Integrating Advanced Weather Forecast Technologies Into .

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evans, Weber, and MoserIntegrating Advanced Weather Forecast Technologies into Air Traffic Management Decision SupportIntegrating Advanced WeatherForecast Technologies intoAir Traffic ManagementDecision SupportJames E. Evans, Mark E. Weber, and William R. Mosern Explicit integration of aviation weather forecasts with the National AirspaceSystem (NAS) structure is needed to improve the development and executionof operationally effective weather impact mitigation plans and has becomeincreasingly important due to NAS congestion and associated increases in delay.This article considers several contemporary weather-air traffic management(ATM) integration applications: the use of probabilistic forecasts of visibilityat San Francisco, the Route Availability Planning Tool to facilitate departuresfrom the New York airports during thunderstorms, the estimation of en routecapacity in convective weather, and the application of mixed-integer optimizationtechniques to air traffic management when the en route and terminal capacitiesare varying with time because of convective weather impacts. Our operationalexperience at San Francisco and New York coupled with very promising initialresults of traffic flow optimizations suggests that weather-ATM integrated systemswarrant significant research and development investment. However, they will needto be refined through rapid prototyping at facilities with supportive operationalusers.Airspace demand has increased steadily in thelast twenty years. Some major terminals anden route sectors are approaching maximumcapacity with current technology and procedures. Asnoted in related articles in this issue of the Journal,thunderstorms in en route or terminal airspace or lowclouds and impaired visibility at airports can reducecapacity significantly below today’s demand levels, resulting in widespread delay events. Aviation plannersanticipate a need for at least a twofold increase in thecapacity of the air transportation system in the nexttwenty years [1]. To prevent disruptive delays during adverse weather, we must develop better weatherforecasts and air traffic management (ATM) decisionsupport systems that facilitate the optimal utilizationof the available capacity of weather-impacted airspace.Figure 1 shows the operational decision process formitigation of adverse weather impacts.Lincoln Laboratory’s role in developing and prototyping integrated weather sensing and processing systems such as the Integrated Terminal Weather System(ITWS) [2, 3], the Corridor Integrated Weather System (CIWS) [4, 5] and the San Francisco stratus-cloudforecast system [6] has lead naturally to considerationof improving the air traffic management process. Amajor goal of the operational testing of these systemshas been to understand in detail how their meteorological products and forecasts are used by the FederalVOLUME 16, NUMBER 1, 2006LINCOLN LABORATORY JOURNAL81

Evans, Weber, and MoserIntegrating Advanced Weather Forecast Technologies into Air Traffic Management Decision SupportOperational decision loopCurrentweatherDetermine weather impactWeathermeasurementsystems Weather radar Satellite SurfaceobservationsDetermine ATC impactUserdisplaysForecastproductsDevelop mitigation plansTraffic flowmanagementdecisionsupport toolsDecide on mitigation planExecute mitigation planFIGURE 1. Decision process for use of weather products for air traffic management and/or flight planning. Delays are averted orminimized only if an appropriate mitigation plan is executed in a timely manner.Aviation Administration (FAA) air traffic managersand airline operations personnel such as dispatchersto develop strategies for reroutes, ground and airbornedelay programs, cancellations, and diversions.Documented examples of improved operational decision making using these Lincoln Laboratory–developed systems are described in the references listed inthe preceding paragraph. While the associated reductions in weather-related delay have been impressive, wehave observed that the complexities of quantitativelyassessing the impacts of weather on airspace capacity,developing candidate response strategies, and coordinating these strategies among multiple operationalfacilities often result in suboptimal response strategies. During situations when airspace demand exceedscapacity for a significant period of time, even modestincreases in throughput—realizable by using betterATM strategies—can significantly decrease overall delay by limiting the length and duration of the aircraftqueues that form.In 1998, the Port Authority of New York andNew Jersey funded a program at Lincoln Laboratoryto establish an ITWS prototype supporting operations at the major New York City airports (Newark,LaGuardia and John F. Kennedy International Airport). Highly motivated FAA and airline personnelhave worked closely with the Laboratory to adapt thisprototype to the unique operational requirements ofNew York City’s highly congested terminal area. Thisinteraction led to important insights into the mecha82LINCOLN LABORATORY JOURNALVOLUME 16, NUMBER 1, 2006nisms of weather-related delay at pacing airports (thoseairports which control air traffic throughout a region)and the benefits derived from the ITWS products [7].In addition, feedback from these operational users emphasized that purely meteorological products do notfully meet user needs and spurred the developmentof a simple but highly effective operational decisionsupport system called the Route Availability PlanningTool (RAPT). As described later in this article, RAPTintegrates three-dimensional (3D) convective weatherforecasts from the CIWS with National Airspace System (NAS) structure information and an explicit model for pilot preferences in avoiding convective weatherto predict the availability of the filed departure routeand alternative departure routes for an aircraft. RAPTpermits air traffic control (ATC) and airline decisionmakers to focus on managing departure scheduling asopposed to weather interpretation in the context ofthe NAS structure.Insights gained from the operational testing ofRAPT and our other integrated weather system prototypes continue to refine our appreciation of the challenges associated with translating meteorological diagnosis and forecast products into more operationallyrelevant terms. Broadly stated, more effective ATMduring adverse weather requires enhancements in thefollowing four areas.(1) Continued improvement in forecasts of aviation-impacting meteorological conditions (e.g., thunderstorms, low ceiling and visibility) generated at fine

evans, Weber, and MoserIntegrating Advanced Weather Forecast Technologies into Air Traffic Management Decision Supporttime steps that span the zero-to-six-hour window necessary for flight planning. These forecasts must includeparameters that support quantitative characterizationof airspace capacity.(2) Models for translating the weather forecasts intotime-varying estimates of the capacity reductions in affected en route sectors, terminal airspace, and airports.These estimates must include uncertainty bounds.(3) Automatically generated, broad-area ATMstrategies that utilize time-varying estimates of airspacecapacity and demand to anticipate overload situationsand suggest optimal reroute strategies or, when necessary, minimally disruptive ground or airborne delayprograms.(4) Application of modern statistical decision-making and risk-management techniques as a basis for developing ATM strategies, given probabilistic weatherand airspace capacity forecasts.In this article we discuss insights on the ATM challenge developed during ongoing operational prototyping of Lincoln Laboratory–integrated weather sensing and decision support systems, and recent work todevelop more quantitative operational guidance, asjust described. We begin with a discussion of LincolnLaboratory’s experiences in operational prototyping ofexplicit capacity impact forecasts generated by the SanFrancisco stratus-forecast system and RAPT. Then wediscuss our follow-on efforts to develop and validatemore general airspace capacity models based on meteorological forecasts. We conclude with a descriptionof preliminary efforts to develop and apply a robustoptimization model for post facto performance assessment and real-time broad-area planning needs.Operational Use of the San FranciscoCeiling/Visibility Capacity ForecastsThe Lincoln Laboratory San Francisco stratus-cloudforecast system deals with what in some respects is arelatively straightforward ATM problem [6]. The airport’s arrival acceptance rate can be one of two distinctvalues, depending on a well-defined meteorologicalcondition (low-ceiling conditions from May throughOctober due to the intrusion of marine stratus alongthe Pacific coast) at a specific location, the approachpath to San Francisco.The low cloud conditions prohibit dual paral-lel landings of aircraft on the airport’s closely spacedparallel runways, thus effectively reducing the arrivalcapacity by a factor of two. The behavior of marinestratus evolves on a daily cycle, filling the San Francisco Bay region overnight, and dissipating during thedaylight hours. Often the low-ceiling conditions persist throughout the morning. The FAA puts a grounddelay program into effect under these conditions, sincethe scheduled demand into San Francisco from midmorning to early afternoon typically exceeds the SanFrancisco low-ceiling arrival capacity of approximatelythirty aircraft per hour. These ground-delay programsdelay departures at their origin such that the arrivalflow for San Francisco matches the airport capacity.The result of the ground-delay program is a substantial number of delayed flights originating at airports asfar away as Chicago.The Lincoln Laboratory San Francisco forecastsystem uses physical and statistical models to providean estimate of the most likely capacity transition timeand estimates of the cumulative probability that thetransition has occurred at each forecast time step. Theoriginal Lincoln Laboratory benefits projections forthe San Francisco forecast system envisioned the proactive ending of these ground-delay programs so thatthere would no longer be a one-to-two-hour periodwhen the low ceiling/visibility conditions had ended,but the rate of arrivals was much less than the actualairport capacity [8].To date, however, there have been very few eventsin which a ground-delay program was cancelled proactively. The current FAA policy is to add two hoursto the projected burn-off time to arrive at a grounddelay program cancellation time. If there is high confidence in the burn-off time, a higher airport acceptancerate—forty-five aircraft per hour, which is intermediate between the low capacity rate of thirty aircraft perhour and the fair-weather capacity of sixty per hour—is used to modify the ground-delay program for thetwo hours after the forecast burn-off time. Since thevast majority of stratus events dissipate well before twohours after the projected burn-off time, a significantfraction of the projected benefit from the San Francisco ceiling/visibility capacity forecast is not beingachieved.We have identified several key problems in the opVOLUME 16, NUMBER 1, 2006LINCOLN LABORATORY JOURNAL83

Evans, Weber, and MoserIntegrating Advanced Weather Forecast Technologies into Air Traffic Management Decision Supporterational utilization of what appears to be a technicallysuccessful probabilistic forecast. The first is that AirRoute Traffic Control Center (ARTCC) operationalusers are concerned about the possibility of too manyaircraft holding in Oakland center airspace. Effectively, they have assigned a very high cost to the possibilitythat an overly optimistic forecast will result in moreplanes arriving at San Francisco than can be accommodated with available capacity. Second, the FAA andairline-traffic flow management-unit personnel do nothave academic training or practical experience in usingprobabilities for decision making. Indeed, importantforecast information that would be needed to applystandard techniques for decision making under uncertainty is not being provided to the users by the currentforecast.Making decisions by using well-defined probabilityforecasts (probabilities that can be manipulated by thestandard rules for probability use) involves the application of statistical decision theory. The key elementsin the context of this problem are (1) the available actions (e.g., ground-delay program parameters); (2) thepossible states of nature (the marine-stratus dissipationtimes); (3) the consequences for a given action takenwhen nature has some state (e.g., amount of delay,number of aircraft in a holding pattern); (4) the probability of the various possible states of nature, givensome measurements (these probabilities for variousstates would be generated by the San Francisco forecast algorithm); and (5) the strategy used to choose between the actions, given the forecast probabilities [9].It should be noted that there is extensive literatureon optimizing ground-delay program parameters, given a probabilistic forecast of the future capacity. Forexample, A. Mukherjee and M. Hansen show contemporary results and provide references to the past literature [10]. These studies did not explicitly consider thecost to air traffic personnel from too many aircraft in aholding pattern (e.g., if the ground-delay program wasended proactively in error). In addition, they generallyassume that the costs and benefits could be expressedby a combined metric such that the ground-delay program parameters could be optimized by using an expected loss criterion.These considerations suggest that a substantiallydifferent, risk-management-based approach to pre84LINCOLN LABORATORY JOURNALVOLUME 16, NUMBER 1, 2006sentation and use of the San Francisco probabilisticweather forecasts could increase their operational utility. Specifically, FAA traffic flow managers and airlineoperations managers need to be provided the expectedconsequences of ground-delay programs—given theforecast probability distribution of expected dissipation time. This operational consequences-orientedpresentation would include key factors such as expected average delays, expected unnecessary avoidable delay, average holding time, and probabilities of variousnumbers of aircraft (e.g., ten, twenty, or thirty) in airborne holding within the Oakland ARTCC for various ground-delay program options.In addition, we need to pay much more attentionto how to mitigate the risk of very late stratus dissipation events that would cause an excessive number ofholding aircraft. There are at least two elements to thisrisk mitigation: improved use of the daytime forecasts(e.g., 15Z, or 8 a.m. Pacific Daylight Time) to extenda ground-delay program that was put into effect inthe predawn period (e.g., 13Z), and developing a fairand equitable system by which San Francisco–boundplanes in a holding pattern would be diverted to analternative airport in the event that the number ofholding aircraft exceeds an agreed-upon threshold. Itshould be noted that the diversion option would haveto be developed in collaboration with the airlines. Thisalternative approach to decision making with the SanFrancisco probabilistic forecast has been proposed bythe Laboratory as an initiative for the FAA/AirlineCollaborative Decision Making program [11].The above experience in achieving operational benefits with what we would regard as a meteorologicallysuccessful probabilistic forecast for a situation in whichthe consequences of various actions are fairly well understood highlights the challenges ahead for the muchmore complicated problem of developing and utilizingprobabilistic forecasts of chaotic convective weathercapacity impacts.Route Availability Planning ToolDeparture delays during thunderstorms have beenidentified as a significant problem in the NAS. Thereport of the FAA/Airline Severe Weather SystemReview identifies airport departures during a SevereWeather Avoidance Plan (SWAP) as one of the five

evans, Weber, and MoserIntegrating Advanced Weather Forecast Technologies into Air Traffic Management Decision SupportKilometers 102major NAS severe weather prob2.5lems to be addressed [12]. LowTime of flight (min)departure rates when convectiveTEB – 202.0weather is within two hundredEWR – 22miles of the airports has been aJ95LGA – 23major problem for years at the1.5JFK – 27New York airports. S. Allan etStormal. found that increased depar1.0motionture rates when a SWAP was ineffect provided the highest New0.5York City ITWS delay reduction benefit during convectiveweather [7]. However, even withEWR0the ITWS in use, there were stillJFKTEBLGAmajor delays for departures, uding situations of gridlock on 102Kilometersthe airport surface due to the arrival rate exceeding the departureFIGURE 2. Potential interactions of released aircraft with thunderstorms in the Newrate for prolonged periods ofYork City area. The challenge is determining aircraft/weather intersections along specific routes at times in the future. The question raised at various times is “If at this timetime. A major problem was thean aircraft is released on this route, will it encounter hazardous weather?” The identilong time required to execute thefication codes for the New York City region airports are TEB (Teterboro), EWR (Newoperational decision loop shownark), LGA (LaGuardia), and JFK (Kennedy).in Figure 1 under circumstancesin which the departure capacitywas rapidly changing due to convective weather.Previously, ATM personnel had to answer theseOn the basis of feedback from the New York Terquestions by estimating flight profiles for departingminal Radar Approach Control (TRACON), Lincolnaircraft and comparing these to the ITWS forecast ofLaboratory developed a concept for a decision toolstorm locations, as illustrated in Figure 2. RAPT autothat would translate the convective forecasts into amates these mentally taxing calculations, making acprediction of the availability of departure routes as acurate departure impact predictions readily availablefunction of takeoff times so that ATC and airline deto the supervisors and air traffic flow managers for allcision makers could focus on ATM for departures asthe important routes in the airspace. The RAPT disopposed to interpreting ITWS thunderstorm forecastsplay shown in Figure 3 illustrates the tool’s usage forrelative to New York airspace structure.key westbound routes for the New York airspace.The RAPT combines thunderstorm forecasts withOperational Insights Based on RAPT Field Evaluationsan explicit model for pilot preferences in avoidance ofconvective weather, the structure of departure routesOperational evaluation of RAPT by New York Cityfrom the New York airports, and nominal flight timesITWS users commenced in August 2002 and has conto various locations on a departure route. These foretinued until the present. Our analysis of operationalcasts help FAA traffic managers and airlines answerusage is based on data gathered from four differentthree questions: Will a candidate future departure ensources: (1) references to RAPT in operational logs;counter hazardous weather at some point along its in(2) interviews of air traffic control personnel; (3) ditended path? Will there be opportunities to route therect observation of ATC operations in FAA facilitiesaircraft through significant gaps in evolving weather?during convective weather events; and (4) unsolicitedIf so, at what times can the aircraft depart to be able tocomments received from users via e-mail.utilize the gaps?In 2003, traffic managers used RAPT primarily toVOLUME 16, NUMBER 1, 2006LINCOLN LABORATORY JOURNAL85

Evans, Weber, and MoserIntegrating Advanced Weather Forecast Technologies into Air Traffic Management Decision SupportFIGURE 3. Route Availability Planning Tool (RAPT) display. The forecast movie loop display (upper region) showsanim

Integrating Advanced Weather Forecast Technologies into Air Traffic Management Decision Support VOLUME 16, NUMBER 1, 2006 LINCOLN LABORATORY JOURNAL 83 time steps that span the zero-to-six-hour window nec-essary for flight planning. These forecasts must include parameters that support quantitative characterization of airspace capacity.

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