INVITED PAPER A Hierarchical Flight Planning Framework for Air Traffic Management This paper aims to manage high-altitude air traffic flows by incorporating each flight operator’s preferences and aircraft type while considering weather risks and airspace capacity constraints. By Wei Zhang, Member IEEE, Maryam Kamgarpour, Student Member IEEE, Dengfeng Sun, Member IEEE,andClaireJ.Tomlin,Fellow IEEE ABSTRACT | The continuous growth of air traffic demand, tralization approach developed in this paper would also skyrocketing fuel price, and increasing concerns on safety and provide useful insights into the design of decision and infor- environmental impact of air transportation necessitate the mation hierarchies for other large-scale infrastructure systems. modernization of the air traffic management (ATM) system in the United States. The design of such a large-scale networked KEYWORDS | Air traffic control (ATC); cyber–physical systems system that involves complex interactions among automation (CPSs); decentralized optimization; hierarchical systems; path and human operators poses new challenges for many engi- planning neering fields. This paper investigates several important facets of the future ATM system from a systems-level point of view. In particular, we develop a hierarchical decentralized decision I. INTRODUCTION architecture that can design 4-D (spaceþtime) path plans for a The air traffic management (ATM) system of the United large number of flights while satisfying weather and capacity States is a large-scale, safety-critical, cyber–physical sys- constraints of the overall system. The proposed planning tem (CPS), which involves more than 50 000 flights daily, framework respects preferences of individual flights and en- being monitored and regulated by thousands of air traffic courages information sharing among different decision makers controllers based on weather and traffic measurements in the system, and thus has a great potential to reduce traffic obtained through numerous weather stations and radar delays and weather risks while maintaining safety standards. facilities located across the entire country. The physical The framework is validated through a large-scale simulation component in the system consists of a network of fast- based on real traffic data over the entire airspace of the conti- moving aircraft, whose coordination and control rely cru- guous United States. We envision that the hierarchical decen- cially on many cyber components such as weather and traffic prediction algorithms, decision-support software, and radio communications among pilots, dispatchers in Manuscript received April 15, 2011; revised June 17, 2011; accepted September 6, 2011. Airline Operation Centers (AOCs), and air traffic Date of publication September 6, 2011; date of current version December 21, 2011. This work was supported in part by the National Science Foundation (NSF) under controllers. Grant CNS-0931843, by the Air Force Office of Scientific Research (AFOSR) under Since its birth in 1920s, the ATM system has gradually Grant FA9550-06-1-0312, and by a National Science and Engineering Research Council of Canada (NSERC) fellowship. evolved from its primitive form that consisted of a set of W. Zhang and C. J. Tomlin are with the Department of Electrical Engineering and simple operation rules to its current version that is a com- Computer Sciences, University of California at Berkeley, Berkeley, CA 94720 USA (e-mail: [email protected]; [email protected]). plex network of sensing, communication, and control sub- M. Kamgarpour is with the Department of Mechanical Engineering, University of systems. Although various automation systems have been California at Berkeley, Berkeley, CA 94720 USA (e-mail: [email protected]). D. Sun is with the School of Aeronautics and Astronautics, Purdue University, West continuously introduced, the backbone of the current Lafayette, IN 47907 USA (e-mail: [email protected]). systemwasformedduringthe1950swhentheintro- Digital Object Identifier: 10.1109/JPROC.2011.2161243 duction of radar surveillance and radio communication 0018-9219/$26.00 Ó2011 IEEE Vol. 100, No. 1, January 2012 | Proceedings of the IEEE 179 Zhang et al.: A Hierarchical Flight Planning Framework for Air Traffic Management technologies revolutionized the way the system was B. Next Generation of ATM as a operating [1]. After more than half a century, another Cyber–Physical System major evolution of the ATM system to incorporate modern Clearly, the current air transportation system is sensing and information technologies is currently under- approaching its capacity and safety limits. To resolve its way [2] in order to address the growing concerns about its existing issues as well as to be able to support the rapid operational and energy efficiency, environmental impacts, growth of traffic demand, we need to automate the system and safety. at a faster pace. It is a common vision shared by the Federal Aviation Administration (FAA), air traffic controllers, and A. Notable Issues in Current ATM airline companies that the efficiency, environmental, and Air traffic demand in the past 20 years has grown by safety concerns of the current ATM system can be over 64%, while human traffic controllers and airspace considerably alleviated by properly incorporating modern resources such as airports and runways have not kept up sensing and information technologies to enable reliable with this growth rate [3]. It has been estimated that communications, real-time common situation awareness, domestic air traffic delays in 2007 cost the U.S. economy and prompt safety-guaranteed decision supports. Such a about $41 billion, including more than $19 billion in direct vision clearly coincides with the CPS viewpoint of modern operating costs [4]. The delays also contributed to about engineering systems, and is currently being implemented 740 million extra gallons of jet fuel, and an additional through the concept of Next Generation Air Transpor- emission of about 7.1 million tons of carbon dioxide. The tation System (NextGen) in the United States [2]. The situation will be further aggravated by the expected two- to NextGen concept advocates for an evolution from the cur- threefold increase in air traffic demand over the next two rent ground-based navigation system to a satellite-based decades [5]. Meanwhile, the need to constrain the rapid ATM system, where verbal communications and ground growth of aviation’s impact on the global climate is be- radar systems are replaced with more reliable and accurate coming increasingly clear. Global carbon dioxide emis- data-link communications and global positioning systems sions from aircraft grew about 45% between 1992 and (GPSs), so that many traffic control tasks can be handled 2005. It has also been forecasted that aviation emissions (semi)automatically. In addition, the increased automation will increase an additional 150% above the 2006 level by in conflict detection and resolution would facilitate 4-D 2036 [6], [7]. (space-time) trajectory-based operations (TBOs), in which Aside from being strained by the current level of individual flights would have freedom to adjust their tra- demand, air transportation safety has recently been jectories according to real-time traffic and weather condi- compromised to a level requiring immediate attention. It tions, rather than having to follow fixed nominal flight was reported that the number of certified air traffic plans as in the current clearance-based operations [9]. controllers in 2008 reached the lowest level in 15 years, The implementation of NextGen not only calls for an causing many major air traffic control (ATC) facilities to integrated engineering effort, but also poses new chal- declare staffing emergencies. The lack of enough air traffic lenges in many research disciplines as listed in Fig. 1, controllers has caused an upsurge of operational errors, including transportation engineering, human factors, many of which could have turned into major accidents. For communications, sensor networks, cyber security, opera- example, the plane crash at Lexington, KY, on August 27, tion research, and machine learning [2]. Information 2006, was partly due to the fatigue of the sole tower sharing has already played an important role in the current controller causing him to not respond promptly to the system. For example, many pilots report the actual weather incorrect runway use. As a more recent example, the sole conditions experienced in flight to air traffic controllers tower controller in the Ronald Reagan Washington through verbal communications. These reports are being National Airport (DCA), who was on his fourth straight updated continuously (see Fig. 2 for a snapshot of these overnight shift on March 23, 2011, fell asleep, forcing two reports) and used heavily for making aviation decisions commercial aircraft to land without assistance. [10]. With the vision of NextGen, one can imagine that the The efficiency and safety issues make the system even future air transportation system will soon evolve from this more vulnerable to weather disruptions. It was found that verbal information sharing platform to an automatic hazardous weather such as storms or high winds Bsensing and action web[ in the sky, in which onboard accounted for more than 70% of the air traffic delays in sensed data are disseminated through secure communica- 2007 [4] and about 30% of all aviation accidents [8]. tions, and are processed and analyzed in real time to Although various