Hamsa Balakrishnan Massachusetts Institute of Technology NSF−UC Berkeley−MIT ActionWebs Kickoff Meeting December 17, 2009 ActionWebs: Energy-efficient Air Transportation Systems

The Air Transportation System  Key player in global travel and commerce 2 billion passenger enplanements in 2006 (US: ~700 mil.) 29 million flights worldwide in 2007 (US: ~30,000 flights per day) Number of flights expected to grow ~2-3x by 2025 Jet fuel prices are volatile

Air traffic delays  In 2007, domestic air traffic delays cost the US economy $41 billion 24% of arrivals at least 15 min late (avg. delay: 46 min) ~20% of total domestic flight time was delay 1,565 flights delayed on the ground (not at gate) for over 3 hours 60% rise in rate of passenger complaints ( ) $19 billion in direct operating costs to the airlines $12 billion cost to passengers Data sources: IATA, FAA ASPM and OPSNET databases, Bureau of Transportation Statistics, Joint Economic Committee, Airline Quality Rating 2008

Air Traffic Management: current functional architecture Approved handoffs Clearances/ advisories [Adapted from A. Haraldsdottir (Boeing), 1998] Flight Planning Flight schedules Weather National Flow Planning Facility Flow Planning Filed flight plans Capacity schedule Aircraft Guidance & Navigatio n Aircraft state < 5 min Pilot Recorded ETMS data Hrs-day Facility Traffic Control 5 min Facility ATC Airline Operations Center Central Flow Mgmt Unit Traffic Mgmt Unit Facility Traffic Planning Approved flight plans/ planned flow rates Traffic situation 5-20 min Desired traffic loads Negotiate handoffs Airlines Facility Traffic Manager Efficiency Safety Planning Execution Throughput

Consequence: Delay propagation!

Key research objectives  More decentralized decision-making  More flexible and dynamic trajectories  Increase efficiency of operations  Increase operational robustness in the presence of weather  Decrease fuel burn and environmental impact  Multi-objective control techniques for balancing tradeoffs The use of onboard sensing in ActionWebs, combined with the development of hybrid systems models of aircraft trajectories can help us achieve these objectives

 More decentralized decision-making

An Eulerian model for distributed feedback control s 1 |s 2 s 2 |s 3 s 2 |s 4 s 3 |s 2 s 2 |s 1 s 4 |s 2 s 3 |s 5 s 5 |s 3 s 3 |s 6 s6s6 Sector 1 Sector 2 Sector 3 Sector 4 Sector 5 Network model has two nodes for each sector boundary (one on each sector) Links correspond to the regions of airspace Set of queues associated with each node, each containing aircraft currently in that region of the airspace Aircraft move from one node to another, at rates determined by the flow rates along the links Le Ny and Balakrishnan, ACC 2009]

An Eulerian model for distributed feedback control At every node, there is a queue corresponding to each destination Then, we model the dynamics of queue m at node i by: is the rate allocation on link ( i, j ) to flow m (control variable) Putting this together, airport arrivals/departures inflow outflow

Advantages of this framework  Can apply distributed feedback control policies For example, MaxWeight  Attractive idea, because sector controllers only need to talk to their neighbors (much like today!)  Build model from archived ETMS (surveillance) data Le Ny and Balakrishnan, ACC 2009; Kannan, Harvard BA thesis, 2009]

For example, the airspace surrounding SFO Numbers denote maximum inter-sector handoff rates in aircraft/min

Scheduling with routing No routing (predefined routes): With routing: (better balanced loads in two routes) Time (in hrs) Sector load (# of aircraft)

 More flexible and dynamic trajectories  Increase efficiency of operations  Increase operational robustness in the presence of weather

Routing using convective weather forecasts  Convective weather has a significant impact on NAS operations, especially in summer  As the time horizon increases, forecast errors increase (especially when we are trying to forecast storm intensity in a 1 km x 1 km pixel) 5 min30 min

Route flexibility improves accuracy Forecast Actual B

 Decrease fuel burn and environmental impact  Multi-objective control techniques for balancing tradeoffs

Environmental impacts of air transportation  Aviation is responsible for 3% of total global carbon emissions Aircraft contribute about 12% of CO 2 emissions from the transportation sector According to the European Union, international aviation is one the largest growing contributors to CO 2 emissions, having increased 87% between 1990 and 2004  The aviation sector was responsible for million metric tons of CO 2 emissions in the US in 2007 (about 3% of total emissions) [Commission of the European Communities, 2006; EPA 2007]

Environmental impact of air traffic delays  Air traffic delays have an environmental cost, in addition to the inconvenience to passengers, airline costs and impact on the economy  In 2007, domestic air traffic delays Cost airlines an additional $1.6 billion in fuel costs Consumed an additional 740 million gallons of jet fuel Released an additional 7.1 million tons of CO 2 into the atmosphere  Enhancing system capacity and improving efficiency will result in environmental benefits as well [Joint Economic Committee of the US Senate, 2008]

Surface emissions from taxiing aircraft  In 2007, aircraft in the US spent over 63 million minutes taxiing in to their gates, and over 150 million minutes taxiing out to their runways An estimated 6 million tons of CO 2, 45,000 tons of CO, 8,000 tons of NOx and 4,000 tons of hydrocarbons are emitted annually by aircraft taxiing out for departure  These flights burn fuel and contribute to emissions at low altitudes, and adversely impact local air quality  Taxi-out emissions correspond to about 5% of the fuel burn and emissions from aircraft operations  How do we optimize surface traffic movement to reduce aircraft emissions from taxi processes? [FAA ASPM database; Balakrishnan et al. 2008]

Aircraft taxi trajectories from surface surveillance data

Effect of stopping and starting while taxiing  Potential fuel burn impact from stopping on the surface No significant impact

Effect of stopping and starting while taxiing  Impact depends on pilot actions No significant change in throttle setting

Using CFDR data to estimate impact of different taxi profiles  ICAO emissions databank assumes that aircraft taxi at a constant throttle setting of 7%  Using CFDR data (from Swiss Air) corresponding to taxi profiles of various aircraft, we Developed a regression model for fuel burn, that considers the baseline fuel burn and the impact of stop-start events  Stop-start impact: Estimate of the form “The extra fuel burn from a start-stop event is equivalent to x additional minutes of taxi time” Developed a (linear) regression model between fuel burn and throttle settings Conducted above analysis for 9 aircraft types Fuel burn = Baseline fuel burn rate  (taxi time) + (Stop-start impact)  (# of stop-start events)

CFDR vs. ICAO fuel burn estimates Impact of a stop-start event Labels indicate throttle settings

Minimizing fuel burn impacts of aircraft trajectories Multi-objective control of taxi trajectories Identification of hybrid system model of taxi trajectory Surface surveillance Flight data recorder Identification of fuel burn model Surface surveillance Flight data recorder (archival data) (real-time data)

Multiple real-world objectives  Maximize throughput  Minimize average delay  Minimize maximum delay  Maximize robustness  Minimize fuel consumption  Minimize fuel costs  Minimize operating costs  Minimize passenger delays  Multiple stakeholders with differing objectives, tradeoffs involved [Balakrishnan and Chandran, Operations Research, to appear; Lee and Balakrishnan, Proceedings of the IEEE, 2008]

Summary  ActionWebs concepts can help achieve More decentralized decision-making More flexible and dynamic trajectories Increased efficiency of operations Increased operational robustness in the presence of weather Decreased fuel burn and environmental impact  The Air Transportation System test bed will be an exciting application of these concepts!