National Airspace System: Comprehensive FAA Plan for Global Positioning
System Is Needed (Letter Report, 05/10/95, GAO/RCED-95-26).
Pursuant to a congressional request, GAO reviewed the Federal Aviation
Administration's (FAA) augmentation of the Global Positioning System
(GPS) for use in civil aviation navigation, focusing on whether FAA: (1)
will have sufficient time under its new milestones to augment GPS; and
(2) has taken appropriate actions to better manage its GPS-related
efforts.
GAO found that: (1) although FAA has met all of its milestones to date,
its future milestones involve more complex and difficult tasks; (2) FAA
may not have enough time to develop and implement its wide area system
augmentation by 1997, although civil aircraft are expected to use the
augmented GPS without relying on other navigation aids for backup; (3)
FAA estimates that system software development alone may take 24 to 28
months; (4) implementation of the wide area system may be delayed by
factors beyond FAA control, such as the launching of commercial
satellites needed to support the system; (5) in 1994, FAA strengthened
its GPS management by integrating its GPS activities, securing the
necessary funding to accelerate the wide area system's development, and
issuing plans for developing and implementing augmentation systems and
transitioning to GPS; and (6) the FAA GPS plans are not comprehensive,
since they omit a schedule for implementing the local area system, cost
estimates for the local and wide area systems, and the probabilities of
meeting schedule and cost estimates.
--------------------------- Indexing Terms -----------------------------
REPORTNUM: RCED-95-26
TITLE: National Airspace System: Comprehensive FAA Plan for Global
Positioning System Is Needed
DATE: 05/10/95
SUBJECT: Navigation aids
Transportation safety
Air traffic control systems
Communications satellites
Research and development costs
Computer software
Geographic information systems
Systems conversions
Systems management
Weather forecasting
IDENTIFIER: NAVSTAR Global Positioning System
GPS
FAA Satellite Navigation Program Master Plan, FY 1994-1999
FAA GPS Implementation Plan for Air Navigation and Landing
FAA National GPS/CNS Transition Plan
FAA Wide Area Augmentation System
GPS Communications, Navigation, and Surveillance Systems
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Cover
================================================================ COVER
Report to the Committee on Transportation and Infrastructure, House
of Representatives
May 1995
NATIONAL AIRSPACE SYSTEM -
COMPREHENSIVE FAA PLAN FOR GLOBAL
POSITIONING SYSTEM IS NEEDED
GAO/RCED-95-26
Global Positioning System
Abbreviations
=============================================================== ABBREV
CNS - Communications, Navigation, and Surveillance
DOD - Department of Defense
DOT - Department of Transportation
FAA - Federal Aviation Administration
GAO - General Accounting Office
GPS - Global Positioning System
ICAO - International Civil Aviation Organization
INMARSAT - International Maritime Satellite Organization
Letter
=============================================================== LETTER
B-260614
May 10, 1995
The Honorable Bud Shuster
Chairman
The Honorable Norman Y. Mineta
Ranking Democratic Member
Committee on Transportation
and Infrastructure
House of Representatives
The Federal Aviation Administration (FAA) is augmenting (enhancing)
the Department of Defense's (DOD) Global Positioning System (GPS)
because this satellite-based system will provide major benefits to
civil aviation. When fully integrated as a navigation aid in the air
traffic control system, GPS will be superior to the ground-based
navigation aids in current use, thereby enabling civil aircraft to
fly more fuel-efficient routes.
GPS satellites transmit radio signals that allow properly equipped
air, land, and sea users to calculate the time and their position and
speed in any location and weather condition. Because it was designed
for military purposes, however, GPS does not satisfy civil air
navigation requirements dictating, for example, that the system's
signals be available in sufficient number virtually all of the time
and be accurate enough to support aircraft landings in the worst
weather conditions. When augmented by wide and local area systems
that FAA intends to implement,\1 GPS is expected to satisfy the above
requirements.
After FAA established its schedule in February 1992 for using GPS to
support civil air navigation, governmental and aviation industry
groups recommended that the agency accelerate some of the schedule's
milestones to permit full use of the system by civil aviation as soon
as possible. In January 1994--following the recommendations of an
industry task force on satellite navigation and The National
Commission to Ensure a Strong Competitive Airline Industry--the
Secretary of Transportation charged the FAA Administrator with, among
other things, accelerating the use of GPS by civil aviation.
In response, FAA modified its schedule for using GPS by accelerating
several milestones, in general, from 2000 to 1997. As a result, your
offices asked us to assess whether FAA will have sufficient time
under the new milestones to augment GPS and whether the agency has
taken appropriate actions to better manage its GPS-related efforts.
--------------------
\1 The wide area system will use commercial communication satellites
to augment GPS' signals in the airspace between and around airports
so that civil aircraft can navigate in air routes and land on airport
runways. The local area system will use ground-based communications
equipment to augment the signals in the airspace around airports so
that aircraft can land in the worst weather conditions.
RESULTS IN BRIEF
------------------------------------------------------------ Letter :1
Although FAA has met all of its milestones to date, the agency will
face more complex and difficult tasks in achieving future milestones.
We are concerned that the revised schedule will not give the agency
enough time to develop and implement its wide area system for
augmenting GPS by 1997, when civil aircraft are expected to use the
augmented GPS without having to rely on other navigation aids for
backup. This commitment is ambitious because the FAA contractor must
develop and implement the wide area system, and the agency must
accept and commission it over a 28-month period--although FAA
estimates that software development alone may take from 24 to 28
months. Also, FAA's efforts to develop and implement the wide area
system may be slowed by potential difficulties--some of which are
beyond FAA's control. For example, the launching of the commercial
communication satellites needed to support the system may be delayed.
FAA took several actions in 1994 to strengthen its ability to manage
its GPS efforts. FAA's actions include integrating GPS activities
within the agency, securing the necessary funding to accelerate the
development of the wide area system, and issuing plans for developing
and implementing augmentation systems. These actions are
encouraging. However, the plans for GPS are not comprehensive
because they do not provide complete or detailed schedule and cost
information, needed for making sound programmatic and budgetary
decisions regarding these augmentation systems. The plans omit (1)
milestones for implementing the local area system to augment GPS, (2)
cost estimates for this system and the wide area system, and (3)
information on the probabilities of meeting schedule and cost
estimates, given known potential problems that may affect the
development of these systems.
BACKGROUND
------------------------------------------------------------ Letter :2
DOD designed GPS to support military missions, such as military air,
land, and sea navigation; missile guidance; search and rescue; mine
placement; and precision surveying. GPS has space and ground
components, as depicted in figure 1. The space component consists of
a worldwide constellation of 24 satellites in six orbits at
approximately 11,000 miles above the earth. These satellites are
positioned so that a user will have at least four satellites in view
at any given location. The satellites transmit radio signals that
permit adequately equipped users to calculate the time as well as
their speed and tridimensional position (latitude, longitude, and
altitude) anywhere on or above the earth's surface and in any weather
condition. The ground component includes a master control station,
five monitoring stations, and three ground antennae located
throughout the world. The master control station tracks and directs
the GPS satellites through the monitoring stations and ground
antennae, respectively.
Figure 1: GPS' Components
(See figure in printed
edition.)
\a Other GPS satellites not shown.
\b Other GPS ground antennae not shown.
\c Other GPS monitoring stations not shown.
Source: Based on DOD's data.
As mentioned earlier, because GPS was designed for military purposes,
the system, by itself, cannot satisfy key safety-related civil air
navigation requirements, such as those dictating that a sufficient
number of the system's satellite signals be available virtually all
of the time. Currently, GPS is used domestically as a supplemental
means of navigation because on-board-the-aircraft augmentation
systems--which use altimeters, gyroscopes, and other equipment to
augment GPS--do not address all civil air navigation requirements,
particularly those related to the system's availability.
In accordance with the direction provided by the Department of
Transportation (DOT), FAA is supporting the development of a wide
area system and local area systems that will permit GPS to fulfill
all civil air navigation requirements and become a primary means of
navigation.\2 This month, FAA plans to award a contract for
developing the wide area system. The agency has not announced a date
for awarding a contract to develop local area systems. (See app. I
for a description of civil air navigation requirements and the wide
and local area systems that FAA intends to implement.)
FAA and the aviation industry expect that the augmented GPS will
result in a navigation capability that will provide major benefits to
the agency, civil aviation, and others because of its superiority
over currently used navigation aids. For example, because FAA
expects that the augmented GPS will be able to support runway
approaches and landings in all weather conditions, the agency
recently canceled its multibillion-dollar project to acquire
microwave landing systems--a key element of the program to modernize
the air traffic control system.\3 Also, FAA foresees that the
augmented GPS will permit the agency, after a transition period, to
start decommissioning its ground network of navigation and landing
aids. Moreover, airlines expect that the augmented GPS and its
applications will result in major operational and economic benefits
by reducing flying times and fuel consumption. In addition, DOT and
FAA anticipate that the augmented GPS will benefit not only aviation
users but also other federal agencies and land and sea users having a
need for navigation information.\4
--------------------
\2 DOT's direction to FAA agrees with the recommendations proposed in
two reports: A Report to the Secretaries of Defense and
Transportation, The Global Positioning System: Management and
Operation of a Dual Use System, Joint DOD/DOT Task Force (Dec. 1993)
and A Technical Report to the Secretary of Transportation on A
National Approach to Augmented GPS Services, Department of Commerce,
National Telecommunications and Information Administration (NTIA),
NTIA Special Pub. 94-30 (Nov. 1994).
\3 Our report Airspace System: Emerging Technologies May Offer
Alternatives to the Instrument Landing System (GAO/RCED-93-33, Nov.
13, 1992) discusses the need for FAA to reassess its requirements for
precision landing systems. (See fn. 2.)
\4 One of our recent reports highlights the need for a governmentwide
response to the GPS needs of federal agencies. See Global
Positioning Technology: Opportunities for Greater Federal Agency
Joint Development and Use (GAO/RCED-94-280, Sept. 28, 1994).
FAA MAY NOT ACHIEVE FUTURE GPS
MILESTONES
------------------------------------------------------------ Letter :3
Although FAA has met all milestones for GPS to date, the agency will
face more complex and difficult tasks in achieving future milestones.
We are concerned that the revised schedule for augmenting GPS will
not give the agency enough time to develop and implement the wide
area system by 1997, when civil aircraft are expected to use the
augmented GPS domestically as a primary means of navigation. The
schedule is tight, and potential problems could affect the system's
development and implementation.
FAA HAS MET INITIAL GPS
MILESTONES
---------------------------------------------------------- Letter :3.1
In 1993, FAA met several milestones for GPS when the agency approved
the use of the system as a supplemental means of navigation for
oceanic and domestic air routes as well as nonprecision approaches.\5
Also, in December 1994, FAA met one of two 1995 milestones ahead of
schedule when the agency approved the use of GPS--augmented by
on-board-the-aircraft systems--as a primary means of navigation over
oceans and remote areas.\6 In addition, FAA will likely meet the
other 1995 milestone when the agency completes assessing the
feasibility of using local area systems to support all types of
precision approaches.\7 Agency officials responsible for GPS
activities see little chance for delays in meeting this milestone.\8
Although FAA has been confident for some time that local area systems
will be able to support all types of precision approaches, the agency
is sponsoring research by various institutions to confirm the
feasibility of these systems. For example, in June 1994, FAA awarded
contracts to Wilcox Electric Inc. and E-Systems to develop and test
two different local area systems for supporting precision approaches.
According to FAA officials responsible for GPS activities, the
preliminary testing of demonstration systems has been encouraging.
These agency officials expect that the reports on the performance of
these systems will be completed on schedule by the summer of 1995.
--------------------
\5 On a nonprecision approach, an aircraft receives electronic
guidance for flying toward the runway's centerline. On a precision
approach, an aircraft receives not only this guidance but also
guidance on the slope of descent to the runway. As a result, on a
precision approach, an aircraft can safely descend closer to the
ground while attempting to land in bad weather.
\6 These augmentations must have an automatic dead reckoning
navigation capability, which uses airspeed, altitude, and heading
information to guide the aircraft in case GPS is not available.
Also, these augmentations must be enhanced by operational procedures
and, when GPS is not available, be operated with restrictions.
\7 According to FAA, its augmentation systems will permit aircraft to
rely solely on GPS for flying precision approaches. The wide area
system is expected to support Category I precision approaches, under
which an aircraft receives guidance as it descends to a height of 200
feet when the runway's visibility is at least 1,800 feet. The local
area systems are expected to support not only these precision
approaches but also Category II and III precision approaches, under
which an aircraft receives greater navigational assistance when
approaching a runway.
\8 These officials include the Director of the Integrated Product
Team for GPS and Navigation, the Manager of the Satellite Navigation
Program, and the Manager of the Wide Area Augmentation System
Project.
FAA MAY NOT MEET FUTURE GPS
MILESTONES
---------------------------------------------------------- Letter :3.2
FAA may not be able to meet its 1997 milestones for civil aircraft to
use GPS domestically as a primary means of navigation. These
milestones are based on the implementation of an initial wide area
system by 1997. (See app. II for a depiction of FAA's milestones
for GPS.) The schedule for implementing the initial system is tight,
and potential problems could affect the system's development. This
commitment is challenging because the system's schedule may not
provide enough time for FAA to complete all necessary steps. Over a
28-month period, from May 1995 to September 1997, the FAA contractor
must develop and implement the system, and the agency must accept and
commission it. However, FAA estimates that the system's software
development alone may take from 24 to 28 months, thereby leaving
little time for the agency to accept and commission the system.
Also, potential difficulties may be encountered during the system's
development. These difficulties include the following:
Software-related problems. Although FAA has taken measures such as
strengthening its oversight capabilities, the contractor selected may
face difficulties while attempting to develop, integrate, test, and
certify the wide area system's software. The agency estimates that
when measures to mitigate potential software development problems are
considered, the software schedule has about a 60-percent probability
of success. FAA has noted its concerns about potential software
problems since it decided to adopt the accelerated schedule for
developing and implementing the system.
Satellite-related problems. The space component of the wide area
system requires that three commercial communication satellites be in
place by late 1997--an undertaking that is beyond FAA's control.
However, enough satellites may not be in orbit on time because the
International Maritime Satellite Organization (INMARSAT)--the only
commercial entity that has publicly announced its intention to launch
satellites capable of supporting this space component--could delay
launches or could launch an insufficient number of satellites to
fully support this component. INMARSAT recently delayed launching
the first of these satellites from late 1995 to early 1996 because
the rocket to launch the satellite would not be available on
schedule.
FAA recently estimated that its 1997 milestones may slip up to 18
months if potential problems are realized. However, the agency did
not provide information on the likelihood of meeting the milestones
within this period of time.
FAA'S ACTIONS ARE ENCOURAGING,
BUT PLANS PROVIDE INCOMPLETE
INFORMATION TO DECISIONMAKERS
------------------------------------------------------------ Letter :4
In 1994, FAA took several actions to strengthen its capacity to
manage its GPS-related efforts, including integrating GPS activities
within the agency, securing additional funding to develop the wide
area system, and issuing plans for developing and implementing the
augmentation systems and a draft plan for transitioning to GPS.
These actions are encouraging. However, the plans are not
comprehensive because they exclude schedule and cost estimates for
implementing augmentation systems and information on the likelihood
of achieving these estimates.
FAA HAS IMPROVED ITS ABILITY
TO AUGMENT GPS
---------------------------------------------------------- Letter :4.1
FAA recently took several management actions to better position
itself for augmenting GPS. First, FAA integrated pertinent GPS
research, development, and acquisition activities that had been
fragmented across the agency. In October 1993, FAA named a Director
of GPS/Communications, Navigation, and Surveillance (CNS) Systems,
and in May 1994, it created the GPS/CNS Development and
Implementation Service. In November 1994, FAA consolidated the
Service with units responsible for current ground-based navigation
aids, such as instrument landing systems. This new organization,
headed by the former Director of the GPS/CNS Service, is called the
Integrated Product Team for GPS and Navigation and is under the
jurisdiction of the Associate Administrator for Research and
Acquisitions. According to the head of this organization, the
consolidation was intended to improve the integration and
coordination of the agency's efforts to augment GPS.
Second, after deciding to accelerate the implementation of the wide
area system, FAA obtained $82.8 million for fiscal year 1995, an
increase of $61.9 million over its appropriation for fiscal year
1994. This funding includes $67.9 million to develop and implement
the wide area system. In fiscal year 1996, the administration is
requesting $86.9 million to fund the system.
Third, in mid-1994, FAA released plans for guiding the development,
acquisition, and implementation of GPS' augmentations and drafted an
agencywide plan for directing the transition to GPS.\9
Although these actions are encouraging, they may not address
potential problems that may affect the development of the wide area
system. Some of these problems are beyond FAA's control, such as the
difficulties that may be experienced during the launching of
commercial communication satellites.
--------------------
\9 FAA Satellite Navigation Program Master Plan, FY 94-99, June 15,
1994; GPS Implementation Plan for Air Navigation and Landing, Aug.
1994; and FAA National GPS/CNS Transition Plan, Draft, July 1994.
GPS-RELATED PLANS PROVIDE
INSUFFICIENT INFORMATION
---------------------------------------------------------- Letter :4.2
Among other things, the GPS development and implementation plans and
the draft of the transition plan (1) present information on FAA's
planned efforts to augment GPS, including schedule information on the
wide area system and related milestones for using GPS as a primary
means of navigation; (2) identify requirements that GPS must satisfy;
and (3) highlight benefits that GPS will provide the agency and
aviation users. Also, after the wide and local area systems are
implemented, the transition plan proposes tentative schedules for
transitioning to GPS and for decommissioning navigation aids in
current use.
However, these plans provide insufficient information to
decisionmakers in the administration and the Congress on the systems
needed for augmenting GPS.
The plans issued in 1994 do not provide a timetable for implementing
local area systems that will be needed to support precision
approaches. FAA recently canceled its microwave landing system
project because it is confident that the local area systems will be
able to support all types of precision approaches. Without a
timetable, decisionmakers cannot evaluate the extent to which
schedules being considered are timely and minimize the need to keep
instrument landing systems operational.
The GPS plans exclude information on the level of financial resources
needed by FAA to implement the wide area system. Also, they do not
present information on the funding required to implement the local
area systems needed for supporting precision approaches.
When plans do not identify financial resource needs, past experience
shows that decisionmakers may not have a sound basis for assessing
budget requests or considering alternative courses of action. For
example, because FAA's 1992 GPS development plan did not include cost
information,\10 the Congress did not have the necessary information
to evaluate the administration's budget request for funding FAA's GPS
effort for fiscal year 1993. After we reported to the Congress that
this budget request was less than half of what FAA needed to keep
these efforts on schedule, the Congress had a basis to fully fund the
agency's needs.\11
The plans omit information on the likelihood that FAA will meet its
milestone and cost estimates, given the effect of potential problems
on the system's development and implementation. Identifying the
probability (low, medium, and high) of successfully meeting the
schedule and cost estimates would enable decisionmakers to understand
the level of confidence that the agency has in these estimates.
FAA has the above information for the wide area system. Also,
according to agency officials responsible for GPS activities, FAA
expects to complete the development of similar information on the
local area systems by late 1995.\12
--------------------
\10 FAA's 1992 Research and Development Satellite Navigation Plan.
\11 See Hearing on the Department of Transportation and Related
Agencies Appropriations for 1993, before the Subcommittee on the
Department of Transportation and Related Agencies, Committee on
Appropriations, U.S. House of Representatives (102nd Cong., 2nd
Sess., Apr. 6, 1992) and Airspace System: Emerging Technologies May
Offer Alternatives to the Instrument Landing System (GAO/RCED-93-33,
Nov. 13, 1992).
\12 FAA recently submitted to the Congress comprehensive air traffic
control automation plans, including sensitive schedule and cost
information regarding system procurement. However, these plans did
not provide information on the likelihood that FAA would meet its
schedule and cost estimates. See Air Traffic Control Automation
Program Master Plan, Sept. 27, 1994, and Office of Air Traffic
Systems Development, Program Master Plan, Feb. 3, 1995.
CONCLUSIONS
------------------------------------------------------------ Letter :5
FAA has been successful in meeting its GPS milestones to date.
However, the agency faces more complex and difficult tasks in
achieving future milestones. We are concerned that the revised
schedule will not give the agency enough time to develop and
implement the wide area system by 1997, when civil aviation is
expected to use the augmented GPS as a primary means of navigation.
To strengthen its ability to manage its GPS efforts, FAA recently
took various actions, such as integrating GPS activities across the
agency, securing additional funding for accelerating the development
of the wide area system, issuing development and implementation
plans, and drafting a transition plan. These actions are
encouraging. However, the plans are not comprehensive enough to
provide the administration and the Congress with a sound basis for
making programmatic and budgetary decisions concerning GPS'
augmentation systems. For example, the plans omit important schedule
and cost information on these systems.
A comprehensive plan--including (1) complete milestones for
augmenting GPS and transitioning to it, (2) the financial resources
needed to achieve those milestones, and (3) information on the
likelihood that FAA will meet its milestone and cost estimates--would
help FAA guide and coordinate its efforts, marshall its resources,
and assess its progress. Also, this plan would help the
administration and the Congress ascertain the scope of FAA's efforts,
in terms of schedules and costs; assess whether the agency can meet
milestones on time, given the level of resources requested; consider
alternative courses of action; and monitor whether the agency's
progress toward accomplishing these milestones and transitioning to
GPS is on schedule and within budget. Finally, the plan would help
aviation users map out their transition to GPS in terms of both
equipping aircraft and training pilots. With the development of
additional information on local area systems by late 1995, FAA will
soon have the information needed to prepare a comprehensive GPS plan.
RECOMMENDATION
------------------------------------------------------------ Letter :6
We recommend that the Secretary of Transportation direct the FAA
Administrator to prepare a comprehensive plan for augmenting GPS and
transitioning to it and to update this plan regularly. The plan
should include, among other things, schedule and cost estimates for
developing and implementing the wide and local area augmentation
systems as well as information on the probability that FAA will meet
these estimates.
AGENCY COMMENTS
------------------------------------------------------------ Letter :7
We gave copies of the draft report to DOT and FAA officials,
including FAA's Director of the Integrated Product Team for GPS and
Navigation, the Manager of the Satellite Navigation Program, the
Manager of the Wide Area Augmentation System Project, and the Manager
of the Local Area Augmentation System Project. These officials
generally agreed with the report's findings, conclusions, and
recommendation and did not have concerns about its contents. The
officials gave us information and suggestions to help us clarify and
qualify the report. We incorporated their suggestions where
appropriate.
SCOPE AND METHODOLOGY
------------------------------------------------------------ Letter :8
We obtained information on FAA's efforts to augment GPS from FAA
officials responsible for pertinent GPS activities, including the
Director of the Integrated Product Team for GPS and Navigation and
the Manager of the Satellite Navigation Program. Also, we reviewed
key documentation on civil air navigation requirements, reports on
different augmentation systems being developed to augment GPS, plans
and studies that identified various time frames for augmenting GPS,
and schedule and cost information on FAA's efforts related to GPS.
In addition, we attended various professional meetings sponsored by
FAA and other aviation organizations at which GPS issues were
discussed. Finally, we obtained information on satellite navigation
technology through discussions with representatives from airlines,
the Air Transport Association, the Aircraft Owners and Pilots
Association, the GPS industry, the International Civil Aviation
Organization (ICAO), and DOD, including the Executive Secretary of
the U.S. GPS Industry Council; the Chairman of ICAO's Special
Committee on Future Air Navigation Systems, Phase II; and the Senior
Staff Specialist for Navigation and Air Traffic Control Systems in
the Office of the Assistant Secretary of Defense. We conducted our
work from August 1993 through April 1995 in accordance with generally
accepted government auditing standards.
---------------------------------------------------------- Letter :8.1
As arranged with your offices, unless you publicly announce its
contents earlier, we plan no further distribution of this report
until 30 days after the date of this letter. At that time, we will
send copies to interested congressional committees; the Secretary of
Transportation; the Administrator, FAA; the Director, Office of
Management and Budget; and other interested parties. We will also
This work was performed under the direction of Allen Li, Associate
Director, who may be reached at (202) 512-3600 if you or your staff
have any questions. Major contributors to this report are listed in
appendix III.
Sincerely yours,
Kenneth M. Mead
Director, Transportation and
Telecommunications Issues
CIVIL AIR NAVIGATION REQUIREMENTS
AND GPS' AUGMENTATIONS
=========================================================== Appendix I
The Global Positioning System (GPS), by itself, cannot fulfill civil
air navigation requirements related to the various phases of flight.
The Federal Aviation Administration (FAA) is working on two major
systems for augmenting (enhancing) GPS so that it can meet these
requirements and become a primary means of navigation.
GPS, ALONE, DOES NOT MEET CIVIL
AIR NAVIGATION REQUIREMENTS
--------------------------------------------------------- Appendix I:1
GPS does not satisfy civil air navigation requirements, including
availability, integrity, and in the case of precision approaches (see
fn. 2) accuracy requirements.
The availability of a navigation aid is defined as the amount of time
that the system is available for use. Availability requirements for
the different phases of flight dictate for safety-related reasons
that the system's signals be available more than 99.9 percent of the
time. However, under the current GPS constellation of 21 operational
satellites and 3 spares, satellites are available only 98 percent of
the time. Through its augmentations to GPS, FAA plans to provide
users with several satellite signals similar to those provided by GPS
so that signals are available virtually all of the time.
The integrity of a navigation aid is defined as its ability to
provide timely warnings to users about the system's malfunctions.
Integrity requirements for the different phases of flight dictate
that warnings be provided to users within seconds of a system's
malfunction. However, GPS' integrity warnings can take 15 minutes or
longer. Through its enhancements to GPS, FAA intends to provide
timely integrity warnings to users so that they know when GPS or its
enhancements are malfunctioning.
The accuracy of a navigation aid is defined as the difference between
the true and measured position of an aircraft, the latter position as
calculated by on-board-the-aircraft equipment. Accuracy requirements
for precision approaches range from a few meters to under a meter.
However, GPS, by itself, provides accuracies of about 100 meters.\1
Through its augmentation to GPS, FAA plans to provide accuracy
corrections to users so that the system can support all types of
precision approaches.
--------------------
\1 GPS satellites have two signals. One signal provides information
only to U.S. government-authorized users. The other signal provides
similar information to all users. This information allows users to
calculate the time and their speed and tridimensional position
(latitude, longitude, and altitude). For national security reasons,
the accuracy of the positioning information provided by the second
signal to all users is currently degraded to at least 100 meters.
When this signal is not degraded, its accuracy ranges from 21 to 53
meters.
GPS' AUGMENTATIONS
--------------------------------------------------------- Appendix I:2
FAA is working to develop and implement wide and local area
augmentation systems for augmenting GPS.
WIDE AREA AUGMENTATION
SYSTEM
------------------------------------------------------- Appendix I:2.1
FAA is working on the development and implementation of a
satellite-based wide area system that will permit GPS to satisfy the
integrity, availability, and accuracy requirements needed to make it
a primary means of navigation for supporting all phases of flight,
including precision approaches.
FAA plans to use the wide area system to augment GPS in two phases.
Under the first phase, FAA will use the system to enhance the
availability and integrity of GPS. The system will transmit
satellite signals similar to those provided by GPS, which will
provide integrity warnings within 6 seconds of a malfunction. Under
the second phase, FAA intends to enhance the accuracy of GPS for
meeting the requirements of Category I precision approaches.\2
FAA recently received authorization to implement this accuracy
enhancement.
The wide area system will have ground and space components for
augmenting GPS. Figure I.1 depicts the wide area augmentation
system.
Figure I.1: Wide Area
Augmentation System for All
Phases of Flight
(See figure in printed
edition.)
Legend
WAAS = wide area augmentation system.
\a Other communication satellites not shown.
\b Other GPS satellites not shown.
\c Other communication stations not shown.
\d Other WAAS master stations not shown.
\e Other WAAS reference stations not shown.
Source: Based on FAA's data.
The ground component will consist of a network of stations, including
reference, master, and communication stations. Reference stations
will, among other things, monitor the GPS satellite signals to
generate integrity warnings and calculate corrections to improve the
accuracy of the signals. Master stations will monitor the
performance of the system, control reference stations, and process
the integrity and accuracy information needed for augmenting GPS.
Master stations, which will be located at several reference station
sites, will send this information to communication stations. The
latter will transmit the information to communication satellites--the
space component--that in turn will broadcast the information to users
with augmented signals similar to GPS signals. In addition to this
operational wide area system, FAA plans to implement a smaller wide
area system--called a functional verification system--to support
related developmental, operational, and maintenance efforts.
FAA's strategy is to implement an initial wide area system by
September 1997. The initial system, through a series of
enhancements, is expected to become a final system by 2001. The
initial system will consist of 2 master stations, 24 reference
stations, and 6 communication stations. These stations will be
joined by ground telecommunications. The system will use three
communication satellites to deliver augmented signals similar to
those provided by GPS to users. FAA envisions that the final system
will consist of about 4 master stations, up to 40 reference stations,
and up to 16 communication stations. The final system may use up to
eight communication satellites. The functional verification system
will consist of two master stations, five reference stations, and one
communication station. It will require one communication satellite.
The initial system and the functional verification system will use
the same software. This software will contain an estimated 150,000
lines of code. The final system's software may contain about 200,000
lines of code. This additional software code is intended to make the
system capable of supporting Category I precision approaches and
interfacing with other wide area augmentation systems implemented
around the world.
To limit risks during the integration of the system and ensure proper
interfaces between the system's components, FAA plans to award a
contract for the wide area system to a single contractor. The
contract will be a cost-plus contract because uncertainties
affecting, for example, the software's development and integration do
not permit FAA to estimate costs with the accuracy required for using
a fixed-price contract. The contract will include incentives for the
contractor to meet technical and cost goals. FAA expects to award
the contract in May 1995. The contract, including four options,
could extend for up to 8 years and will be funded incrementally.
--------------------
\2 According to FAA, the wide area system will permit aircraft to
rely solely on GPS for flying Category I precision approaches. Under
a Category I approach, an aircraft receives guidance as it descends
to a height of 200 feet above the ground when the runway's visibility
is at least 1,800 feet. The system will not support Category II and
III precision approaches, which are used by aircraft when they
require greater navigational assistance under worse weather
conditions. Under a Category II approach, an aircraft receives
guidance as it descends to a height of 100 feet when the runway's
visibility is at least 1,200 feet. Under a Category III approach, an
aircraft receives guidance that permits it to descend and land when
the runway's visibility is greatly reduced. Local area systems will
be able to support Category II and III precision approaches.
LOCAL AREA AUGMENTATION
SYSTEM
------------------------------------------------------- Appendix I:2.2
FAA is working on the development of a ground-based local area system
that will allow GPS to satisfy the integrity, accuracy, and
availability requirements needed to make it a primary means of
navigation for supporting precision approaches. This local system
uses a ground component for augmenting GPS. Figure I.2 depicts one
of the systems under development. The ground component has one or
more GPS monitoring stations located at known locations for detecting
malfunctions and calculating accuracy corrections near or at the
airport. After processing this information, the stations transmit it
with an augmented signal similar to those provided by GPS to users.
Figure I.2: Local Area
Augmentation System for
Precision Approach Phase of
Flight
(See figure in printed
edition.)
\a Other GPS satellites not shown.
Source: Based on FAA's data.
Currently, FAA is sponsoring various efforts to develop local area
systems to support all types of precision approaches. For example,
in 1994, the agency awarded contracts to Wilcox Electric and
E-Systems, at a cost of $1.67 million and $2 million, respectively,
to develop and test demonstration systems using two different
technologies.
FAA'S CHANGES TO GPS MILESTONES
========================================================== Appendix II
Figure II.1 shows the milestones in the schedule for enhancing GPS.
Also, it displays the extent to which FAA has accelerated some
milestones since they were introduced in 1992. Future milestones in
the schedule depend on the implementation of a wide area system for
augmenting GPS nationwide by 1997.
Figure II.1: FAA's Fiscal Year
Milestones for GPS
(See figure in printed
edition.)
Legend
A: GPS for multisystem navigation. Under this mode, a pilot uses
the system in conjunction with one or more commissioned air
navigation aids for obtaining reliable information on the aircraft's
position. The aircraft must carry equipment for both GPS and the
navigation aids, and the pilot must constantly cross-check the
GPS-derived positioning information with the other systems'
information.
B: GPS augmented for supplemental navigation. Under this mode, the
pilot uses the augmented GPS by itself for determining the aircraft's
position. However, because the GPS signals may not be available
during one of the phases of flight, the aircraft must carry equipment
for a commissioned air navigation aid as a backup.
C: GPS augmented for primary means navigation. Under this mode, the
pilot uses the augmented GPS by itself. However, the aircraft does
not have to carry equipment for a commissioned air navigation aid as
a backup.
B* and C*: Milestones based on the implementation of the wide area
augmentation system.
D: GPS augmented for special Category I precision approaches. Under
this mode, a pilot uses GPS augmented by privately owned local area
systems for flying this type of precision approach.
E: Feasibility determination of GPS' augmentation for supporting
Category II/III precision approaches. FAA determines whether GPS
augmented by local area systems can support these types of precision
approaches.
Source: Based on FAA's 1992, 1993, and 1994 development plans and
1994 implementation plan.
MAJOR CONTRIBUTORS TO THIS REPORT
========================================================= Appendix III
RESOURCES, COMMUNITY, AND ECONOMIC
DEVELOPMENT DIVISION, WASHINGTON,
D.C.
Allen Li, Associate Director
Robert E. Levin, Assistant Director
Juan F. Tapia-Videla, Evaluator-in-Charge
Stephanie K. Gupta, Staff Evaluator
Gregory P. Carroll, Staff Evaluator