NASA/TM–2010-216389

Concept of Operation for Tactical Separation Assurance 

in Super-Density Operations

Dallas G. Denery

UARC, University of California at Santa Cruz

Ames Research Center, Moffett Field, California

Huabin Tang and John E. Robinson

Ames Research Center, Moffett Field, California

August 2010
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NASA/TM–2010-216389

Concept of Operation for Tactical Separation Assurance 

in Super-Density Operations

Dallas G. Denery

UARC, University of California at Santa Cruz

Ames Research Center, Moffett Field, California

Huabin Tang and John E. Robinson

Ames Research Center, Moffett Field, California

August 2010

National Aeronautics and

Space Administration

Ames Research Center

Moffett Field, California 94035-1000
Available from:

NASA Center for AeroSpace Information National Technical Information Service

7115 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161

(301) 621-0390 (703) 487-4650
iii 

TABLE OF CONTENTS 

INTRODUCTION ................................................................................................................................ 1

SUPER-DENSITY OPERATIONS ...................................................................................................... 1

TACTICAL SEPARATION ASSURANCE FUNCTION ................................................................... 3

STORY BOARDS FOR TACTICAL SEPARATION ASSURANCE ................................................ 7

PATHWAY TO IMPLEMENTATION ............................................................................................... 9

REFERENCES ................................................................................................................................... 10

LIST OF FIGURES 

Figure 1. Major functions required for Super-Density Operations. ...................................................... 2

Figure 2. Notional depiction of displayed information......................................................................... 4
iv 
1 

CONCEPT OF OPERATION FOR TACTICAL SEPARATION ASSURANCE 

IN SUPER-DENSITY OPERATIONS 

Dallas G. Denery1, Huabin Tang, and John E. Robinson 

Ames Research Center 

INTRODUCTION 

NASA is committed to supporting the Next Generation Air Transportation System (NextGen) 

through research and development in select areas. One such area, referred to as Super-Density 

Operations, is conducting research to develop technologies and procedures that will safely increase 

throughput in busy terminal area environments that involve multiple airports. As part of this effort 

there is a requirement to develop a Concept of Operations for Super-Density Operations that is consistent with the Joint Planning and Development Office (JPDO) NextGen Concept of Operations 

(ref. 1). 

This document develops a Concept of Operations for the Tactical Separation Assurance function, 

one of the functions included in Super-Density Operations. The Tactical Separation Assurance function detects and resolves conflicts that are predicted to occur within a two- to three-minute time 

horizon. Several conflict-detection and -resolution algorithms for the Tactical Separation Assurance 

function have already been devised and evaluated (refs. 2 and 3). 

The document is organized to first provide an overview of Super-Density Operations. A functional 

architecture along with a general description of each function and a discussion of the role of automation in the near-term, mid-term, and end-state implementations are presented. This overview of 

Super-Density Operations is expanded in reference 4. The overview is followed by a more detailed 

description of the Tactical Separation Assurance function. The next section presents several story 

boards to illustrate how the Tactical Separation Assurance function is envisioned to be used operationally. The last section presents a suggested pathway to implementation. 

SUPER-DENSITY OPERATIONS 

A functional architecture for Super-Density Operations is provided in figure 1. The architecture is 

based on a new concept for airspace operations, referred to as the Advanced Airspace Concept 

(AAC) (ref. 5). The AAC architecture achieves a high level of safety by including a two-layered 

architecture for separation assurance, a strategic layer and a tactical layer. The Merging and Spacing 

and Off-Nominal Recovery functions shown in the figure represent the strategic layer, while the 

Tactical Separation Assurance function represents the tactical layer. A third layer of protection is 

provided by an independent collision-avoidance system similar to the Traffic Alert and Collision 

 

1

 UARC, University of California at Santa Cruz, Ames Research Center, Moffett Field, CA 94035-1000. 
2 

Avoidance System (TCAS) that is located on the aircraft. The Extended Terminal Area Routing and 

Scheduling functions have been added to complete the description of capabilities required for SuperDensity Operations. A brief description of each function is provided in the following sections. The 

descriptions are followed by a brief discussion of the role of automation as applied to separation 

assurance in the near-term, mid-term, and end-state implementations. 

Extended Terminal Area Routing: This function provides optimized routes for efficiently routing 

en-route traffic to the desired airport and runway and for routing surface traffic to en-route airspace. 

The routing is based on many factors, including weather and airport configuration. 

Scheduling: This function provides a schedule for achieving a smooth flow of arrivals and departures along the defined terminal area routes. The scheduling of flights along the routes is coordinated 

with the user (i.e., Airline Operations Center, or AOC), the airport, and en-route operations. 

Merging and Spacing: This function provides minor adjustments to the schedule and routing to 

maximize the flow rate along the routes while meeting the separation requirements. This function 

may be implemented on the ground or in the air. 

Tactical Separation Assurance: This function provides an independent prediction of a conflict (loss 

of separation) and, if a conflict is predicted, defines a short-term conflict-free path that resolves the 

conflict. In doing this task, it provides a layer of safety to protect against an operational error 

(blunder) or trajectory error introduced by any of the other functions. 

2

Super Density Operations

Controller

Interface

Data Link Voice Link

Emerging Cockpit Technologies

Traffic Alert & Collision Avoidance System (TCAS)

Merging,

& Spacing

(2-20 min time horizon)

Tactical Separation 

Assurance

(0-3 min time horizon)

Extended Terminal Area

Routing

(20 min – 2 hr time horizon)

Scheduling 

(20 min – 1 hr time horizon)

AOC AOC

Data Link

Off-Nominal Recovery

(2-10 min time horizon)

Airport/En Route Coordination

Updated 4D Trajectory

Ground-Based

Aircraft-Based

Distributed 

air/ground

Coordination

Unequipped

Figure 1. Major functions required for Super-Density Operations. 
3 

Off-Nominal Recovery: This function provides options for reinserting an aircraft into the stream of 

traffic if the aircraft is sufficiently out of conformance that the original sequencing and scheduling 

cannot be maintained by minor path perturbations or speed control. An aircraft that responds to a 

resolution issued by the Tactical Separation Assurance function is an example of an aircraft that 

would have to be reinserted into the sequence. 

Controller Interface: This function provides the means by which the controller can interact with the 

automation and surveillance systems to conduct Super-Density Operations. 

In the near-term concept (2015), the controller and pilot procedures are essentially the same as 

today. The traffic management coordinator uses Traffic Management Advisor and other information 

sources to schedule the flights along the nominal routes. The controller is responsible for the Merging and Spacing, Off-Nominal Recovery, and Tactical Separation Assurance functions without the 

benefit of computer-generated advisories. The major difference from today’s operations is an 

improved capability for predicting an impending loss of separation. 

In the mid-term concept (2025), the Merging and Spacing, Off-Nominal Recovery, and Tactical 

Separation Assurance functions provide the controller with computer-generated advisories to assist 

in the performance of these functions. It is also expected that the controller may delegate merging 

and spacing to the flight deck under some conditions. However, the controller is responsible for the 

control of traffic and identifies the function that is appropriate to the situation. 

In the end-state concept (2035), the system is largely automated. Under routine conditions, the 

Merging and Spacing and Tactical Separation Assurance functions are performed without controller 

intervention. The Off-Nominal Recovery function is highly automated but is likely to require some 

controller interaction. It is assumed that a controller is responsible for monitoring the health of the 

system and is able to engage in the control of traffic if required or in cases such as when an aircraft 

is unable to receive data-link. 

TACTICAL SEPARATION ASSURANCE FUNCTION 

This section contains a more complete description of the Tactical Separation Assurance function and 

its operational use in the near-term, mid-term, and end-state concepts. 

Near-term concept (2015): In the near-term concept, the Tactical Separation Assurance function is 

the responsibility of the controller. A conflict-detection capability is included to assist the controller 

in identifying potential conflicts, but the controller is responsible for resolving the conflicts without 

the benefit of computer-generated resolution advisories. 

The controller procedures, interfaces, and responsibilities are similar to those used with Conflict 

Alert (CA) (ref. 6), and those being planned for Automated Terminal Proximity Alert (ATPA) 

(ref. 7). Although the displays for ATPA have not yet been completely defined, a notional depiction 

of the CA and the planned ATPA displays is provided in figure 2. The figure shows a sequence of 

in-trail traffic designated by the characters “H” moving from left to right along a defined course. 

The sideways V represents a site-specific landmark. A Conflict Alert results in the characters “CA” 
4 

being added to the upper line of the data block where they are blinked. A CA also results in an 

audible warning. ATPA provides a “Cautionary Alert” and an “Immediate Attention Alert” based 

on time to predicted loss of separation. A “Cautionary Alert” causes the display to show a cone (see 

fig. 2) in yellow. The apex of the cone begins at the aircraft track and extends along the direction of 

flight. The length of the cone is related to the separation requirements. An “Immediate Attention 

Alert” turns the ATPA display orange. In the figure, the orange cone indicates an “Immediate 

Attention Alert” for EFG650 and EFG423. 

The “Immediate Attention Alert” is activated when the predicted loss of separation is less than a 

predefined time, TIA. The “Cautionary Alert” is activated when the time to a predicted loss of separation is greater than TIA but less than a predefined time, TC, where TC>TIA. Depending on the phase 

of flight, it is expected that the values for TIA and TC will range between 22 and 60 seconds and 

between 45 and 120 seconds, respectively. Because the intended purpose of ATPA is to allow the 

safe control of traffic as near to the separation minima as possible while Conflict Alert is to 

protect against a potential collision by generating an alert of a potential or actual infringement of 

separation minima, the Conflict Alert is activated when the predicted loss of separation is less than a 

predefined time, TCA, where TCA ≤ TIA. 

The controller may decide that a tactical resolution is necessary at any time, independent of the alert 

status. The displays and alerts are provided to improve the controller’s awareness of the situation, 

but they do not require a controller response. If the controller decides that a resolution is required, 

the controller determines the resolution and transmits it to the flight deck via voice. 

Figure 2. Notional depiction of displayed information. 

AAL1109 

18R 

MD80 

H 

EGF423 

18R 

B737 

H 

DAL341 

18R 

B757 

H 

EFG650

18R 

SF34 

H <

>

ATPA Cone Data Block 
5 

The major difference between the near-term Tactical Separation Assurance function and that used 

today for CA and proposed for ATPA is the use of improved trajectory predictions and a strict use of 

Federal Aviation Administration (FAA) separation standards to provide the controller with earlier 

alerts and reduced false-alert rates. The improved conflict-detection algorithm drives both the CA 

warnings and the ATPA displays. The improved trajectory-prediction algorithm, referred to as the 

Flight Intent Algorithm, uses knowledge of area navigation system (RNAV) routes and site-specific 

terminal area procedures to infer the intended flightpath of the aircraft. The Flight Intent Algorithm 

combines this limited-intent information with dead-reckoning trajectory predictions to define the 

trajectories that are examined for a conflict. A comparison with other approaches to conflict detection using fast-time simulation of recent arrival and departure operations, some of which included 

operational errors, demonstrated that this algorithm achieves a significantly reduced false-alert rate 

with slightly improved alert lead times (ref. 3). 

Mid-term concept (2025): The major differences from the near-term operation are in the improvement of the conflict-detection algorithm and in the addition of automation to assist the controller in 

resolving a conflict involving one or more aircraft pairs. The conflict-detection algorithm differs 

in that it is modified to take advantage of improved surveillance data and knowledge of specific 

terminal routes to provide a better understanding of the intended flightpath of an aircraft, thereby 

potentially allowing earlier detection of an impending loss of separation and a reduced false-alert 

rate (ref. 2). The conflict-resolution automation assists the controller by identifying a clearance that 

results in a 2-minute conflict-free flightpath for each aircraft that must be maneuvered to avoid the 

conflict (ref. 3). It is expected that 2 minutes is adequate for the Off-Nominal Recovery function to 

intervene. 

The algorithm for resolving a conflict results in a set of speed, altitude, and/or vector changes. Since 

there are usually many possible resolution clearances, they are prioritized. Each item in the prioritized list is a set of maneuvers for the aircraft involved. Depending on the location and the encounter 

geometry of the aircraft involved, the priorities of the clearances may be different. For example, 

during sequential final approaches, the relative speeds of the aircraft are small and speed maneuvers 

may be preferred over vector or altitude clearances. Also altitude clearances may be more efficient 

and less interrupting than vector clearances and so are preferred. On the other hand, in the downwind 

and base turn area, altitude and vector clearances may be preferred over speed maneuvers. To 

minimize interference with the Traffic Collision Avoidance System (TCAS), three additional rules 

are used in developing a prioritized list of clearances. First, because a TCAS Resolution Advisory 

(RA) is restricted to “climb” or “descend,” the Tactical Separation Assurance function resolutions 

are restricted to the horizontal plane when there is concern that a TCAS RA may also be activated. 

Second, horizontal resolutions are prioritized so as to reduce the likelihood of inducing a TCAS RA. 

Third, when possible, altitude resolutions are restricted to those that do not cause the two aircraft to 

cross each other’s altitude. A trial maneuver set is then selected from the prioritized list and validated by computing the trajectories that would result from the trial maneuver set using realistic 

aircraft performance parameters and determining if the resulting separations meet the separation 

standards. If the resolution does not provide a 2-minute conflict-free path, the process is repeated 

using the next trial set of maneuvers within the prioritized list. A detailed description of the algorithm is contained in reference 3. 
6 

As in the near-term implementation, the conflict-detection algorithm generates a “Cautionary Alert,” 

an “Immediate Attention Alert,” or a “Conflict Alert,” depending on the time to a predicted loss of 

separation. In a “Cautionary Alert” situation, the ATPA displays are shown in yellow. In an “Immediate Attention Alert” situation, the ATPA displays change to orange. For a “Conflict Alert” the 

characters “CA” are added to the upper line of the data block. 

How and under what conditions the resolution is presented is subject to debate and will be a matter 

of research. Two options are considered here. In the first option the controller can call on the Tactical Separation Assurance function to provide a suggested conflict resolution for a “Cautionary 

Alert,” an “Immediate Attention Alert,” or a “Conflict Alert” by a simple manual entry. The 

conflict-detection alerts are used only to increase the controller’s awareness of a potential loss of 

separation but not to directly cause the resolution to be displayed. The concern with this approach is 

that it requires a manual entry in a high-workload situation. Another option being considered is similar to the first option with the exception that in a “Conflict Alert” situation the resolution is automatically displayed in a simplified format. The concern with this approach is that it may replace an 

existing advisory that the controller still believes will resolve the problem or result in conflicting 

advisories if both are retained. With either option, upon requesting a conflict resolution, the Tactical 

Separation Assurance function generates a clearance that results in a 2-minute conflict-free flightpath for each aircraft that requires maneuvering to resolve the conflict. If the controller accepts the 

resolution advisory, the controller provides the resolution to the flight deck via voice and data-link 

and upon concurrence by the flight deck is used to automatically update the trajectory information 

for that flight. If the controller issues a clearance that is not generated by the Tactical Separation 

Assurance function, the controller must enter it manually into the system or the flight will be treated 

as a nonconforming flight that is managed by the Off-Nominal recovery function. 

End-state concept (2035): In the end-state concept the Tactical Separation Assurance function is 

similar to that for the mid-term concept except that the controller is no longer responsible for routine 

separation of traffic. The conflict-detection algorithm still generates a “Cautionary Alert,” an 

“Immediate Attention Alert,” or a “Conflict Alert.” However, since the controller is no longer 

responsible for separation assurance, these alerts control which function is responsible for the 

aircraft involved in the conflict at a given instant in time. For a “Cautionary Alert” or an “Immediate 

Attention Alert,” the functions responsible for managing the involved flights at the time of the alert 

receive notice of the alert but continue to manage the flights (i.e., Merging and Spacing or OffNominal Recovery function). For a “Conflict Alert,” there is a transition of control of the involved 

flights from the functions in control at the time of the alert to the Tactical Separation Assurance 

function. The Tactical Separation Assurance function generates the necessary 2-minute conflict-free 

path that is automatically transmitted to the appropriate aircraft via voice and data-link and upon 

concurrence by the flight deck is used to automatically update the trajectory information for that 

flight. 

The “Cautionary Alert,” “Immediate Attention Alert,” and “Conflict Alert” for aircraft in conflict 

are also shown on a plan-view display so that a controller in charge can monitor the overall health of 

the system. The controller in charge can request an automatically generated 2-minute conflict-free 

maneuver for an aircraft in conflict or intervene in the management of a specific flight at any time. 

The controller is also required to handle special cases such as those in which an aircraft is not 

equipped to receive data via data-link. 
7 

STORY BOARDS FOR TACTICAL SEPARATION ASSURANCE 

The purpose of the story boards is to assure that the concept of operations for the Tactical Separation 

Assurance function leads to a similar set of procedures for a wide range of possible scenarios. To 

illustrate the similarity in operation in different situations, complete story boards are presented for 

two scenarios: 1) both aircraft are in three-dimensional (3-D) conformance and on the same route 

and 2) the aircraft are on different routes with one of the aircraft being out of 3-D conformance. An 

aircraft is said to be in 3-D conformance if it is on the assigned horizontal route at the correct altitude. Mid-term operations together with the first option where the controller must make a simple 

manual entry to be provided with an automatically generated resolution are used as the basis for 

developing the primary story board for each scenario. Differences in near-term and end-state operations are then discussed. 

Aircraft A1 and A2 are in 3-D conformance on the same route: 

Situation: Aircraft A1 and A2 are on downwind. A1 is flying at 210 knots ground speed. A2 is 

assigned an airspeed based on altitude and winds that would position A2 behind A1 with the correct 

spacing. Because of errors, the clearance leads to A2’s closing on A1 faster than expected, causing a 

potential loss of separation. The hypothesized sequence of actions in case of such an error follows: 

Mid-term implementation follows: 

• A loss of separation is predicted to occur at a time less than TC but more than TIA, thereby 

activating a “Cautionary Alert.” 

– A yellow ATPA cone, which extends from the trailing aircraft, A2, in the direction of 

flight, is displayed on the controller’s screen. 

– The “Cautionary Alert” can be transmitted to the automation within the Merging and 

Spacing function for use if required. 

– The “Cautionary Alert” can be transmitted to the aircraft for use via voice and/or datalink if required. 

– The controller continues to use the Merging and Spacing function to provide speed and 

path adjustments to maintain spacing. 

• A loss of separation is predicted to be less than TIA seconds, thereby activating an “Immediate Attention Alert.” 

– The ATPA cone on the trailing aircraft is changed to orange on the controller’s screen. 

– The controller reviews the situation, determines that a resolution is required, and requests 

a tactical resolution advisory from the Tactical Separation Assurance function. 

– The Tactical Separation Assurance function generates a suggested 2-minute conflict-free 

path for A2 that resolves the predicted conflict. 

– The controller accepts the automatically generated 2-minute conflict-free path and transmits the resolution in the form of a clearance to the flight deck of A2 via voice and datalink. 

– Upon concurrence by the flight deck the resolution is used to automatically update the 

trajectory information for that flight. 
8 

Near-term implementation follows: 

In the near-term implementation, the scenario is the same except that the controller is required to 

define a resolution without the benefit of a computer-generated advisory. 

End-state implementation follows: 

In the end-state implementation, the system is largely automated. The Merging and Spacing function 

maintains control over the involved flights until a “Conflict Alert” is issued. For a “Conflict Alert,” 

the Tactical Separation Assurance function automatically generates a 2-minute conflict-free path that 

is transmitted to the appropriate aircraft via data-link and computer-generated voice without requiring controller intervention. 

Aircraft A1 and/or A2 are out of 3-D conformance: 

Situation: A1 is following a nominal terminal area arrival route. A2 is a departure from a nearby airport along an RNAV departure route. A2 incorrectly believes that it was given a clearance to do a 

“direct to.” In executing the “direct to,” A2 is on a path that will lead to a loss of separation with A1. 

A1 is under responsibility of the Merging and Spacing function. It is recognized that A2 is not following the assigned clearance and is being managed by the Off-Nominal Recovery function. Both 

aircraft are in radio contact with the terminal radar approach control facilities (TRACON). The 

hypothesized sequence of actions in case of such an error follows: 

Mid-term implementation follows: 

• A loss of separation is predicted to occur at a time less than TC but more than TIA, thereby 

activating a “Cautionary Alert.” 

– ATPA displays are presented in yellow on the controller’s screen. (The actual displays to 

be used in this situation have not yet been defined.) 

– The “Cautionary Alert” can be transmitted to the Merging and Spacing and Off-Nominal 

Recovery functions for use if required. 

– The “Cautionary Alert” can be transmitted to the aircraft via voice and data-link for use if 

required. 

– The controller or controllers continue to use the Merging and Spacing and Off-Nominal 

Recovery functions to provide strategic resolutions to A1 and A2, respectively. 

• A loss of separation is predicted to be less than TIA seconds, thereby activating an “Immediate Attention Alert.” 

– A1 and A2 ATPA displays are changed to orange on the controller’s screen. 

– The controller reviews the situation, determines that a tactical resolution is required, and 

requests a tactical resolution advisory from the Tactical Separation Assurance function. 

– The Tactical Separation Assurance function generates clearances that will provide 2-

minute conflict-free paths for both A1 and A2 that resolve the predicted conflict (a resolution involving only one of the aircraft was not found). 

– The controller accepts the automatically generated clearances and transmits the clearances to the two aircraft via voice and data-link. 

– Upon concurrence by the flight deck the resolution is used to automatically update the 

trajectory information for that flight. 
9 

Near-term implementation follows: 

• In the near-term implementation the scenario is the same except that the controller is required 

to determine a resolution without the benefit of computer-generated advisories. 

End-state implementation follows: 

• In the end-state implementation the system is largely automated. The Merging and Spacing 

and Off-Nominal Recovery functions maintain control over aircraft A1 and A2, respectively, 

until the “Conflict Alert” is issued. Upon activation of the “Conflict Alert,” the Tactical 

Separation Assurance function generates 2-minute conflict-free paths for A1 and A2 that are 

transmitted to the appropriate aircraft via data-link and computer-generated voice without 

requiring controller intervention. The resolution is automatically added to the trajectory 

information for the involved flights. 

PATHWAY TO IMPLEMENTATION 

The pathway to implementation is highly uncertain and will depend on further research. Nevertheless, it is advantageous to at least envision how this capability may eventually be implemented into 

the National Airspace System (NAS). 

In preparation for the near-term time frame, NASA will engage with the FAA to determine the feasibility and benefits that would be derived by modifying the ATPA and CA to include an improved 

conflict-detection capability based on some of the concepts developed as part of the NASA Airspace 

Systems Program. Although a direct comparison has not yet been conducted, fast-time simulation of 

recorded arrivals and departures in a busy terminal area has demonstrated that the Flight Intent 

Algorithm with a strict use of FAA minimum separation requirements may provide earlier detection 

of a conflict with a lower false-alert rate than those currently being used with CA and ATPA. A next 

step would be to conduct a more thorough evaluation of the different approaches to conflict detection and take the best of each approach to develop the conflict-detection algorithms that would form 

the basis of the automation included in the near-term Tactical Separation Assurance function. 

Similarly, in the mid-term time frame, it is proposed to work with the FAA in the development and 

evaluation of the algorithms for conflict resolution. Although an initial conflict-resolution algorithm 

has been developed under the NASA Airspace Systems Program, it has not been tested in simulation 

with FAA controllers. The next step will be to further refine the algorithm through controller-in-theloop simulations. In parallel, the conflict-resolution algorithm will be tested against live traffic data 

to determine its ability to successfully resolve a conflict. Upon FAA concurrence, the algorithms 

will be evaluated by active controllers in a shadow mode at an FAA-selected facility. The shadowmode evaluation will be followed by a field evaluation. Upon successful completion of the field 

evaluation, the technology will be transferred to the FAA for implementation into the terminal area 

automation system. 

In the end-state time frame, the Tactical Separation Assurance Function is meant to automatically 

detect and resolve conflicts without controller intervention. The clearances would be automatically 

transmitted to the flight deck via data-link and upon concurrence by the flight deck they are 

uploaded into the flight management system (FMS) or flight control system for execution. This 
10 

scenario clearly represents a major departure from the mid-term concept where the automation 

provides the controller with resolution advisories but the controller is still responsible for separation. 

The transition will depend on confidence that the automation will lead to safe and acceptable operations. To gain the necessary level of confidence, the resolution advisories provided in the mid-term 

concept will be monitored and evaluated for accuracy, robustness, and acceptability and a comprehensive risk analysis will be conducted. In parallel, the end-state version of the Tactical Separation 

Assurance function will be tested in fast-time simulations to assure statistically significant results 

and in human-in-the-loop simulations to understand the feasibility of controller intervention in 

emergency situations. Initial use of the Tactical Separations Assurance function for controlling traffic will be in low-density traffic conditions with controller oversight. As confidence improves (based 

on use in low-density conditions and safety analysis), the end-state Tactical Separation Assurance 

function will be used with increasing levels of traffic until it is accepted for routine operations. 

REFERENCES 

1. Concept of Operations for the Next Generation Air Transportation System, Joint Planning and 

Development Office, version 2.0, June 2007. 

2. Tang, H.; Robinson, J.; and Denery, D.: Tactical Conflict Detection in Terminal Airspace. AIAA 

Aviation, Technology, Integration, and Operations conference, Fort Worth, TX, Sept. 2010. 

3. Tang, H.; Denery, D.; Erzberger, H.; and Paielli, R.A.: Tactical Separation Algorithms and Their 

Interaction with Collision Avoidance Systems. AIAA, GNC conference, AIAA-2008-6973, Aug. 

2008. 

4. Isaacson, D.; Swenson, H.; and Robinson, J.E.: A Concept for Robust, High-Density Terminal 

Air Traffic Operations. AIAA Aviation, Technology, Integration, and Operations Conference, 

Fort Worth, TX, Sept. 2010. 

5. Erzberger, Heinz: Transforming the NAS: The Next Generation Air Traffic Control System. 24th 

International Congress of the Aeronautical Sciences (ICAS), Yokohama, Japan, Aug. 30, 2004. 

6. Common ARTS Computer Program Functional Specification (CPFS) Conflict Alert, NAS-MD632, U.S. Department of Transportation, Federal Aviation Administration, April 2007. 

7. Functional Description Narrative, N32422 Automated Terminal Proximity Alert (ATPA)-Final 

Approach Course, ATO0T-CARTS-1055, Version 20, Federal Aviation Administration, Oct. 

2008.