Development and Integration of a Human-Centered Volumetric Cockpit
Situation Display for Distributed Air-Ground Operations

Stacie Granada and Arik Quang Dao Dominic Wong Walter W. Johnson and
Vernol Battiste

San Jose State University QSS Group Inc. NASA Ames Research Center

Moffett Field, CA Moffett Field, CA Moffett Field, CA

In the Distributed Air Ground Traffic Management (DAG-TM) simulation
environments pilots flew desktop simulators, which included a Cockpit
Situation Display (CSD). Within the current paper we will briefly review
the tasks pilots were responsible for in the simulations and
subsequently evaluate the tools made available on the CSD to assist the
pilots in executing their tasks. Some of the tasks pilots were
responsible for in the simulations included the following: to create and
evaluate user-preferred routes, meet flight scheduling requirements at
the meter fix, self-space behind designated aircraft, and maintain
separation with other aircraft. Some of the tools offered within the CSD
to facilitate these tasks included a Route Analysis Tool (RAT), a
Waypoint table with capabilities to input scheduling requirements, a
Spacing tool, and Conflict Detection and Alerting logic. A detailed
examination of these features and others will be discussed

In 1995, the RTCA Task Force 3, Free Flight Implementation (1995) cited
a need for a Cockpit Display of Traffic Information (CDTI) that could
increase situation awareness on the flight deck in order to develop and
progress the notion of free flight. While numerous definitions of free
flight have surfaced, a seminal view expressed in the final report was
that *any* move toward removing restrictions on behalf of the user is a
step toward free flight. In order to support free flight, the task force
suggested that a CDTI needed to provide information that would allow the
flight deck to maintain separation with other aircraft, perform
rerouting operations en route, and engage in limited delegation to
maintain spacing en route or in the terminal area.

The NASA Ames Flight Deck Display Research Laboratory has devoted many
years of research and development to a Cockpit Situation Display (CSD; a
high fidelity aviation navigational display) due to the increase in
endorsements toward advanced flight deck displays by the FAA and NASA's
Advanced Air Transportation Technologies (AATT) program (Johnson,
Battiste, & Holland, 1999). Work on the Ames 3D CSD described in this
paper was conducted for two reasons. First, there is an accepted need
for displays that provide vertical and horizontal situation information.
In an assessment of both these display formats, Wickens, Olmos, Chudy, &
Davenport (1997) found that information about relative altitude was not
naturally available when viewing traffic on a horizontal situation
display, and lateral position information was not available on vertical
situation displays. In today's flight deck where display space is at a
premium, having a single display to view both vertical and horizontal
situation information seems to be the practical solution.

Second, an advanced flight deck display was needed to facilitate the
examination of potential free flight concepts. In order for Air Traffic
Controllers (ATC) to manage higher traffic flows they will not only need
advanced tools on their end, but they also will need pilots to share in
some of the air traffic management roles and responsibilities. By
providing a tool such as a CSD on the flight deck pilots can maintain
better situation awareness, which inadvertently gives ATC greater
flexibility with what options they can use to manage their own workload,
such as with having pilots manage to a required time of arrival at the
meter fix. Overall, an advanced flight deck system is needed to
facilitate the examination of free flight concepts.

Multiple simulations were conducted at NASA Ames Research Center to
examine Distributed Air Ground Traffic Management (DAG-TM) solutions for
free flight. These proposed solutions aimed to examine three concept
elements - CE-5: En Route Free Maneuvering; CE-6: En Route Trajectory
Negotiation; CE-11; Self-Spacing for Merging and In-trail Separation for
Terminal Arrival - which were designed to evaluate various roles and
responsibilities by which free flight could be achieved (Battiste et
al., 2005; Johnson et al., 2005). The goal of the current paper is to
review a Decision Support Tool (DST; specifically, the Ames 3D CSD)
utilized by pilots in these simulations. The main tools developed within
the Ames 3D CSD are described in detail. We address some of the benefits
of the Ames 3D CSD and the tools within the CSD, both of which provided
the platform with which we could test the concepts proposed under
DAG-TM.

The CSD and DAG-TM

The goal of DAG-TM was to propose a prototype of an air/ground system
with a human-centered approach. That is, the research team reevaluated
the roles and responsibilities of the stakeholders to enhance user
flexibility and user efficiency with, for example, user-preferred
routing to increase airspace capacity without impeding upon safety or
airspace accessibility.

Within the concept elements tested, pilots flew desktop simulators and
were responsible for the following tasks: 1) maintaining separation 2)
meeting their assigned RTA (Required Time of Arrival) 3) modifying
Ownships flight path for traffic and RTA compliance 4) sending and
acknowledging trajectory changes, and 5) self-spacing behind a
designated lead aircraft. Several DSTs were provided to aid pilots in
accomplishing these new tasks and to meet their responsibilities in the
simulations. The remaining portion of this paper addresses the Ames 3D
CSD, which provided pilots with the ability to achieve the tasks
outlined above.

CSD Display Overview

The primary DST for the flight deck was the 3D CSD (see Figure 1), which
dynamically depicted traffic, flight plans, conflicts, and more. With
this airside interface, pilots had the ability to view traffic
information in a planar view, profile view, and to dynamically position
the display in some combination between these two choices with a 3D
perspective. An earlier paper describes some of the features of a
previous 2D version of the CSD in detail (Johnson, Battiste, & Holland,
1999).

![](media/image1.png){width="2.7604166666666665in"
height="2.834722222222222in"}

The goal of the Ames 3D CSD was to integrate several tools into a single
interface and expand the user's situation awareness by providing a 3D
depiction of the airspace. 3D displays have some advantages compared to
2D displays. First, 2D planar displays do not visually render altitude
information in as optimal a manner as was desired. It is possible to use
coplanar displays exhibiting both top down and profile views of traffic,
but they use excessive display space and cannot depict some conflict
geometries. It was intended that pilots have the ability to view any and
all geometric traffic situations, thus the display needed to have the
ability to depict any and all geometric traffic situations. Second,
future work with the current CSD will include the integration of
traffic, weather, and terrain within the same display. 3D renderings may
provide more realistic depictions of weather and terrain, as well as
provide greater global situation awareness within the flight deck.

*CSD - Display Basics.* Due to limited space, only the key components of
the DSTs within the Ames 3D CSD are described in this paper[^1]. In
general, the Ames 3D CSD presents the standard navigational elements at
the top-most portion of the display and Ownship is depicted as magenta.

The Ames 3D CSD offers two modes in which a user can view traffic. At
start-up, the primary display projection (the standard view) is set in
*Expanded mode, planar view*. In this mode a compass rose, depicted at
the top-most portion of the CSD, displays 100 degrees of heading value
with Ownship depicted at the center of the display. In the *Expanded
mode*, the user can only view the CSD in a 2D top-down (i.e., planar)
view. When the display is switched to *Full mode,* the user can
manipulate the CSD to examine the display as a 3D depiction on a 2D
surface (i.e., perspective display). In this mode, the compass rose is
displayed as a full 360 degrees around Ownship (except in temporal view,
which is described below).

The benefit of providing the Full mode in the Ames 3D CSD is that two
projection views are offered: *Orthographic* and *Perspective*. From the
orthographic view, the sizes and perspective of elements on the screen
are discrete and constant which makes it easier for the viewer to make
judgments regarding the distance and direction of the aircraft on the
display. In contrast, the perspective view affords making relative
judgments regarding the relative distance between aircraft; as aircraft
that are farther away diminish in size.

In addition to orthographic and perspective views, the full mode
provides a *Central* and *Temporal* view which are dependent upon the
relative position of Ownship. The *Central* view positions Ownship in
the center of the rings on the display affording detection of aircraft
by a distance parameter around the Ownship. The display range provides
the ability for pilots to zoom in for a detailed look at the airspace
around Ownship (10nm) or zoom out as far as 640nm to facilitate in
viewing or planning far-term trajectories. Table 1 lists the display
range tool and indicates how usable and useful pilots in the simulations
found this tool.

The *Temporal* view positions Ownship closer to the bottom edge of the
display, which maximizes the view in front of Ownship. The depiction of
traffic is relative to a time parameter, where for example, any aircraft
displayed can reach Ownship within 10 minutes.

The Ames 3D CSD provides four memory settings whereby users can set and
quickly flip through multiple views. For example, a user may choose a
top-down planar view of the traffic, a vertical rear-view, a vertical
side-view (or profile view), and a 3D view. With visual momentum, the
display will move into any of the preference settings by simply clicking
the corresponding buttons. Additionally the display can be manipulated
into any 3D view by simply right clicking and dragging the display
toward the desired angle. Although it is not likely that a mouse will be
used on a flight deck to manipulate such a display, this input device
works for simulations and other control devices can eventually adopt
similar strategies for acquiring display motion. Further research is
needed to explore this issue as implementation of CSDs come closer to
reality.

*Usefulness of the display*. Research shows that there are advantages
and disadvantages to 3D displays and 2D coplanar displays, and the
benefits of each are task dependent (Wickens, Olmos, Chudy, & Davenport,
1997). The 3D CSD outlined here has the benefit of being manipulated to
display a top down view of the traffic situation, a profile view, or
*dynamically* moved to display some rare conflict geometries that are
not discernable from simple 2D or coplanar displays. Having the option
to view traffic from several viewpoints allowed pilots to look ahead at
any conflict situation and determine where the paths of two aircraft
would cross while searching for an efficient route through the meter
fix. In the DAG-TM simulation of autonomous flight operations, pilots
flying in an Advanced Concepts Flight Simulator (ACFS) and those flying
single-pilot stations (both using Ames 3D CSDs) were able to meet their
meter fix crossing restrictions while maintaining separation with other
aircraft (Kopardekar et al., 2004). Pilots reported using the Ames CSD
in 3D 36% of the time and in 2D 64% of the time. Table 1 provides
pilots' ratings of features within the Ames CSD in terms of usability
and usefulness (each item is addressed in the text).

Table 1

Pilot Ratings of CSD Tools

**Tool** **Usability** **Usefulness**

[M]{.underline} [SD]{.underline} [M]{.underline} [SD]{.underline}

# Display settings

Display range 4.9 0.32 5.0 0.00

3D View 4.2 1.14 4.1 1.29

*Route information*

3D flight plans 4.3 1.34 4.7 1.00

Path predictors 5.0 0.00 4.7 0.67

# RAT features

RAT path 4.5 0.53 4.6 0.70

RAT: drag/drop 4.5 0.85 4.6 0.84

# Alerting system

Alert warning 4.5 0.71 4.5 0.71

Alert symbology 4.4 0.52 4.0 1.05

N = 10; Scale: 1 = not very usable/useful, 5 = very usable/useful.

Pilots found the display range, 3D views, and 3D flight plans usable and
useful. Overall, the 3D display settings provided pilots with enough
situation awareness to maintain separation and make strategic flight
modifications, and the pilots seemed to like these features.

*CSD - Aircraft Intent*. With the Ames 3D CSD, properly equipped
aircraft (i.e., those with Automatic Dependent Surveillance Broadcast,
ADS-B) have the ability to transmit and receive intent information, or
flight plan information, from aircraft within ADS-B broadcast range. The
Ames 3D CSD allows users to view intent information in two ways. First a
user may choose to display the entire flight plan of one or more
aircraft on a case-by-case basis. Flight plan intent information is
depicted as a linear path relative to the direction of the aircraft
heading and includes information regarding level flight and descent or
ascent segments of flight. To view the flight path of an aircraft, a
user must simply click on the aircraft symbol within the CSD and the
flight path is rendered on the display. Again, for specific details
regarding intent depiction see the Ames 3D CSD User Guide
([http://human-factors.arc.nasa.gov/
ihh/cdti/](http://human-factors.arc.nasa.gov/ ihh/cdti/) download.html).

The second option to view intent is for users to display "fast-time
predictor" information simultaneously for *all* or selected aircraft
within the selected altitude surveillance band and broadcast range.
Fast-time predictors are shown along the depicted flight path of all or
selected aircraft. The users can select the amount of time they would
like the intent information "forecasted". That is, traffic may be
displayed with path intent information ranging from 0 to 20 minutes
ahead. The fast-time predictor is shown as a pulse traveling the length
of the predictor line(s) and reflects the speed the aircraft are flying.
Due to the nature of flight, intent information may change at any
moment. Intent information is depicted for the "current" status of the
aircraft and updates as the flight status for each aircraft changes.

The pulse predictor also traverses any flight plan (option 1 from above)
that is selected by the user as long as the pulse predictor is set
anywhere from 2 -- 20 minutes. The major distinction here is that flight
plan information yields *all* of the aircraft's registered intent
information, whereas the predictor lines only show up to 20 minutes of
intent information. Again, the flight plan of individual aircraft may be
turned on or off by clicking on the desired aircraft symbol, then the
predictor can be turned on for the selected aircraft, or on for all
aircraft.

*Usefulness of aircraft intent*. There are benefits associated with the
predictor tool and having access to visualizations of entire flight
plans. For example, Xu and Rantanen (2003) demonstrated that perceptual
cues regarding motion prediction afford less error in collision
estimations. This supports the notion that the predictor tool can offer
robust situation awareness in detecting conflicts as it provides
perceptual information regarding future locations of the target
aircraft. That is, combined with a 3D display the pulse predictor
provides 4D flight information, which fosters low workload for examining
the threat potential of existing traffic.

Additionally, as users have access to rendering of full flight plan
information they are less likely to fall subject to the perceptual
illusions. Research has demonstrated that there are particular geometric
collision angles that may elicit a bias in position prediction and
create a false sense of safety when predictor lines are short (Comerford
& Uhlarik, 2001; Holland, 1998). Therefore, the full flight plan
implementation allows the user to scrutinize possible conflicts more
closely for safer operations. As Table 1 indicates, pilots found the
flight plans and pulse predictor tool highly usable and useful.

*CSD - Route Assessment Tool (RAT)*. The RAT provides the user with the
ability to create and visualize in-flight route modifications, submit
proposed route modifications to ATC, receive route modifications from
ATC, and execute any of these modifications depending on flight status.
The planning and implementation of these flight plan modification
possibilities are subject to provisional alerting and are made available
for 1) strategic conflict resolution, 2) RTA requirements, 3) weather
avoidance, 4) direct route efficiency, 5) dynamic Special Use Airspace
(SUA) avoidance, and eventually 6) terrain avoidance.

To perform any of the functions outlined above, the user must first turn
the RAT on by clicking the RAT button on the CSD toolbar. This provides
the user with access to a waypoint table, a flight path that can be
manipulated (see Figure 2), and options for execution or datalink. The
RAT tool allows the user to enter new waypoints or to use the waypoint
table to scroll through existing waypoints.

![](media/image2.jpeg){width="1.729861111111111in"
height="1.7895833333333333in"}

Once a waypoint is identified, the user can enter an RTA for the
waypoint, enter a new altitude for that waypoint, or move the waypoint
to a new lateral position. All of the RAT functions can be visualized
and evaluated before execution, which helps reduce the need to make
numerous changes to the flight plan since pilots can verify whether the
modification reflects the desired action.

*Usefulness of the RAT*. In the recent DAG-TM simulations, the RAT
allowed pilots to solve conflicts strategically as opposed to
tactically. That is, pilots were able to modify their flight plans to
avoid a loss of separation (Kopardekar et al., 2004), whereas with
existing TCAS systems, collision threats can only be avoided tactically
when the threat is imminent.

The RAT provided an easy method for visualizing, manipulating, and
changing flight information, which required little mental effort or
calculations on behalf of the flight crew. For example, if a pilot
wanted an altitude change, the only work required by the crew was to
insert a start point on the flight path and to enter the newly desired
flight level. The aircraft's most economical climb or descent is
determined by the system and is based on how large the change in
altitude is. Since the RAT provides immediate visual feedback and
provisional alerting information, flight crews know whether the proposed
flight change will have an adverse impact on safety before executing the
plan, and can continue to visually search for path variations until a
safe trajectory is found. In the recent DAG-TM simulations, pilots were
able to use the RAT to strategically solve conflicts when the traffic
levels exceeded the capacity of today's airspace (Kopardekar et al.,
2004). Table 1 also indicates that pilots found the design of the RAT
path and the drag and drop features of the RAT to be usable and useful.

*CSD - Alerting.* The Ames 3D CSD alerts are depicted for strategic
conflict detection as opposed to tactical conflict detection. This type
of alerting is designed to encourage less drastic changes to the flight
plan in order to resolve the conflict to help reduce time, cost, and to
increase safety. The alerting logic detects conflicts (or losses of
separation) based on an algorithm of temporal proximities, which takes
into account the aircraft intent information or aircraft state
information (current heading, altitude, speed). For more detailed
information regarding logic behind the Conflict Detection and Resolution
within the CSD see Canton, Refai, Johnson, and Battiste (2005).

The CSD depicts 3 levels of alert (See Figure 3a, b, c). Alert level 1
is the lowest level of alert and is

![](media/image3.wmf){width="0.7638888888888888in"
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depicted on the CSD when Ownship and the conflicting aircraft become
yellow or amber. At Alert Level 2, an amber glow is added to the
existing Alert Level 1 symbology. Finally at Alert Level 3, yellow
predictor lines with intersecting Loss of Separation (LOS) rings are
added to the alert symbology. These depictions provide information
regarding how imminent any particular alert may be.

*Usefulness of alerting*. The alerting techniques utilized by the CSD
were useful in providing enough information to keep pilots aware of
possible safety concerns (i.e., possible losses of separation) without
committing to numerous false alarms (Kopardekar et al., 2004). Xu (2003)
recommends that effective alerting systems provide continuous measures
of conflict detection as opposed to dichotomous measures. That is,
rather than provide pilots with an all or nothing view of whether a
conflict is likely, it is beneficial to utilize and consider the
dynamics of flight. Again, the alerting system outlined here took into
account winds, future flight plan information (such as a descent
profile), and the alert level based on proximities. Additionally pilots
had access to the time-to-contact information (with early notification),
which overall contributed to the pilots' ability to view possible
conflicts at farther time increments, allowing strategic resolutions
rather than tactical. As with the other CSD tools, Table 1 indicates
that pilots found the alert warning and alert symbology usable and
useful.

*CSD - Spacing*. The CSD allows users to self-space behind designated
lead aircraft (e.g., maintain 90 seconds behind aircraft XYZ). With the
spacing tool users can input the assigned spacing value while algorithms
work to adjust Ownship's speed in order to maintain the required
interval (Abbott, 2002).

The CSD renders a spacing box that represents the target location of
Ownship based on the spacing interval that was set. This provides the
user with updated visual information regarding the current spacing
status. For example, if Ownship is targeted at the correct interval
behind its lead aircraft, the spacing box will appear green and Ownship
will visually appear *in* the box. Similar visual feedback is provided
if Ownship is too early or late for its spacing assignment. A temporal
indication of the spacing status also appears in Ownships data tag when
the spacing is set.

*Usefulness of spacing.* In the DAG-TM simulations, pilots were able to
effectively use the spacing tool and they found workload to be low when
spacing clearances were issued early (Battiste et al., 2005). With the
spacing tool available on the Ames 3D CSD, it is possible to test
several concepts aimed at improving airspace bottlenecks as aircraft
transition from en route through the meter fix into the terminal area.

Ames 3D CSD Effectiveness

Overall, the Ames 3D CSD utilized in the DAG-TM simulations provided
pilots with the type of situation awareness necessary to effectively
maintain separation, meet their assigned RTA, modify Ownships flight
path, send/acknowledge trajectory changes, and self-space behind
designated lead aircraft.

The tools within the Ames 3D CSD offered a flexible and comprehensive
backbone of information that pilots could use in testing the autonomous
operations, self-spacing spacing operations and more. In this simulation
we had the opportunity to evaluate how pilots interacted with the
aforementioned tools and how they in turn facilitated flight in this
futuristic free flight concept (Kopardekar et al., 2004). The data
indicated that flight crews flying the ACFS and pilots flying the single
(desktop) station CSDs were able to meet their assigned RTA's as well as
the speed and altitude restrictions at the meter fix, whether they were
under ATC control or operating autonomously. It is also worth noting
that an increase in traffic did not alter the CSD pilots' performance in
meeting these requirements. Finally, all CSD pilots were able to
maintain separation with both the managed and autonomous aircraft, even
with the increase in traffic. This demonstrates the potential for free
flight concepts with the use of CSDs, such as the one described here.

The Ames 3D CSD presented here has incorporated visually dynamic traffic
information, such as aircraft intent, route planning, and conflict
alerting. Future work will address the integration of traffic, weather,
and terrain on a 3D display. Preliminary work on incorporating weather
into the CSD is currently undergoing investigation, and recommendations
have been made regarding possible design issues to consider for this
type of integration (Comerford, 2004).

References

Abbott, T. (2002). *Speed Control Law for Precision Terminal Area
In-Trail Self Spacing*. NASA Technical Memorandum 2002-211742. Hampton,
VA: National Aeronautics and Space Administration.

Battiste, V., Palmer, E., Johnson, W., Smith, N., Prevot, T., Mercer,
J., Granada, S., Johnson, N., Dao, Q., Lee P. (2005). Human Centered
Decision Support Tools for Arrival Merging and Spacing. *Submission to
the 2005 International Symposium on Aviation Psychology,* Oklahoma City,
OK

Comerford, D. (2004). *Recommendations for a cockpit display that
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[^1]: For more information, download the Ames 3D CSD User Guide at
    http://human-factors.arc.nasa.gov/ihh/cdti/download.html