสุด รวมแบบยืน aprons และเครื่องบิน หลังจากปรับปรุงบางอย่างจำเป็นและเพียงพอผลการทดสอบในหลากหลายสภาพแวดล้อมสนามบิน แพ็คเกจชนิดนี้อาจมีวางแผนสนามบินภายในไม่กี่ปีมีการตั้งค่าการ ใช้งานง่าย และรวดเร็วมากของเครื่องมือสำหรับการศึกษาของปัญหา airside4.1.2. Airside Simulations. General-purpose simulation models of airside operations first became viable in the early 1980s and have been vested with increasingly sophisticated features since then. Three models currently dominate this field internationally: SIMMOD, The Airport Machine, and the Total Airport and Airspace Modeler (TAAM). A report by Odoni et al. (1997) contains detailed reviews (somewhat out-of-date by now) of these and several other airport and airspace simulation models and assesses the strengths and weaknesses of each. At their current state of development (and in the hands of expert users), they can be powerful tools in studying detailed airside design issues, such as figuring out the best way to remove an airside bottleneck or estimating the amount by which the capacity of an airport is reduced due to the crossing of active runways by taxiing aircraft. Unfortunately, these models are frequently misused in practice, at great cost to the client organization. This happens when they are applied to the study of “macroscopic” issues that can have only approximate answers because of the uncertainty inherent in the input data. An example is a question that often confronts airport operators: When will airside delays reach a level that will require a major expansion of an airport’s capacity (e.g., through the construction of a new runway)? Questions of this type, often requiring a look far into the future, are best answered through the approximate analytical models surveyed earlier, which permit easy exploration of a large number of alternative scenarios and hypotheses. Detailed simulation models, by contrast, cannot cope well with the massive uncertainty involved because they require inputs that are difficult to produce (e.g., a detailed schedule of aircraft movements at the airport for a typical day 10 or 15 years hence) and lack credibility under the circumstances. 4.1.3. Optimizing Airside Operations. The airside models discussed so far are descriptive in nature. Their objective is to help users understand and predict the operational characteristics of the various airside facilities under different operating scenarios. A considerable amount of OR work with an optimization focus also exists, much of it concerned with the effective use of runway systems. The capacity of a runway is largely determined by the separation requirements specified by the providers of ATM services (e.g., the FAA in the United States). For any pair of consecutive runway operations these requirements depend on the type of aircraft involved. For example, in the United States, when an arriving “heavy” (H) aircraft—defined as one with a maximum takeoff weight (MTOW) greater than 255,000 lbs—is immediately followed by an arriving “small” (S) aircraft (MTOW < 41,000 lbs), the required separation between them, at the instant when H is about to touch down on the runway, is 6 nautical miles (∼10.9 km). This is because “heavy” aircraft (wide-body jets) may generate severe wake turbulence, which may be hazardous to other aircraft behind it. By contrast, when an aircraft of type Sis followed by one of type H, the required separation is 2.5 nautical miles (∼4.5 km). Note that given a number n of aircraft, all waiting to land on a runway, the problem of determining the sequence of landings, such that the time when the last aircraft lands is minimized, is a Hamiltonian path problem with n points. However, this is only a static version of a problem which in truth is a dynamic one: Over time the pool of aircraft available to land changes, as some aircraft reach the runway while new aircraft join the arrivals queue. Moreover, minimizing the “latest landing time” (or maximizing “throughput”) should not necessarily be the objective of optimal sequencing. Many alternative objective functions, such as minimizing the average waiting time per passenger, are just as reasonable. A further complication is that the very idea of “sequencing” runs counter to the traditional adherence of ATM systems to a first-come, first-served (FCFS) discipline. Deviations from FCFS raise concerns among some airside users about the384 Transportation Science/Vol. 37, No. 4, November 2003
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