1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
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Design and Operational Evaluation of the Traffic Management Advisorat the Fort Worth Air Route Traffic Control Center
By
Harry N. Swenson*, Ty Hoang*, Shawn Engelland*Danny Vincent¤, Tommy Sanders
Beverly Sanford£, Karen Heere¦
Summary
NASA and the Federal Aviation Administration (FAA) have designed and developed an automation toolknown as the Traffic Management Advisor (TMA). The TMA is a time-based strategic planning tool thatprovides Traffic Management Coordinators (TMCs) and En Route Air Traffic Controllers the ability toefficiently optimize the capacity of a demand-impacted airport. The TMA consists of trajectory prediction,constraint-based runway scheduling, traffic flow visualization and controller advisories. The TMA was usedand operationally evaluated for thirty-nine rush traffic periods during a one month period in the Summer of1996 at the Fort Worth Air Route Traffic Control Center (ARTCC). The evaluations included all shifts of airtraffic operations as well as periods of inclement weather. Performance data were collected for engineeringand human factor analysis and compared with similar operations without the TMA. The engineering dataindicate that the operations with the TMA show a one to two minute per aircraft delay reduction during rushperiods. The human factor data indicate a perceived reduction in en route controller workload as well as anincrease in job satisfaction. Upon completion of the evaluation, the TMA has continued to be a primarytraffic management tool of daily operations at the Fort Worth ARTCC.
1. Introduction
The growth of commercial air travel within theUnited States has put a severe strain on thenationÕs air traffic capacity. This coupled with theÒHub & SpokeÓ procedures used by the major aircarriers and the marketing requirements to take-off and land at optimum times has led to the needto improve the air traffic control system. Thereare two ways to increase the capacity of thesystem. The first is the building of more runways.Though this might be the obvious solution, theeconomic, geographic and political difficultiesmake this an undesirable solution for mostairports and communities. The second is theaddition of decision support tools that allows thecapacity to be more efficiently utilized. TheCenter-TRACON Automation System (CTAS) is aset of decision support tools being developed toimprove airport capacity and reduce delays while
maintaining controller workload at a reasonablelevel1.
CTAS is comprised of three major decisionsupport tools: the Traffic Management Advisor(TMA), the Final Approach Spacing Tool (FAST),and the Descent Advisor (DA). The goal of thesetools is to assist air traffic controllers efficientlymanage and control arrival traffic within theextended terminal area (100 to 200 miles fromtouchdown to landing). The core element of eachtool is the CTAS 4-Dimensional (4D) trajectorysynthesis algorithms2,3. These algorithms, similarto those used for Flight Management Systems(FMS) for modern equipped commercial airtransports, have a demonstrated 20 min.prediction accuracy of approximately 15 sec.root-mean-square error4. Each tool is beingdesigned to provide a level of automation andcapability that is not dependent on the other toolfunctions, but can work in concert to provideenhanced benefit. The primary capabilities of theTMA are time-based arrival traffic flowvisualization, strategic planning based uponaircraft separation and flow rate constraints, andlimited tactical ARTCC controller advisories formetering. The capabilities of FAST are to providelanding sequence and runway assignments thatassist Terminal Radar CONtrol (TRACON)controllers to efficiently manage arrival traffic inthe complex terminal environment5. FAST hasbeen operationally evaluated at the Dallas/Ft.
* Research Engineer NASA Ames Research Center Moffett Field, CA, USA¤ Traffic Management Supervisor Traffic Management Coordinator Federal Aviation Administration Fort Worth Air Route Traffic Control Center Fort Worth, TX USA£ Human Factors Engineer¦ Engineering Analyst Sterling Software Redwood Shores, CA, USA
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Worth airport and has demonstrated a 13%increase in airport throughput without asignificant increase in controller workload6. DA isbeing designed to assist en route controllers bygenerating accurate, fuel-efficient conflict-freeclearance advisories to meet TMA-generatedschedules2.
The primary users of the TMA are the TrafficManagement Coordinators (TMCs), whoseprimary function is to predict the ÒdemandÓ of airtraffic and the ÒcapacityÓ of their facility. TheTMCÕs key responsibility is to ensure theÒdemandÓ in excess of the facilityÕs capacity issafely and efficiently absorbed throughout theairspace. A simple definition of ÒdemandÓ is thenumber of aircraft destined to a common mergepoint within a facilityÕs airspace during a specifiedtime interval. Two obvious examples of mergepoints are the runway threshold and the TRACONgate/fix. The TRACON gate/fix is a position orarea through which the primary flow of trafficenters from enroute to terminal airspace. Thisposition will be referred to as a meter fixthroughout this paper. ÒCapacityÓ is the maximumnumber of aircraft that a facility can safelytransition through its boundaries during a givenperiod of time, usually measured as a flow rate orthe number of aircraft per hour. A facilityÕscapacity can be very dynamic and is heavilyinfluenced by weather conditions, runwayavailability, capacity changes of nearbyfacilities, and controller staffing level. Therealization of this complexity as well as thecurrent demand of the National Airspace System,has lead to the growth of the Traffic ManagementUnit (TMU) and TMC specialty.
A major problem the TMCÕs need to address is aphenomenon known as an air traffic ÒrushÓ. Arush is a period of time when the number ofaircraft destined to the same point exceeds thenumber that can be accommodated withoutsignificant delay and controller and pilotinteraction. During these rush periods TMCsimpose restrictions upon air traffic movement toinsure that a facilityÕs capacity is approximatelymet, but not exceeded.
The current tools available to a TMC to predictdemand are a combination of 1) historicalknowledge 2) radar derived positional informationfrom both the facilityÕs radars and the AirportSituation Display(ASD), which providesintegrated but somewhat limited radar informationfrom all ATC facilities and 3) the En RouteSpacing Program (ESP)/ Arrival SequencingProgram (ASP)7,8. These tools require a
significant amount of heuristics and guess-workon the part of the TMC to predict the current andfuture demand. The numerous uncertaintiesassociated with the National Airspace System(NAS) and air traffic movement in general makethis prediction a highly challenging task.
The demand prediction requirement of a TMC hasto be coupled with his/her understanding of afacilityÕs capacity. Capacity in arrivalmanagement is based on such physicalconstraints as runways, traffic mix, size ofusable airspace for traffic movement andweather. Also the TMC needs to consider theintangibles; which controller or controller teamsare working, how long they have been working,and the agreed-upon coordination with adjoiningfacilities. Again, there is limited information that aTMC can draw upon to make this capacityevaluation. Mostly the TMC uses historicalknowledge, experience and attempts to err on theconservative side. The tools that the TMCs haveat their disposal to affect the period of time whenthe demand exceeds capacity are flow reductiontechniques. The primary technique used is therequirement that the in-trail separation for aseries of aircraft is to be greater than the legalminimum of 5 miles; these restrictions are knownas miles-in-trail (MIT) restrictions. Some limitedresearch has been conducted to developautomation to assist in the efficient use of MIT9.The operational use of MIT restrictions is basedupon vast experiential knowledge and manyheuristics that are not mathematically tractable.The TMCÕs also have the ability to close or openparticular aircraft routings to affect trafficdemand. The final current tool available to theTMC is the ASP flow rate algorithm7. The tooluses demand predictions based upon the filedspeed and current ARTCC routing coupled to avery simple route from the ARTCC boundary to acommon point within the TRACON representingall runways, known as a vertex. Aircraft are thenscheduled to this vertex to meet an airportacceptance rate (AAR) without regard toseparation requirements or standards atindividual runways or adjacent dependentrunways.
This paper will present a brief description of theTMA and how it is used to optimize the capacityof a demand impacted airport. This will befollowed by a discussion and analysis of anoperational evaluation of the TMA conducted atthe Fort Worth Air Route Traffic Control Center(ARTCC) managing the traffic flows into theDallas/Fort Worth airport, the second busiestairport in the world10.
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2. TMA System Description
The TMA is a time-based strategic planning andcontrol tool that consists of trajectory prediction,constraint-based runway scheduling, traffic flowvisualization and controller arrival sequence,time and delay advisories. The TMA softwarecomponents are hosted on a network of modernUNIX workstations. A simple hardware/softwarediagram is shown in figure 1. On the left side isthe operational air traffic control system fromwhich the TMA receives aircraft track data, flightplans and various controller entries. These dataare passed to the communications manager (CM)for distribution to the prediction, scheduling andvisualization processes. The CM also transfersthe atmospheric data to the prediction andvisualization algorithms. The time predictionprocess generates estimated times of arrival(ETA) for all aircraft to the meter fixes and alleligible runways. This is the most computationallyintensive process and is a function of the numberof aircraft in the system. It was thus designed tobe scaleable with more computers. The figureshows four processors allocated for thispurpose. The ETA data are used with ATCconstraints to generate scheduled time ofarrivals (STA). The ETA, STA and otherinformation of interest are displayed in variousgraphic formats on the TMA displays. The CMalso transmits STA and ETA information back tothe operational ATC HOST computer in the formof aircraft sequence, scheduled meter fix andouter metering arc crossing times and delayadvisories to be presented on the controllersÕPlanview Displays (PVD).
Constraint-Scheduling
Communication-Manager-
&Host Interface
ATC-Host
Atmospheric-Data
Operational ATC TMA Workstations
ControllerPlanviewDisplay-
Flow-Visualization-and Control
TimePrediction
Figure 1. TMA simplified hardware/softwarediagram
2.1 Time Prediction
The time prediction algorithms are the foundationof TMA. The fundamental basis of the timeprediction process are algorithms designed forflight management systems of moderncommercial aircraft. The time prediction is
separated into two modules: the route analyzer(RA) and trajectory synthesis (TS). The RAgenerates, based upon user generated sitespecific adaptation logic and heuristics, a two-dimensional path from the aircraftÕs currentposition to its final destination. The complexity ofthis path is determined via the necessaryadaptation. This two-dimensional path is coupledby the TS with the aircraftÕs current energy stateand atmospheric data to calculate a fuel optimalfour-dimensional trajectory using aircraft specificmathematical performance models. ETAs areextracted from this trajectory for specific pointsof interest. The TS trajectories include all modesof flight including ascent, cruise and decent. Acomplete description of the trajectory synthesiscan be found in reference 3 along with predictionaccuracy performance measurements inreference 4.
Meter Fix
ATC Standard Arrival Routes
Outer Fix
Outer Metering Arc
Direct-to Route
Runways
Meter Fix to Runway Routing
Figure 2. Typical TMA routeing
The typical routing used by the TMA for ETAdetermination is the one which will generate theearliest time of arrival for a particular aircraft.This routing is referred to as the Òdirect-toÓ route.The direct to route extends from the aircraftÕscurrent location to the transition fix between theARTCC and TRACON (meter fix) as shown infigure 2. At the meter fix transitional routes aregenerated to all eligible runways based uponcurrent airport landing configuration. The figureshows the example of possible TRACON routingsfor an aircraft landing in a South flow airportconfiguration from a Northwest meter fix. Thesetransitional routes are also based upon theshortest possible path from the meter fix to therunway. The RA determines these potentialroutings based upon the adapted airportconfiguration information. As discussed earlier,the route information is used in the TS todetermine the earliest ETAÕs to the meter fix, an
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
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outer metering arc, shown in figure, and alleligible runways. The ETAÕs for each aircraft areupdated with each track or flight plan update.The grouping of the ETAÕs represents the arrivalÒdemandÓ on the runways, airport and meterfixes. This demand information is the inputrequired for the constraint based scheduling.
2.2 Constraint Scheduling
The constraint scheduling logic and algorithmsnecessary for the diverse operationalrequirements of ATC is beyond the scope of thispaper and will only be covered briefly. A completediscussion can be found in references 11 and 12.The functional logic for the scheduling algorithmis a modified first-come-first-serve (FCFS)algorithm. The scheduling constraints used tomodify the FCFS schedule are the factorsassociated with the separation safetyrequirements specified by FAA regulations. TheFCFS algorithm is coupled with delay reductionrunway allocation logic and a Center/TRACONdelay distribution function (DDF). The schedulingalgorithms ensure conflict-free schedulessimultaneously at both the meter fix and runwaythreshold or the final approach fix (FAF) duringvisual meteorological conditions.
2.2.1 Meter Fix ConstraintsScheduling is accomplished in a multi-stepprocess. First is the generation of an initialschedule to each of the meter fixes. Thesequence is determined based upon the earliestETA to the meter fix. The first aircraft in thesequence is scheduled at its earliest ETA. Thenext aircraft in sequence is then scheduled to itsearliest ETA or the time necessary to ensure in-trail separation constraints are met. The in-trailseparation constraints can be specified as anyvalue greater than or equal to the minimumseparation standards of 5 miles for similar aircrafttypes crossing the same meter fix to the sameairport destination. Thus an initial meter fixseparation based schedule is established for allfixes.
2.2.2 Runway ConstraintsScheduling to ensure required threshold or FAFseparation is met is the next major step. Thethreshold separation requirements are theminimum of the FAA wake vortex standardsbased on aircraft weight class. The TMC mayincrease these values due to weather or othersignificant events. The scheduling algorithmselects the first aircraft from each of the initialmeter fix schedules. From this group of aircraftan Òorder of considerationÓ (OOC) is generated by
using the ETA to the runway threshold. Theaircraft with the earliest runway is selected as thefirst aircraft of the OOC. Then, using the meterfix scheduled time of arrival (STA) and the meterfix to runway transition time, the first aircraft inthe OOC is scheduled to the threshold. The nextaircraft from that meter fix is added to the order ofconsideration for possible selection. The nextaircraft is scheduled using its meter fix STA,transition time and the specified thresholdseparation requirements. Once the second andsubsequent aircraft are scheduled, thresholdseparation delay is known. If this delay is greaterthan the Center/TRACON DDF then the amountgreater than the DDF is fed back to the meter fixSTA. The modified meter fix STA causesmodification to the aircraftÕs in-trail separationbased meter fix schedule. The process isrepeated until all aircraft are scheduled.
2.2.3 Flow Rate ConstraintsOnce these separation based constraints areconsidered the flow rate constraints areevaluated. The primary flow rate consideration isthe Airport Acceptance Rate (AAR). Flow ratescan also be placed on a particular runway, meterfix or even the TRACON as a whole. The AAR isnormally defined as the rate of aircraft permittedto land at the airport over a specified time period.This flow rate constraint is added becausecontrollers cannot land aircraft at minimumseparation for an extended period of time, due toworkload and other considerations. Among theseconsiderations that affect the selection of anAAR by a TMC are: airport ground movement orcongestion, departure demand, airspacecomplexity as well as the basic capacity factorsdiscussed earlier. The current scheduled flowrate is computed by a simple algorithm thatcounts the number of aircraft scheduled to landover an adaptable time interval. This scheduledflow rate is compared with the specified flow rateconstraint. If the scheduled flow rate during thespecified time interval exceeded the specifiedrate, the excess aircraft are pushed back into thenext time interval.
2.2.4 Runway AllocationThe runway allocation algorithm within thescheduling process is event driven. The eventsare (1) initial aircraft knowledge as determined byTMA receipt of an estimated or departed flightplan from the ATC computer; (2) a stable track-based ETA is determined; (3) freezing of theschedule prior to transmission to the ATC Hostcomputer for display on the controllersÕ PVDs. Ateach of these events the total system delayassociated with the particular aircraft scheduled
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
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to its current runway is compared with the totalsystem delay if the aircraft was allocated to analternate runway. The comparison includes anydelay incurred in the TRACON due to a longermeter fix to runway routing. The runwayallocation algorithms are controlled by TMCheuristics. These heuristics are captured inadaptation parameters that are a function ofairport configuration and aircraft type. Theparameters are eligible runways, primary,secondary, and in some cases tertiary along withthe amount of system delay savings necessaryto allocate to an alternate runway. Theadaptation can also be used to favor longerTRACON routes if it is beneficial for controllerworkload due to airspace complexity issues.
2.2.5 Center/TRACON Delay DistributionThe allocation of economically efficient delaybetween the Center and TRACON for commercialjet transports is discussed in references 11 and13. The basic premise is that the delaydistribution is a function of the uncertainty of theactual meter fix delivery time and fuel burn as afunction of altitude. Another key consideration,not discussed in the references, is efficientworkload distribution between the Center and
TRACON airspace. Delay is directly related tocontroller workload and the scheduler has aparameter that allows the delay distribution to beset between the Center and TRACON. The effectof the delay distribution is to place enoughpressure on the TRACON to maintain a fullyutilized final approach course throughout a rush.Typically the TMA DDF is set to maintain a 3 to 4aircraft final with the TRACON controllers usingheading and speed control. The effect of thedelay distribution in the Center is to postpone theonset of holding thereby reducing the overallamount of time that holding is required.
3.0 Flow Visualization
The TMC interaction with the TMAÕs timeprediction, schedule and delay information is agraphically based TMA traffic flow visualizationuser interface. Figure 3 shows a suite of fourTMA displays as installed at the Ft. WorthARTCC. The display formats are the timelines(lower left), load graphs (upper left), planviewdisplay (upper right) and linear list (lower right).The display formats are described in detail inreference 12. Each of the displays presentsdifferent views of the flow of air traffic in the
Figure 3. TMA display Suite at Ft. Worth ARTCC
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arrival airspace. The timelines display thepredicted arrival demand, schedule, and delay foreach aircraft in an analog format. The format is aseries of vertical lines with time reference to themeter fixes and runway threshold. The individualaircraft identification size and track status aredisplayed juxtaposed to the time-to-go reference.The bottom of the timeline is current time. Theload graphs display a running average of theaircraft demand, schedule and delay. The loadgraphs provide flow information that allowdemand size and duration to be determined. ThePlanview display provides a spatial display ofindividual aircraft track information. Theinformation is presented over scaleable chartoverlays of the Center and TRACON airspace.The final format is a list or tabular presentation of
demand, schedule and delay. This format wasdeveloped just prior to the operational evaluationand is similar to the existing ASP TMC displaywith color coding enhancements. Itsdevelopment was necessary to accommodatethe current TMC staff training, familiarity andextensive experience with the ASP format.
4.0 Controller Advisories
TMA generates controller advisories which aretransmitted to the operational ATC Hostcomputer. The advisories are displayedsuperimposed on the sector controller PVD as alist of aircraft designators in a time orderedsequence. The aircraft identifier is displayedadjacent to the scheduled crossing time and
Figure 5. Controller PVD with TMA advisories displayed
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delay to be absorbed. These advisories arereferenced to both the meter fix and outermetering arc for jet aircraft and only the meter fixfor low altitude turbo prop and prop aircraft. Onlythe advisories relevant to a specific sector aredisplayed on that controllerÕs PVD. The delaysare distributed between the sector controllersworking the jet traffic in both high (above 24,000ft.) and low altitude. The high altitude controllerabsorbs all but an adapted minimum amount ofthe center required delay where jet aircraft aremost fuel efficient. The delay distributed to lowaltitude controllers is for both workloaddistribution and to maintain pressure on theTRACON meter fixes to ensure a volume ofaircraft are available in the event that theTRACON determines that capacity can beincreased. The low altitude controllers are alsorequired to absorb delays associated with allother traffic.
The advisories are similar to those used currentlyby ASP with the following exceptions. Theadvisories are presented to the high altitudecontrollers in a single time ordered list referencedto the outer metering arc. The outer metering arcis at an adaptable fixed radial distance from themeter fix. The outer metering arc is usually 50 to60 n.mi from the meter fix. Figure 5 shows thecontroller advisory presentation to the outermetering arc on a sector PVD. The PVD is for theNortheast corner of the Ft. Worth Centerairspace. The advisory list is on the left side ofthe picture with AAL1557 as the first aircraft inthe sequence, currently crossing the outermetering arc. The photo was taken when theCenter was not engaged in flow control, thus thenegative delays indicate that no controller flowcontrol action is required. This presentation isdifferent from the current ASP advisories whichare referenced to outer fixes and presented inmultiple lists per arrival sector. Another TMAenhancement is the ability for the controller toswap or change sequence of the aircraft withinthe list for sector tactical considerations.
5.0 Evaluation Description
TMAÕs flow visualization elements and its timeprediction capabilities were evaluated at theDenver ARTCC and TRACON15. The studydocumented benefits associated with the TMAuse as it relates to TMC traffic managementdecisions. The evaluation conducted at the Ft.Worth ARTCC and DFW TRACON extends theprevious research and focuses on the time-based scheduling aspects and controlleradvisories. A complete description of the
evaluation along with its challenges are availablein the references 16 and 17. As described in thereferences, field evaluation of the TMA in anoperational ATC facility is opportunistic in nature.There are innumerable independent variablesover which the evaluator has little or no control.In response to this fact, a two-phase approachwas taken in the evaluation. The first phase wasdesigned as an engineering and suitabilityevaluation. The two goals were to operate theTMA and present controller advisories duringevery normal rush period, and then progresstowards the use of the TMA throughout eachoperational shift that required flow control.Systematic data collection was conducted duringthe second phase of the evaluation.
The first phase of the evaluation was conductedover a three week period followed by a two weeksecond phase. Both phases were conductedduring the summer of 1996. The evaluation teamconducted operations in the Traffic ManagementUnit (TMU) and the DFW arrival sectors in allareas of the Ft. Worth ARTCC. The controlleradvisories were transmitted to 8 to 12 sectorPVDs depending on Center configuration andstaffing. Human factor observers were stationedin the busy arrival sectors as well as the TMU.Engineering performance and human factors datawere collected throughout the evaluation. Theevaluation included a total of 39 rushes in whichthe TMA was used for flow control operations.Prior to and during the evaluation period,engineering performance data were alsocollected for rush periods when ASP was beingused for flow control. This data is referred to asÒshadowÓ data, and was collected withoutintervention with actual ATC operations.
The TMA is designed to allow flow controlschedules for multiple airports, however theevaluation concentrated on the arrivals into theDFW airport, the second busiest airport in theworld. The DFW TRACON used a four corner postoperation to land at the three primary DFW arrivalrunways. There were eight rush periods per daywhen the DFW airport demand required flowcontrol. Since the evaluation, this operation hasbeen modified to a dual arrival fix at each cornerpost. This modification was made to make moreefficient use of the increased DFW capacityenabled by the addition of a new runway.
6.0 Results and Discussion
The TMA operated successfully throughout theentire evaluation period. Because the evaluationwas conducted in an operational Air Traffic
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Control facility, considerable planning andprocedures were necessary to be able to react toa wide range of conditions16. Nevertheless, at notime during the evaluation were the backupprocedures necessary. The TMAÕs entireoperational envelope was explored during theevaluation period. The TMAÕs operationalenvelope went beyond their current ASP flowcontrol system, including periods of dynamicweather-related phenomena, and periods ofairport closure and reopening due to the passage
of storm fronts. The reason that the TMA canremain operational is that the TMA updates theprediction on every radar track update, whereasthe ASP system stops updating if its frozenscheduled arrival time passes current time.
A representative example of a rush period underTMA flow control is shown in figure 6. The plotshows the radar tracks for all arrivals to the DFWairport from 15:43 to 17:20 universal timecoordinates (UTC). The plot covers the airspace
x (n.mi.)
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.................
...............
.........................
.............................
DAL2062
..... ........ ... .......................... .. ...................... .............................................................................................................
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...........
...............................
AAL1560........................................................................................
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AAL1549
..........
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EGF920
.....................................................................................................
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EGF124
...
....
....
..
.........
.......
...........
........
..........
.......
.........
........
..........
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..............
......................................
AAL1176
.....................................................................................................................................................................................................................................................
ASE924
........................ ................. ........................................ ............... ............ ...... .. ........ ... ........ ............................................................................................................
DAL1074...........................................................................................................................................................................................................................................................................
AAL1308
...........................................................................................................................................................................................................................
AAL1472
..............................................................................................
........................................
AAL720
...........................................................................................................................................................................................................................................................................
EGF750
.........................................
...............
...........
...........
...........................
EGF696
... .... .......... ........................................
.............................................. ....... ........ ..........
.. ...... .. . . . .......... ...... ... ......................
...........................
..............
...........................................
DAL1262
.............................................................................................................................................................................................................................................................
EGF958
.......................................................................... . .. ...... ......... .......... ...... ... ....... ........................................................................................................
DAL614
.........................................................................................................................................................................................................
AAL420
........... .................................................................................................................................................................................................................................. ..
DAL1192
............ ..........................................................................................................................................................................
.......................
...........................
............
...............
................................
DAL756
..................................................................................................................................................................................
..............
.............
............
...............
............................................
AAL1887
..........................................................................................................................................................................
ASE633
......................................................................................
.......................... . .. ...... ......... .......... ...
... ... ....... ............... ........................
..........................
............
................................
AAL1428
. . ............................... ..............................................................................................................................................................................
DAL1086 ............................................................................................................................................................................
AAL1645
................................................................................................................................................................................................................
AAL841
..................................... ......................................................... ..................................................................................................................................................................
AAL488
.........................................................................................................
EGF708
........................................................................................................................
EGF508
........
.............................................................................................
.............
....................................
AAL724
....
....
....
....
....
...
............
........
.........
........
.........
..........
.........
............
................
..................
......................
AAL2078
...................................................................................................................... .....................................................................................
AAL1934
.............................................................................................................................................................................................................
AAL1396
. .... .... .......... ............................ ......... ........ ....................
...............
..................................................................................................................................................
AAL1864
............................................................................................................................................................................................................................................................................................
ASE645
.............................................................................................................................................................................................................
EGF634
...............................................................................................................................................................................................................
DAL2102
............................................................................................................
..........
..............
...............
.............
ASE722
....................................................................................................................................
EGF578
............... ....................................................... ...............................................................................................
AAL538
.............................................................................................................................................................
AAL2217
............................................................................................ ...... ... ......................................................................................................
DAL594
.....................................................................................................................................................................................................................................................................................
ASE603
................................
.........
.........
.........
.........
..........
..........
..........
...........
..............
......................................
DAL834
..............................................................................................................................................................................................
ASE695
.............. ......... .......... ...... ... ....... ...............................................................................................................
AAL1670
....................................................................................................................................................................................
DAL2118
.. ...... ......... .......... ...... ... .......................................................................... ...........................................
AAL552
................
.............
..............
...........
..............
................
................
..................
.............
...........
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ASE482
..............................................................................................................................................................................................................................................
ASE478.................................................................................................................................................................................
UAL359
...............................................................................................................
DAL161
..........................................................................................................................
.........................................................
ASE424
........................................................................................................
AAL1381
................
............................
......................................................................
...............................
..............
EGF078
.................................... ................................................................................................................................................................
DAL306
..........................................................................................................................................................................................
............
.............
.....
......
......
................
DAL431
.........................................................................
..............................................................
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.....
ASE494
..............................................................................................................................................
ASE414
......................................................................................
...................................................
...........
............
EGF390
.................................. ................................................................................................
AAL1406
...........................................
..............................
............................
............................
.......................
......................
EGF022
.....................................................................................................................................................................................................................
.............
......SCT2000
..................
................
..................
......................
................
..............
..................
.............
..............
..........
AAL535
..................................................................
.............
...........................................
DAL1194
............................................................................................................................................................
EGF728
..............................................
AAL70
...........................................................................................................................................
ASE442
..............................AAL296............AAL1928
...........................................................................
DAL1706
............................................................................................................................... ASE464
.............................................................................................................................
EGF710
...................................................................................
AAL1544
...............................
EGF664
........................................................................
EGF640
...............................................................
.......................
EGF824
................................
EGF544
...........................
....................
..
EGF792
................EGF532
..........EGF852
KH - Tue Sep 3 14:43:14 PDT 1996
Figure 6. Arrival radar tracks from Ft. Worth ARTCC to DFW airport
x (n.mi.)
y (n
.mi.)
440 450 460 470 480 490 500
200
210
220
230
..
..
. ..
..
. ..
..
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..
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......
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..
...
.. .
. . . .. .
.
.
.
...
AAL1066
..
....
..
...
...
...
..
...
...
...
..
..
...
....
AAL1171 ...
............
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...
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...
.
.....
......
AAL1211..
..
..
...
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..
..
...
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....
.
.
..
AAL1223
..
.
..
. . ..
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...
..
..
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.. ..
AAL1256
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. ...
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AAL1268
...
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.....
AAL1295
..
..
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...
.
AAL1308
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......
AAL1356
..
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...
AAL1361
. . . . . . . . . . . . .. . . .
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.
AAL1396
...
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...
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AAL1411
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AAL1428
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...........
AAL1472
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......
AAL1502
....
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....
AAL1549
..
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AAL1554
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AAL1560.
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AAL1625
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AAL1645..
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AAL1714
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AAL1719
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AAL1752
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AAL1842
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AAL1864
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AAL1887
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...
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AAL1934
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.......
AAL1936.
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. .........
AAL1940.
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AAL1969
.. .
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AAL2012
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AAL2030 ..
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AAL2078
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AAL2213.
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AAL2217
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AAL410
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.........
AAL420.
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AAL486. .
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AAL504
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AAL535
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AAL579
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AAL606 .
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AAL720. .
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AAL724 .
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AAL807
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AAL841.
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AAL85
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AAL858.
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ASE414.
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ASE424
...
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ASE442.
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ASE478
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ASE482.
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ASE494
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ASE603
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ASE633
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ASE645.
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ASE671
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ASE695
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ASE722
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ASE924..
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DAL1074
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DAL1086. . ..
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DAL1192
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DAL1194.
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DAL1262.
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DAL1670..
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DAL2062
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DAL2102
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DAL2118
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DAL286
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DAL306
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DAL428
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DAL431
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.
DAL450..
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DAL594..
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DAL614
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DAL650
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DAL678
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DAL756.
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DAL759.
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DAL834
...
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EGF002
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EGF006
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EGF058
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EGF166
...
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EGF292
.
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EGF302
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EGF324
..
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EGF390.
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EGF526
..
..
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USA1217
Figure 7. Meter fix to runway aircraft arrival radar tracks
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
9
controlled by the Ft. Worth ARTCC (approximately 800 by 500 n.mi.), with the DFWairport at its approximate center. As can be seenin figure 6, aircraft arrive from all directions andmerge to the four meter fixes prior to TRACONentry. The figure also illustrates that ATCvectoring is being conducted prior to each meterfix, thus imposing traffic delay. The TRACONportion of figure 6 is expanded in figure 7. Figure
7 shows the tracks from the meter fixes to therunways. The DFW runways are also displayed.The tracks are shown only to the outer markerdue to an artifact of the radar data source. Ascan be seen in fig. 7 the final approach courseintercept point is extended to approximately 15n.mi. during the rush period.
Figure 8 shows individual aircraft delay as a
time (UTC)
Del
ay (
sec)
14000 16000 18000 20000
-100
0-5
000
500
1000
15:40 15:50 16:00 16:10 16:20 16:30 16:40 16:50 17:00 17:10 17:20 17:30
mean (all data) std dev
start.stat stop.stat
Figure 8. Aircraft delays for the sample rush
time (UTC)
Thr
ough
put (
10 m
in a
vera
ge)
010
2030
16:00 16:10 16:20 16:30 16:40 16:50 17:00 17:10 17:20 17:30
o
oooooo
oo
o ooo
ooooo
ooo
oooo
ooooooooo
o
oooooooo
o
oooo
o
oooooo
ooo
oooooo
ooooooooo
oooo
o
oooo
oo
oo
ooo
o
oo
ooo
oo
ooooo
o
oo
oo
oo
oooo
o
oo
oo
o o
AAR = 108/hr
Predicted ThroughputActual Throughput
Figure 9. DFW predicted and actual throughput with TMA
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
10
function of time. Delay is defined by using theaircraft's earliest ETA to the meter fix at areference time of 19 minutes from the meter fix(approximately 150 n.mi. from the meter fix). Thisearliest ETA value is then subtracted from theactual meter fix crossing time to determine delay.The delay for each aircraft is shown. The meandelay for all aircraft and the 1-sigma standarddeviation, averaged using a sliding ten minuteperiod, are plotted as a function of time. Thestart and stop references, determined as thetimes when the mean delay crosses the zerodelay axisThese references are used todetermine periods of time when significant delayis imposed on a large number of aircraft foranalysis.
The predicted throughput or ÒdemandÓ of the DFWairport is shown in figure 9. This prediction isbased on each aircraftÕs ETA to the runwaythreshold at the 19-minute from the meter fixfreeze point. The predicted, or demand,throughput, shown as a dashed line, representsthe number of aircraft with predicted arrival timeswithin a 10 min. sliding averaging interval. Thedemand on the airport shows a characteristicarrival rush. The rush starts with a steady state(pre-rush) demand of approximately ten aircraftper a 10 minute interval (60 aircraft/hour). Therush starts to ramp up from this steady statevalue at 16:25 to predicted arrival demand of 180aircraft per hour at 16:38. The desired AAR wasspecified by the TRACON as 108 aircraft per
hour, shown as a reference line on the plot. Thesolid line is the actual airport throughput orlanding rate. Note that for an initial period of time,the actual throughput exceeded the AAR. This isdone purposely and is called Òfront loading.ÓSince the airport has been operating below theAAR, exceeding the AAR by front loading permitsa faster buildup to the actual airport capacity.The front loading period lasts for approximately15 minutes during which the TRACON is landingaircraft at a rate of approximately 132 aircraft perhour. This front loading period is followed by thesteady state landing rate of 108 aircraft per hourfor the next 30 minutes. The amount of frontloading is controlled by the choice of theCenter/TRACON DDF. It is interesting to notethat this desired ATC response shows a classicwell damped second order dynamic systemresponse to a step function.
As discussed earlier, the TMA was used duringthe evaluation period for all DFW rush periods todemonstrate its adaptability to a wide range ofoperational situations. The TMA has beendesigned to provide an accurate, usable flowcontrol system to support safe and efficienttraffic management operations. The system alsowas being evaluated to determine if benefits wereprovided when compared to the existing ASP flowcontrol metering system. Because of theresource requirements of the evaluation, it wasnot possible to collect enough rush periods tomake a true statistical comparison for all rushes.
Number of Aircraft in Rush
Del
ay (
sec)
20 40 60 80 100 120
-200
020
040
0
·
-
-
·
-
-
·
-
-
·
-
-·
-
-
·
-
-
·
-
-
·
-
-
o
-
-o
-
-
o
-
-
o
-
-
o
-
-
· ASP corr. coeff. = 0.48o TMA corr. coeff. = 0.53
Figure 10. TMA and ASP statistical delay comparison for 11:30 am rush
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
11
Therefore the comparison results indicate trends.Shadow data was collected for all rushes.However, due to the complex nature of the ATCenvironment and the opportunistic nature of fieldevaluations, the comparison of the TMA and ASPfocused on the 11:30 am rush period. This periodwas chosen because the 11:30 am rush period isone of the more difficult to manage. The rushnormally starts with a moderate to heavy demandfrom the East and light traffic from the West. Thedemand direction then switches to be very heavyfrom the West with moderate traffic from theEast. This directional shift is one of the morechallenging problems for TMCs, and wastherefore chosen to stress the TMA for thestatistical comparison. During the weeks leadingup to the TMA evaluation, comparable data werecollected for the 11:30 am rush period when ASPwas operational. Figure 10 shows thecombination of all the delay data for the 11:30 amrush periods. The data is for rush periods whileeither the TMA or ASP was being used for ATCflow control. Figure 10 shows the mean delaysurrounded by the 1-sigma standard deviation foreach 11:30 am rush as a function of the numberof aircraft with in the rush. The ASP operationaldata are represented as a filled circle and theTMA data are shown as an open circle. The delaydata are shown as a function of the number ofaircraft within a rush. Linear regressions wereperformed on both the ASP and TMA datapointsresulting in 70 second average delay reductionfor the TMA operations. The data also showapproximately 30% reduction in the 1-sigma
delay distributions. This indicates that thedelays were more equitably distributed among theaircraft within the rush while using TMA.
A statistical comparison of the meter fix crossingtime accuracyÕs with TMA and ASP flow controladvisories is shown in figure 11. The plot showsthe mean difference and 1-sigma standarddeviation between the meter fix crossingadvisories and the actual aircraft crossing timesduring the 11:30 am rush periods. The plot showsthe crossing times were more precise with theTMA advisories, as demonstrated by the meanerror being much closer to zero and the 40%reduction in the 1-sigma standard deviation. Thefact that the mean and standard deviation of theerror was smaller using the TMA indicates that itsignificantly improves the controllers ability tometer traffic.
Human factor data were also collected from thecontroller staff and the TMC users both in theCenter and TRACON. The data consisted ofquestionnaire, observations, and post rushinterviews. The detailed results of this data will bepublished in the future and only highlights arepresented. The sector controllers indicated thatthe TMA considerably reduced the workloadassociated with metering based flow control. Themost significant reasons cited for the workloadreduction: 1) the development of a single outermetering arc reference for high altitude jetsectors, 2) more representative aircraft crossingsequences, 3) more accurate and realizable
Number of Aircraft in Rush
Cro
ssin
g tim
e A
ccur
acy
(sec
)
20 40 60 80 100 120
-300
-200
-100
010
020
030
0
·
-
-
·
-
-
·
-
-
·
-
-
·
-
-
·
-
-
·
-
-
·
-
-
o
-
-
o
-
-
o
-
-
o
-
-
o
-
-
· ASPo TMA
Figure 11. TMA and ASP meter fix crossing accuracy for 11:30 am rush
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
12
crossing advisories, 4) the added crossingadvisory feedback provided by the delaycountdown feature, and 5) the added ability tomodify the sequence of the meter list via thecontroller sequence swap function thus, allowingtactical considerations to be reflected in theadvisories. Facility personal also subjectivelyreported a 2 to 3 min. delay reduction while theTMA was in operation. The difference betweenthe data in figure 9 and this perception wasdiscussed during the post evaluation period whenthe analysis was shown to the controllers. Thecontrollers indicated that their experience spansthousands of rushes using ASP and that if TMAoperational data were collected over a similarnumber the results in figure 9 would be closer tothe 2 to 3 min. delay reduction value. TheCenterÕs TMCs reported that the time basedinformation provided by the TMA allowed them tobe more aware of the arrival situation within theCenter and TRACON airspace, and allowed themto be more proactive in their traffic managementactivities.
The TRACON TMCs reported that the accuracyand predictability provided by the TMA allowedthem to increase the airport acceptance rate byabout 5% from an average of 102 to a 108aircraft per hour. The TRACON TMCs alsoreported that using TMA for flow control provideda smoother traffic flow into the TRACON. Thisobservation is currently under analysis but, islikely due to two primary factors. First, theamount of delay assigned to be absorbed in theTRACON is directly controllable by a parameter inthe scheduler. Second, the TMA uses acontroller derived model of the TRACON runwayeligibility rules in its scheduling, thus theschedules are closer to actual operations.
The original evaluation plan called for the removalof the TMA at the conclusion of the evaluationperiod. However, due to the benefits observedduring the evaluation period and the positiveresponse from facility personal, the Ft. WorthARTCC, DFW TRACON, The National Air TrafficController Association (NATCA) and the AirTransportation Association requested that theFAA and NASA maintain the TMA in operation atthe Ft. Worth ARTCC and DFW TRACON. TheFAA and NASA agreed to support the TMAsystem until the FAA implements a system that isfully supported by the appropriate FAAoperational support organizations. This decisionhas led to significant challenges in systemdevelopment primarily due to the completeredesign of the Ft. Worth ARTCC and DFWTRACON Airspace. The Airspace was changed
to accommodate the opening of a new runway atDFW as well as projected traffic growth. Theairspace redesign was completed in October1996 after 10 years of planning and preparation.This change required the equivalent of adaptingthe TMA for a completely new Center andTRACON. Since, the TMA software was designedto be highly adaptable, it was operating when theDFW airspace change (a.k.a. DFW MetroplexPlan) was put in place on October 10,1996, andthe TMA has been used on a daily basis since.
7.0 Concluding Remarks
TMA, an air traffic control decision support toolthat integrates time prediction, ATC constraintbased scheduling, flow control visualization andcontroller advisories has been developed andevaluated extensively at the Ft. Worth ARTCC.The tool generates minimal delay advisories thatdistribute delay efficiently between Center andTRACON operations. The tool was used toachieve delay reductions of an average of 70seconds per aircraft when compared with currentoperations during periods when ATC demandexceeded capacity. The TMA also allowed theTRACON to increase the average airportacceptance rate by 5%. The system was utilizedfor all periods requiring flow control at Dallas/Ft.Worth Airport, the worlds second busiestincluding periods of dynamic inclement weatherconditions. The system reduced controllerworkload and increased traffic managementcoordinators arrival traffic awareness. The toolhas been integrated into the daily operations atthe Ft. Worth ARTCC and DFW TRACON facilities.
References
1. Erzberger, H.; Davis T. J.; and Green, S. M.:Design of Center-TRACON Automation System.Proceedings of the AGARD Guidance and ControlPanel 56th Symposium on Machine Intelligence inAir Traffic Management, Berlin, Germany, 1993.
2. Erzberger, H.; Tobias, L.: A Time-BasedConcept for Terminal Area Traffic Management.Proceedings of the 1986 AGARD Conference,No. 410 on Efficient Conduct of Individual Flightsand Air Traffic, Brussels, Belgium, 1986.
3. Slattery, R.; Zhao, Y.: En-Route DescentTrajectory Synthesis for Air Traffic ControlAutomation. American Control Conference,Seattle, WA, June 21-23, 1995.
4. Green, S.; Vivona, R.: Field Evaluation ofDescent Advisor Trajectory Prediction Accuracy.
1st USA/Europe Air Traffic Management Research & Development SeminarSaclay, France, June 17 - 19, 1997
13
AIAA Guidance Navigation and ControlConference, San Diego, CA, July 29 -31, 1996.
5. Davis, T. J.; Krzeczowski, K. J.; Bergh, C.:The Final Approach Spacing Tool. Proceedingsof the 13th IFAC Symposium on AutomaticControl in Aerospace, Palo Alto, CA, 1994.
6. Davis, T. J.; Isaacson, D., R.; Robinson, J.,E.; den Braven, W.; Lee, K., K.; Sanford, B. S.:Operational Field Test Results of the PassiveFinal Approach Spacing Tool. 8th IFACSymposium on Transportation Systems, Chania,Greece, June 1997.
7. Cherone, R.L.; Ostwald, P. A.: TrafficManagement Coordinator UserÕs Guide forESP/ASP. The MITRE Corporation TechnicalReport MTR-90W00111, Sept. 1990.
8. Sokkapa, B.G.: The Dynamics of Arrival FlowManagement. Journal of ATC, June 1987.
9. Synnestvedt, R.G.; Swenson, H.N.;Erzberger, H.: Scheduling logic for Miles-in-TrailTraffic Management. NASA TM 4700, Sept. 1995.
10. AdmistratorÕs Fact Book. Federal AviationAdministration, ABC-100, Feb. 1997.
11. Erzberger, H.: Design Principles andAlgorithms for Automated Air TrafficManagement. AGARD Lecture Series 200,AGARD-LS-200, Nov. 1995.
12. Wong, G.: The Dynamic Planner. NASATechnical Memorandum.
13. Hunter, G.; et. al.: CTAS Error Sensitivity,Fuel Efficiency, and Throughput BenefitsAnalysis. Seagull Technology, Inc. 96150-02,Cupertino CA, July 1996.
14. Traffic Management Advisor TMA ProcedureSummaries under Solaris Release 5.0.0t. AirTraffic Management Branch, NASA AmesResearch Center, Moffett Field, CA., January 31,1997.
15. Harwood, K.; Sanford, B.: Denver TMAAssessment. NASA Contractor Report 4554,October 1993.
16. Hoang, T.; Swenson, H.N.: The Challenges ofField Testing of the Traffic Management Advisorin an Operational Air Traffic Control Facility.Proceedings of the AIAA Guidance, Navigationand Control Conference, New Orleans LA, August1997.
17. Nichol,R.: Good Times at Ft. Worth Center.Journal of Air Traffic Control, Oct-Dec 1996.
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