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NASA Researchers Assist FAA with Initial NextGen Deployment
The Federal Aviation Administration (FAA) Traffic Management Advisor (TMA) Program Office recently requested NASA's assistance in improving features within the operationally deployed TMA, which is an important component in the achievement of NextGen goals.
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The Center air traffic controllers and Traffic Management Coordinators (TMCs) control arriving aircraft that enter the Center from an adjacent Center or depart from feeder airports within the Center. On the basis of the current and future traffic flow, the TMC creates a plan to deliver the aircraft, safely separated, to the TRACON at a rate that fully subscribes, but does not exceed, the capacity of the TRACON and destination airports. The TMC's plan consists of sequences and scheduled times of arrival (STAs) at the meter fix, published points that lie on the Center-TRACON boundary. The Center air traffic controllers issue clearances to the aircraft in Center so that they cross the meter fixes at the STAs specified in the TMC's plan. Near the TRACON, the Center controllers hand the aircraft off to the TRACON air traffic controllers.

Image of TMA Scheduling Reference Points. Click on the D-link for a detailed description.D
Figure 1

The Traffic Management Advisor (TMA) assists, but does not replace, the Center TMCs and air traffic controllers in several ways. TMA increases situational awareness through its graphical displays and alerts. TMA also generates statistics and reports about the traffic flow. In addition, TMA computes the undelayed estimated time of arrival (ETA) to the outer meter arc, meter fix, final approach fix and runway threshold for each aircraft. Furthermore, TMA computes the sequences and scheduled times of arrival (STAs) to the outer meter arc, meter fix, final approach fix, and runway threshold for each aircraft to meet the sequencing and scheduling constraints entered by the TMC. The TMA also assigns each aircraft to a runway to optimize the STAs. Although the TMA computes the STAs and runway assignments for each aircraft in Center, FAST may overrule these STAs and runway assignments when the aircraft enters the TRACON airspace. TMA continually updates its results at a speed comparable to the live radar update rate in response to changing events and controller inputs.

The TMA software suite consists of the following CTAS processes.

Communications Manager (CM)
The CM provides the communication and common database between each of the processes.
Radar Daemon
The Radar Daemon serves as the interface between CTAS and the air traffic control facility's host computer.
Weather Daemon
The Weather Daemon receives and processes live weather information from the National Oceanic and Atmospheric Administration (NOAA) or the National Weather Service (NWS).
Timeline Graphical User Interface (TGUI)
The TGUI receives input from and displays information to the TMCs.
Planview Graphical User Interface (PGUI)
The PGUI receives input from and displays information to the controllers and TMCs.
Route Analyzer (RA)
The RA computes the projected horizontal route that each aircraft will follow. This information is then passed to the Trajectory Synthesizer (TS).
Trajectory Synthesizer (TS)
The TS computes the ETAs and 4-D trajectory, including both the horizontal route and descent profile, for each aircraft.
Dynamic Planner (DP)
The DP computes the runway assignment for each aircraft and computes the sequences and STAs to the outer meter arcs, meter fixes, final approach fixes, and runway thresholds.
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An important feature of TMA is its ability to sequence and schedule aircraft to the outer fix, meter fix, final approach fix, and runway threshold in such a way as to maximize airport and TRACON capacity without compromising safety. In addition, TMA will assign the aircraft to runways to optimize the schedule. All of this activity takes place while the aircraft is in the Center's airspace (approximately 40 to 200 miles from the arrival airport). Moreover, scheduling of some aircraft takes place before the aircraft have even entered the Center's airspace as long as that aircraft's flight plan is received by CTAS.

TMA will schedule aircraft based on the aircraft's flight plan information that may be received as much as 90 minutes before the aircraft enters the Center's airspace. TMA will update these sequences, schedules, and runway assignments constantly to adapt to changes in the traffic situation, changes in the environment, or in response to inputs by the TMCs. This process of sequencing, scheduling, and assigning runways is described below.

Scheduling Events

TMA will reschedule all or some of the aircraft in response to various events. Some of these events will trigger a reschedule immediately. These immediate scheduling events are as follows.
  • Addition/deletion of a gate blocked interval
  • Addition/deletion of a meter fix blocked interval
  • Airport acceptance rate change
  • Change in the occupancy time or required separation distance at a runway
  • Gate acceptance rate change
  • Meter fix acceptance rate change
  • Super stream class redefinition or separation distance change
  • TRACON acceptance rate change
  • Addition of a meter fix sequence constraint
  • A Find Slot operation initiated by the TMC
  • A meter fix STA manually set for an aircraft by the TMC
  • A runway STA manually set for an aircraft by the TMC
  • A request by the TMC to reschedule one or more aircraft
  • Time passage of at least 6 seconds since the last schedule
In addition, other events are placed in a pending list for rescheduling later. Events in the pending list trigger a reschedule when an immediate rescheduling event is received. Pending rescheduling events also trigger a reschedule when a pending event of a different type is received. The pending list is processed and subsequently flushed. Pending rescheduling events are as follows.

  • Flight plan amendment that changes an aircraft's runway
  • Flight plan amendment that changes an aircraft's coordination fix
  • Aircraft's ETA is "hovered" (see description below)
CTAS receives the flight plans for aircraft before they become active, and an aircraft becomes active when its radar track is received. An active or inactive aircraft's Scheduled Time of Arrival (STA) is constantly updated until the aircraft's meter fix ETA is less than or equal to 19 minutes in the future. At that point, the aircraft's STA is frozen. This point 19 minutes in the future is known as the freeze horizon.
Example: Suppose it is 12:00 noon. The freeze horizon is located 19 minutes in the future at 12:19pm. Delta flight #678 has a meter fix ETA of 12:18pm which is less than 19 minutes in the future. Therefore, its STA is frozen. However, United flight #525 has a meter fix ETA of 12:20pm. This is more than 19 minutes in the future, so its STA is not frozen.

One minute later, at 12:01pm, United flight #525 has its STA frozen because its meter fix ETA of 12:20pm is now 19 minutes in the future.
If the aircraft was supposed to become active before it reaches the freeze horizon, but it is still inactive, then the aircraft's meter fix ETA is increased by a few minutes to keep it outside of the freeze horizon. When the aircraft's meter fix ETA is modified in this manner, the aircraft is said have had its ETA "hovered." When the aircraft finally becomes active, its STA will be frozen when its meter fix ETA becomes less than or equal to 19 minutes in the future.


An important part of the scheduling process is the construction of the sequence of aircraft. Aircraft are sequenced in first-come first-served (FCFS) order within each super stream class according to their meter fix ETA. A super stream class is a group of aircraft that share similar scheduling characteristics. Super stream classes are typically based on engine type (jet or prop), destination airport, and meter fix.

In addition, sequence constraints entered by the controllers and TMCs will override the FCFS order. Each sequence constraint involves two aircraft in the same super stream class, and each sequence constraint can be one of two types. The first type of sequence constraint is a direct sequence constraint. Such a constraint restricts one aircraft directly behind another aircraft in the sequence. The second type of sequence constraint is an indirect sequence constraint. This is a weaker constraint than a direct sequence constraint, and it restricts one aircraft anywhere behind another aircraft in the sequence. Other aircraft may be sequenced between these two aircraft without violating the indirect sequence constraint.

TMA also contains code to resolve sequence constraint conflicts. If sequence constraints are found to conflict with one another, then the sequence constraint with the lower priority at the time of the scheduling is ignored. If the sequence constraints are of equal priority, then the older sequence constraint is ignored. Note that conditions may change from scheduling cycle to scheduling cycle and may affect which sequence constraints are in conflict with each other. Thus, a sequence constraint might be obeyed during one scheduling cycle, but may be ignored during a later scheduling cycle due to changes in the situation.


Once a sequence to the meter fix has been determined, the scheduled time of arrival (STA) at the meter fix is computed for each aircraft. No aircraft is assigned an STA that is earlier than its nominal ETA to the meter fix. Moreover, the aircraft may be assigned an STA that is later than its ETA due to the scheduling constraints and its position in the sequence. The difference between the STA and the ETA is known as the aircraft's delay. The aircraft have their preliminary meter fix STAs computed in the order that they appear in the meter fix sequence computed above. For each aircraft, the aircraft's meter fix STA is set equal to the aircraft's nominal meter fix ETA. The aircraft's STA is then increased (thus delaying the aircraft) so that the aircraft's STA complies with all of the following scheduling constraints set by the TMC.

TRACON Acceptance Rate
The maximum number of aircraft per hour that can be scheduled to enter the TRACON.
Meter Fix Acceptance Rate
The maximum number of aircraft per hour that can be scheduled to cross a meter fix. Each meter fix has its own meter fix acceptance rate.
Gate Acceptance Rate
The maximum number of aircraft per hour that can be scheduled to cross any of the meter fixes contained within a gate. Each gate has its own gate acceptance rate.
Super Stream Class Miles In Trail Separation
Separation, in nautical miles, between aircraft as they cross the meter fix. Each super stream class has its own miles in trail restriction.
Meter Fix Blocked Intervals
Time intervals during which aircraft may not be scheduled to cross the meter fix.
Note that an aircraft's meter fix STA will be computed to comply with all of the scheduling constraints. This effectively means that the most stringent constraint will have the greatest effect on an aircraft's STA. However, which constraint is the most stringent one will vary from aircraft to aircraft.

Next, aircraft have their runway STAs computed according to an "order of consideration." This order of consideration is based on the order of preliminary meter fix STAs and the runway ETAs. The aircraft with the earliest meter fix STA within each super stream class is examined. From this set of aircraft, the aircraft with the earliest runway ETA is considered for scheduling to the runway. A rigid sequence at the runway is not possible because, under certain conditions, the runway sequence may conflict with the meter fix sequence. The order of consideration maintains the sequence at the meter fixes and gives preference to aircraft with earlier runway ETAs when computing the runway STAs.

For each aircraft in the order of consideration, the STA is computed to the runway such that the STA is no earlier than the sum of the meter fix STA plus the TRACON transition time. The TRACON transition time is the nominal time to fly from the meter fix to the runway if there were no other aircraft in the airspace. This is computed according to:

TRACON Transition Time = (Runway ETA) - (Meter Fix ETA)

The aircraft's STA is increased, thus adding delay, as necessary to comply with the following scheduling constraints.

Airport Acceptance Rate
The maximum number of aircraft per hour that can be scheduled to land at a particular airport.
Runway Acceptance Rate
The maximum number of aircraft per hour that can be scheduled to land on a particular runway.
Wake Vortex Separation
Separation, in nautical miles, between aircraft as they land. The amount of separation varies depending on the engine type and weight class of the two aircraft to be separated from each other.
Runway Occupancy Time
Additional time between arriving aircraft to account for various stopping conditions and the amount of time required by a landed aircraft to clear the runway.
Runway Blocked Intervals
Time intervals during which aircraft may not be scheduled to land.
These runway scheduling constraints are applied either at the runway threshold or at the final approach fix (FAF) depending on the airport configuration. For configurations associated with Instrument Flight Rule (IFR) conditions, the scheduling constraints are applied at the runway threshold. For configurations associated with Visual Flight Rule (VFR) conditions, the scheduling constraints are applied at the final approach fix. The other runway STA is computed by adding or subtracting (as appropriate) the nominal flight time between the two points. For example, under IFR, the STA at the runway threshold is computed to comply with the scheduling constraints. The STA at the final approach fix is then set to the runway threshold STA minus the nominal time to fly from the final approach fix to the runway threshold.

Heavy traffic conditions and bad weather can contribute to delays within the TRACON. The TRACON can absorb only so much of this delay. Therefore, some of this delay must be fed back into the Center airspace. An aircraft's delay at the runway is computed according to:

delay = (Runway STA) - [(Meter Fix STA) + (TRACON Transition Time)]

If this delay exceeds an amount preset for a particular TRACON, then the excess delay is added to the aircraft's meter fix STA. This will most likely delay other aircraft in the Center that are sequenced behind this aircraft. Their meter fix STAs will be increased as appropriate to meet all of the scheduling constraints while maintaining their position in the sequence.

Finally, once the final meter fix, runway threshold, and final approach fix STAs have been computed for all aircraft, the Outer Meter Arc (OMA) STAs are computed. There are no scheduling constraints at the OMA. Therefore, the OMA STA for each aircraft is computed according to:

OMA STA = (Meter Fix STA) - [(Meter Fix ETA) - (OMA ETA)] - AMDT,

where AMDT is the amount of delay to be absorbed in the low altitude approach sector.

Runway Allocation Events

TMA will assign aircraft to runways which reduce the delay of all aircraft in the system in a process known as Runway Allocation. From the TMC's point of view, it is undesirable to have an aircraft switch runways constantly even if this would continually optimize the schedule. Therefore, only certain events trigger the runway allocation process. Some of these events will cause an immediate runway allocation. These immediate allocation events are as follows.
  • Addition/deletion of a runway blocked interval
  • Change in the acceptance rate of one or more runways
  • Departure of an aircraft from an airport in Center
  • Aircraft is about to have its STA frozen
  • Change in an aircraft's priority status
  • Aircraft has been reset
  • Resumption of an aircraft that has been suspended from scheduling
  • A flight plan is received which changes an aircraft's gate
  • A flight plan is received which changes an aircraft's meter fix
  • A flight plan is received which changes an aircraft's destination airport
  • Receipt of the initial set of flight plans when TMA is first brought up
  • Manual request by the TMC to reallocate one, some, or all aircraft
In addition, other events are placed in a pending list for later runway allocation. Events in the pending list trigger a runway allocation when an immediate runway allocation event is received. Pending runway allocation events also trigger a runway allocation when a pending event of a different type is received. The pending list is processed and subsequently flushed. Pending runway allocation events are as follows.

  • Change in the airport configuration of an aircraft
  • Receipt of the first ETA for a new flight plan or newly active aircraft

Runway Allocation

The schedules computed by TMA can be optimized by allocating runways to aircraft to reduce delay. Although FAST will overrule any runway assignments made by TMA, TMA's runway assignments and schedules ensure that the Center schedules apply the right amount of pressure on the TRACON so that the TRACON's scheduling constraints are met but not exceeded.

The following describes TMA's allocation process in response to a given event. The event may either be a current event that requires immediate allocation, or an event that was taken from the pending list. (See Runway Allocation Events.)

Determine which aircraft require allocation.
Which aircraft are involved depends on the time of the allocation event, the type of event, and which runways have an increasing, decreasing, or steady acceptance rate as a result of the event.

If the event changes the acceptance rate of one or more runways, then the algorithm will allocate aircraft which were previously assigned to runways which now have a decreasing acceptance rate. The goal is to reduce overall delay by moving aircraft off of a runway with a reduced capacity. In addition, the algorithm will try to allocate aircraft from their previously assigned runways to runways whose acceptance rates are increasing. The goal in this case is to take advantage of a runway's increased capacity to reduce overall delay.

Runway Allocation Example
Runway Acceptance Rate Before Event
Acceptance Rate After Event Acceptance Rate Change Considered for Allocation
A 54 aircraft/hour 36 aircraft/hour Decreasing Yes
B 27 aircraft/hour 36 aircraft/hour Increasing No
C 40 aircraft/hour 40 aircraft/hour Steady Yes

The table above shows an example where various runway acceptance rates are changed as part of an allocation event. As a result of the allocation event, Runway A has a decreasing acceptance rate, Runway B has an increasing acceptance rate, and Runway C has an unchanged acceptance rate. Aircraft assigned to Runway A are considered for allocation since Runway A has a decreasing acceptance rate. At the same time, aircraft assigned to Runway C are considered for allocation because Runway B has an increasing acceptance rate. However, aircraft on Runway B are not considered for allocation at all since no other runway has an increasing acceptance rate.

The addition or deletion of a runway blocked interval will trigger a runway allocation. The algorithm treats adding a blocked interval to a runway the same as decreasing the acceptance rate of that runway. Similarly, the deletion of a runway blocked interval is treated the same as increasing the acceptance rate of that runway.

Finally, there are some events which trigger runway allocation for a single aircraft. For instance, when an aircraft is new to the system and it's runway ETAs have just been computed, then an allocation event is triggered for this aircraft. In this case, all available runways are considered during the runway allocation of a single aircraft.

Determine Allocation Mode.
The Allocation Mode is dependent on the event type. The mode directs the allocation algorithm to follow specific rules when allocating aircraft to runways.
For each aircraft, follow the site-specific allocation rules.
The first step is to determine the runway allocation category for the current aircraft. The runway allocation category depends on the aircraft's destination airport and the airport's configuration since these two pieces of data indicate which runways are available. The runway allocation category also depends on the aircraft's assigned meter fix because some runways are favored more when the aircraft crosses over one meter fix than when it crosses over another. Finally, the runway allocation category depends on the aircraft's engine type (jet, turbo-prop, or piston) and the runway allocation mode determined in the previous step.

Once the runway allocation category has been determined, the site-specific runway allocation rules corresponding to that category are followed. These rules give the order in which each runway is examined for the current aircraft. The aircraft is temporarily assigned to the runway which the rules say should be examined next. Subsequently, that aircraft and all aircraft following it are rescheduled (see Scheduling). The STAs of all of these aircraft are added together to arrive at the System Schedule Time. The allocation rules specify how much this System Schedule Time must be better than the System Schedule Time for the best runway trial-assignment seen so far. If this runway assignment is sufficiently better than the best seen so far, then this runway assignment becomes the best assignment seen so far. Note that the amount by which the current trial-runway assignment must be better allows the runway allocation algorithm to favor some runways over others within a runway allocation category. For instance, if it is determined that Runway X should be favored over Runway Y, then the rules for the current allocation category may specify that Runway Y may only be selected over Runway X if the savings in System Schedule Time is over M minutes.

Image showing Runway Allocation Considerations. Click on the D-link for a detailed description.D
Figure 2
The rules also specify which runways to consider for allocation. This is particularly important in cases where the acceptance rates of one or more runways have changed as a result of an allocation event. Referring to Figure 2, the aircraft on Runway A will consider both Runway B and Runway C for allocation because Runway A has a decreasing acceptance rate. Also, the aircraft on Runway C will consider Runway B because the acceptance rate of Runway B is increasing.

The rules work in a similar manner for runway blocked intervals. In this case, adding a runway blocked interval results in the same allocation rules as when the acceptance rate of that runway is decreasing. Also, removing a blocked interval has the same set of rules as when the acceptance rate of that runway is increased.

Compute a schedule using the newly assigned runways.
A schedule is computed for the aircraft affected by the allocation event (see Scheduling). During this scheduling process, the newly assigned runways are used.
A Schedule message is sent out containing the STAs just computed.

Each aircraft's airport configuration is updated.
As a result of the allocation and reschedule, the aircraft may end up on the other side of a configuration change event.
Flight plan amendments are sent to the other CTAS processes.
As a result of allocation and scheduling, the aircraft's airport configuration and assigned runway may have changed. For those aircraft that have changed, a flight plan is assembled and sent to the other CTAS processes informing them of the change in configuration, runway assignment, or both.
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Graphical User Interfaces

What follows is only a brief summary of TMA's graphical user interface. More detailed information may be found in the TMA Procedures Summaries.

TMA provides a number graphical features that improve situational awareness while accepting inputs from the controllers and TMCs. The graphical features that improve situational awareness include timelines, load graphs, planview displays, sequence lists, traffic count overlays, aircraft watch windows, rush alerts, data degradation alerts, and other text overlays. The TMCs and controllers can interact with TMA through control panels, buttons, sliders, pop-up menus as well as clicking and dragging various graphical entities on the displays. These graphical features are displayed by the TGUI, PGUI, and, to a limited extent, the CM.


The timeline, a basic feature of TMA, improves situational awareness and accepts input from controllers and TMCs. Full featured timelines, a portion of one is shown in Figure 3, appear on the TGUI while partial featured timelines appear on the PGUI (see Figure 4). Each timeline displays its own time scale and reference point type. A reference point type can be a meter fix, final approach fix or runway threshold. An abbreviation below the timeline indicates the reference point type. For example, the reference point type for the timeline shown in Figure 3 is a meter fix as indicated by the green "MF." The abbreviations below this timeline also indicate that only aircraft assigned to any runway and the meter fix ACTON (as indicated by "AQ") are displayed on this timeline. The TMC can configure the timeline to display whichever aircraft is desired. The bottom of the timeline represents the current time, and each tick mark represents a minute after the hour. Timelines also show the ETAs and STAs of arriving air traffic. The sample timeline shown in Figure 3 displays the ETAs along the left side and the STAs along the right side of the timeline.

Image of a TGUI Timeline. Click on the D-link for a detailed description.D
Figure 3 - TGUI Timeline
Image of a PGUI Timeline. Click on the D-link for a detailed description.D
Figure 4 - PGUI Timeline

Each aircraft is represented by an aircraft tag that contains the airline company and the flight number. For example, the TMC can view the timeline in Figure 3 and see that American Airlines flight number 652 (AAL652) has an ETA of almost 5 minutes after the hour and an STA of almost 7 minutes after the hour. The green "2" next to the STA indicates that TMA's scheduler has delayed this aircraft by 2 minutes (rounded to the nearest minute) to meet certain scheduling constraints entered by the TMC. The aircraft tags along the timelines convey additional information. The symbol next to the flight number indicates the wake vortex class of the aircraft. For example, DAL1991 is a heavy aircraft, NTS172 is a small aircraft, EGF586 is a large aircraft, and AAL652 is a Boeing 757 (a large aircraft creating a wake like a heavy). The symbol for DAL1991 is orange indicating that CTAS has not received any radar tracks for that aircraft, and TMA has computed the ETA and STA using the filed flight plan of the aircraft. The color of each aircraft tag is also significant. ETAs are displayed in green. Unfrozen STAs are displayed in yellow while frozen STAs are displayed in turquoise. A frozen STA means that the aircraft is close enough to the meter fix that TMA's scheduler will not change that aircraft's STA except in response to extraordinary events.

The TMC can also input information to the TMA via the timeline. When the TMC clicks on an aircraft tag, a pop up menu (see Figure 5) allows the TMC to select from a set of operations on that particular aircraft or on that particular aircraft plus all aircraft following that aircraft. Aircraft sequences and schedules can also be manually changed by clicking and dragging the aircraft tag to the desired position in the sequence or location on the timeline. In addition, blocked intervals during which TMA's scheduler will not schedule any aircraft can be indicated by dragging a line on the timeline. Additionally, a TMC can create a blocked slot by clicking on a point on the timeline and selecting, from the pop-up menu (see Figure 6), the aircraft type (specified by wake vortex category and engine type) of the blocked slot.

Image of the TGUI Aircraft Dwell Menu. Click on the D-link for a detailed description.D
Figure 5 - Aircraft Dwell Menu

Screenshot of the TGUI Timeline Menu. Click on the D-link for a detailed description.D
Figure 6 - Timeline Menu


An overlay feature is available to allow the TMC access to detailed information about a particular aircraft. With this featured switched on, the TMC can point to an aircraft tag, and a display (see Figure 7) shows the aircraft's type, stream class, assigned meter fix and runway, and various ETA and STA information. In the example shown in Figure 7, DAL135 is a Boeing 767, its weight class is "heavy", it has been assigned to the meter fix BUJ and the runway 18R, and its stream class is DFW_BLUERIDGE_JETS. The various ETAs and STAs are also visible.

Image of Aircraft Overlay. Click on the D-link for a detailed description.D
Figure 7 - Aircraft Overlay

TMCs are often called upon to record the number of aircraft that have landed or crossed a meter fix during various intervals in time. TMA assists with this process by displaying a Traffic Count Overlay. Displayed on this overlay are the number of ETAs and STAs to the runway threshold and the number of meter fix crossings during various time intervals in the past, present, and future. Figure 8 shows an example of this overlay where the current time is somewhere between 1700 and 1709. The time intervals are each 10 minutes in size, and the numbers indicate the number of aircraft that have threshold ETAs, threshold STAs, and have crossed the meter fixes (Fdg is an abbreviation for Feeder Gate which is the same thing as a meter fix) in each 10 minute interval.

Screenshot of Traffic Count Overlay. Click on the D-link for a detailed description.D
Figure 8 - Traffic Count Overlay

Load Graphs

Another TMA feature that improves situational awareness is the Load Graph. The Load Graph can be configured to show present and future traffic flow to various reference points. The example shown in Figure 9 shows the traffic flow to the DFW airport. The vertical axis is the number of aircraft in a 10 minute period while the horizontal axis represents time in the future in a manner similar to the timelines. The numbers on the horizontal axis represent the number of minutes after the hour. The green line is based on ETA data; it shows the expected traffic demand in 10 minute periods. In this example, the expected demand peaks at 33 aircraft in a 10 minute period (198 aircraft per hour). The red line shows the airport acceptance rate that has been set in TMA by the TMC. In this example, the airport acceptance rate has been set at 18 aircraft per 10 minute period (108 aircraft per hour). The yellow line shows the planned arrivals to DFW as computed by TMA's scheduling algorithms based on the desired airport acceptance rate. In this example, we see that the scheduling algorithm has scheduled aircraft so as to come as close as possible to the airport acceptance rate without exceeding it. Far in the future, the demand decreases, and hence the number of planned arrivals does not fully subscribe the airport acceptance rate.

Screenshot of a TGUI Load Graph. Click on the D-link for a detailed description.D
Figure 9 - Load Graph

Rush Alert

Air traffic often arrives in bunches in a manner similar to rush hour traffic on the roadways in any major city. In air traffic control terms, this is called a "rush." TMA contains a graphical display known as a Rush Alert that informs a TMC that such a rush has been detected and when the rush will occur. The TMC can specify the interval size in minutes and the number of aircraft within that interval size which constitutes a rush. When the number of aircraft during any interval of the specified size equals or exceeds this threshold level, a pair of red brackets is displayed showing the earliest time when a rush has been detected (see Figure 10).

Screenshot of a Rush Alert. Click on the D-link for a detailed description.D
Figure 10 - Rush Alert

Data Degradation Alert - "Big Red X"

The TMA's TGUI can also detect when the data it expects from other CTAS processes is missing or is incomplete. The TMC is alerted to this via a large red "X" across the TGUI display. A dialog box is displayed which indicates which pieces of data are missing. For example, in Figure 11, the TGUI has detected that no scheduled times (STAs) have been received for 3 minutes. It has also detected that ETA updates for less than 80% (61% in this case) of the aircraft have been received.

Screenshot showing a Data Degradation Alert 'Big Red X'. Click on the D-link for a detailed description.D
Figure 11 - Data Degradation Alert "Big Red X"


Figure 12 shows the panel used to enter an airport acceptance rate change. In this example, the user is about to set the airport acceptance rate for Dallas/Fort Worth to 108 aircraft per hour. The user has indicated that the time of the acceptance rate change is 0010 Zulu. The airport acceptance rate panel is representative of the many panels that allow the TMC to alter CTAS parameters to meet current and future air traffic control needs.

Image showing the (F4) Flow Parameters panel. Click on the D-link for a detailed description.D
Figure 12 - TGUI Flow Parameters Panel

Planview Display

Figure 13 shows a portion of the PGUI. It shows the tracks, headings, speeds, altitudes, and IDs of arriving traffic. In this example, the traffic shown is arriving over the Bridgeport (BPR) meter fix at Fort Worth ARTCC.

Screenshot showing aircraft tracks on a PGUI. Click on the D-link for a detailed description.D
Figure 13 - Aircraft Tracks on the PGUI

Sequence List

The PGUI can also display timelines as shown in Figure 4. This same information can be displayed in text form in the sequence list (see Figure 14). This overlay example shows the aircraft's ID, weight class, CID, assigned meter fix, and its meter fix ETA and STA. Across the top of the overlay is displayed the time of day, airport configuration, and airport acceptance rate.

Screenshot of a PGUI Sequence List. Click on the D-link for a detailed description.D
Figure 14 - PGUI Sequence List

Watch Window

Figure 15 shows a watch window for a particular aircraft. A number of watch windows for individual aircraft may be brought up on the CM. Since CM serves as a central database for TMA, most of the information about an aircraft may be viewed via CM's watch window. The watch window shows the aircraft identification, type, and flight plan. It also shows the current track information such as the flight level (FL), true airspeed (TAS), heading, and area (Center or TRACON). The aircraft's assigned gate, meter fix, runway and sectors are also shown. Near the bottom are the various ETAs that CTAS has computed to various reference points.

Screenshot of CM Aircraft Watch Window. Click on the D-link for a detailed description.D
Figure 15 - CM Aircraft Watch Window
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Field Activities

TMA Operational Evaluations at ZFW & DFW

June 17-21, 1996

A full operational evaluation of the CTAS tool known as the Traffic Management Advisor (TMA) was conducted for eleven rushes during the week of June 17 - 21, 1996. In all evaluated rushes the TMA reduced advisory delays from ZFW into DFW by at least 1 -2 minutes when compared to the Arrival Sequencing Program (ASP). The TMA advisory delays in three of the rushes evaluated were on the order of 4 to 5 minutes less than ASP. Feedback from the sector controllers indicates that not only were the advisory delays reduced but also control delays reduced. This control delay reduction is attributed to the decreased metering sector controller workload when using the TMA generated crossing time and countdown delay advisories. The overall feedback from this first week of evaluations is that the TMA reduces advisory delays, reduces control delays and proves that the delay benefits predicted by Dr. Heinz Erzberger are highly conservative estimates. Feedback from the Traffic Management Coordinators, sector controllers and ZFW and DFW Traffic Management Officers is that the TMA system is significantly better than the existing ASP tool and should be used regularly.

A brief synopsis of each TMA scheduled (metered) rush is as follows:

Monday, June 17, 1996, 8:30 p.m. rush
DFW was recovering from an airport shutdown due to thunderstorms during the 6:30 PM rush. The thunderstorms were also in the area and closed down the BUJ arrival gate. BUJ later reopened and the SCY gate closed. The TMA was used to schedule and provide controller advisories to meet a 96 airport rate requiring approximately 12 minutes of delay. The rate was low because the airport was experiencing approximately 1 hour ground delays. During the post evaluation debrief the TMC lead congratulated the TMA evaluation team stating that the ASP system is not usable with a gate closed due to weather. Without TMA the TMU would have resorted to an antiquated miles-in-trail plan to meet the TRACON restrictions.
Tuesday, June 18, 1996, 6:30 p.m. rush
The 6:30 p.m. rush was a more nominal situation, the airport rate was 102 and ASP was advising 8 minutes maximum delay and the TMA a maximum of 6 minutes. The TMA advised free-flow for the 8:30 PM rush while ASP was advising 2-3 minutes of delay. The TMC lead decided on TMA free-flow.
Wednesday, June 19, 1996, 9:00 a.m. rush
During the 9:00 a.m. rush, an extremely heavy east side rush was evaluated. The TMA was advising 3-5 minutes of delay and ASP 5 - 7 minutes. The sector controllers did not follow their sector advisory lists very closely (the controllers were sending aircraft in 2 - 3 minutes early). The impact on the TRACON was that they came very close to shutting off the Center over BUJ. The positive feedback from the evaluation was that the TMCs had the information real-time due to the fact that the delay advisories will count up as well as count down. The ZFW TMC evaluation team and CTAS NATCA representative plan to resolve this issue through further education regarding the accuracy of TMA advisories and how overall delays and workload are reduced if the advisories are followed.
Wednesday, June 19, 1996, 11:30 a.m. rush
During the 11:30 rush (noon balloon), TMA required maximum delays of 8-9 minutes and ASP (prior to its termination) 10 - 11 minutes. The TMC in-charge of the metering position commented that without the TMA the Center would be in a National Airspace Performance Reporting System (NAPRS) delay reporting situation.
Thursday, June 20, 1996
The TMA was used operationally from 6:30 a.m. until 3:00 p.m. for all rushes, and sector times were displayed for the 8:00 a.m., 9:00 a.m., 11:30 a.m., 1:00 p.m. and the 2:30 p.m. rushes. In each rush the TMA delay advisories were 1-2 minutes less than ASP and during the 2:30 p.m. rush ASP was advising 6-8 minute delays while the TMA was advising only 1-3 minutes.
Friday, June 21, 1996, 9:00 a.m. rush
The TMA was used for the 9:00 a.m. rush prior to the NASA TMA evaluation team departing for the weekend. For this rush the ASP system was advising 6-8 minutes and the TMA was advising 2-4 minutes of delay.
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TMA Operational Evaluations at ZFW & DFW

June 14, 1996

The CTAS tool known as the Traffic Management Advisor (TMA) was operated in its full operational mode during the noon rush from the Fort Worth Air Route Traffic Control Center (ZFW) to the Dallas Fort Worth (DFW) TRACON on Friday June 14, 1996. The noon rush is often characterized as an extremely heavy rush with typical delays of 5 - 10 minutes per aircraft. It is also considered to have heavy sector controller workload due to the predominance of flights from the West coast.

At 11:00 a.m. CDT, the TMA Traffic Management Coordinator Lead advised the Traffic Management Unit and the Traffic Management Officer of the intention of the NASA/FAA TMA evaluation team to run the TMA as the primary flow control and advisory system for ZFW. The TMC lead coordinated with the DFW TRACON advising them of the fact that the TMA was to be used operationally for the noon rush. The DFW TRACON gave ZFW the approval and a DFW airport arrival rate of 108 (nominally the AAR is 102). The CTAS NATCA Technology representative and TMC controller coordinator advised ZFW's operational floor of the use of TMA for the noon rush. The NASA TMA engineering team placed the appropriate configurations and settings into the TMA as per instructions by the TMC lead. After observing the TMA and ASP system for a few minutes the decision was made to run the TMA operationally instead of ASP. The delays indicated by the TMA were on the order of 2-3 minutesand 3-4 minutes for ASP. At 11:15 the TMA sector advisories were transmitted to the sector Plan View Displays (PVDs). The sector controllers were advised to start using the TMA generated advisories at 11:25 for the high altitude controllers and 11:33 for the low. The CTAS NATCA representative took the initiative to coordinate and advise his counterpart at DFW TRACON as well as coordinating throughout the operational floor at ZFW.

The evaluation was successfully conducted from 11:25 until 12:05 CDT when the last aircraft in the rush was placed into the TMA sequence. The feedback from the ZFW floor, as reported by the CTAS NATCA representative, was that once the controllers had sequenced the aircraft, the vast majority of the TMA sequences and crossing advisories fell right into place. The CTAS TMC lead indicated that the decision to issue the TMA advisories was based upon the information from the TMA and that for this situation it could have gone either way. The DFW TRACON indicated that the flow supplied from ZFW was workable. Once the evaluation was completed at 12:05 a return to normal ZFW operations was initiated with the normal post noon demand drop-off. The initial data analysis indicated that the airlines were saved one to two minutes per aircraft.

The TMA's first operational evaluation is considered an unqualified success by the NASA/FAA evaluation team.

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