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2nd USA/EUROPE AIR TRAFFIC MANAGEMENT R&D SEMINAR Orlando,1st - 4th December 1998

Terminal Routing Using Speed-control Techniques (TRUST): Initial Concept Evaluation Report

D. R. Barker, T. A. Becher, E. J. Blassic, S. P. Chase, J. L. Harding, and S. C. MohlejiCenter for Advanced Aviation System Development (CAASD)

The MITRE Corporation1820 Dolley Madison Blvd.

McLean, Virginia 22101(703)883-6000/Fax: (703)883-1911

AbstractThis paper describes some of the intrinsic

problems that lead to less than optimal TRACONoperations. It also identifies available technologyand proposed procedures that can be applied in asynergistic fashion to mitigate such problems via aterminal routing concept called TRUST. Theprototype development plan including verificationand validation activities is discussed along withprogress to date. Preliminary results are reported aswell as possible future applications of the TRUSTfunctions.

IntroductionProblem Description

PredictabilityVariabilityAircraft Equipage MixTRACON SpecificityDemand and Throughput Mismatch

Available TechnologyConcept Description

Predefined RoutesArrival PlanningSpeed AdvisoriesArrival and Departure CoordinationEn Route Metering Interface

Mapping of Problems to Solutions

BenefitsOperationalEconomicSafetyResults of Paper Study

Development PlanMethodologyEvolving and Iterative ProcessCore CapabilityVerification and Validation Role

ProgressDeveloped Core CapabilityVerification CompletedIndependent Verification and Validation

ResultsOperational AcceptabilityMetrics and Their DeterminationRoute DesignPath Comparison

ApplicationsProcedure EvaluationAir Traffic ManagementSpeed Advisory

SummaryReferences

Note: The contents of this material reflect the views of the authors.Neither the Federal Aviation Administration nor the Department ofTransportation makes any warranty or guarantee, or promise, expressedor implied, concerning the content or accuracy of the views expressedherein. 1998 The MITRE Corporation.This paper can be viewed at http://ATM-seminar-98.eurocontrol.fr/

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IntroductionDuring high traffic demand periods, arriving

aircraft may encounter significant delays at airports.The major contributors to the delays are largevariances between flight paths/times considered forplanning traffic flows and actual paths/times flown.

In this paper we report on the continuingevaluation of a concept which combines the use ofpredefined terminal routes with automation to reducevariation in terminal flying times. The predefinedroutes are defined from entry fixes to touchdown foruse by Flight Management System (FMS) and AreaNavigation (RNAV) equipped aircraft andunequipped aircraft. The automation system consistsof arrival and departure coordination, sequencing,scheduling and accurate flight time estimation, withspeed control effected via speed advisories to dealwith residual flight time variances.

This concept envisions a different end state fromprevious automation efforts [1,2,3] for the efficientcontrol of aircraft in the Terminal Radar ApproachControl (TRACON). The concept can be introducedin near term with changed procedures and ultimatelydeveloped evolutionarily towards a fully automatedsystem.

Problem Description

Predictability

The aircraft arriving at major airports in the U.S.typically follow Standard Terminal Arrival Routes(STAR)s from the en route transition airspace to theestablished fixes in the TRACON area. Aircraftnavigate these STARs using VHF omnidirectionalrange (VOR)/distance measuring equipment (DME).From the end of STARs to the final approaches, theaircraft fly under approach control using ad hocvectors (headings).1

The use of vectoring to achieve spacing creates asignificant difficulty for any automation system in

1 Similarly departing aircraft are vectored after take off toconnect to departure procedural routes.

predicting landing times, or indeed, times at othermeaningful nodes in the TRACON.

Variability

Compounding the problem of flying timeprediction are the variations in several systemelements. Included in these variations are errors inassessment of the wind field; differences innavigational precision and execution of maneuvers[4,5] from aircraft to aircraft; variation in pilotresponse and actions; and variation in controllergenerated clearance times. Any or all of thesevariables can lead to less than optimal spacing andtiming for aircraft arrivals or departures.

Wind Estimation and Prediction Error

Scheduling and planning algorithms rely uponpredicting flight times for a given path and altitudeprofile. Integral to flight time estimation isknowledge of the wind. Wind error, defined as thedifference between the forecast winds and the actualwinds, is a major source of perturbation in estimatingflight times.2

Navigational Precision

When each aircraft is vectored by the controller,there is inherently large variability in the paths.3 Thisis due to large flight technical error when in a manualmode of flight. Even among FMS equipped aircraftwith autopilot flying a given route, there can be somevariation in maneuver timing and the ability of theaircraft to capture the new course.

RNAV/FMS/Global Positioning System (GPS)equipped aircraft can perform point-to-pointnavigation. Precision in lateral navigation is requiredto maintain route conformance. Improved route

2 For example, consider an aircraft descending from15,000 ft to 10,000 ft while maintaining a constantindicated airspeed of 250 kts and descending through alinearly varying wind field with an initial magnitude of45 kts and a wind shear of 3kts/1000ft. Further assuminga tailwind, a 20% error in the estimated wind causes a4.5% error in the flight time estimate.3 Indeed, in lieu of other techniques for adjusting spacingthe controller can alter the spacing by judicious selectionof turns and timings of turn initiation.

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conformance reduces the differences betweenassumptions made during the maneuver planningversus actual execution of maneuvers. Onesignificant source of nonconformance is the executionof turns. RNAV/FMS equipped aircraft can executea smooth coordinated turn, whereas an unequippedaircraft may start a turn too soon or too latedepending upon the time the ground clearance isissued. Systematic differences in navigation can leadto unexpected and undesirable effects on subsequentspacing.4

Pilot Variation

Pilots do not all respond identically whenrequested to initiate a maneuver, whether it be a turnor deceleration. Variation is seen also by aircrafttypes, and even by airlines.

At Seattle, it was found that for FMS procedureswhich were designed with speed managementconstraints in mind, varying pilot techniques in theirexecution of the necessary speed reductionsintroduced an "accordion" effect. In other words, thespacing between aircraft was not uniform and flightcrew- induced "holes" or gaps were created in thetraffic stream [4,5].

Controller Variation

In today’s environment, final spacing of aircraftdepends upon the timely generation of clearances andthe hand off of aircraft from one controller to another.Sometimes there is a significant difference inefficiency between controllers [6].

A recent example of this was conveyed to someof the authors during a visit to the Seattle TRACON.At Seattle, there are two feeder controllers, east andwest, who hand off the aircraft to the final controller.The final controller must interleave all traffic streamson the final. The rates at which the feeder controllerscould provide a uniform stream of traffic to the final

4 One example gleaned from discussion with operationalpersonnel is that departing aircraft on vectors are oftenovertaken (separation reduced) when followed by FMSaircraft, since the FMS turns are typically smooth. Forarrivals, when an aircraft on vectors is followed by anFMS aircraft, an analogous situation can occur.

controller vary with ad hoc demand and anyabatement of this variation would improve operations.

Aircraft Equipage Mix

Contemplating the use of RNAV/FMS equippedaircraft to help reduce variability in some aspects ofthe control system, begs the question of howunequipped aircraft can be planned with a commonset of procedures. FMS operations at Seattleindicated some problems with merging equipped withunequipped aircraft (without additional automationaids).

Also, there were problems with sequencingsuccessive FMS arrivals from different starting pointsand the sequencing of FMS with other aircraft. Sincethe performance of FMS aircraft was “predictable”,controllers tended to work other traffic around them.This is not true integration of FMS technology intothe terminal area traffic management process.

TRACON Specificity

Wide differences in TRACON and airportspecific characteristics pose challenges to traffic flowplanning when attempting to use a generalizedsolution. Examples of site dependent operationaldifferences are:

• the number of runways and runway geometry• airspace restrictions due to noise and

adjacent or satellite airports• the coordination procedures between

surrounding en route centers and TRACONs• the percentage of operations under

Instrument Meteorological Conditions (IMC)versus Visual Meteorological Conditions(VMC) weather

Often traffic problems and flow managementsolutions grow up around a specific TRACON orairport and are not easily applied to or ported to othersites. There is always a trade off between solving aparticular operation's problems and being general,flexible, and adaptable. When evaluating candidatesolutions, it is important to be able to balance generalversus specific requirements.

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Demand and Throughput Mismatch

Arrival capacity for an airport is a function of thesum of required time separations between successiveaircraft in a continuous stream of traffic. The timeseparations depend upon the approach and landingspeeds of the aircraft and the distance separationsestablished based on wake vortex considerations forthe weight classes of lead/following aircraft.Depending upon the aircraft type pairs, the separationstandards vary among 2.5, 3, 4, 5, and 6 nmi.Without well defined paths all the way to touchdown,it is difficult to establish landing times and effectivesequences. Unless landing sequences are known, it isdifficult to determine time separations and thereforedetermine airport capacity. As such, the ATC systemuses hourly airport acceptance rates (AAR) or miles-in-trail restrictions based on individual operatorexperience to meter traffic to the airports. Theestimation of capacity becomes even more difficult ifthe runways are shared for both arrivals anddepartures. During time periods when traffic demandexceeds AARs, the aircraft are vectored not only fornavigation, but also for separation resulting inextended flight paths, increased flight times (costingfuel) and increased air/ground communications.

Figure 1 shows some actual track data fromSeattle. The tracks reflect the fact that Seattle is afour-post operation (FLAAK is for turbo-props only).Wide path variations in the turn from the downwindonto baselegs to final are a superposition of theproblems just described. The laboratory predefinedpaths are also shown in Figure 1 along with two FMSarrival routes designed and used at Seattle from theJAKSN and OLYMPIA fixes. The northeast JAKSNarrival has been in use whereas the OLYMPIA BayFMS route from the southwest was discontinued.

Available Technology FMS/RNAV equipped aircraft have the ability to

precisely navigate from point to point. A majority ofaircraft operating at major airports today haveRNAV. In order to better serve these aircraft in theterminal environment, the TRUST concept has beendeveloped. The concept is intended to improveoverall efficiency of operations at those airportswhere a significant number of aircraft are equippedwith FMS/RNAV.

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Figure 1 Illustration Of Variation In Paths Actually Flown. Also shown are the laboratory-defined routes and two FMS procedure routes developed by SEA-TAC.

Navigational precision will improve even morewith the advent of satellite based navigation offeredby GPS as more aircraft acquire GPS receivers. Anyimprovement in navigational capability, andsubsequently, route conformance, will increase theaccuracy of terminal operations planning and aircraftadherence to the plan, thereby maximizing airportcapacity.

Concept Description Each of the problems discussed in the previous

section can be mitigated through the application ofimproved procedures and appropriate technology,with a paradigm which at once exploits thattechnology and facilitates a more structured, more

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efficient means of operation. This paradigm isembodied in the TRUST concept which has itsfoundation in the Route Oriented Planning andControl (ROPAC) concept [7,8,9]. ROPAC and nowTRUST is designed to monitor aircraft progressagainst an established schedule and generate speedreduction advisories to be used by the controllers atappropriate times. Proper timing of the advisoriesenable aircraft to maintain schedule conformance bymitigating the flight time variances.

Predefined Routes

The concept assumes that aircraft fly from meterfixes to runway threshold via predefined but flexibleroutes. Efficient paths from the meter fix all the wayto touchdown are defined. Presumably FMSequipped, or RNAV equipped aircraft could navigatewithout guidance from the ground (ad hoc vectors orheading commands). Unequipped aircraft areexpected to be vectored by the controllers essentiallyalong the same route(s) as the FMS equipped aircraft.The routes are designed to be conflict free (laterally).Maintaining overall aircraft separation is still theresponsibility of the controllers.

Figure 1 shows the conventional flight paths forabout one hour of actual traffic at a busy airport.The aircraft enter the terminal area using STARs, andat some intermediate points as shown in the figure,the aircraft are vectored over downwind and/orbaseleg paths to their final approaches. Because thepilots can not turn after the end of STARs untilreceiving clearances from the ATC system, theaircraft paths vary over a large segment of airspacedue to overshoots and undershoots.

Since FMS/RNAV equipped aircraft cannavigate over any predefined path regardless of thelocation of navigation aids, if a route structure weredefined from the terminal area entry (meter) fixes tothe final approach, not only could the aircraft flighttimes be predicted accurately over different segmentsof flight, but also the aircraft could navigate preciselyto meet these times. This could enhance the en routemetering function’s ability to efficiently schedule

aircraft and minimize delays resulting from largeplanning uncertainties.

Arrival Planning

The TRUST logic acquires each aircraft as itenters the terminal area, and then determines anestimate of its flight time to threshold assuming thepredefined route, and considering winds and aircraftspecific performance parameters. This is done for allaircraft in turn. From the estimated flight times atentative sequence is determined. The sequence isused to establish a schedule, (i.e., scheduled landingtimes for each aircraft are determined) by applyingappropriate separation criteria based on wake vortexseparation considerations between lead and followingaircraft at the threshold, or when the aircraft areestablished on the final approach.

Speed Advisories

Having determined a scheduled landing time foreach aircraft, the TRUST logic continually monitors(on some regular time basis) the progress of therespective aircraft towards the threshold. Built intothe routes are segments where pre-established speedchanges will be made. The speed reduction process isbased on routine speed clearances issued by thecontrollers in the current environment. The nominallocation of the speed advisory points are chosen toexpedite each aircraft so that it flies as fast aspossible over the shortest paths to the final approach,in lieu of other constraints. Each time the TRUSTlogic monitors an aircraft, it calculates a newestimated landing time using a Flight Time Estimator(FTE). As deviations (greater than some thresholdvalue) are noted against the planned schedule, theTRUST logic moves the speed advisory point in anattempt to keep the aircraft on schedule. In thismanner, various perturbations (uncertain wind,aircraft non-conformance, reaction time delays, etc.)can be mitigated to keep aircraft on schedule. Speedadvisory points are illustrated in Figure 2.

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Figure 2 TRUST Laboratory Routes With Speed Advisory Locations.

Arrival and Departure Coordination

After allowing for speed controllability in theTRACON (discussed later), the desired terminal areaentry times are established and communicated to theTraffic Management Unit (TMU) in the center. Insituations where the departure times are known apriori, the departure time slots can be automaticallyinserted in the gaps in the arrival stream. For someaircraft, where landing times may need to be pushedback, their terminal entry times are adjustedaccordingly while the aircraft are still at higheraltitudes in the en route airspace. The slots fordepartures, popups, and reentry of missed approachescan be manually inserted into the schedule, andTRUST will recalculate the TRACON entry times forthe subsequent aircraft. If needed, TRUST allowslimited path extension for aircraft already on STARsin the TRACON. Once the departure times areestablished, TRUST can also compute the terminalexit times for coordination with en route using defined

paths and aircraft performance data. Time predictionat a departure “fix” are subject to large variationbecause of the variation in taxi times and in climbperformance for departing aircraft. However, earlyinformation on departures transmitted to the en routeCenter can improve management of traffic withcrossing traffic and overflights.

En Route Metering Interface

Desired “TRACON entry times” for arrivingaircraft are communicated to the en route meteringfunction based on the planned scheduled arrivals andthe known flight paths that the aircraft would follow.This would alleviate the need for vectoring aircraft.If needed, TRUST could also generate TRACON exittimes for the en route Center using the analogousalgorithms and updated aircraft performance database to include climb and acceleration parameters.

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Mapping of Problems to SolutionsTable 1 indicates the conceptual mapping of the

relevant perceived problem(s) to components oraspects of the TRUST concept that provide somedegree of solution. Associated with each problem andsolution are intermediary activities linking theabstraction to a solution of real world problems.

Benefits

Operational Benefits

The design of terminal and en route routes werepreviously tied to the physical location of groundbased navigation aids. With the advent of RNAV andFMS equipped aircraft, procedures can be developedwhich no longer have this dependency [5,10]. Moreflexibility in designing the routes is now availablemaking it easier for procedure designers to efficientlymeet noise and airspace constraints. The integrationof multiple routes with aircraft separation managedvia speed control would create a more uniform arrivalstream. Finally, due to the increased predictabilityand route conformance, design of procedures whichintegrate arrivals and departures, become viableproviding increased runway utilization, especially forshared arrival and departure runway operations.

Economic Benefits

Minimized Flying Times

The predefined terminal routes are designed to beminimum flying time paths subject to environmentaland ATC constraints. Aircraft following these routeswill have reduced TRACON flying times. Thereduced flying times result in fuel savings and alsoreduce aircraft direct operating costs.

Problem

Activity

Solutions

Predictability

• Route definition • Algorithmic

development

• Route "design" • Route integration • Wake vortex based

separations

Variability

• Training • Advisories

• Modified Procedures • Speed Control • Route Conformance • Estimation of Winds

Equipage Mix

• Identify sites withhigh FMS equipage

• Integrate RNAV,

FMS, and GPStechnology

• Develop procedure toaccommodate mixedequipage

• Does not require data-

link

TRACON Specificity

• Design modular routeand site independentdata structures

• Understand site

constraints for routes • Route (re-)design

• Flexible siteadaptation needs

• Algorithms are site-

independent • Route design tool

Demand Mismatch

• Identify mechanisms

for TRACON and enroute centerinteraction

• Involve TMC in

simulations andconcept

• Investigate transition

airspace tools

• Arrival management • TMC aid • Feedback optimal

entry times to enroute

• Arrival and departure

sequencing andscheduling

Table 1 Correspondence of TRUST toTRACON Problems

Improved Throughput

As mentioned earlier, gaps can occur in thearrival stream for a variety of reasons, the primarybeing the mismatch of demand to airport capacity.Application of the TRUST concept would close thesegaps so more aircraft could land per unit time,thereby increasing runway utilization. Given a priorideparture times, coordination between arrivals anddepartures would result in an optimal use fornaturally occurring gaps in the arrival stream. Gaps

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could be maintained or widened for purposes ofallowing for departures. A shared runway operationwould realize a larger gain in airport throughput.

Adaptability

The TRUST concept described herein could havedifferent operational instantiations. Some of thesepossible solutions would require new or enhancedsoftware. Deployment of software systems which arenot easily adapted to additional sites can be costly. Ithas already been demonstrated that this system iseasy to adapt to most airport configurations.Additionally, economic benefit would be obtained ifthe procedure development and deployment cyclecould be shortened. At airports where a majority ofaircraft are equipped with RNAV/FMS, TRUST mayexpedite the design, testing, and implementation ofroutes and FMS arrival and departure procedures.

Safety Benefits

Reduced Air and Ground Communications

Self-navigation will reduce the need forcommunication between the pilot and controllercurrently used to vector aircraft. This will allow thecontroller to focus on maintaining separations andallow the pilot more time to efficiently fly the aircraft.Reduced air and ground communication will reduceoperational errors due to miscommunication andalleviate some of the voice congestion. Also, routeconformance will naturally lead to a more orderly,safely separated arrival stream.

Reduced Workload

Clearing aircraft to fly a predefined routeprovides the controllers with additional time to focuson other air traffic concerns such as vectoring theunequipped aircraft. Because of reducedcommunication between pilots and controllers, thepilots will have more time to focus on their situationalawareness versus focusing on management of theaircraft.

Results of Paper Study

Operational data from a major airport trafficsample were analyzed as a baseline to determine

preliminary benefits of using the concept. Thefollowing Table 2 provides a summary of thesepreliminary benefits [8].

Item Results Average Delay Reduction per Aircraft 3 min

Average Fuel Savings per Aircraft 54 gal

Maximum Fuel Savings for One

Aircraft

338 gal

Increase in Runway Throughput 14%

Reduction in Number of Vectoring

Commands

30%

Table 2 Paper Study Estimates of Benefits

Precision navigation capabilities in conjunctionwith predefined terminal routes managed using speedcontrol provide a range of operational, economic, andsafety benefits. Development of procedures basedupon the TRUST concept would complement existingand planned decision support systems and, in turn,help these systems realize additional benefits [11].Table 3 summarizes the potential benefits fromapplying the TRUST concept.

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Benefits

Operational

Economic Safety

Procedure independent

of navaid location

Reduced flying times Reduced air-

ground

communications

Route design

flexibility

Improved Throughput Reduced workload

Arrival and departure

integration

Reduced

implementation and

maintenance costs

Reduced

TRACON/Center

coordination

Table 3 Qualitative Benefits of TRUST

Development Plan

Methodology

Part of the process of concept exploration andconcept development is the use of prototypes andsimulations to further define and refine technicalissues. A simulation has been developed forexploring the concept of defining new proceduresrooted in pre-defined terminal routes and speedcontrol. A connection is made between theconcept/possible solutions and the end state/perceivedproblems via a computerized model. Thecomputerized model provides a means for evaluatingpotential concepts as viable solutions. Verificationand Validation (V&V) plays a central role to thisevaluation process [12]. As a result, a V&V planwas developed as means of creating a solidfoundation for work progression and future success[13].

Evolving and Iterative Process

The V&V process is iterative and may expand orcontract according to the needs of the project and thepath taken. A V&V plan provides a valuable tool forresponding to project scrutiny since it is a standardtechnique embraced by the simulation and modelingcommunity. The path taken by a project as it evolvesfrom a concept to a laboratory prototype to a fieldprototype changes in response to environmentalstimuli.

Core Capability

In order to evaluate the feasibility of the TRUSTconcept, a core capability was developed to serve as alaboratory prototype of TRACON operations usingTRUST. The core capability was based on anexisting Air Traffic Control (ATC) simulationrunning on a UNIX workstation, which consisted of areal-time flight model, along with simulated controllerdisplay, and Pseudo-pilot capabilities. The TRUSTconcept was integrated into the existing legacysimulation [14,15] by adding a TRUST algorithmcomponent as illustrated in Figure 3. The followingsubsections describe the core elements of the TRUSTdesign. Basic algorithms for each function have beendeveloped with the intent of making site adaptationeasier.

Flight Model

PseudoPilot(s)

TRUSTspeed advisories

• flight time estimator• sequencer• scheduler• delay monitor• speed advisor

voiceController Display(s)

aircraft maneuvers

aircraft info

Figure 3 Schematic for Core CapabilityFunctionality Used for Concept Evaluation

Information Infrastructure

The information infrastructure used for buildingthe TRUST laboratory prototype is site independent.Capabilities already existed to simulate the terminalarea. These capabilities include the presentation ofsite-specific video map, aircraft with data blocks,system clocks, controller interactions via keyboardand trackball, controller communication to pseudo-pilots, and several modes of moving aircraft: routes,scripts, and flight trajectory models based on aircraftperformance data which are specific to aircraft type.

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Site Configurable Routes

The TRUST route structure was designed so thatit is not specific to any airport. The routes are brokendown into straight level and descent segments andturns, with speeds and altitudes defined for eachsegment. Adapting the routes for another site is assimple as defining a set of segments with latitudesand longitudes, with speeds and altitudes defined atthe beginning and at each endpoint. This flexibilitywas demonstrated when the TRUST prototype wasadapted to Brussels National Airport within a fewweeks.

Sequencing and Scheduling

Aircraft landing sequences and correspondingscheduled arrival times at the runway threshold areestablished by taking into consideration the desiredseparations among different weight classes ofaircraft. Departure slots are allowed to be built intothe arrival sequences/schedules by permittingcontrollers to interactively reserve departure slots atspecific times between the arrivals.

Speed Advisory Generation

Aircraft typically enter the TRACON at speedsabove 250 knots Indicated Airspeed (IAS), andreduce to 250 knots when they reach an altitude of10,000 ft. The ATC system typically uses two speedreductions to 210 knots and 180 knots in thedownwind/baseleg region. The aircraft reduce to thefinal approach speeds of about 150 knots before theouter marker. The same speed reduction process isused by the TRUST speed control logic5. Acontinuous descent from the terminal entry altitude tothe desired outer marker altitude is assumed todetermine flight levels at intermediate points along thedefined path segments, after properly accounting forsmooth turns and level decelerations.

The aircraft scheduled landing times are plannedon the assumption that the reduction to the nextpermissible speed along each path segment would beinitiated near the end of each path segment.Managing the speed control point to achieve an

5 The actual speeds are parameterized in the datastructure.

earlier speed reduction could correct deviations fromthe scheduled landing times. The speed controlalgorithm adjusts the current segment's speedreduction location to correct for delay. If delaycannot be alleviated by taking an early speedreduction in the current segment alone, the algorithmlooks ahead to future segments and shifts future speedreduction points as necessary. When an early speedreduction is needed in the current segment, anadvisory will be displayed to the controller. Thecomputer human interface (CHI) for this advisory ispreliminary and yet to be determined. One way tocommunicate the information to the controller is via adot which could appear on the screen. This indicatesan advisory to the controller to issue a clearancebased on the desired speed reduction over the flightsegment. The speed advisory information could alsobe shown in the third line of the data block on theradar display.

Estimation of Terminal Entry and Exit Times

TRUST computes the earliest landing time foreach aircraft using the defined route structure, windsand aircraft-specific parameters (speed profile,descent, deceleration, and turn rates) from anappropriate data base. A tentative landing sequencefor aircraft is established based on first-come-firstserved approach to the runway. The scheduledlanding time for the first aircraft is set equal to itsearliest landing time. The scheduled landing times forthe subsequent aircraft are derived by adding thedesired time separation between each pair of aircraftto the scheduled landing time of the lead aircraft. Adelay is defined as the time difference between theaircraft’s scheduled landing time and its earliestlanding time. In the case where the earliest landingtime of any following aircraft is later than itscomputed scheduled landing time, the scheduledlanding time is set equal to the aircraft’s earliestlanding time. A negative delay in such casesindicates a gap in the arrival stream. Analogous logicwould define TRACON exit times.

Flight Time Estimator (FTE)

The FTE is used to obtain flight time estimatesfor aircraft following the predefined routes. Eachroute is a union of straight line segments and turns.

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The FTE assumes the aircraft maintains constantindicated airspeed in descents and that the aircraftdecelerates at a constant altitude. Turns are alsoassumed to be performed at a constant altitude. Alinear wind shear model is considered to estimate theimpact of the along-track wind component [16]. Theinput parameters for the flight time estimationalgorithms are aircraft performance data (based uponaircraft type) and the route definition (planned flightprofile). Eventually the FTE algorithms will estimateflight time biases arising from composite sources andcorrect for these biases.

Flight Model

The flight model is used to update the aircraftstate in the simulation. Based upon default settingsor user input, the flight simulation will update eachaircraft's state based upon various operational modes.In addition, the flight model was enhanced to includea trajectory-following capability, which could modelan aircraft flying in FMS or RNAV mode. A griddedwind model was implemented to be used by both theflight model and TRUST components. Furthermore,several error models were implemented in thesimulation, including from navigational errors,variation in pilot response time, controllers’ speedinstructions response time, and errors betweenforecast winds (used by flight time estimationalgorithms) and real winds (used by the flight model).

Scenario Generator

The Scenario Generator has the capability tocreate traffic scenarios either from prerecordedaircraft track data or by specifying scenarioparameters. To create a scenario from prerecordeddata, the Scenario Generator determines the times atwhich each aircraft is closest to a meter fix entrypoint. That time will be used for creating the aircraftin the scenario entering the system at that meter fix.If two aircraft are violating separation at the starttime, then they are separated according to separationrules. This capability allows the user to createrealistic scenarios based on what actually occurred inthe prerecorded data.

The Scenario Generator also allows the user tocreate a scenario based on the following parameters:

duration of traffic demand, arrival rate, percentage ofsmall, large, or heavy aircraft, of FMS/RNAV orunequipped aircraft, of arrivals over each meter fix,and a maximum meter fix delivery time perturbation.Once the input parameters have been selected, thetraffic scenario is generated by creating a successivesequence of aircraft and assigning them times on therunway. The runway times are based on wake vortexseparations, landing speeds and a specified intrailbuffer to allow for final approach deviations. Theaircraft are then assigned to the desired route andtheir time to fly the route is calculated. Then theaircraft time is projected back to the meter fix and thesimulation start time is calculated.

Once a scenario is created, any of the aircraft’sfields may be changed. The Scenario Generator willreestablish the rest of the scenario accordingly.

Verification and Validation Role

As an integral part of the development process ofTRUST, a formal Verification and Validation (V&V)Plan has been developed [13,17,18]. The V&V Plandefines numerous tests to be applied to the TRUSTlaboratory prototype. The verification tests ensurethat the algorithms and prototype are performing asdesigned. The validation tests indicate the suitabilityof the concept for meaningful ATC applications,viability of operations under what set of conditions.Validation includes controller-in-the-loop evaluations,which determine controller effective use of theTRUST generated information and display needs.

Results are reported on the robustness of thesystem within designed bounds assessed throughclosed-loop testing of simultaneous parametervariation. Sensitivity analysis parameters wereassigned to three different categories: conceptparameters, prototype parameters, and environmentalparameters. The prototype parameters are specific tothe computer model, the environmental parametersrefer to items which do not change radically and arenot the focus of the study; and the concept parametersare the key parameters of interest by determiningwhether the concept makes sense for a particular site.

The concept parameters are meter fix timeaccuracy, FMS/RNAV equipage ratio, accuracy ofwind information, and arrival rate/traffic density.

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Prototype parameters are intrail buffer, speedadvisory clearance time, speed advisory deliverybuffer, and the aircraft movement conformanceupdate cycle. Environmental parameters includetolerance of wind error, tolerance of navigationerrors, aircraft performance parameters,controller/pilot response delay, and surveillance error.

In controller-in-the-loop simulations, FMSequipped aircraft will fly their nominal routes withoutthe requirement for controller vectoring. Unequippedsimulated aircraft will be conventionally vectored.The ratio of FMS to RNAV equipped and unequippedaircraft will be varied to determine the level ofequipage that is necessary to make the concept work.Feedback from controllers on the issuance anddisplay of the speed advisories and specifically, torecord and study their reaction to a paradigm thatallows them to control aircraft via speed control withlimited vectoring contributes to an assessment of theconcept viability. After successful V&V, it isexpected to test the concept in an operationalenvironment using a field prototype.

Progress

Developed Core Capability

The initial prototype development will supportcontroller-in-the-loop evaluations which will notincorporate pop-ups or missed approaches. It isintended to support preliminary controller feedbackand highlight controller CHI issues versus pilot CHIissues [19].

The current core capability will support sensitivitystudies on:

• minimum percentage of FMS/RNAVequipped versus unequipped aircraft

• timing thresholds and buffers• navigational error• knowledge of winds• meter fix delivery time precision

The core capability will be extended to allow:

• changing sequences or changing schedules• creation of slots for pop-ups or missed

approaches

• conformance monitoring• enhanced speed advisory logic All of the components required to simulate traffic

and test the TRUST system response have beendeveloped.

Verification Completed

Before using the core capability to assess theoperational validity of the TRUST concept, it wasnecessary to verify that the algorithms for sequencing,scheduling, flight time estimation, speed advisorygeneration, trajectory-following and other functionshad been implemented properly in the simulationsoftware. To this end, a series of 16 verification testswere designed as part of a V&V Plan. For each test,the purpose of the test, basic methodology forconducting the test, and verification criteria weredefined. The tests covered all aspects of the corecapability, including: FMS/RNAV trajectory-following capability, error models, wind model,aircraft performance parameters, conversionsbetween indicated air speed and ground speed, flighttime estimation algorithms, and speed advisoryalgorithms.

In order to conduct the verification tests, a set ofoutput data was defined to be collected during eachverification run. The output data was parsed andanalyzed using a combination of Perl scripts and theMATLAB® software package.

The verification effort spanned a period ofseveral months, and was extremely useful inpreparing for laboratory validation activities.Preparation of the core capability for the verificationeffort uncovered some missing features thatsubsequently were implemented in the core capability.

For certain verification tests, initial results didnot match the Verification Criteria for passing thetest, which enabled developers to detect and correctbugs in the software. This led to an iterative processof de-bugging and re-executing the verification testsuntil the results achieved matched expectations. Ofthe 16 tests defined in the V&V Plan, 15 have beencompleted successfully [20]. The remaining test,which consists of a series of Monte Carlo studies, iscurrently in progress.

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Independent Verification and Validation

A personal computer (PC) based simulation hasbeen developed for exploring the concept of definingnew procedures for using pre-established routes inconjunction with speed control in the terminal area[21]. As a part of the Independent Verification andValidation effort of the TRUST concept andautomation, the PC-based simulation allows real andfast time simulation of route-bound aircraft receivingspeed control advisories to effect threshold spacing.The PC simulation includes many self- verifyingfeatures via animation linked to the movement ofaircraft and the response of the TRUST system. Thesimulation implements all algorithms independent ofthe laboratory prototype, usually in a simplified butconsistent form. The degree of simplification andresulting fidelity compared to results obtained fromthe laboratory prototype is itself interesting and auseful validation technique. The PC-based simulationcan be used for iterative, quick time studies and forthe rapid prototyping of new algorithms, methods orother ideas pertaining to validating the TRUSTconcept or its variants.

The simulations share some common datastructures (e.g., Automated Radar Terminal System(ARTS) data input, aircraft track recording, etc.) tofacilitate direct comparison of scenarios and tests.

Results

Operational Acceptability

Industry Feedback

The core capability has been used to demonstratethe TRUST concept to various stakeholders in theaviation community, including representatives fromFederal Aviation Administration (FAA)Headquarters, FAA Regional Offices, National AirTraffic Controllers Association (NATCA)representatives, National Airspace System (NAS)Users including (American Airlines, USAirways andComAir), industry representatives (including Airbus),and representatives from the international community.In addition, demonstrations of the TRUST conceptreceived wide exposure as part of an exhibit at the

Fall 1998 Radio Technical Commission forAeronautics (RTCA) Conference.

Reaction to the concept demonstrations has beengenerally positive. Some demonstrations haveprompted suggestions for new applications of theTRUST algorithms, or for ways of combining theTRUST concept with other tools such as theConverging Runway Display Aid (CRDA), which isbaselined in the ARTS, or Data Link.Demonstrations have also elicited comments on issuesthat may affect the operational implementation of theTRUST concept, including integration of pop-upsand missed approaches into the sequence,accommodation of dynamic re-routing due toweather, methods of handling aircraft that are out ofconformance with their assigned FMS/RNAV route,and issues surrounding the ability of en routecontrollers to meet assigned meter fix times with therequired accuracy.

Site Feedback

Concurrent with our simulation development andtesting efforts, we have continued our interactionswith staff and controllers at Seattle-TacomaInternational Airport (SEA-TAC), to betterunderstand their operations and to properly adapt oursimulation [22]. During the most recent site visit wewere able to use the PC-based simulation on a laptopcommuter to facilitate interactions with the staff andcontrollers. The reaction to the TRUST concept wasvery encouraging. The site interactions wereunanimous in indicating that the concept made senseand had merit. They recognized the opportunity tointegrate FMS/RNAV routes, rather than having towork unequipped aircraft around the routeconstrained for FMS equipped aircraft. They wereamenable to partial solutions; thought SEA-TAC wasan appropriate site; and wanted to be involved in thedevelopment of new procedures and automation.

SEA-TAC provided suggestions on route design.Furthermore, SEA-TAC has experience dealing withFMS aircraft and also has some experience with theuse of speed control on FMS routes. SEA-TACpersonnel explicitly indicated that they would beinterested in partial solutions (for example, improving

15

the coordination of the feeder controllers' hand-off tofinal).

Controller Feedback

A preliminary assessment of the feasibility of theTRUST concept was conducted in September 1998during a visit to the Center for Advanced AviationSystem Development (CAASD) by a controller fromSEA-TAC. The controller was shown ademonstration of the TRUST concept using thedeveloped core capability. The demonstrationincluded the initial assessment of TRUST routedesign for Seattle, and a sample traffic scenariocreated with the Scenario Generator.

The Seattle controller provided suggestions formodifying the TRUST routes to avoid noise-sensitiveareas, and to conform to current airspace restrictionswith respect to the altitudes at which aircraft shouldbe at specific points along the TRUST routes. Thecontroller also provided input on making the trafficscenarios more realistic in terms of typical levels oftraffic arriving at each meter fix, and more realisticmix of jets and props. In addition, other necessarysimulation features were discussed, includingrequirements for handoffs between controllers,specific pseudo-pilot functions, and specific displayfunctions. The Seattle controller did not have anyimmediate suggestions for changes or improvementsto the proposed CHI for displaying speed informationto controllers. He expressed an interest to gain moreexperience working with the simulation beforecommenting further.

Metrics and Their Determination

Controllability

An important metric for the TRUST automationis the amount of control (time adjustment to meetlanding time via speed control) in the system for agiven aircraft. All other things being equal, andrelying on no other control mechanism including routeextensions, the controllability would help define theminimum requirements for metering fix deliveryaccuracy to be dealt with by a control system such asTRUST.

For measuring the controllability6, a monitorlooks at the current status of the aircraft. It comparesthe estimated landing time (ELT) (obtained via theflight time estimator + clock ) to the scheduledlanding time (SLT) of the aircraft. Ordinarily, whenthe ELT and SLT are sufficiently different, themonitor will set the aircraft status accordingly, andthen the speed advisor (SA) will move the point (ineach of three SA segments per route) at which thespeed advisory is issued so as to minimize oreliminate the difference between ELT and SLT. Theextremes to which the SA point(s) can be moved,determine the amount that the flight time can beadjusted. The total amount that the flight time can beadjusted from TRACON entry to the final approachsegment is termed as the controllability.

The technique that was used to measurecontrollability is as follows. By design, the simulationincludes various extreme-test switches. One suchswitch is a monitor-status-override. This allows ascenario to be executed with the aircraft status set toone of the following values: nominal, on time, late, orearly. By comparing flight times between thescenarios executed with status equal "late" and statusequal "early" the amount of controllability is easilydeduced since the SA will be issued at the extremelimits for the respective cases. Using this technique,the estimates of controllability of the current lab-defined routes (refer to Figure 1) found are indicatedin Table 4.

EntryFix/

Route

Sector MeasuredControllability

(seconds) OLYMPIA SE 84

RADDY SW 92

JAWBN NE 53

JAKSN NW 61

Table 4 Estimates Of Controllability

The range of controllability measured andreported here is consistent with previous studies [23].

6 The results and methodology reported here are from[21] and are consistent with the laboratory prototype.

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All times were measured with a “leveldeceleration” model with nominal deceleration valuesof 50 kts/min and descent values of 350 ft/nmi [24].

The routes entering from the north (JAWBN andJAKSN) have less controllability, since the STARSturn directly over the baselegs to the threshold in thesouth operation we are prototyping (refer to Figure1).

Flight Time Variation

Another evaluation conduced as a part of theIV&V of the TRUST laboratory prototype concernsthe determination of how much flight time variationcan be introduced for a given route due only tovariation of the descent and deceleration parameters.The data represent over 100 hours of simulated time.

The TRUST flight time estimator makesassumptions about how the aircraft will fly (routeconformance, and values for deceleration and descentgradients, etc.). This begs the question “what if theaircraft does not perform as expected?” Can TRUSTprovide enough speed control to handle the flight timevariation? The conclusion from these simulationsshow that, all other things being equal, the range offlight time variations introduced by aircraft nominaldeceleration and descent performance is well withinthe measured controllability over the routes tested(OLYMPIA, RADDY, JAWBN and JAKSN).

These results were consistent across threedifferent variants of the flight model(s) that wereimplemented— (1) simultaneous7 deceleration &descent allowed, (2) "level decel"— aircraft levels offduring any deceleration phase with 100 feet/nmimaximum downward drift during the decelerationphase, and (3) truly level descent (i.e., zerodownward drift during any deceleration phase). Routeconformance and final approach performance washeld constant for all tests.

Note that these tests were performed with thespeed advisor "locked" at the nominal positions for all

7 Some combinations of deceleration and descent valuesfor a given route will not necessarily result in concurrentexecution of the deceleration and descent, but should they"overlap," simultaneous/independent decelerations anddescents are allowed.

aircraft, i.e., all aircraft received the decelerations atexactly the same points on the routes. In effect thespeed advisor is "turned off." Otherwise, TRUSTwould have been affecting the flying times by tryingto keep the aircraft on schedule, which would haveobscured the measurement in question. The findingsare summarized below:

• All flight models show, that for a reasonableassumption for the performance envelope, theflight times changed by no more than 20-30seconds.

• Whether one models "level deceleration" or"truly level deceleration" as defined here,makes very little difference in flight times.However there are significant differences inthe level deceleration model flight times vs.the simultaneous deceleration/descent model.

• The variation is exceeded by the measuredcontrollability.

While conducting these tests we noticed that notall nominal aircraft performance values allowed theaircraft to "fly the lab-defined routes". The aircraftcould not complete the planned flight profile byadhering to the assumptions of the profile. Theassumptions are that an aircraft must complete adescent or deceleration before initiating a turn, orbefore another deceleration and descent maneuverbegins.

Route Design

Approach to Route Design

An important result of the effort to date is thedesign and implementation of an adaptable routedefinition data structure [9]. Routes are specified bysegments characterized by the expected maneuversand are delimited by lat/lons. In effect, the route andmaneuver segments could be adapted to meet therequirements at a particular TRACON. Indeed, allTRUST algorithms built on this data structure (suchas the flight time estimator) are, at the computerimplementation level, oblivious to site specific routesand procedures. This approach has proved veryvaluable in the rapid prototyping, modularization, andverification of the system.

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Site Participation in Route Design

To begin development of the simulation ofTRUST for SEA-TAC, some reasonableapproximations were made to construct routesconsistent with observed aircraft flight paths for theoperation in question. Routes were constructed whichoriginated at the respective meter fixes and wereoriented (“vectored”) according to ground basednavigation aids (VORs). As appropriate, downwindand baseleg segments were laid out, and all routesjoined the extended final at a thirty degree angle ofintercept (please refer again to Figure 1).

Concurrently we began a study of theappropriateness of the lab-defined routes, both interms of their “flyability”— an aircraft performanceissue; and in terms of the particular constraints of thesite— an operational issue. Interactions with the siteconcerning the previous efforts to understand theirestablished FMS procedures were useful in helping toidentify design criteria for the routes.

The routes were also redrafted8 to moreaccurately account for site-specific noise abatementconstraints (see Figure 4).

Flyability of the Lab-Designed Routes

While conducting verification tests for thelaboratory prototype, it was noticed not all aircraftcould fly the lab-defined routes9 using nominalperformance values while adhering to the constraintsof the flight profile. The constraint were thatmaneuvers (turns, descents and decelerations) beindependent.10 The redesigned routes were thenslightly modified for flyability. In this regard thesimulation is clearly a valuable tool for evaluatingproposed routes.

8 There is no indication that the redesign as currentlyunderstood will change the conclusions reached hereregarding flight time variation and controllability. The"final" lab-designed routes will be compatible with site-specific constraints and with most aircraft performance.9 This fact was observed not only in the laboratoryprototype but in the independently developed PC-simulation and other analyses [25]. This is a goodexample of the benefits of the V&V process.10 Concurrent executions of descents, decelerations andturns are not modeled in the flight model software.

Route Adaptation

The general structure of the routes is notchanged, however to accommodate the siteconstraints and aircraft performance constraints, thesegment definitions (lat/lon, expected maneuvers,etc.) were changed. For example, some downwindsegments extended. The site-independent nature ofthe data definition allows the straightforwardadaptation of the relevant TRUST algorithms fromone site to another. Adapted simulations have beenimplemented already for Seattle, Brussels andPhiladelphia.

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Figure 4 Redesigned Laboratory Routes Consistent With Noise Abatement Procedures At Seattle.

Route Design Tool

Since it may be necessary to define new routes ormodify candidate draft designs for routes at aparticular site, CAASD has begun development of aroute design tool. In its simplest form it allows layoutand definition of a route structure with links to theFTE and flight model so that fly-ability can beconcurrently evaluated. An interface will bedeveloped that would allow online modification of theroute data structure being used by TRUST. This may

not only facilitate route design and exploration ofrelated airspace redesign issues, but also will providean opportunity to explore the notion of the dynamicmodification of the site route structure forapplications such as weather avoidance, pathextension, etc.

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Path Variation Comparison

A sample of track data from Seattle was used forcomparing actual flight times and distances basedupon current operations with the laboratory terminalroutes. Flight times and distances were computed foreach route along with flight times and distances foractual tracks associated with each particular route.Not surprisingly, the use of pre-defined routes whichoverlay the de-facto average path of arriving aircraftalong with RMS/RNAV self-navigation reduces theaverage path distance and time of aircraft flying frommeter fix to threshold; also— and this is the point:reduces the overall variability.11

The baseline data used for comparison wasobtained from SEA-TAC ARTS tapes and wascarefully filtered and reduced so that onlyrepresentative arrivals to runway 16L were analyzed.Tracks which had holding patterns or which did notsignificantly overlap the TRUST routes were notused. The actual track was assigned to theappropriate TRUST route based upon the closestmeter fix when the aircraft entered the TRACON. Inorder to obtain means for the variability analyses, theaverage routes lengths and variation were thencomputed and compared to simulated traffic flyingthe lab-defined routes as shown in Figure 1.

With a preponderance of FMS-equipped aircraftfor each route the variability (of both time anddistance) was reduced for aircraft flying the TRUSTroutes.

The following Table 5 indicates the statisticalcomparison (n=14) for the OLYMPIA route (fromthe southwest). Data from the other routes are notreported statistically due to small sample size.

11It is a premise of the TRUST concept that similarreductions in variation would be seen regardless of theactual positioning of the routes.

OLYMPIATRUSTRoute

σARTS Baseline

σTIME (sec) 17 103

DISTANCE (nmi) 0.6 4.4

Table 5 Standard Deviation of Flight Times andDistances

In the future we will repeat the comparisons withcontroller-in-the-loop simulations.

ApplicationsThe components of the TRUST concept and

associated automation can be selected according tothe needs and requirements of ATC applications.There are three basic modes in which TRUST canoperate: Procedure Evaluation, Air TrafficManagement, and Speed Advisory.

Procedure Evaluation

There are four subactivities that define theprocedure evaluation mode.

Controller-in-the-Loop Simulations

TRUST can be used to facilitate the evaluation ofthe impact of new routes and procedures usingscenarios based on the prerecorded flight operationsdata. After it is determined in a lab environment(using a controller-in-the-loop mode of thesimulation) that the procedures are effective andusable by the ATC operators, the core capabilitycould be used to familiarize the air traffic managersand planners. The procedures could then beimplemented for actual operations.

Training

Used in an offline setting, TRUST is valuable forassisting controllers to become proficient with use ofspeed control. With all routes integrated by theautomation and correlated by the adopted procedure,controllers can learn techniques and skills to usespeed control on route-bound aircraft, includingunequipped aircraft, and become comfortable with anew paradigm of control.

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Route Definition and Evaluation

Route design requires collaborative effort of theairlines and the site. Often the process is iterative.Routes must be constructed that satisfy the needs ofboth parties, and meet the particular constraints ofeach. Use of TRUST can facilitate the interaction andcan be used to evaluate the performance aspects ofthe routes.

Terminal Airspace Design

Extending or applying the route design capabilityfurther, it is clear that automation tools such asTRUST can be used as part of the larger problem ofairspace design. The connection or extension ofSTARS to FMS-like routes would facilitate thesimplification of the overall terminal structure.

Air Traffic Management

Passive Mode

In this mode, the TRUST algorithms require onlya one way real time data feed from the AutomatedRadar Tracking System (ARTS). Live traffic is seenand evaluated by the TRUST automation accordingto the pre-defined route structure so that schedulesand sequences are indicated. This simple level ofsituational awareness is apparently useful at somesites. In particular this is the design requirement forthe Brussels application of TRUST. The ATCoperators could use these times to regulate the flow of

traffic in and out of the terminal area to minimizedelays at the airport. In effect, a TMC positionutilizes the improved view of the evolving traffic forplanning purposes resulting in a more efficientoperation.

Arrival and Departure Coordination Mode

Taking the planning capability one step further,an external processor with a graphical user interfaceallows interactive operator (typically the TMC)inputs to reserve slots for departures, unmeteredaircraft, and missed approaches, as well as displayaircraft schedules and en route/terminal transit times.Table 6 illustrates the interface for displaying theschedule.

Speed Advisory

This mode, as originally conceived in theROPAC paper, allows information on speedadvisories to be communicated to the controllersthrough an interface with ARTS. This modefacilitates keeping all aircraft on schedule resulting ina more efficient operation. Controllers can expectequipped aircraft to maintain their route-boundapproach, thus reducing the workload to theinteraction of speed control for those planes.Meanwhile the controller is free to vector anyunequipped aircraft for route conformance.Unequipped aircraft also get speed advisories.

ACID Type Route Class # Delay SLT SDT ARRIVAL

Spacing

DLH4306 EA32 KLENE H 1 -11 00:23:44 -- --

SAB756 ARJ TOLEN H 2 -2 00:26:31 -- 167

DLH5198 CRJ KLENE H 3 0 00:28:27 -- 117

FIN817 MD80 KLENE L 4 10 00:30:47 -- 140

SAB415 B737 DEPARTURE L -- -- -- 00:32:37 --

DLH516 CHJ DEPARTURE H -- -- -- 00:34:07 --

SAB465 BA46 KOKSY L 5 34 00:36:32 -- 345

Table 6 Facsimile of Arrival and Departure Interface

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TRUST coordinates the integration of all routes andall aircraft, equipped or not. Computer humaninterface evaluations are planned to determine how tobest present the speed advisory information on thecontroller displays.

Summary

The typical TRACON presents challenges withrespect to managing the arriving aircraft (anddepartures) so as to reduce variability, improvepredictability, and optimize time-varying demand andcapacity. The TRUST concept allows a synergy ofavailable navigation technology (FMS, RNAV, andsoon GPS) and new procedures (terminal routes) tofacilitate a different and more efficient end state forthe TRACON operations. Aircraft self-navigatingpredefined routes are integrated with unequippedaircraft which receive controller vectors, and allaircraft are monitored with respect to a schedule, withresidual timing perturbations mitigated via speedcontrol. A simulation environment has been created toevaluate the possible application(s) of TRUST. AV&V Plan is being followed to determine theconditions under which TRUST can be applied and todemonstrate operational acceptance. Preliminaryresults indicate that the concept has merit.

References

[1] Denery, D. G., Erzberger, H., Davis, T. J., Green,S. M., McNally, B. D., Challenges of Air TrafficManagement Research: Analysis, Simulation, andField Test, AIAA-97-3832, AIAA Guidance,Navigation, and Control Conference, New Orleans,Louisiana, August 1997.

[2] Erzberger, H., and Nedell, W., Design ofAutomated System for Management of ArrivalTraffic, NASA Technical Memorandum 102201,Ames Research Center, June 1989.

[3] Lee, K. K. and Davis, T. J., The Development ofthe Final Approach Spacing Tool (FAST): ACooperative Controller-Engineer Design Approach,Journal of Control Engineering Practice, Vol. 4, No.8, August 1996, pp. 1161-1168.

[4] Davidson, T., Letter to Frank Alexander,Chairman of Seattle Flight Management SystemDemonstration Project, July 12, 1994.

[5] Alexander, F., Seattle FMS Project Objectivesand Benefits, Northwest Airlines, July 9, 1993.

[6] Forman, J. M., 10 April 1998, Terminal AreaOperations and Needs, F045-M-022, The MITRECorporation, McLean, VA.

[7] Mohleji, S. C., June 1989, Route OrientedPlanning and Control for Terminal Automation,MTR-88W00223, The MITRE Corporation,McLean, VA.

[8] Mohleji, S.C., 1996, A Route-Oriented PlanningAnd Control Concept for Efficient Flight OperationsAt Busy Airports, Control Engineering Practice, Vol.4, No. 8, pp. 1143-1151.

[9] Barker, D. R., Becher, T. A., Chase, S. P, andHarding, J. H., September 1997, Flexible TerminalRouting: Concept Description and PrototypeDesign, MTR-97W0000108, The MITRECorporation, McLean, VA.

[10] Boan, L. M., Sanders, S. and Mohleji, S. C.,1998, FMS/GPS/RNAV Routes in the TransitionAirspace Briefing Book, WN-98W0000052, TheMITRE Corporation, McLean, VA.

[11] Hunter, G., et. al., July 1996, CTAS ErrorSensitivity, Fuel Efficiency, and Throughput BenefitsAnalysis, Seagull Technology, Inc., Cupertino, CA.

[12] Defense Modeling and Simulation Office, 1996,Verification, Validation, and AccreditationRecommended Practices Guide, U.S. Department ofDefense, Washington, D.C.

[13] Becher, T. A. and Barker, D. R., September1997, Flexible Terminal Routing: ConceptValidation and Prototype Verification Plan, MTR-98W0000029, The MITRE Corporation, McLean,VA.

[14] Taraken, R. M., Huang, C. L., Pollio, C. L.,1992, Integration and Interaction Laboratory Initial

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Experimentation Capability: Terminal/TASF, MTR-92W0000192, The MITRE Corporation, McLean,VA.

[15] Harding, J. L., and Chase, S. P., September1996, Transition from En Route to TerminalAirspace: Operational Concept Exploration,WN960000120, The MITRE Corporation, McLean,VA.

[16] Etkin, B., 1972, Dynamics of AtmosphericFlight, New York, Wiley.

[17] Law, Averill M. and W. David Kelton, 1991,Simulation Modeling and Analysis, Second Edition,McGraw Hill, Chapter 5.

[18] Sargent, Robert G., 1992, Validation andVerification of Simulation Models, Proceedings ofthe 1992 Winter Simulation Conference, ed. J.J.Swain, D. Goldsman, R. C. Crain, and J. R. Wilson,p.104ff.

[19] Lee, K., K., Sanford, B. D., and Slattery, R. A,August 1997, The Human Factors of FMS Usage inthe Terminal Area, AIAA Modelling and SimulationTechnologies Conference, New Orleans, LA.

[20] Harding J. L., September 1998, Results ofVerification of Terminal Routes Using Speed-controlTechniques (TRUST) Laboratory Prototype, MTR-98W0000123, The MITRE Corporation, McLean,VA.

[21] Barker, D. R., December 1998, PersonalComputer Based Simulation of Terminal RoutingUsing Speed-control Techniques, MTR-98W000130,The MITRE Corporation, McLean, VA.

[22] Barker, D. R., T. A. Becher, September 1998,Transmittal of Supplemental Deliverable “TripReport: Visit to Seattle-Tacoma InternationalAirport,” F045-L-076, The MITRE Corporation,McLean, VA.

[23] Vandevenne, H. F. and Andrews, J. W., 1993,Effects of Precision and Terminal Controllability onRunway Throughput, Air Traffic Control Quarterly,Vol. 1(3), John Wiley & Sons, Inc.

[24] Hunter, George, January 1992, Aircraft FlightDynamics in the Memphis TRACON, SeagullTechnology, Inc., Sunnyvale, CA, TM92120-01.

[25] Becher, T. A., September 1998 AircraftPerformance and TRUST Route Design, F045-M-045, The MITRE Corporation, McLean, VA.