**THE HUMAN ELEMENT IN AUTOMATIC DEPENDENT**

**SURVEILLANCE---BROADCAST (ADS-B) FLIGHT OPERATIONS \*\*\***

**Gary Spencer Livack and James I. McDaniel**

**Federal Aviation Administration**

**Washington, DC**

**Vernol Battiste and Dr. Walter W. Johnson, Ph.D.**

**National Aeronautics and Space Administration**

**Ames Research Center, Moffett Field, CA**

**OVERVIEW**

There is a growing awareness within the aviation community that one of
the more fundamental and challenging issues impacting the acceptance and
implementation of Free Flight and ICAO's Communications, Navigation,
Surveillance, and Air Traffic Management (CNS/ATM) concepts is the need
to establish early consensus on pilot and controller responsibilities
for collaborative, aircraft-based separation. Separation, as used in
this paper, is defined as safe aircraft-based separation from hazardous
weather, from terrain and obstacles, from established airspace
boundaries, from proximate traffic, and from other hazards *external* to
an aircraft.

Embedded in this fundamental issue of defining overall pilot and
controller separation roles and responsibilities is the more focused and
specific debate of the role of Automatic Dependent
Surveillance---Broadcast (ADS-B) information. This new surveillance
technology has been proposed to be flight deck-based to support a
variety of aircraft-based separation applications for use during
oceanic, domestic en route and terminal area flight operations, as well
as to provide collision avoidance protection when operating on the
airport surface. Additionally, although ADS-B is viewed primarily as a
surveillance technology in the United States, it also has the ability to
provide a limited data link communications capability. In this context,
ADS-B ground stations could provide functionality to the controller and
to the pilot. A difficult issue that must be resolved is how air traffic
will safely delegate airborne separation responsibilities between the
flight deck or cockpit and air traffic control.

This paper discusses some of the technical and institutional human
factors-related issues surrounding the subject of the human element in
ADS-B flight operations. It also proposes a procedural-based rulemaking
strategy. This strategy would facilitate further development and
implementation of the human factors and enabling flight technical
standards and operational procedures needed to make free flight
acceptable to the pilot, controller, the user community, and to the
certification authorities. The principal finding of this paper is that
we are now at the brink of having sufficient knowledge from which to
develop a new set of operating rules---Free Flight operational "rules of
engagement"---termed Electronic Flight Rules (EFR).

**INTRODUCTION**

As we continue our journey into the digital age, general aviation (GA)
and air carrier cockpits will continue to evolve, becoming ever more
sophisticated "work spaces" where pilots will manage on board systems,
in addition to actively "fly," their aircraft. New technological
advancements will bring a quantum leap in aircraft avionics functional
capabilities. A number of new and evolving technologies are responsible
for this leap. Some of these enabling technologies include:

-   The Avionics Computer Resource (ACR) with its \"open systems\"
    architecture and its modular software

-   Multifunction displays such as navigation displays (NDs), primary
    flight displays (PFDs), and head-up displays (HUDs), along with the
    Electronic Flight Bag (EFB)

-   Augmented Global Navigation Satellite Systems (GNSS) permitting
    highly accurate Required Navigation Performance (RNP)

-   Digital voice and Controller-Pilot Data Link Communications (CPDLC)

-   ADS-B multipurpose data link

-   Textual and graphical Flight Information Service (FIS) data links

-   Onboard terrain, obstacle, airspace, noise-impacted area data bases,
    and airport map data bases

    These and other related technologies in the hands of well-trained
    pilots, flight crews, and controllers, integrated into supportive
    flight management and air traffic management (ATM) systems, are the
    enabling tools needed to support collaborative decision making
    within the framework of an emerging global Free Flight
    infrastructure. This paper will focus on the human elements involved
    in ADS-B technology.

    In managing this avionics suite of the future and the operational
    implementations thereof, pilots of varying knowledge and skill
    levels will need to perform two generic kinds of decision making.
    One type of decision making involves how best to manage the flight
    of the aircraft. The second type pertains to managing risks. Pilots
    today have limited tools for managing risks. As risk assessments
    become more complex, pilots will need to have available the tools to
    effectively monitor those operational variables that occur both
    within and outside the cockpit environment. They will also need a
    decision making process that helps them compare possible adjustive
    strategies against potential outcomes. This decision making process
    is called risk assessment and risk reduction management.

    One of the newest technology-based tools to assist pilots in
    obtaining a better, more informed sense of what is happening in the
    vicinity of their aircraft, i.e., a technology that augments their
    existing level of situational awareness, is provided by the emerging
    technology called ADS-B. ADS-B is a technology that allows suitably
    equipped aircraft within sensor range (both in flight and on the
    airport surface), selected surface vehicles, and other specialized
    ADS-B broadcast sites such as uncharted towers or ADS-B transmitters
    on catenary wires (e.g., wires suspended across a valley), to
    transmit their:

-   Identification (who or what they are)

-   Position (where they are)

-   Approved flight or surface trajectory (i.e., "intent information";
    where they intend to go)

    This information, along with other pertinent data, will be
    transmitted for reception by any ADS-B equipped receiver, either
    airborne or ground-based, that is within range.

    ADS-B is a fundamentally revolutionary communications and
    surveillance tool. Additionally, and especially for GA units, its
    built-in GNSS receiver can also provide a navigation function as
    well. This new technology will be far superior to the old, and
    actually continues the trend of history repeating itself. Railroad
    tracks supplanted water canals. Screw propellers supplanted wind
    sails. Diesel electric engines supplanted steam locomotives. And now
    the potential is for ADS-B to provide surveillance where radar is
    unavailable, and to supplement or even supplant radar (or at least
    secondary surveillance radar) where a dual surveillance capability
    is required.

    The fundamental issue is not this new technology, per se, but how
    the information from this evolving technology can best be presented
    and utilized by the users (e.g., pilots, dispatchers, vehicle
    operators, and controllers) in support of their respective
    responsibilities. One issue revolves around pilot and controller
    acceptance which, of course, is preceded by questions about
    operational procedures and human factors. Another related issue is
    one of building a trusting and collaborative work ethic or
    "partnership" between pilots, controllers, and certification
    authorities, so that liability concerns pertaining to safety and of
    non-compliance with established separation minima are adequately
    addressed. To this end, one of the core issues that must be
    addressed and resolved is how best to define and delegate pilot and
    controller roles and responsibilities for aircraft-based separation.

    It is easy to over simplify what separation entails, because
    separation takes on different forms in various kinds of airspace
    situations. However, keeping this in mind, we can generally
    distinguish differences among at least three prevailing views as to
    how best to allocate aircraft-based separation responsibility. One
    view is that separation responsibility must remain with the
    controller at all times. A second view suggests that with proper,
    timely, and up-to-date information, the pilot or flight crew can
    assume partial or full responsibility (i.e., delegated
    responsibility) for separation, especially during the en route
    phase. A third view, the one that is emphasized in this paper, is
    that with timely information and tools available in the cockpit,
    flight crews could modify and coordinate their preferred or desired
    routings with air traffic control for approval (i.e., their own
    "de-conflicted" trajectories for routes and/or altitudes).

    The information and tools needed would include a suitable display
    that included "intent" information of nearby traffic along with
    certified conflict detection and resolution software. As ground and
    flight systems became more robust and interoperable, flight crews,
    within established parameters, could further modify their in-flight
    trajectory, as circumstances warrant, and communicate those changes
    to air traffic and nearby aircraft.

    Using this third approach, the flight deck would not directly assume
    any aircraft-based separation responsibility but would, in effect,
    be *authorized* by air traffic control to effect flight operations
    within established parameters using Electronic Flight Rules (EFRs).
    Like existing Instrument Flight Rules (IFR), and based on adequate
    pilot training, certified equipment, well-crafted procedures, and
    aircraft equipage, these new rules could permit aircraft-based
    separation based upon specific equipage and procedures requirements
    codified by a new set of internationally harmonized operating rules.

    Given the three separation responsibility alternatives above, this
    latter EFR approach seems to optimize evolving pilot and controller
    roles and responsibilities with emerging ADS-B capabilities.
    However, before any transfer of separation responsibility or
    codification of EFRs can begin, technical methods must be developed
    to disseminate timely aircraft "intent" and other air
    traffic-related information to support a distributed decision making
    process.

    **THE DISPLAY---THE COCKPIT-ENABLING PILOT INTERFACE DEVICE**

    There is considerable work underway, both in the various government
    research organizations and in the private sector, to develop an
    effective Cockpit Display of Traffic Information (CDTI). Definition
    of the necessary cockpit symbology needed to communicate ADS-B
    position and intent information to the flight crew on a single
    function or multifunction display is key to this work. Initially,
    information presented on the CDTI is expected to support improved
    traffic situational awareness and visual traffic acquisition.
    However, as flight deck information requirements and associated
    procedures for en route and terminal operations become better
    understood and defined, the design and use of the CDTI and
    supportive user interfaces will continue to improve. What
    information will be displayed will be a direct function of how the
    display is to be used, e.g., for situational awareness, for early
    warnings, for active avoidance, etc. One of many challenges that
    must be solved in the near-term is the fused presentation of
    dissimilar information from multiple data sources onto a single
    display. An immediate challenge is the presentation of
    (GNSS-enabled) ADS-B position data with today's TCAS II cockpit
    display presentations.

    **ADS-B / CDTI Implementation**

    The first certified, albeit, limited implementation of an
    operational ADS-B/CDTI system approved for revenue service in
    commercial aviation occurred in the United States in April 1999
    under the sponsorship of the Cargo Airline Association (CAA) in
    association with its integrating contractor, the II Morrow
    Corporation of Salem, Oregon. The initial customers for this new
    Free Flight-enabling technology are three U.S. cargo airlines:
    Airborne Express, Federal Express, and United Parcel Service. Plans
    are to initially equip 12 Boeing 727 and DC-9 aircraft with first
    generation, "baseline" ADS-B/CDTI technology. Starting with a
    limited evaluation that gradually progresses toward greater detail,
    objectivity, and complexity, they will conduct a limited in-service
    and operational evaluation of this technology. This evaluation will
    perform the singular operational function of providing enhanced
    situational awareness information from which to facilitate improved
    "see and avoid" of other aircraft under various operational
    conditions.

    During the summer of 1999, a dedicated operational evaluation of
    these and other ADS-B equipped aircraft is planned to gather
    additional technical and human factors information that may lead to
    full fleet-wide implementation of ADS-B/CDTI technology and
    associated procedures in the U.S. cargo fleet. It is expected that,
    as a direct result of this evaluation effort, several other ADS-B
    operational applications may also be identified and requested by the
    CAA during their full fleet-wide implementation and operational
    approval process. It is anticipated that the symbology and display
    controls used in the initial CAA hardware implementation may be
    modified somewhat to reflect new human factors and operational
    knowledge gained during these initial flight operations. Both the
    U.S. Federal Aviation Administration (FAA) and the National
    Aeronautics and Space Administration (NASA) are copartners with the
    CAA in this fundamentally important activity.

    Other important work on ADS-B technology is being conducted in
    Europe, and in particular, in Northern Europe. A group led by
    Swedavia (a wholly owned subsidiary of the Swedish Civil Aviation
    Authority), Scandinavian Airlines, and Lufthansa, is making
    considerable and important progress in the conceptual development of
    a multipurpose data link system that provides multiple CNS/ATM
    functionalities to the cockpit, including ADS-B functionality.

    Other important on-going technical and human factors research is
    being conducted in various laboratories across Europe and North
    America, such as the National Aerospace Laboratory NLR in The
    Netherlands; the EUROCONTROL Experimental Center in Bretigny,
    France, and NASA's Ames Research Center in California. Fundamentally
    important ADS-B human factors work is underway at these locations.

    ADS-B implementation requires global harmonization. Take, for
    example, an airliner that starts its day in Los Angeles in the
    morning, arrives in Washington, DC by evening, and is in London,
    Frankfurt, or Paris early the next morning. Because of this
    globalization, it is imperative that the technology, as well as the
    supporting human factors and flight technical procedures, be
    standardized and made seamless across airspace boundaries or at
    least harmonized to the maximum extent possible. There is also a
    need to develop intuitive symbology standards and appropriate (but
    perhaps not identical) pilot and flight crew interfaces to provide
    adequate information with which to make timely, collaborative
    decisions. This symbology might be similar to the icon displays used
    in automobiles.

    The underlying objective of this work is to develop new operational
    procedures that will result in defined and substantive operational
    benefits. In this regard, it is our view that an "approved" ADS-B
    operational application is the culmination of certified equipment
    and procedures, and operational approval for use in both revenue and
    non-revenue service.

    **REDUCED SEPARATION STANDARDS---**

    **A CRITICAL HUMAN FACTORS DEBATE**

    There is an emerging need to develop and agree upon international
    policy that clearly defines the overall roles and responsibilities
    of pilots, controllers, and dispatchers in the digitally-enabled
    world of cockpit-based separation. In this paper, we will limit our
    discussion and focus to the use of ADS-B technology for
    aircraft-based separation. In this context, aircraft-based
    separation is narrowly defined as the maintaining of minimum
    acceptable (or greater) distance between two aircraft as determined
    by the aircrew(s) with airborne equipment, rather than by the air
    traffic controller(s), possibly using ground-based equipment.

    Aircraft-to-aircraft separation standards are generally specified in
    air traffic publications, with most being policies, not rules, e.g.,
    FAA Order 7110.65, PANS-RAC, ICAO Doc 7030, etc. There are various
    minimum IFR separation minima specified for en route and terminal
    operations. Additionally, there are certain airspace width
    protections applied to operations on either side of the centerline
    of a charted airway, or along the border of restricted airspace. In
    non-radar airspace, or when the ground-based radar surveillance
    system temporarily fails, separation is generally accomplished by
    applying either time- or distance-based separation procedures,
    usually dependent on the type of navigation equipment being used.
    Also, certain military aircraft may sometimes operate over the high
    seas with "due regard" for the safety of civil aircraft, but not
    necessarily in conformance with globally established separation
    minima.

    There is considerable debate as to how ADS-B technology can be used
    to help facilitate the reduction of both longitudinal and lateral
    separation. One thought is that by using the precise and highly
    accurate ADS-B technology, and sharing this information with other
    aircraft and air traffic ground sites, both pilots and controllers
    can make better use of today's established IFR minimum separation
    standards.

    The separation standards utilized within radar coverage today are
    based on primary and/or secondary radar surveillance systems. For
    example, use of the three-mile radar-based IFR separation standard
    applied within 40 miles of a radar antenna was begun in the early
    1950's with the introduction of radar for air traffic control (ATC)
    purposes. Before the introduction of radar, ATC utilized non-radar
    time-and-distance-based separation standards. These standards were
    well suited for aircraft of that era, such as the DC-3. However,
    with the introduction of faster turbine-powered aircraft in the
    1950's, and the substantial increase in air traffic, the need to
    revisit the existing separation standards became evident.
    Notwithstanding, the three-mile in-trail standard represented a
    safety-related distance familiar to pilots, many of whom were
    initially reluctant to accept ground-based radar control. For most
    aircraft, the three-mile standard for terminal operations has stood
    to this day. Radar equipment limitations were the underlying
    rationale for the choice of five miles as the standard for aircraft
    operating more than 40 miles from a radar antenna.

    Times and technologies have changed. The introduction of ADS-B, with
    its anticipated high level of position accuracy regardless of the
    distance from ground receivers, may enable pilots and controllers to
    see other aircraft with much greater accuracy, resolution, and
    integrity. Using conflict detection and collision alerting software,
    ADS-B---for what is anticipated to be a fraction of the cost and
    with a higher level of certitude than existing TCAS II
    technology---can provide notification when the airspace in the
    immediate vicinity of an aircraft will be transgressed by other
    aircraft. How small a protected volume of airspace is small enough?
    How close ought one aircraft fly in proximity to another aircraft,
    and yet remain safe? What will be the "comfort factors" for possible
    task-saturated pilots, or pilots who focus on the safe operation of
    their aircraft more than on any "big picture" and who may not have
    the time to concentrate on developing the best executed separation
    strategy? At what point would controllers be expected to note
    potential problems and offer assistance? These are a few of the core
    human factor issues that are being debated. It's all about
    risks---and risk taking. It's all about the notion of when might one
    be willing to trust a new technology. Human factors questions,
    questions about situational awareness, surveillance workload and
    performance, causes of errors and lapses---all are relevant to
    change.

    Change is difficult. In his scientific autobiography, Max Planck,
    the Nobel laureate known best for his discovery of the revolutionary
    quantum theory, reported what he had observed in the development of
    physics:

    > This experience gave me also an opportunity to learn a fact---a
    > remarkable one in my opinion: A new scientific truth does not
    > triumph by convincing its opponents and making them see the light,
    > but rather because its opponents eventually die, and a new
    > generation grows up that is familiar with it.

    From the earliest flight training, pilots are taught not to trust
    merely their senses, and not to rely on any one specific data source
    or system as a "sole means" input to their decision making process.
    Trust, yes, but also verify. When things do not look or feel right,
    verification is critical and instruments should be cross-checked
    with other independent instruments. One such technique is the
    "critical triangle method" whereby experienced pilots rely on not
    just one independent system but on three independent systems. If one
    system fails or provides inaccurate data, a pilot can cross-check
    with the other two independent sources of data to determine which
    one of the three is in error. Two independent systems are
    insufficient.

    This same critical triangle method is part of the current debate
    over the role of ADS-B, and whether it has sufficient merit and
    end-to-end system integrity and certitude to satisfy the airborne
    separation assurance function. If so, what then should be the role
    of TCAS II? Should TCAS II be accepted as a "last ditch" back-up
    system, especially if it is found to have less end-to-end system
    integrity than ADS-B? Also, how might one combine data of dissimilar
    quality onto a common CDTI? Likewise, what should be the role of the
    controller as an additional and independent means of back-up to the
    pilot in the event that an agreed-upon separation standard or
    operating parameters cannot be met or complied with? Of course, we
    must address not only separation criteria but also traffic flow
    management objectives that extend beyond the surveillance and
    trajectory envelopes of individual aircraft. Underlying these
    questions is the notion that detected loss of separation must always
    involve a culprit. Such an adversarial approach (devoid of an actual
    accident) between the pilot, the controller communities, and the
    various certification authorities, seems to somehow contradict the
    notion of systems safety and safety root-cause analysis. One of the
    reasons why pilots and controllers may be willing to accept TCAS is
    that if an aircraft responds to an RA, then the human is not held
    liable---an important lesson for ADS-B/CDTI?

    **PILOT AND CONTROLLER PRESPECTIVES**

    Some pilots and controllers appear guarded in their willingness to
    embrace ADS-B technology and any associated reduced separation
    standards, at least not without first having the appropriate
    equipment and associated procedures developed, along with the needed
    education, training, and collaborative decision making processes in
    place. Also, they want adequate operational tests and evaluations to
    have been conducted beforehand. Ironically, while some pilots may be
    hesitant to embrace ADS-B as an enhanced separation or spacing tool,
    or as a means for conflict detection and resolution advisories, they
    appear more willing to support TCAS II and its limited
    functionalities. This appears to be a dichotomy, given the expected
    increased accuracy and capability of ADS-B over TCAS II. Such a
    viewpoint may be based on a lack of understanding by pilots of the
    underlying technologies of both ADS-B and TCAS II, coupled with a
    lack of operational experience and use of this new technology.

    **The Airline Pilot's Perspective**

    A focused educational effort targeted to the commercial pilot
    community has not yet begun, and is long overdue. In the meantime,
    some pilots, especially those associated with the several pilot
    labor organizations, have voiced concerns about ADS-B. These union
    representatives assert that flight crews should never accept
    responsibility for maintaining minimum separation standards.
    Instead, they believe that the proper maintenance of these standards
    is the role and responsibility of the controller. Under certain
    controlled conditions (such as when operating in visual
    meteorological conditions) pilots may elect to accept and visually
    apply reduced separation standards. Some pilots want the controller
    to be the safety valve and to identify if separation has been
    reduced to at or below the established IFR separation standards. In
    the practical reality, in the United States, most visual approach
    operations are conducted with the pilot assuming separation, often
    at less than the established IFR standards, while taking into
    account any wake vortex risks.

    In comparison to the airline pilot, GA pilots operating under visual
    flight rules (VFR) routinely perform aircraft-based separation from
    other traffic, often without radio contact with air traffic control.

    There is also concern about cockpit workload, both in the en route
    and terminal areas. The right tools must be designed and validated
    to ensure any new flight deck application can be accomplished safely
    and with no unacceptable increase in workload or diversion from
    current safety related tasks.

    Airline pilot union representatives also want specific procedures in
    place to address contingency procedures in the event that their
    ADS-B unit or the ADS-B unit of the other pertinent aircraft fails,
    or if someone's application of established procedures somehow goes
    amiss and an escape maneuver is needed. For example, if procedural
    de-confliction and/or disengagement are warranted, they want ATC to
    be part of the oversight process. They specifically want a collision
    detection and avoidance system in place that works as a safety
    backup. They also want an adjudication procedure whereby any loss in
    separation may not always be addressed by the certification
    authorities in punitive proceedings, but in a process and in a
    spirit of committed partnership.

    **The Controller's Perspective**

    The professional controller community also has certain specific
    concerns regarding the future role of the controller in any proposed
    wide-scale ADS-B implementation. Their specific concerns fall into
    at least three basic categories:

-   When separation responsibility is shared or delegated to the
    cockpit, and there is a loss of separation or an accident occurs,
    who will be held liable---the controller, the pilot(s), or the air
    traffic service provider?

-   When a cockpit "crisis" or other unusual situation necessitates that
    the pilot return delegated separation responsibilities to the
    controller, will the controller have the time, information, or other
    resources at hand (e.g., the pertinent intent information,
    communications capability, control authority) immediately available
    to quickly accept separation responsibility?

-   How will ADS-B technology (and its use in the cockpit as a tool for
    separation) affect the overall mission of the air traffic
    controller? Specifically, from a systems safety perspective, will
    the role of the pilot to perform cockpit-based separation complement
    or hinder the controller's overall mission?

    Resolution of these questions and issues is fundamental to achieving
    early and widespread ADS-B implementation. Clearly, human factors
    experts, pilots, and controllers, along with certification
    authorities, must be comfortable that the transfer of today's
    defined pilot-controller separation responsibilities will enhance,
    not degrade, the overall target level of safety. Enhancing safety
    should be a mutual objective of all parties.

    In the case of the controller liability question, controllers today
    often add a safety buffer to the minimum in-trail separation
    distances specified for IFR operations. Though this added separation
    distance may sometimes reduce capacity, it also helps reduce the
    chances that a controller will incur an operational error because of
    a loss of separation. This safety buffer is there just in case
    something goes wrong due to the low probability of human or
    equipment lapses. As a result, the traditional three mile in-trail
    separation standard in the terminal area might become five miles,
    and five miles in-trail separation might become seven miles, and so
    on. The fact is that in today's controlled airspace environment and
    in today's litigious social and business environment, when
    instrument meteorological conditions (IMC) prevail, and controllers
    have full responsibility for traffic separation, they may apply
    extra spacing to minimize the chances for an operational error.
    ADS-B may provide the controller with a tool to keep this safety
    buffer at a minimum. When operationally appropriate, it may also
    provide a technical means to shift separation responsibility to the
    cockpit for those equipped aircraft with pilots who are willing to
    accept that responsibility.

    One controller concern, as noted, deals with the potential for the
    temporary or limited delegation of controller responsibility to the
    pilot. What might happen to the controller's workload if the flight
    crew temporarily accepts separation responsibility, then needs to
    return it to the controller at a moment's notice. What if the
    controller is using the productivity gained by the earlier transfer
    of responsibility to accomplish an expanded workload, such as
    allowing other aircraft to enter the sector? What happens if the
    controller, due to some emergency or other unforeseen event, must
    then take back separation responsibility? Will the controller be
    able to react quickly in such a situation; will the controller be
    immediately overloaded? Will other air traffic services (to include
    separation assurance for other aircraft) be jeopardized? These
    questions perhaps can best be resolved with contingency-based
    procedures. We may be able to equate this to today's current visual
    approach procedures where the pilot loses sight of the aircraft
    being followed and the controller has to resume the role of
    providing separation assurance. This procedure of retaking visual
    approach spacing has been successful for many years and we would
    expect that ADS-B based procedures can be equally successful,
    recognizing that procedure formulation is needed to accommodate
    specific kinds of situations.

    Controllers also need to be aware that an ADS-B aircraft-based
    separation system is not a panacea. It will not perform many of the
    "other" tasks that a controller does, such as managing dynamic
    metering restrictions affecting handoffs to nearby sectors, managing
    the impact of flow control and weather impacts on routings, and
    other multi-faceted, "constraint generating" issues---all of which
    are outside the scope of ADS-B. These "limitations," along with the
    notion that controllers optimize the system by assisting all
    aircraft in making the best decisions for the welfare of the overall
    system (and not necessarily for the welfare of a single aircraft)
    indicate that an ADS-B aircraft-based separation system may not be
    able to optimally support the overall air traffic control mission.
    Some controllers thus argue that ADS-B cannot accomplish all air
    traffic control tasks and therefore, as an emerging technology, has
    only a limited application in any future air traffic management
    system.

    **ELECTRONIC FLIGHT RULES---A POSSIBLE ADJUSTIVE STRATEGY?**

    Given the above set of pilot and controller concerns, there are
    times when one must just lean back and ask, rhetorically, "What does
    all this really mean, and what will it take to go forward?"
    Restated, what solution or set of evolutionary strategies might best
    be used to resolve these complex issues to the satisfaction of all
    the parties concerned?

    Rather than adopting a "park it" and simply ignore it attitude---and
    not moving forward at all---why not move forward through a series of
    small, evolutionary steps rather than through a revolutionary
    approach? The thought is to take many small but deliberate steps,
    each supported by limited but focused air traffic and cockpit
    procedural changes that are subjected first to rigorous test and
    evaluation.

    One part of this evolutionary approach would be to develop and
    implement a new set of operating rules called Electronic Flight
    Rules (EFR) that would codify CDTI-based tasks performed by
    aircrews. These rules must, however, remain consistent with
    procedural rules applied by air traffic controllers, who retain
    overall responsibility for air traffic safety and flow control.

    These new operating rules would be clearly written and highly
    procedural: "I do this, and you do that. I turn right, and you stay
    where you are." EFR would define the roles and responsibilities of
    aircraft operating between city pairs in a Free Flight global
    airspace system. These rules would codify the "when and how" of a
    cockpit-based ADS-B separation system and would be used to establish
    precise procedures for its use as an airborne separation and as a
    conflict detection and resolution system. These new rules would also
    define when and under what circumstances ADS-B could be used as an
    independent means for separation assurance. (To effect this, the
    technical community will first need to define appropriate air-to-air
    separation standards in terms of total required system performance
    and other technical parameters.)

    Additional issues that would fall within the scope of the new rules
    would include large versus small aircraft right-of-way rules as well
    as the role of TCAS II or other technology as a potential back up to
    ADS-B. Specifically to be addressed: Is TCAS II really needed, or
    will it be obsolete given the notion that pilots have been quite
    clear that they will not accept an aircraft-based separation system
    that does dual duty, i.e., maintaining separation and use as a
    last-ditch backup? Yet another aspect of EFR would be the downlink
    coordination transaction between an aircraft with its RNP-based
    flight path and air traffic's ground-based conflict probe.

    One suggestion for a possible EFR-based ADS-B airspace system
    implementation might be as follows: Flight plans could be initially
    filed with an air traffic service provider as a "3D" trajectory
    "contract" between city pairs, where the pilot selects the preferred
    routes, altitudes, and airspeeds. Upon departure, and while en
    route, potential aircraft-to-aircraft conflicts would be identified.
    Any potential conflict would obviously need to be resolved
    compatibly with overall traffic flow management objectives and
    procedures. Solving these strategic conflicts would require either
    onboard conflict detection and resolution software or a ground-based
    conflict probe, including collaborative decision making with air
    traffic controllers. Execution of the onboard software would result
    in a suggested modification to the filed flight plan to resolve the
    conflict---either a lateral, vertical, and/or speed adjustment.

    In most low-density airspace, the role of the controller would most
    likely become one of managing rather than controlling the flight. In
    higher density airspace, the controller would most likely control,
    rather than manage, using ground-based automation, and would assign
    specific "4D" waypoints to eliminate conflicts. Pilots, using
    aircraft systems, would be assigned the responsibility of
    maintaining aircraft-based separation, including in-trail separation
    behind other aircraft while on final approach. Aircraft-based
    conflict detection and resolution software, supported by a
    redundant, ground-based air traffic control surveillance and
    automation infrastructure, would be used to ensure safe separation
    in the unlikely event of a failure of an aircraft's avionics. A
    famous American poet once wrote:

    *I shall be telling this with a sigh*

    *Somewhere ages and ages hence:*

    *Two roads diverged in a wood, and I --*

    *I took the one less traveled by,*

    *And that has made all the difference.*

    Robert Frost, American poet (1864-1963)

    Before implementing EFR, the aviation community must reaffirm its
    desire for and commitment to move "down the road" toward Free
    Flight. The Free Flight final report, published in October 1995, was
    a consensus document. Are we still eager to embrace a Free Flight,
    user-preferred, trajectory-based separation system, as opposed to
    the existing airspace-based separation system? Do we as a world
    community still share the same CNS/ATM vision? If so, let us
    continue down the road less traveled.

    **ENHANCED PILOT DECISION MAKING**

    In any future ADS-B or CNS/ATM technology implementation, the "human
    element" will likely be only as good as the education and training
    received. Work done by Embry-Riddle Aeronautical University (ERAU),
    FAA, NASA, Transport Canada, and others since the early 1970's all
    paved the way for three fundamental enhancements in aviation safety.
    At the air carrier level, the first two fundamental enhancements are
    cockpit resource management (CRM) and line oriented flight training
    (LOFT). At the GA level, the third is known as pilot decision making
    (PDM) training.

    The airlines have done a credible job in maturing and fine-honing
    CRM and LOFT, while the GA constituency is still working on maturing
    PDM training. Nevertheless, the opportunity now exists to use some
    of the original GA PDM training concepts to create an entirely new
    training curriculum tailored to support ADS-B, including how best to
    use the new digital avionics technology to enhance pilot judgment
    and pilot decision making. What is specifically needed is focused
    lesson plans to teach air carrier and general aviation pilots how
    best to use these new technologies to enhance their situational
    awareness and reduce accidents. Needed are ways to teach the use of
    multifunction displays so as to gain the maximum safety benefits
    possible from the technology-enabled four fundamentals of enhanced
    (i.e., electronic) aircraft-based separation. These can also be
    considered the four fundamentals of enhanced situational awareness,
    and include:

-   RNP-based moving maps

-   Terrain and obstacle databases which provide controlled flight into
    terrain and approach and landing phase accident protection

-   Adverse weather avoidance based upon data linked weather information
    to the cockpit

-   ADS-B enabled aircraft-based traffic separation and mid-air and
    airport surface collision avoidance

The technology-based tools are now nearing the commercialization phase
of their product life cycle. Lacking are the needed cockpit equipment
and air traffic integration systems combined with pilot judgment
training materials to gain the maximum safety benefits possible.

**MANAGING CHANGE IN A GLOBAL AIRSPACE SYSTEM**

In summary, how do we implement global airspace change when certain user
groups are still somewhat hesitant to embrace change? Should we require
change? Should we take small steps over time to build acceptance? Should
we create a process to develop, simulate, validate, demonstrate,
evaluate, change, modify, and then implement change? Such an
evolutionary schema is called the scientific process. We should embrace
this latter approach and support the further development and operational
use of the predominantly cockpit-based, Free Flight enabling, digital
avionics technologies, along with the proposed codification of new
operating rules that would enable cockpit-based self-separation within
the context of a trajectory-based global airspace system. Last, we
should support an initiative to develop materials to teach the four
fundamentals of enhanced situational awareness as part of any advanced
pilot judgment and decision making training curriculum.

The human element if not thoughtfully integrated into a system can and
generally will be the weakest link in any endeavor. We now have, or will
soon have, the opportunity to implement new ADS-B technology that can
significantly reduce accidents caused by human error. ADS-B technology
also affords the opportunity for reduced separation standards, increased
capacity and efficiency of flight operations, and it provides for
greater airspace flexibility while, at the same time, maintaining or
enhancing the quality of our environment. This vision is called Free
Flight. The technology, the procedures, and the human factors are all
now available or will be within the very near-term. The real challenge
is to build and maintain a consensus that is willing to accept change.
Once this is done, the next task is to develop an ATM system in which
the human element is properly integrated into the overall system and
pilot and controller roles and responsibilities are clearly defined,
delineated, and understood. These, indeed, *are* the real challenges.

**BIBLIOGRAPHY**

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