August 18, 2000

The Potential Impact of Unmanned Aerial Vehicles

On the National Airspace System and other resources

by

Del Weathers NASA Ames Research Center

Abstract

This paper briefly discusses NASA's current work on Unmanned Aerial
Vehicles (UAVs), indicates where additional information may be obtained,
and presents some of the potential impacts of UAVs on the United States
National Airspace System (NAS) and its users. Three operational
scenarios using UAVs in the NAS are presented, relevant operational
issues are discussed, and specific research topics identified. This
paper treats all the various forms of semi-autonomously operating (SOVs)
or remotely piloted vehicles (RPVs) as UAVs. See the glossary for other
terms.

Overview

In January 2000, Jeff Griffith, who is Program Manager of the Federal
Aviation Administration's (FAA) Air Traffic Service Planning and
Procedures Program asked the NASA Ames-led Advanced Air Transportation
Technologies (AATT) project to investigate what kinds of Unmanned Aerial
Vehicles (UAV) work NASA was actively pursuing. During discussions with
the AATT project, he indicated that his primary concern was the
potential impact that UAV operations within the NAS could have on the
operations of current and future users. He explained that he had
received information that perhaps thousands of such vehicles may
eventually be operating in the NAS. Indeed, some sources do indicate
that in the next few years that there may be hundreds, perhaps thousands
of such vehicles operating throughout the United States.[^1] He
suggested that many operational issues should be appropriately
considered before such general operations could take place. These issues
include certification, liability, legal, procedures, communications, and
flight safety. His visit to the NASA Ames Research Center was, in part,
to request some insight into how NASA approaches the challenge of
operating UAVs in the NAS.

The topic of UAVs is quite complex in the range of possible aerial
vehicle types, their performance capabilities, payload capabilities, and
their guidance, navigation, and control (GN&C) systems. The types range
from very small (a few feet---literally radio-controlled "model"
airplanes) to quite large (the size of a commercial aircraft---Helios
has a wingspan exceeding 200 feet and Global Hawk has a wingspan of 116
feet which exceeds that of a Boeing 737). Their operating performance
capabilities range from being able to slowly operate only a few miles
from their departure point to 350+ knot, multi-day global operations
(e.g., Global Hawk). Their payloads can vary in mass from a few
kilograms or less to almost a metric ton (e.g., Predator). Their GN&C
systems can either be autonomous from ground control, using the Global
Positioning System (GPS) navigation to provide input to their guidance
(much like DoD's cruise missiles), to vehicles completely slaved to a
remote pilot station which provides all the UAV commands via a
communications link.[^2] Several current UAVs are effectively industrial
versions of the hobbyist radio-controlled aircraft available to the
public.

During the next few years, UAV technologies will become smaller,
lighter, more technologically advanced, and less costly to operate. As
propulsion technology becomes more sophisticated, there will be tests of
vehicles that will be able to remain aloft for weeks perhaps months at a
time. A recent Aviation Week and Space Technology article discussed the
Helios vehicle being developed for NASA's ERAST effort by
AeroVironment.[^3]

The continuing technological maturation of UAV technologies will create
opportunities for the aerospace industry to offer civilian and military
customers a wide range of vehicles and capabilities (based on NASA and
DoD[^4] research and development and operational efforts). These
customers will want to use these vehicles in some portion of the NAS and
operate in as free a manner as is possible without endangering other
users or creating problems on the ground. To demonstrate possible uses
of UAVs, several representative missions are listed in Table 1 below.

## Table 1. Representative UAV Missions

> Military Operations and Support
>
> (ranging from reconnaissance to weapons delivery)
>
> Atmospheric Sensing/Sampling
>
> Polar and Oceanic Science
>
> Fishing Monitoring
>
> Hurricane Reconnaissance
>
> Search and Rescue (at least, assist)
>
> Around-the-World Demonstrations
>
> Fire (all types)/HAZMAT Monitoring
>
> Telecommunications
>
> Cargo Delivery (e.g., FedEx, UPS)
>
> Commercial Imaging
>
> Pipeline/Powerline/Infrastructure/Traffic Monitoring
>
> Disaster Real-time Observation/Photography and Sensing
>
> Law Enforcement/Regulatory Support
>
> Agriculture/Forest/Geological/Land use Imaging
>
> Earth Resources Management

As UAV customer usage pressure increases, as part of their regulatory
responsibilities, the FAA will need to develop, coordinate, and sustain
for the UAV community:

General operating procedures and Federal Aviation Regulations,

Official agency and stakeholder points of contact,

Vehicle and remote pilot certification standards,

Training and maintenance requirements, and

Flight inspection regulations and protocols.

Given that the UAV aeronautical technologies are rapidly developing, the
essential issue for employing these vehicles will center upon their safe
use in large numbers within the NAS. There is no question that in a few
years industry will be prepared to offer UAV customers a wide range of
capabilities that will stress the operational services of the current
NAS. [^5] How the FAA, NASA, DoD and other organizations deal with this
demand on services will need careful consideration and active
participation by industry, user groups, and other stakeholders.

Finally, there does not seem to be any solid information to aid in
predicting how many UAVs will be built in the next few years. The
briefing discussed in footnote 1 indicates that potentially hundreds and
even thousands of UAVs may exist if the civilian and military market
emerges. The book *The Innovator's Dilemma* by Clayton Christensen
points out that since there is no previous market for a new technology
or product, there is no realistic way to predict future market
volume.[^6]

Discussion of NASA's Work

Since its creation in 1958, NASA has worked on many technical aspects of
UAVs, particularly guidance, navigation and control (GN&C) systems,
vehicle structures, and propulsion research. Currently this research on
UAV technologies has matured to the point of creating and operating very
sophisticated aerial vehicles that can carry a wide range of advanced
sensors, and GN&C systems with fuel-efficient, even solar powered
engines for a science mission-focused payload (see footnote 3). To
demonstrate and further test the rapidly advancing capabilities of these
vehicles, there exists an emerging need to consider their operation
outside of normally restricted airspace environments. For example,
operating such vehicles outside of the Edwards Air Force Base's R-2508
restricted area for weeks will require careful coordination among FAA,
NASA, and DoD organizations. NASA's primary UAV project, the
Environmental Research Aircraft and Sensor Technology (ERAST) effort, is
planning to semi-autonomously operate a UAV in airspace normally
reserved for Instrument Flight Rule (IFR) operating vehicles. NASA's
work on UAVs is located at Ames Research Center, Dryden Flight Research
Center, Langley Research Center, and Glenn Research Center.[^7]
Currently the only active flight program involving UAVs is the ERAST
project being conducted at Dryden.[^8]

In February 2000, NASA headquarters released a NASA Research
Announcement (NRA-99-OES-XX) to demonstrate UAV-based science for a
variety of scientific applications. This program will require some
operation of a UAV in the NAS. One researcher for this effort stated
that they "\...want to get away from using chase planes to monitor the
UAV and go with semi-autonomous operation in the NAS." It is unclear
whether there would be continuous ground monitoring of the flight. While
there will be considerable coordination between FAA and NASA on this
program and its use of the NAS, the opportunity exists to examine many
of the salient issues facing general NAS usage by UAVs.[^9] See footnote
8 second paragraph. If this project desires to use portions of the NAS,
they will a reliable approach for providing positive separation of this
vehicle from other users of the NAS and weather phenomena. Much research
remains to be accomplished in order to realize even simple operations in
the NAS without a chase aircraft being present. Perhaps requesting that
Air Traffic Services provide a temporarily sanitized corridor is one
approach.

Within the above mentioned NRA is the following discussion of UAVs:

"UAVs are available with varying capabilities. The most important
performance parameters for consideration are altitude, endurance (time
in flight), range (distance covered in flight), and payload-carrying
capability (weight and volume). Other payload-related considerations are
the operational flexibility of the UAV to land and take off in areas of
interest and on a time-schedule to exploit the observational targets, as
well as the environment experienced by the payload (controlled or
subject to ambient variations), location on the aircraft (important for
air sampling, viewing, etc.), electrical power, and ease of
installation. Operational considerations include communications options
for both platform command and control and payload control and data down
link. These features need to be considered when selecting a platform
suitable for science and applications.

> It is the intent of this NRA that proposers seek out those UAV
> platforms which meet their science or applications objectives and with
> which unique missions can be performed. An excellent resource for
> information about UAVs is the web page of the industry trade
> association, the Association of Unmanned Vehicle Systems International
> (AUVSI) at
> [www.erols.com/auvsicc/index.html/](http://www.erols.com/auvsicc/index.html/)"

At the Ames Research Center there are several UAV technology efforts
being conducted by both NASA and the Army. Much of this work is focused
on rotorcraft technologies.[^10] Specifically, Ames is:

• investigating automated reasoning as part of NASA Intelligent Systems
research using a semi-autonomous rotorcraft;

• developing an integrated simulation environment of UAV flight dynamics
and control (in cooperation with Carnegie Mellon University);

> • providing flight control law analysis support on the Navy's VTOL
> Tactical UAV (VTUAV) and Kaman Aerospace's BURRO (Broad-area Unmanned
> Responsive Resupply Operations)[^11] demonstrator aircraft;

• performing aerodynamic performance and acoustics analysis of UAV
ducted fans; providing engineering support and technical analysis in
support of DARPA's UAV research;

• examining revolutionary swashplateless and variable diameter tilt
rotor concepts using UAVs;

> • performing conceptual design and rotor technology development for an
> autonomous[^12] vertical flight platform on the planet Mars; and,
>
> • starting to examine semi-autonomous systems and their interaction
> with the general environment.

Currently, all NASA-sponsored UAV flights are part of flight testing
programs that require several individuals be continuously involved
during the operational phase of any mission. When using the Dryden
facility, part of this involvement is the prior notification to the
tower at Air Force's Edwards AFB (R2515 and R2508) of the proposed
flight and appropriate flight and mission profile information.

In summary, NASA is pursuing some focused efforts, mostly based around
the Earth Observation System's (EOS) ERAST project, to pursue the
aeronautical technology aspects of UAVs. NASA is also starting an effort
to examine semi-autonomous operations of UAVs primarily within NASA's
Ames Research Center.[^13] Finally, NASA's Dryden Flight Research Center
is collaborating with the Department of Defense (primarily DARPA and the
Air Force) on their UCAV activity. Some of the UAV flights in the ERAST
project are planning to use portions of the NAS.

Discussion of Department of Defense Work

To support a broad range of tactical and strategic missions the DoD has
long been investigating the use of UAVs. For most of the history of UAVs
DoD has driven the technology primarily the need for flight test drones
and remote reconnaissance missions. (See Table 1.) Recently in the
Kosovo operations, UAVs provided reconnaissance support for many NATO
missions. Building on the successes in Kosovo and taking advantage of
some of the emerging UAV technologies the DoD is currently studying how
to employ large numbers of UAVs primarily to limit exposure of their
human assets. They are looking for UAVs to assist military operations
across tactical and strategic missions. Two examples are the anti-radar
drone missions and air attack and transport missions which both use
vehicles called Unmanned Combat Air Vehicles (UCAVs). The Air Force
recently issued a contract to Boeing to build a prototype for testing
the UCAV concept. This one effort has the potential to produce scores
perhaps hundreds of such vehicles.[^14] It is currently unclear how
these vehicles will use the NAS.

The Air Force Research Laboratory (AFRL) at Wright Patterson Air Force
Base is supporting the UCAV effort by starting to examine the challenge
of "Concurrent Airspace Operations (UAV Deconfliction)". NASA Dryden is
partnered with DARPA, the Air Force (AFRL and Air Force Systems Command)
and Boeing on the UCAV program to develop semi-autonomous ground
operation control laws, mid-air collision avoidance guidance, and
interaction with air traffic control. The Air Force AFRL is pursuing the
deconfliction (i.e., conflict prediction and avoidance) of multiple UAVs
in the same airspace. The Air Force will be developing, integrating and
flight testing an automatic air-to-air collision avoidance systems
applicable to both military and civilian manned and unmanned aircraft.

In addition, AFRL's Integrated Tactical Aircraft Control (ITAC) and UAV
Autonomous Control (UAVAC) programs are developing software architecture
and software agents for multi-vehicle operations. AFRL is also
investigating research in cooperative control and close-coupled
formation control. AFRL is also supporting a program called Reliable and
Affordable Control of Cooperative Non-piloted Systems (RACCOONS).[^15]

DoD's Defense Advanced Research Project Agency (DARPA) is researching a
very small size class of UAVs called Micro Air Vehicles (MAVs).[^16]
These tiny aircraft could be used for a variety of missions. One
source[^17] stated that:

> "We're at the Wright Brothers stage" with this effort, Richard Wlezen,
> DARPA's acting program manager for micro air vehicles, told an
> Association for Unmanned Vehicle Systems International symposium
> audience here recently. "We could see something out there in a very
> short time \[with a basic capability\]\...but when you start adding
> autonomy," fielding will take considerably longer.

Although the technology for MAVs is maturing it will probably be several
years before MAVs have the capability to operate in the NAS.

A fundamental question yet to be answered by DoD is whether they will
require that UAV's be allowed to operate in the NAS or will need to be
handled as a form of an advanced drone requiring chase aircraft.

Operational Scenarios

To aid in discussion of various operational issues, three scenarios are
postulated below.[^18] These scenarios serve only as possible uses of
UAVs, not planned activities. These scenarios assume a constant or
continuous level of demand of UAVs on the NAS and its services. Further,
by considering all three scenarios in parallel, a larger scenario that
borders on a "worst case" situation could be created. If only one UAV
was occasionally involved over a long time, then the issues could be
handled on a case-by-case basis. These scenarios attempt to go beyond
that situation. Each scenario considers both the remotely piloted
vehicle (RPV) and semi-autonomously operated vehicle (SOV) classes.
These classes, while artificial, aid in the discussion of
pilot-in-the-loop and no pilot distinctions. There may be some
situations where a pilot will be needed for departing and arriving, but
during the rest of the phase of flight, the vehicle is semi-autonomous.
In addition, none of the scenarios considers the use of "expendable"
UAVs. It is quite possible that UAVs could be used as "one time only"
type assets and, hence, have significantly less demand on the NAS than
those that would be used over and over again.

> [Scenario 1. High Altitude Monitoring Scenario]{.underline}. Everyday
> one UAV takes off from an airport, climbs to altitude in en route
> airspace (or perhaps above 60,000 feet), cruises for several hours,
> adapts to different mission profiles, completes the missions, descends
> to terminal, and lands. Possible missions: atmospheric
> sensing/sampling, polar science, hurricane reconnaissance,
> around-the-world demonstrations, fire monitoring, and
> telecommunications. This scenario essentially duplicates some of the
> capabilities of high altitude reconnaissance aircraft such as the NASA
> ER-2, although not with the same operating performance profile.
>
> [Scenario 2. Medium Altitude Distance Flight Scenario]{.underline}.
> Everyday in many parts of the United States several UAVs take off from
> various airports, climb to various altitudes in en route airspace
> (Class A), cruise amongst various weather zones, aviate among several
> en route ATC facilities, descend to different terminals, and land.
> Possible missions: cargo delivery, point-to-point atmospheric
> monitoring, and hurricane reconnaissance. This scenario explores the
> part of the NAS airspace normally flown by Part 135 and Part 121
> operators.

[Scenario 3. Routine Low Altitude Flight Operations
Scenario]{.underline}. Everyday in many parts of the United States
several UAVs\--with widely differing missions---take off from non-public
launching facilities, climb to various low altitudes, cruise to various
mission areas (generally in Class G airspace), perform one or more
missions, descend to different recovery locations, and land (or are
recovered). Possible missions: commercial imaging, pipeline or
transmission line monitoring, disaster real-time observation or
photography, local/state/federal law enforcement support, and
agricultural/forest/geological/land use. This scenario explores the part
of the NAS airspace normally flown by general aviation.

The UAVs in these scenarios could fall into two classes:

Class 1: Remotely Piloted Vehicles (RPVs)

To ensure a reasonable level of safety, it may be required that all RPV
type UAVs would at a minimum need to:

> 1\. Provide positive (and unique) identification. One research issue
> would be the need to examine the current Mode C 4096 limit on
> transponder codes. Perhaps using the Mode S system for UAVs would be a
> better solution.
>
> 2\. Provide accurate position information. The update rate would need
> to be similar to that achieved by radar.

3\. Possess some form of reasonable flight planning information for
traffic conflict prediction and metering/scheduling purposes. This is
particularly true for those RPVs that would be flying for many weeks.
Research issues include examining the time needed for approvals or
contact/structure of RPV type clearances.

4\. Have a continuous and qualified staffing of the remote piloting
position(s) during all segments of a RPV's flight. This would probably
require a reliable two-way communications architecture for CONUS
operations, perhaps using commercial telecommunications satellites.
Transition to low altitude operations for approach and landing may
require use of local ground-based communications architecture.[^19]

5\. Have emergency procedures available for air traffic controllers. Two
major research issues would be (1) to examine human ATC monitoring to
assess if they can react fast enough to any developing situations and
(2) to create appropriate operating procedures.

Class 2: Semi-autonomously Operating Vehicles (SOVs)

It is assumed that there will be a human-in-the-loop during some phase
of every UAVs flight operation. While it is possible to build autonomous
vehicles, there are safety and operating considerations that make it
very difficult to foresee how either NASA or the FAA would accept them
as part of normal operations. Therefore, a class of UAVs that has
minimal human-in-the-loop interaction is a viable approach. To ensure a
reasonable level of safety, it may be required that all SOVs would at a
minimum need to:

> 1\. Provide positive (and unique) identification
>
> 2\. Provide accurate position information

3\. Possess some form of reasonable Flight Planning information for
conflict prediction and metering/scheduling purposes. This is
particularly true for those SOVs that would be flying for many weeks.

4\. Possess a method or technique for the air traffic control (ATC)
system to command a specific SOV to immediately perform an emergency
maneuver. Other possible maneuvers could include commanding the SOV to
loiter in a holding pattern chosen by ATC, directly return to some
selected point, or perform a wing-over roll into the ground (perhaps
parachuting the vehicle safely to Earth).

Discussion of Operational Issues

Any discussion of operational issues in the NAS requires coverage of a
wide range of complex and interrelated subjects\--each of which demands
great expertise and lengthy experience to avoid creating more
complexities and perhaps confusion. Table 2 shows the structure of the
operational issues section. This structure comes from Aircraft Owners
and Pilots Association's (AOPA) Airman Information Manual cited in the
reference section. Each issue is discussed using the Scenarios outlined
above and the two class types of UAVs\--RPV and SOV.[^20] With many of
the operational issues research topics are identified and potential
approaches outlined. No attempt is made to either dictate or force a
particular operational solution.

While it may not be initially clear why some topics are included in
Table 2, it is clear for UAVs and their operators to fully participate
in the NAS\--as users and consumers of the various operational
services\--they will need to be sensitive to and compliant with all
relevant aspects of the NAS.

Table 2 -- List of Operational Issue Topics

> Navigation Aids
>
> Aeronautical Lighting and Other Airport Visual Aids
>
> Airspace
>
> Air Traffic Control Services
>
> Radio Communications Phraseology and Techniques
>
> Airport Operations
>
> ATC Clearances/Separations
>
> Collision Prediction and Avoidance
>
> ATC Procedures

UAV Flight Plans

Preflight

Departure Procedures

En Route Procedures

Arrival Procedures

> Pilot/Controller Roles and Responsibilities
>
> National Security and Interception Procedures
>
> Emergency Procedures
>
> Emergency Services available to UAVs
>
> Distress and Urgency Procedures
>
> Two-Way Radio Communications Failure
>
> Safety of Flight
>
> Meteorology
>
> Altimeter Setting Procedures
>
> Wake Turbulence
>
> Bird Hazards, Flight over National Refuges, Parks and Forests
>
> Potential Flight Hazards
>
> Safety, Accident and Hazard Reports
>
> Medical
>
> Aeronautical Charts and Related Publications
>
> Remote Pilot Interfaces
>
> UAV Software Certification
>
> Inter-Government Agreements
>
> Science Data Collection and Transmission
>
> Hazards to Persons on the Ground

# Navigation Aids

Since payload mass is at a premium, it is expected that the vast
majority of UAVs will use the GPS System as their primary navigational
and guidance input. For safety reasons, this probably will result in
UAVs needing to support antenna configurations that can receive and
transmit in all directions.

In Scenario 1 this would not be a big issue since such vehicles\--either
RPV or SOV\--are very expensive and will probably possess redundant
navigational capabilities. In the SOV case, legal and safety issues
would probably require an on-site physical presence by someone at the
departure and arrival points.

In Scenarios 2 and 3, having hundreds of RPV-type UAVs operating in the
system would probably require some robust form of remote navigational
capabilities on the UAV so that a remote pilot could know the position
of the UAV relative to published aeronautical information. In the SOV
case, it is difficult to understand what the solution would be if a set
of SOV-type UAVs develop problems with GPS and proceed to deviate from
their flight profiles.

Part of UAV research will need to establish some minimum navigational
performance parameters that the RPV and SOV classes must meet.

# Aeronautical Lighting and Other Airport Visual Aids

In considering Scenarios 1 and 2, since all UAVs (both RPV and
SOV-types) are effectively blind, there will need to be some way for
remote pilots to be aware of the status of various airport terminals'
aeronautical lighting and other airport visual aids during a UAV's
operational phases. These phases include preflight, taxi, liftoff,
approach, landing, taxi, and shutdown. This is not a trivial problem.
Airport operators use those visual aids to inform aircraft pilots of the
status of various systems and objects at the airport. It is unclear how
this situation would involve the SOV-type UAVs since they are
essentially on autopilot. The air information acquired visually can be
flight critical. There is currently no program in FAA's Architecture 4.0
documentation that is targeted to provide this data to either RPVs or
SOVs.

In Scenario 3, this is less of a problem if the UAV takes off and lands
within the owner or customer's facility. The owner/customer has
effectively assumed the liability for the situation.

There will need to be some research done to create systems
(capabilities) which permit UAVs and/or their operators to be aware of
the visual cues (from aeronautical lights and other airport visual aids)
provided to piloted aircraft.

# Airspace

Unless a parallel airspace systems is created for use only by UAVs, it
is safe to assume that UAVs in all the scenarios would need to use the
current NAS and comply with the appropriate FAR rules and regulations
governing the use of that system. The airspace definitions used below
come from the AOPA Airman's Information Manual.

Some UAV proponents have suggested pursuing new airspace concepts that
involve segmenting the current airspace system to contain separate
UAV-only long length corridors or large airspace regions. Such concepts
have the potential for creating a large number of regulatory,
maintenance, and operations issues. Further, such airspace separations
would effectively require that IFR systems would need to be implemented
at much lower altitudes in the nation's airspace and require technology
improvements to permit increased operations and capacity in the NAS. One
research issue would be how such separated UAV airspace could be
effectively created and subsequently monitored (to provided separation
assurance services from other NAS users) and by whom. Another research
issue could examine the concept of using a system of UAVs (in service,
entering service, leaving service) to function as nodes in an operating
neural net to manage each node (UAV) for collision avoidance.

In Scenario 1 UAVs operating in Class A[^21] airspace would effectively
be handled on a case-by-case basis. In Scenario 2, RPVs would need to be
appropriately equipped (as discussed above in Case 1) and have a
properly filed flight plan. Further, the remote pilot would need to be
accessible to ATC throughout the entire time that the UAV was in Class A
airspace. In Scenario 3, it is unlikely the any of the UAVs would
penetrate Class A airspace.

In all the scenarios, unless some particular event requires that a UAV
operate in Class B.[^22] airspace, it is highly unlikely that any UAV
would be permitted such access. The potential for a mid-air collision is
just too great.

In Scenarios 1 and 2, it is likely that many UAV operations would start
or terminate at Class C[^23] airspace airports. These scenarios will
require close interaction between the ATC system and the UAV operators.
Most, if not all, of the UAVs will probably be RPVs. Outfitting the RPV
with a Mode C or Mode S transponder will impose some weight penalty.
Moreover, communications access with ATC will require that the remote
pilot possess highly capable equipment in order to maintain robust
communications with the RPV and ATC.

For Class D[^24] and E[^25] airspace types see the discussion of Class C
airspace.

Conducting activities in Class G[^26] airspace will require that the UAV
be capable of "see and avoid" operations. This is a non-trivial research
topic. Much effort will need to be expended to put a "pilot's mind" into
the software on board a UAV that can safely operate in a mixed weather
environment and continue to conduct its activities in a safe and
predictable manner. It is likely that the vast majority of Scenario 3
type operations will be conducted in Class G airspace.

From the start of their development, UAVs have used Special Use
Airspace[^27] (SUA), particularly Military Operating Areas (MOAs) and
Restricted Areas. Most UAVs started as military platforms and hence have
a real need for sterile research, development, testing, evaluation and
operating environments. It is anticipated that UAVs would continue to be
large users of all types of SUAs. UAVs in all scenarios would likely
first be developed and tested in Special Use Airspace.

UAV operators must be aware of the "other airspace areas"[^28] and their
rules and regulations if any part of the UAV's flight plan crosses, or
in some cases comes near, those areas.

# Air Traffic Control Services

The ATC system provides a wide range of services to its users. These
services include access to facilities such as Air Route Traffic Control
Centers (ARTCCs), terminals, towers, and Flight Service Stations.
Real-time services include flight planning, separation assurance, air
traffic advisories, and status information.

In Scenarios 1 and 2, careful and close coordination between ATC and the
UAV operators would need to be performed. The ATC system would provide
the UAV operator with flight planning, some kind of separation assurance
(a critical research topic), advisories (another research topic),
and---very importantly---status information. In Scenario 3, it is
unclear what services would be available to UAVs. Certainly, the flight
planning services would come into play.

A potential Scenario 2 concept could be that around 2015 UPS wants to
start a customer service of guaranteed 24-hour, 7-day hourly cargo
delivery. This service could be between two airports (e.g., Philadelphia
(PHL) and Chicago O'Hare (ORD)) using 50 UAVs (RPV type) each capable of
carrying a metric ton of cargo. The impact of such a stream of traffic
on NAS would be interesting especially on the type and kind of ATC
services that could be available. Now extend this concept to 100 such
operating streams in many places in the United States.

### Radio Communications Phraseology and Techniques

In all the scenarios, where RPV-type UAVs are employed, the radio
communications phraseology and techniques would need to conform to the
standards set by regulation and practice. Any unusual phrases or
techniques would need to be approved before their usage.

In any scenario where an SOV-type UAV is employed, the automation would
need to also conform. This would be a highly controversial research
topic, since how does anyone really know if the robot actually
understood the communication? This would dictate that a
human-in-the-loop would need to intervene and assist the SOV in some
manner.

### Airport Operations

UAVs of all types would need to have information concerning runway and
taxiway surface movement in order to prevent incursions. In all the
scenarios where RPV-type UAVs are employed, the airport operations of
the UAV would need to conform to all rules and regulations, particularly
those involving safety. If the remote pilot does not actually have their
eyes or some visual aid assisting them, then the operations are
essentially "zero-zero" in nature and must have correspondingly greater
safety margins.

For the SOV-type UAV case it is difficult to imagine a robot wandering
around (taxiing on) an airport's surface mostly oblivious to other
traffic or objects (this is a very difficult research topic). This is a
particularly difficult issue since handling any potential problems
(e.g., the UAV running off the taxiway or runway into a ditch) would
cause new on-the-spot procedures to be developed. In addition, how would
ATC divert a UAV to a different taxiway or runway (if it is landing). It
is likely in almost all cases with SOV-type UAVs that a human would
operate the UAV during the ground phases of flight.

### ATC Clearances/Separations

The issue of accurately accepting and fully executing ATC clearances and
maintaining required separations from other aircraft vehicles or other
objects (e.g., clouds) are potentially the most difficult issues facing
the introduction of UAVs into the NAS. Since the safety of users in the
NAS is a fundamental principle of operations, the UAVs, their operators,
and owners must be fully aware of the value in having UAVs that can
accept these clearances and maintain separation. These issues can
**STOP** UAVs from ever becoming a common phenomenon in the NAS
regardless of how well the flight technology works. Much difficult
research needs to be conducted on these issues and there are currently
no programs within the FAA's NAS Architecture 4.0 that are focused on
these issues for UAVs.

### Collision Prediction and Avoidance

In all the scenarios it is clear the any UAV operating in the NAS,
particularly when in positive control airspace (PCA), will need to be
capable of some level of "see and avoid" collision predication and
avoidance. The visual "see and be seen" rule so prevalent in general
aviation operations simply would not work well since the UAV is
effectively visually blind. Although NASA will be researching this issue
for the ERAST Version 3 aerial vehicle (see footnote 8, second
paragraph), the myriad of technical issues and equipping, training, and
informing the rest of the aviation community will take time. Having the
UAV frequently transmit "It's me, here I am and here's where I'm going"
type messages in IFR/VFR airspace is of limited use since many general
aviation aircraft are not anticipated to be equipped with the
appropriate communications systems. Even if the equipage issue can be
overcome, the UAV would essentially be a blind missile in IFR/VFR
airspace unable to follow well-understood rules of the road.

The highest benefit solution is requiring yet-to-be-developed equipage
of UAVs with Identification Friend or Foe (IFF) systems and some form of
on-board collision prediction and avoidance capabilities. This would
permit all NAS users to interact with a predictable level of safety and
acceptable operating risk margin.

# Air Traffic Procedures

### UAV Flight Plans

Although for VFR flights flight plans are not required, it is common
practice for VFR pilots to file a VFR flight plan with the appropriate
FAA Flight Service Station (FSS). This plan contains relevant
information about the flight's departure times, route, and aircraft
equipment capabilities. It is conceivable that when UAVs start becoming
a common operation, not just a few R&D flights, all UAVs will need to
have an appropriate flight plan filed with the FAA. This will require
that somebody be responsible for the UAV during its entire flight
profile. This assumption of real liability is a deep issue and needs
careful consideration by all appropriate parties. Without a flight plan
a UAV could be involved in a collision or disaster and create a
situation where is it unclear who is responsible for the UAV. This
probably means that UAV flight plans would have information concerning
the location and contact numbers for persons remotely flying or
responsible for the UAV. This could potentially involve the FAA in a
lengthy process of a preparing a formal Notice of Proposed Rule Making
for such flight plans.

### Preflight

During the preflight phase, every pilot usually seeks out all relevant
information concerning their flight's path and anything (including
updated charts) that might affect it. This includes acquiring
information about NAS status, the weather, Notices to Airmen (NOTAMs),
and listening to any information that the FSS may deem important (like
operations of other UAVs). After careful consideration of all collected
information, they usually file a flight plan (see above). All flights
that enter controlled airspace (see the prior discussion on airspace)
are required to have a valid flight plan without which they cannot enter
controlled airspace or receive ATC clearances.

### Departure Procedures

Since in Scenarios 1 and 2, remotely piloted UAV will be participating
in the normal flow of departure operations, the UAV operator must be
fully aware and understand what this means. Since any failure to execute
departure directions from ATC will probably result in impacts on other
users, the UAV operators must be ready to fly when required. Normal
operations do not mean that a UAV operator can suddenly remember that
more of something needs to be done before they can take off. In most
situations, any failure will cause the system to react in a manner that
removes that problem from the system and lets the rest of the users
proceed about their business.

In Scenario 3, the departure procedures would either follow those of
Scenario 2 or be totally within the control of an owner/customer
facility's operations. In this case, the owner/customer would need to
ensure that the appropriate FAR part was being followed. There may even
need to be certification of such non-FAA facilities.

### En Route Procedures

During Scenarios 1 and 2, UAV operations in en route airspace would be
part of the normal stream of traffic through ARTCC airspace subject to
all applicable rules and regulations of the airspace (see the discussion
of Class A airspace above). Of critical importance would be the
communications link between ATC and the remote pilot. Further, robust
and thorough emergency procedures during en route operations would need
to be in place before normal UAV operations could take place.

### Arrival Procedures

Part of the ATC system is having the pilot (in this case the remote
pilot) close their flight plan upon canceling or completing their
flight. Canceling a flight plan before landing and leaving the ATC
system will cause termination of all ATC services. RPV operators will
need to close their flight plans. It is not clear who would close an SOV
flight plan unless the human-in-the-loop took on that responsibility.

### Pilot/Controller Roles and Responsibilities

The remote pilot of an operating UAV should be considered as the
"command pilot" or "pilot in charge" of the UAV. In the operating
SOV-type case it is less clear of who is the pilot (i.e., it is the
"software" on board the SOV-type UAV?) and more of a legal problem. ATC
will need to have a robust procedure in order to provide service to the
UAV and the person operating as the "command pilot" of the UAV will need
to fulfill that role and responsibility. One research topic could be to
examine if SOV-type UAVs should have an override by ATC to become an
RPV-type in most emergencies.

Controller roles and responsibilities should not be changed and only
clarified for the case of handling UAVs in controlled and uncontrolled
airspace. There will probably be some additions and modifications to the
Air Traffic Control Handbook FAA Order 7110.65 discussing the procedures
to be followed when handling UAVs. The sections covering communications
procedures and phrases would certainly have to be carefully considered.

### National Security and Interception Procedures

The command and control communications channels to all UAVs would need
to comply with National Standards for Communications Security (COMSEC).
Inadvertent or malicious tampering with the communications signals could
potentially cause collisions with other vehicles or create dangerous
situations on the ground. Further, imagine a "hacker" remotely hijacking
a large UAV and taking it for a joyride. This could potentially be a
serious issue. If the UAV is transponder equipped and is hijacked, then
there would need to be some internal and protected UAV capability to
dial in a 7500 code into the transponder. One research issue could be
determining how an SOV-type UAV would know that it had been hijacked.
This would require special artificial intelligence to distinguish
between unexpected but normal change of commands and intruder or
unauthorized change of commands.

# Emergency Procedures

It is common practice that the remote pilot in command of a UAV is
directly responsible for the operation of that vehicle. While the
legalities governing UAVs need to be carefully considered and made part
of the FARs, this paper considers that the remote pilot is at minimum
required to abide by the general aviation rules governing private pilots
and the rules contained in FAR Part 91. The critical part for emergency
procedures in the FAR is Part 91.3 (b) which states that "in an
in-flight emergency requiring immediate action, the pilot in command may
deviate from any rule of this part \[i.e., PART 91\] to the extent
required to meet that emergency."

In all three UAV Scenarios, the need for clear and unambiguous emergency
procedures, for both distress and urgent situations, would be a
requirement before UAVs would be permitted general access to the NAS.
Although the UAV may initially be dealing with a danger to itself, it is
in the NAS and will probably influence the actions of others. As the
referenced AOPA document states, "safety is not a luxury."[^29]

### Emergency Services available to UAVs

In the current NAS there are several emergency services available to
pilots. These services include:

Transponder emergency operation (squawking Code 7700 on the Mode C
transponder),

> Direction finding instrument approach procedure (using direction
> finder equipment),
>
> Intercept and escort (the use of Search and Rescue (SAR)
> capabilities),
>
> Emergency locator transmitters (required for general aviation
> aircraft), and,
>
> FAA's K-9 explosive detection team program (detecting and dealing with
> bomb threats).

As can be seen from the list above, UAVs and their operators would need
full and complete awareness of how their operational situation would fit
into system. For example, imagine a situation where a UAV with a Mode C
or S transponder has an emergency, does the UAV itself or the remote
pilot dial in the 7700 code? Further, would UAVs be required to have an
emergency locator on board? Moreover, if so, what kind?

UAVs themselves would probably need to contain indestructible labels
that could be referred to as "if found, please call\..."

### Distress and Urgency Procedures

The appropriate handling of UAV emergencies will require that the remote
pilot be adequately trained and aware of the correct steps. In some
situations the UAV itself, besides the remote pilot, may be required to
have radio equipment that has the ability to transmit on 121.5 mHz,
243.0 mHz, and/or 2182 kHz frequencies. These frequencies are guarded by
many ATC facilities and can only be used to transmit emergency messages.

### Two-Way Radio Communications Failure

A potential for major impact on the NAS and its users could arise from a
two-way radio communications failure with the UAV or the remote pilot.
Procedures for handling such situations involve the following of
specific protocols, some of which are covered in FAR Part 91.185. In the
case where the remote pilot loses communications with the UAV, the UAV
itself needs to be able to handle such a situation and safe mode itself.
The in the case where the remote pilot loses communications with ATC,
then they need to somehow reestablish that communications and failing to
do so, safe mode the UAV.

# Safety of Flight

Safety of flight includes taking into consideration: meteorology; wake
turbulence; bird hazards; flight over National Refuges, Parks, and
Forests; potential flight hazards; and, safety, accident, and hazard
Reports. All of these are discussed below.

### Meteorology

To avoid UAV operations from being adversely impacted by weather
phenomena, the UAV operators should follow normal pilot procedures
during the preflight and flight phases to gather and assess relevant
weather information. In all UAV scenarios, weather will have an impact
on their operations. For example, cloud formations or air turbulence may
cause modifications in a UAV's flight profile. In the RPV-case, the
remote pilot has the responsibility to stay aware of the weather
information\--primarily from the National Weather Service, FAA, military
weather services or other sources\--and act accordingly. In the
SOV-case, it is unclear who has this responsibility. SOV-case research
will be needed to address this issue.

It is also unclear how UAV operators would acquire and use weather
information from Pilot Weather Reports (PIREPS), En Route Flight
Advisory Service (EFAS), Automated Weather Observing System (AWOS),
Automated Surface Observation System (ASOS) and weather radars. Each of
these systems requires that the pilot (in their aircraft) locally
interact to acquire the needed information. This will be a large
communications challenge for remote pilots who will be perhaps hundreds
of miles from their UAV. It is an interesting research issue on how
remote pilots will acquire the right signals and remain in clear contact
with appropriate facilities. An Ames researcher pointed out that perhaps
the UAV could act as a relay point for the remote pilot. It is clear
that research would be needed to solve this issue.

### Altimeter Setting Procedures

This may not be an issue if the UAV is using GPS for guidance and
navigation since the altitude is part of that system. Of importance to
the FAA are the local corrections to the GPS signal that would be needed
for UAVs operating in close proximity to populated areas or difficult
terrain. The FAA's WAAS and LAAS programs should address many of the
local correction issues.[^30] Ensuring that the GPS itself is giving the
UAV continually correct information would also needed some
investigation.

### Wake Turbulence

Every aircraft generates a wake while in flight. For UAVs to
successfully operate in a normal fashion, the UAV must be capable of
responding appropriately to wake turbulence and in most cases trying to
avoid it. A small UAV encountering the wake of a large or heavy class
aircraft could spell disaster. In all Scenarios, for the RPV-case the
remote pilot needs to be aware of the potential for wake turbulence and
the appropriate reactions. Research will be needed to see how this would
be accomplished. In the SOV-case the robot would need this same
awareness and reaction capability.

### Bird Hazards, Flight over National Refuges, Parks and Forests

Migratory bird activity increases the risk of bird strikes on all
aircraft. According to the AOPA Airman's Information Manual, "over 90%
of the report bird strikes occur at or below 3,000 feet \[above ground
level\] (AGL)\...ducks and geese are frequently observed up to 7,000
feet AGL and pilot are cautioned to minimize en route flying at lower
altitudes during migration." [^31] Since UAVs in Scenarios 2 and 3 will
be frequently operating at such altitudes, there needs to be some
awareness in UAV design and operation of such migrations. The FAA will
need to be contacted and appropriate information distributed. Some
research will need to be conducted on what the UAV design and operator
community should do about migratory birds.

UAV operators should also be aware of the rules regarding flights in,
above and around National Refuges, Parks and Forests.

### Potential Flight Hazards

To list the ten most frequent causal factors for general aviation
accidents involving the pilot-in-command (in the case of UAVs, the
remote pilot):

1\. Inadequate preflight preparation and/or planning

2\. Failure to obtain and/or maintain flying speed

3\. Failure to maintain direction control

4\. Improper level off

5\. Failure to see and avoid objects or obstructions

6\. Mismanagement of fuel

7\. Improper inflight decisions or planning

8\. Misjudgment of distance and speed

9\. Selection of unsuitable terrain

10\. Improper operation of flight controls

It is clear from this list that the training and qualification of the
UAV's remote pilot is a critical factor towards a successful mission. In
all scenarios, the RPV-case requires a well-qualified and aware remote
pilot. In the SOV-case, it is unclear if the robot pilot should possess
all the knowledge and skill needed to avoid the above flight hazards.
This issue needs carefully consideration and research.

### Safety, Accident and Hazard Reports

The UAV operators would need to be aware of and comply with the
requirements for safety, accident and hazard reports. This includes the
NASA Aviation Safety Reporting Program (ASRS), the aircraft accident and
incident reporting requirements, and the near midair collision reporting
requirements.

# Medical 

In cases, where the UAV is remotely piloted the training and physical
qualifications of remote pilots will require some careful consideration
and examination of the Federal Aviation Regulations governing pilots.
Since the remote pilot is flying the physical vehicle in the actual NAS
there clearly needs to be certified flight training of those pilots
beyond just being able to successfully fly the Microsoft Flight
Simulator 2000 software. Imagine letting your teenage son or daughter
take a turn at flying your company's expensive UAV without proper
supervision or training. Further, since the remote pilot is responsible
for the flight behavior of the UAV, the ATC system requires two-way
communications with the remote pilot.

# Aeronautical Charts and Related Publications

The operators of any UAVs in the NAS should be familiar with and
practiced on the usage of aeronautical charts and related publications.
Much critical flight information is located on such charts and would
factor into a UAV's preflight planning phase. All the scenarios are
impacted by information contained in these charts.

# Remote Pilot Interfaces

Currently the use of remote pilot interfaces is based mostly on the
amateur radio-controlled model aircraft experiences. Future remote pilot
interfaces will need to possess communications, GN&C, database, and
mission command and control capabilities far beyond those commercially
available. Most research efforts piece together the equipment and
software that is needed without much consideration of integrating
together a standard workstation that can be tested and qualified for
general UAV usage beyond that needed by the project at hand. Much
research in human factors and computer interface design will be needed
to produce the first versions of such common standardized workstations.
With such common workstations there could be savings in training remote
pilots since knowing one UAV remote pilot workstation would transfer
knowledge to another. Further, if one remote pilot controls more than
one UAV of different types and capabilities then having a common
workstation should aid in reducing remote pilot workload and potential
confusion. Currently within NASA there are no research programs that are
looking at the generic remote pilot interface issue.

# UAV Software Certification

The issue of certifying a complex set of flight critical, indeed safety
critical software for flight vehicles has received close attention for
many years. RTCA's Special Committee 167 has prepared and updated their
Software Considerations in Airborne Systems and Equipment Certification
(DO-178B).[^32] This document covers a wide range of important topics
concerning the certification of all software on-board flight vehicles.
UAV developers, including the flight system programmers, need to
carefully consider the creation and maintenance of their software
according to the guidelines found in this document. Since some of the
software will be flight critical and used in conflict detection and
avoidance, special emphasis on this software will be needed.

[Inter-Government Services and Agreements]{.underline}

The Government conducts, manages, and oversees many services (e.g.,
letters of transit, overflights, and use of satellites for
communications) which can potentially impact the ability of UAV
operators to conduct their desired mission activities. Many of these
services have agreements associated with them that the UAV industry will
need to understand and comply with. To achieve a broad, national use of
UAVs, there will need to be significant education, cooperation and
coordination amongst the UAV industry and the affected Government
organizations. It is never too early to start the process of getting
government approvals for various UAV requirements.

# Science Data Collection and Transmission

The collection of science data and its transmission are a large part of
the push towards using UAVs. With such collection (e.g., Antarctic ozone
hole monitoring, air and water pollution issues, sea condition
monitoring, ice flow monitoring, etc.), comes the necessary challenge of
getting the data where people need it. Increased Internet and radio
wavelength bandwidth will be needed accommodate greater volume of UAV
communications and data flows. Further, there will be an operational
need to automatically receive and send down, in a timely and accurate
manner, increased information on UAVs including the identification of
the remote pilot(s), their telephone numbers and communication access
codes, and the mission information.

[Hazards to Persons on the Ground]{.underline}

In some cases UAVs will be carrying some kind of hazardous materials
either as cargo, fuel or as part of the UAV itself. When a UAV develops
a problem and crashes, the designers of the UAV need to have considered
and minimized any hazards to persons on the ground.

Summary

This paper discusses the primary NASA work on Unmanned Aerial Vehicles
(UAVs), indicated where further information may be located[^33], and
presented some of the potential impacts of UAVs on the United States
National Airspace System (NAS). Three operational scenarios using UAVs
in the NAS are presented and several relevant Air Traffic and
aeronautical operational issues are discussed. Many research issues are
identified that would need to be successfully conducted and concluded
before general access of UAV into the NAS could be allowed, primarily
for safety reasons.

Some of the UAV issues briefly discussed---not in order of
priority\--include:

-   Liability

-   Negligent operations

-   Remote pilot fitness

-   Remote pilot interference by outside sources (radio, magnetic,
    other)

-   Unauthorized or authorized operations over populated areas

-   Potential mid-air collisions between UAV and passenger carrying
    aircraft

-   Coordination among various Air Traffic Control systems (including
    foreign)

-   Inter-Government agreements and their organizations for existing
    services

-   Science data collection and transmitting of data to scientists on
    the ground

-   Hazards to persons on the ground

It is clear from the discussion in this paper that wide spread UAV
operations would need to fit into an already established NAS and conform
to most of the established rules and practices. The topics discussed in
this paper represent only a beginning that needs to be carefully
considered by the appropriate organizations and efforts put into motion
that will permit the safe and efficient operations of UAVs now and in
the future.

Finally, effective mechanisms need to be developed for soliciting
approaches, problems, issues, and recommendations from various affected
communities. With a solid understanding of the impact of UAVs on the NAS
and ways of solving the various research issues, there should be a
bright future for UAVs.

Glossary

AOV Autonomous Operating Vehicle[^34]

ATC Air Traffic Control

ATM Air Traffic Management

CONUS Continental United States (the lower 48 States)

FAA Federal Aviation Administration

FAR Federal Aviation Regulations

FSS Flight Service Station

GN&C Guidance, Navigation and Control

IFF Identification Friend or Foe

IFR Instrument Flight Rules

Intl International

kHz Kilohertz

OTH Over-the-Horizon

MAV Micro Air Vehicles

mHz Megahertz

NAS National Airspace System

NASA National Aeronautics and Space Administration

ROA Remotely Operated Aircraft

ROV Remotely Operated Vehicles[^35]

RPV Remotely Piloted Vehicles

SOV Semi-autonomous Operating Vehicle[^36]

SUA Special Use Airspace

UAV Unmanned (Uninhabited) Aerial Vehicles

UCAV Unmanned Combat Air Vehicles

VFR Visual Flight Rules

VTUAV Vertical-takeoff Unmanned Air Vehicle

References

Aviation Week and Space Technology weekly aviation magazine.

AOPA's Airman's Information Manuel

FAA Order 7110.65 Air Traffic Control (version M), Federal Aviation
Administration.

1997-1998 International Guide to Unmanned Vehicles, Aviation Week and
Space Technology Special Publication, Washington DC.

[^1]: See Katrina Herrick's presentation of "Highlights of Trends and
    Growth in Civil UAV Markets. This presentation can be downloaded
    from the Internet on
    http://users.erols.com/auvsicc/faaisg/ppt/markets.htm

[^2]: Further information on UAVs is located on the NASA web site
    http://uav.wff.nasa.gov[/index.hmtl]{.underline}. This site is
    well-organized with information on many different UAVs used either
    for research or in production and arranged in chart format that
    permits a user to look at any of the UAVs in some detail, including
    vehicle endurance, payload weight, and altitude capabilities. By
    selecting any specific UAV on the chart, the interface permits a
    user to view the physical and performance characteristics, the
    payload specifications (power, etc.), estimated costs and also
    allows further selection of a link to even more information.

[^3]: Aviation Week and Space Technology, February 28, 2000, pages
    58-61, has an article entitled "Special Fuel Cells Key to
    Months-Long Flight" which describes the technical issues of long
    flight in detail.

[^4]: In particular the Air Force's research laboratory (AFRL) at Wright
    Patterson AFB and the Global Hawk and Predator Special Programs
    Offices are investigating collision avoidance systems and the issues
    and actions necessary to fly unmanned vehicles in controlled and
    uncontrolled airspace. Further, the Air Force Air Combat Command
    (ACC) are evaluating lessons learned from Kosovo and other military
    operations in order to improve the control and effective application
    of UAVs in future military operations. ACC is also actively involved
    in working UAV control and air traffic management issues at the
    international level. See footnote 6.

[^5]: In a 1998 Special Aviation Week issue of Unmanned Vehicles (see
    references), many different UAVs and their technical details are
    presented. UAVs are described with their company information,
    mission, dimensions, weights, maximum fuel capacity,
    propulsion/fuel, performance, payload(s), GN&C information, brief
    operational concept (1 or 2 sentences), and method of
    launch/recovery, system history, program status, and points of
    contact. This special edition also contains a detailed history of
    UAV technology development.

[^6]: *The Innovator's Dilemma: When New Technologies cause Great Firms
    to Fail*, Clayton Christensen, Harvard Business School Press, Boston
    MA., 02163, 1999. From the book jacket "Christensen argues that good
    business practices---such as focusing investments and technology on
    the most profitable products that are currently in high demand by
    the best customers---ultimately can weaken a great firm. Drawing on
    patterns of innovation in a variety of industries, including
    computers, retailing, pharmaceuticals, automobiles, and steel, he
    shows how truly important, breakthrough innovations---or disruptive
    technologies---are initially rejected by mainstream customers
    because they cannot currently use them."

[^7]: Further information about NASA's programs and projects can be
    found at [www.NASA.gov](http://www.NASA.gov/) and following the
    various Enterprise, Organization, and Center information selections.

[^8]: For further information consult
    http://www.dfrc.nasa.gov/Projects/erast/ The ERAST program, lead by
    the NASA Dryden Flight Research Center, Edwards, CA., aims to
    develop aeronautical technologies that will lead to a new family of
    remotely piloted vehicles (RPVs) that will fly:

    SLOWER At subsonic speeds, as slow as 15 miles per hour (24.1
    kilometers per hour)

    HIGHER At altitudes as high as 100,000 feet (30 kilometers)

    LONGER For continuous missions lasting as long as 96 hours

    Such long-duration, high-altitude RPVs could be used in
    upper-atmospheric science missions to help collect, identify, and
    monitor environmental data to assess global change. They also could
    carry telecommunications equipment to high altitudes, serving in
    place of satellites for a fraction of the cost of putting a
    traditional satellite in space.

    See also, Aviation Week and Space Technology, January 31, 2000,
    entitled "NASA Taps General Atomic to Build New Drones." This short
    article discusses the 3 ERAST Predator B versions and their
    projected performance capabilities and propulsion systems. The
    'proof of concept' vehicle is expected to conduct its maiden flight
    during the summer of 2000. The second airframe will have higher
    altitude capabilities and first fly in 2001. The third version will
    have longer endurance, fly in mid-2002 and use L-Band commercial
    satellites for over-the-horizon operation and have a see-and-avoid
    capability to operate in the air traffic control system.

[^9]: A special biweekly newsletter called [Inside FAA]{.underline},
    January 21, 2000 has an article titled "FAA's Integrating UAVs into
    NAS could be affected by NASA Program." This article discusses the
    need for NASA to obtain a certificate of authorization to fly UAVs
    outside of special use airspace. FAA has also prepared draft
    Advisory Circulars on UAV operations. The article also discusses a
    NASA Research Announcement seeking proposals from industry on a
    range of highly capable UAVs and some of the capabilities desired in
    such UAVs. The article mentions that this effort "will probably
    hasten the development of FAA regulations covering the operation of
    commercial UAVs in the \[NAS\] as the contractor makes the
    case-by-case applications to the FAA\..."

    One reviewer of this paper observed that the FAA seems to be
    pursuing a prudent "wait and see" approach towards integrating UAVs
    into the NAS. That is, if the market never emerges then the FAA will
    not have needlessly developed procedures or rules.

[^10]: Internal NASA communications.

[^11]: More information can be found on VTUAV by web searching "VTUAV"
    and on BURRO by web searching about the Kaman Corp.

[^12]: In this case, the vehicle would be almost entirely autonomous due
    to the long communications loop between Earth and Mars. There would
    probably be a human-in-the-loop to initiate a mission, but then the
    vehicle would probably fly autonomously about the planet reporting
    its progress and discoveries to an orbiting satellite for relay back
    to Earth.

[^13]: For further information on NASA's Intelligent Systems Initiative
    effort review the following URL http://infotech.arc.nasa.gov/.

[^14]: For more information review the following web address:
    <http://www.darpa.mil/tto/programs/ucav.html>

[^15]: For further information on the Air Force's AFRL activities
    concerning UAVs or UCAV contact Donald Swihart at Wright Patterson
    AFB on 937.255.8281. He is the Air Force point of contact on these
    topics.

[^16]: There are several web sites that discuss MAVs:

    <http://www.darpa.mil/tto/MAV/mav_auvsi.html>

    <http://www.fas.org/man/dod-101/sys/land/docs/bct/MAV-ORD-31-Jan-00.htm>

    http://www.aero.ufl.edu/\~issmo/mav/Morris/morris.htm

    <http://www.newscientist.com/ns/970405/features.html>

[^17]: This site has an interesting overview of DoD's MAV efforts

    <http://www.infowar.com/mil_c4i/99/mil_c4i_082599d_j.shtml>

[^18]: These scenarios and most of Table 1 "Representative UAV Missions"
    were based on a briefing prepared by Steve Wegener (NASA Ames
    Research Center) entitled "Over the Horizon (OTH) Communications
    Workshop Findings and Future Plans" March 17, 1998.

[^19]: ..Private communications from John McKinley (SAIC) (April 3,
    2000) "\...Transition to low altitude operations for approach and
    landing may require use of local ground-based communication
    architecture to obviate problems with low-power satellite signals,
    atmospheric attenuation during IMC, antenna shadowing, etc."

[^20]: Private communications from Charles C. Ingalls (NASA/ARC) (March
    24, 2000) "The distinction between SOVs and RPVs did not seem clear
    to me. UAV autonomy can range from no automatic functions with full
    external control, to fully autonomous with on-board decision logic
    and no external control. The level of autonomy is going to be pretty
    important with respect to how the UAV interacts with other NAS users
    and controlling agencies. It might be useful to define ranges of
    autonomy to differentiate between UAVs for developing those
    relationships (with intermediate levels). UAV autonomy is currently
    also variable based on "phase of flight" (E.g., Hunter takes off and
    lands under external pilot control using a model airplane radio
    control box). Systems are then transferred to operators in a control
    station who then direct flight paths on a moving map rather than by
    direct control manipulation.

[^21]: Class A---airspace from 18,000 feet MSL up to and including
    60,000 feet MSL over CONUS and Alaska. Unless otherwise authorized
    all aircraft must operate under IFR.

[^22]: Class B---airspace from the surface to 10,000 feet MSL
    surrounding the nation's busiest airports in terms of IFR operations
    or passenger enplanements. The configuration of each Class B
    airspace area is individually tailored and consists of a surface
    area and two or more layers (some Class B airspace areas resemble
    upside-down wedding cakes). An ATC clearance is required to operate
    in the area and all aircraft that are so cleared receive separation
    services within the airspace. Mode C transponders are required on
    board all aircraft. VFR operations are subject to FAR Part 91.215
    and FAR Part 91.131 requirements. Unless otherwise authorized by
    ATC, aircraft must be equipped with an operable two-way radioClass B
    airspace areas include at least the following locations: Andrews AFB
    MD, Atlanta Hartsfield, Boston Logan, Chicago O'Hare Intl Airport,
    Los Angeles Intl Airport, Miami Intl Airport, Newark Intl Airport,
    New York Kennedy Airport, New York La Guardia Airport, San Francisco
    Intl Airport, Washington National Airport, and Dallas/Fort Worth
    Intl Airport.

[^23]: Class C---airspace from the surface to 4,000 feet MSL above the
    airport elevation surrounding those airports that have an
    operational tower, are serviced by a radar approach control, and
    that have a certain number of IFR operations or passenger
    enplanements. Usually an operating two-way radio and a Mode C
    transponder are required.

[^24]: Class D---airspace from the surface to 2,000 feet MSL above the
    airport elevation surrounding those airports having an operational
    control tower. Usually an operating two-way radio is required.

[^25]: Class E---airspace that is not Class A, B, C, or D and is
    controlled airspace is Class E airspace. For example, Federal
    Airways are Class E airspace and extend upward from 1,200 feet MSL
    to, but not including, 18,000 feet MSL. The colored airways are
    Green, Red, Amber, and Blue. The VOR airways are classified as
    Domestic, Alaskan, and Hawaiian. Many offshore areas are also
    classified as Class E airspace. No separation services are provided
    to VFR aircraft operating in Class E airspace.

[^26]: Class G---airspace that is not Class A, B, C, D, or E. Rules
    governing VFR flight assist the pilot in meeting the responsibility
    to see and avoid other aircraft. Minimum flight visibility and
    distance from clouds required for VFR flight are discussed in FAR
    Part 91.155. FAR Part 91.177 includes a requirement for VFR aircraft
    to remain at least 1,000 feet (2,000 feet in designated mountainous
    terrain) above the highest obstacle within a horizontal distance of
    4 nautical miles from the course to be flown.

[^27]: Special Use Airspace---airspace where activities must be confined
    because of their nature or where limitations are imposed upon
    aircraft operations. Special Use Airspace includes Prohibited Areas,
    Restricted Areas, Warning Areas, Military Operations Areas, Alert
    Areas, Controlled Firing Areas and National Security Areas.

[^28]: Other Airspace Areas---including Airport Advisory Areas, Military
    Training Routes, Temporary Flight Restrictions, Flight
    Limitations/Prohibitions, Parachute Jump Aircraft Operations,
    Published VFR Routes and Terminal Radar Service Areas.

[^29]: AOPA Airman's Information Manual, Chapter 6 Emergency Procedures.

[^30]: For more information about FAA's programs, see the web site
    [www.faa.gov](http://www.faa.gov/) and review the NAS Architecture
    details and program status.

[^31]: See the AOPA Airman's Information Manual Section 7-4-1 for
    further information.

[^32]: RTCA, Inc., December 1, 1992, *RTCA/DO-178B Software
    Considerations in Airborne Systems and Equipment Certification*,
    Washington DC.

[^33]: Although not discussed in this paper there are several Web sites
    which have information on UAVs. Any search engine should find
    several which provide information of specific UAV vehicles. Some of
    these are:

    http://www.aerosonde.com/

    <http://www.psl.nmsu.edu/roa/>

    <http://www.shephard.co.uk/pubs/unman/index.htm>

    <http://www.au.af.mil/au/database/research/ay1998/acsc/98-147.htm>

    <http://cws.rams.com/afosr/afr/sab/any/text/any/uavstud.htm>

    <http://users.erols.com/auvsicc/uav.htm>

    If a specific URL does not work, try using less of the address. The
    Shepard URL has a specific publication for UAVs.

[^34]: Where no pilot or controller has input during the operation of a
    UAV. We do not consider this an operationally viable option.

[^35]: Where a controller or pilot has complete control in operating a
    UAV.

[^36]: Where a controller or pilot has some limited input while
    operating a UAV.