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Abstract Air traffic growth has resulted in serious peak-
traffic flight delays in our National Airspace System, and
congestion at key airports has been recognized as one of the
key factors contributing to the problem. Airport expansion
plans designed to increase the airports capacities cannot fully
realize their potential benefits because they tend to increase
the complexity of the airport configurations, thus reducing the
efficiency of the system. The Surface Operation Automation
Research (SOAR) concept was proposed in a previous article
as a collaborative concept to provide automation for surface-
traffic management and the flight deck to enhance the
operational efficiency in complex airport environments.

Development and evaluation of the SOAR concept is being
pursued in a 5-year program. This paper presents a progress
update of the program.
I. I
NTRODUCTION

HE problem of air traffic growth unmatched by
commensurate growth in capacity has been witnessed
with the peak summer flight delays prior to the September
11, 2001 terrorist attack. The flight-delay problem has
been recognized by the Federal Aviation Administration
(FAA), NASA, and other concerned parties. The slow
down in air travel since the 2001 attack was temporary, and
the traffic has already reached a level that led to an FAA
order in January 2004 to limit scheduled operations at
Chicago OHare Airport. In the National Airspace System
Operational Evolution Plan (OEP) [1], FAA has identified
congestion at key airports as a domain where the problem
is most prominent. Airport expansion plans seek to
increase the airports capacities with the addition of new
runways and taxiways. However, the expansion plans
necessarily increase the complexity of the airport
configurations, which tends to reduce the efficiency of the
system, partially offsetting the capacity-related benefits of
the investments. The Surface Operation Automation
Research (SOAR) concept [2] was proposed as a
collaborative concept to provide automation for surface-
traffic management and the flight deck to enhance the
operational efficiency in complex airport environments.
Development and evaluation of the SOAR concept is being

Manuscript received May 1, 2004; revised August 2, 2004. This work
was supported in part by NASA under Contract NAS2-02073.
V. H. L. Cheng is with Optimal Synthesis Inc., Palo Alto, CA 94303.
USA (phone: 650-213-8585; fax: 650-213-8586; e-mail: vcheng@
optisyn.com).
pursued in a 5-year program. This paper provides a
progress update of the SOAR program.
Three air traffic domains are commonly defined in the
National Airspace System (NAS): en route, terminal, and
surface. Whereas air traffic in en route airspace enjoys the
flexibility of variable flight levels and headings to allow
popular ideas such as free flight, taxi operations on the
surface are confined to the planar network of runways and
taxiways that they need to be more orderly for efficiency.
With surface operations constituting a potential
bottleneck, major airlines practicing hub-and-spoke
operations for cost savings often suffer major delays at the
hub airports. In view of landing and departure rate limits,
construction of new runways is ultimately inevitable to
achieve capacity gain. In addition to the cost of
construction, the increase in surface traffic complexity
resulting from the airport expansion will incur other
indirect costs or penalties. The SOAR concept [2], [3] was
proposed to provide automation tools for coordinating
efficient surface traffic movement. Development and
evaluation of the SOAR concept is currently being
supported by the NASA Virtual Airspace Modeling and
Simulation (VAMS) program. An evaluation plan of the
SOAR concept was provided in [4].
II. SOAR

C
ONCEPT

The SOAR concept introduces advanced automation to
the two main environments for surface operation: the tower
control environment and the flight deck. This collaborative
automation concept will provide maximal performance
when these two environments can be tightly integrated in a
Centralized Decision-Making, Distributed Control (CDDC)
paradigm, as illustrated by the block diagram in Fig. 1
describing the roles of the automation components. There
are three core ideas behind the SOAR concept:
I. Surface Traffic Management (STM) automation to
enable efficient surface traffic flow
II. Flight-deck automation to enable Aircraft Control
for performing high-precision taxi operations
III. Integrated operation of automation and other
advanced systems to accomplish CDDC for
optimum surface traffic efficiency
Fig. 1 describes the interaction of the two automation
environments and with the human operators and the
Surface Operation Automation Research for
Airport Tower and Flight Deck Automation
Victor H. L. Cheng, Member, IEEE
T


aircraft. It also reveals the integrated operation of these
systems with advanced communication, navigation, and
surveillance (CNS) systems, which represent major
enabling technologies for the concept. The three core ideas
are discussed individually in the following subsections.

STM Automation
GO-SAFE
Aircraft Control
FARGO
Navigation
Surveillance
Co
mmunica
t
i
ons
Aircraft
Dynamics
Cockpit Crew
Air Traffic Controller
Navigation
Surveillance
Co
mmunica
t
i
ons
Aircraft
Dynamics
Cockpit Crew
Air Traffic Controller

Fig. 1. High-Level Block Diagram of SOAR Collaborative Automation
Concept
A. Surface Traffic Management Automation
The ground-control component of the SOAR concept
consists of an STM automation system to provide the
centralized decision-making functionality. It bases its
decision on the surveillance data, flight plans and Airline
Operational Control (AOC) requirements, to generate time-
based taxi routes for optimum traffic efficiency. The
envisioned STM automation technologies include the
following categories of functions:
Planning functions for generating efficient taxi
clearances
Traffic control functions to facilitate issuance of
clearances to flight deck
Traffic monitor functions to ensure safety of traffic
while executing demanding operations
Graphic user interface (GUI) to support the
aforementioned functions
Optimal Synthesis Inc. (OSI) has previously developed
an experimental STM automation system, known as the
Ground-Operation Situation Awareness and Flow
Efficiency (GO-SAFE) system [5]. The experimental GO-
SAFE system serves as the foundation for building the
ground-control automation system envisioned by the
SOAR concept. The functions of the envisioned GO-SAFE
system are described in more detail in the following.
1) Planning Functions
The GO-SAFE system concept contains the following set
of planning functions:
Automatic Taxi-Route Generation
Manual Taxi-Route Editing
Decision Support Functions for Traffic Optimization
Taxi-Route De-Confliction
Adaptive Airport Configuration Function
Surface Traffic Data Processing
Early investigation of the GO-SAFE concept [5] included
the experimental development of functions to support the
automatic generation of taxi routes, manual editing of the
routes with graphical interaction, automatic de-confliction
of the routes and runway scheduling for the flights. SOAR
involves more advanced technologies to fully realize the
complex functions envisioned for the GO-SAFE software
system: an integrated function for automatic route
generation, de-confliction, and runway scheduling; an
adaptive airport configuration function to access multiple
airport runway configurations simultaneously to aid the
transition from one configuration to another; and data-
processing functions to give the controllers and
coordinators a more strategic view of the traffic.
2) Traffic Control Functions
Air Traffic Management (ATM) automation systems
such as the Center-TRACON Automation System (CTAS)
[6], [7] and GO-SAFE generate advisories that can be
converted to clearances for the flights. The CTAS tools
traditionally assume that the use of verbal clearances, and
not require that all advisories would be issued as
clearances. Instead, the CTAS software system
continuously monitors the traffic under surveillance to
update the advisories. In the case of GO-SAFE, effective
conversion of the time-based taxi-route advisories to verbal
clearances is unlikely; hence the complex clearances will
most likely be transmitted to the flight deck via data link.
GO-SAFE needs to keep track of the clearance status, and
the Clearance Manager in GO-SAFE provides this
functionality. The Clearance Manager software function
keeps track of the possible clearance status for the flights,
whether a new advisory is available and its clearance ready
to be sent, a clearance has been sent, an acknowledgment
has been received to affirm or reject the clearance, etc.
These different conditions can be conveyed to the
controller via the GO-SAFE GUI. In addition, since the
various GO-SAFE functions of manual route editing,
automatic runway-usage scheduler and route de-confliction
can indivi