National Airspace System: Observations on the Wide Area Augmentation
System (Testimony, 10/01/97, GAO/T-RCED-98-12).

GAO discussed the Federal Aviation Administration's (FAA) Wide Area
Augmentation System (WAAS) program, focusing on: (1) the likelihood of
WAAS satisfying key performance requirements within current program cost
and schedule estimates; (2) the importance of avoiding delays in FAA's
timetable for shutting down (decommissioning) ground-based navigation
aids; and (3) the potential impact of cost increases and decommissioning
delays on the benefit-cost analysis for the WAAS program.

GAO noted that: (1) while the developers of WAAS and outside experts are
confident that WAAS is likely to satisfy most key performance
requirements within current program cost and schedule estimates, some
concerns are worth noting; (2) specifically, FAA may make some
procedural changes for aircraft landings if WAAS is not able to deliver
the level of service provided by existing ground-based landing systems;
(3) also, FAA may add more space-based equipment to meet performance
requirements; (4) FAA expects to make decisions on these matters by late
1998 and late 2000, respectively; (5) if the space-based equipment is
added, program costs would grow between $71 million and $192 million
above the current total program cost estimate of $2.4 billion; (6) the
program's schedule can be expected to slip if arrangements are not made
immediately to put this equipment in space; (7) to realize the full cost
savings from WAAS, FAA will need to avoid delays in decommissioning its
ground-based network of navigation aids; (8) FAA estimates that it
incurs costs of $166 million annually to maintain this ground-based
network; (9) FAA's plans--which envision complete decommissioning of the
network by 2010--presume that the full WAAS will become operational
(commissioned) in 2001 and that the aviation industry will install the
necessary equipment in its aircraft during the remainder of that decade;
(10) however, the planned decommissioning could be delayed if the WAAS
program's schedule slips or if safety and economic benefits, such as an
aircraft's ability to take advantage of more fuel-efficient routes, are
not sufficient to cause the industry to switch to satellite-based
navigation technology by the end of the next decade; (11) cost increases
and decommissioning delays, if they occur, would reduce the net benefits
of the WAAS program, but program benefits would still outweigh costs;
(12) FAA's July 1997 benefit-cost analysis found that benefits were: (a)
more than five times greater than costs when passenger time savings were
included and all aircraft gained savings from shorter flights; and (b)
more than two times greater than costs when passenger time savings were
excluded and 30 percent of all aircraft gained savings from shorter
flights; (13) additional analyses done at GAO's request, using
pessimistic cost and decommissioning assumptions, found that the WAAS
program's benefits are still significantly greater than the costs; and
(14) however, if the ground-based navigation network is not
decommissioned or must remain in place much longer than expected, the
net benefits from WAAS would be substantially reduced.

--------------------------- Indexing Terms -----------------------------

 REPORTNUM:  T-RCED-98-12
     TITLE:  National Airspace System: Observations on the Wide Area 
             Augmentation System
      DATE:  10/01/97
   SUBJECT:  Navigation aids
             Air traffic control systems
             Cost effectiveness analysis
             Airports
             Aviation
             Air transportation operations
             Radar equipment
             Satellites
IDENTIFIER:  FAA Wide Area Augmentation System
             NAVSTAR Global Positioning System
             
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Cover
================================================================ COVER


Before the Subcommittee on Aviation, Committee on Transportation and
Infrastructure, House of Representatives

For Release on Delivery
expected at
9:30 a.m.
Wednesday
October 1, 1997

NATIONAL AIRSPACE SYSTEM -
OBSERVATIONS ON THE WIDE AREA
AUGMENTATION SYSTEM

Statement of Gerald L.  Dillingham
Associate Director, Transportation Issues
Resources, Community, and Economic
Development Division

GAO/T-RCED-98-12

GAO/RCED-98-12T


(341525)


Abbreviations
=============================================================== ABBREV

  FAA -
  WAAS -
  GPS -
  GEO -

============================================================ Chapter 0

Mr.  Chairman and Members of the Subcommittee: 

We are pleased to be here today to discuss the Federal Aviation
Administration's (FAA) Wide Area Augmentation System (WAAS) program. 
FAA is planning a transition from a ground-based civil air navigation
system to a satellite-based system using signals generated by the
Department of Defense's Global Positioning System (GPS).  However,
GPS, designed for military purposes, does not satisfy civil air
navigation requirements such as the one requiring that the system be
available virtually all of the time.  FAA is acquiring WAAS--a
network of equipment on the ground and in space--to enhance GPS so
that the system can meet civil aviation requirements. 
Satellite-based navigation, using GPS/WAAS, is expected to improve
the safety of flight operations, allow the fuel-efficient routing of
aircraft, increase airport and airspace capacity to meet future air
traffic demands, and enable FAA to phase out its costly network of
ground-based navigation aids.  By providing positioning information,
GPS/WAAS is also expected to benefit the operators of other modes of
transportation and other types of users. 

The purpose of our testimony today, which is based on ongoing work
requested by your Subcommittee, is to aid congressional oversight by
providing insights into the cost, schedule, and technical issues that
have drawn considerable attention to the WAAS program.  Specifically,
our testimony will discuss:  (1) the likelihood of WAAS' satisfying
key performance requirements within current program cost and schedule
estimates; (2) the importance of avoiding delays in FAA's timetable
for shutting down (decommissioning) ground-based navigation aids; and
(3) the potential impact of cost increases and decommissioning delays
on the benefit-cost analysis for the WAAS program. 

In summary

  -- While the developers of WAAS and outside experts are confident
     that WAAS is likely to satisfy most key performance requirements
     within current program cost and schedule estimates, some
     concerns are worth noting.  Specifically, FAA may use additional
     augmentations and make procedural changes for aircraft landings
     if WAAS is not able to deliver the level of service provided by
     existing ground-based landing systems.  Also, FAA may add more
     space-based equipment to meet performance requirements.  FAA
     expects to make decisions on these matters by late 1998 and late
     2000, respectively.  If the space-based equipment is added,
     program costs would grow between $71 million and $192 million
     above the current total program cost estimate of $2.4 billion. 
     The program's schedule can be expected to slip if arrangements
     are not made immediately to put this equipment in space. 

  -- To realize the full cost savings from WAAS, FAA will need to
     avoid delays in decommissioning its ground-based network of
     navigation aids.  FAA estimates that it incurs costs of $166
     million annually to maintain this ground-based network.  FAA's
     plans--which envision complete decommissioning of the network by
     2010--presume that the full WAAS will become operational
     (commissioned) in 2001 and that the aviation industry will
     install the necessary equipment in its aircraft during the
     remainder of that decade.  However, the planned decommissioning
     could be delayed if the WAAS program's schedule slips or if
     safety and economic benefits, such as an aircraft's ability to
     take advantage of more fuel-efficient routes, are not sufficient
     to cause the industry to switch to satellite-based navigation
     technology by the end of the next decade. 

  -- Cost increases and decommissioning delays, if they occur, would
     reduce the net benefits of the WAAS program, but program
     benefits would still outweigh costs.  FAA's July 1997
     benefit-cost analysis found that benefits were (1) more than
     five times greater than costs when passenger time savings were
     included and all aircraft gained savings from shorter flights,
     and (2) more than two times greater than costs when passenger
     time savings were excluded and 30 percent of all aircraft gained
     savings from shorter flights.  Additional analyses done at our
     request, using pessimistic cost and decommissioning assumptions,
     found that the WAAS program's benefits are still significantly
     greater than the costs.  However, if the ground-based navigation
     network is not decommissioned or must remain in place much
     longer than expected, the net benefits from WAAS would be
     substantially reduced. 


   BACKGROUND
---------------------------------------------------------- Chapter 0:1

In the 1980s, FAA began considering how a satellite-based navigation
system could eventually replace the ground-based system that had long
provided navigation guidance to aviation.  In August 1995, after
years of study and research, FAA contracted with Wilcox Electric to
develop WAAS.  However, because of concerns about the contractor's
performance, FAA terminated the contract in April 1996.  In May 1996,
the agency entered into an interim contract with Hughes Aircraft. 
The interim contract with Hughes was subsequently expanded and became
final in October 1996. 

Under the terms of the WAAS development contract, Hughes will deliver
an initial operational capability (Phase 1 WAAS) to FAA by April 1,
1999.  The original date written into the Wilcox contract was
December 1997.  Phase 1 WAAS will be able to support the navigation
of aircraft throughout the continental United States for all phases
of flight through Category I precision approaches.\1 However, the
Phase 1 system will not have sufficient redundancy to continue
operations in the event of equipment failures and will have to be
backed up by FAA's current ground-based system.  FAA expects to
conclude the operational testing of Phase 1 WAAS in June 1999 and to
commission the system by July 15, 1999.  To make WAAS capable of
serving as a "sole means" navigation system throughout the United
States,\2 FAA plans to expand the system in Phases 2 and 3 of the
contract.  The Phase 3, or full, WAAS is scheduled to be delivered by
October 2001 and commissioned in early 2002. 

Our August 1997 report on WAAS to this Subcommittee and others
provided details on the history of FAA's cost estimates for WAAS.  We
found that although FAA knew that the facilities and equipment costs
for WAAS could exceed $900 million, the agency presented to the
Congress a figure that was some $400 million lower.\3 In September
1997, FAA estimated the total life cycle cost of the WAAS program to
be $2.4 billion.  Of this amount, about $900 million is for
facilities and equipment and $1.5 billion is for operations and
maintenance through the year 2016. 

Accuracy, integrity, and availability are the major performance
requirements for GPS/WAAS.  Accuracy is defined as the degree of
conformance of an aircraft's position as calculated using GPS/WAAS to
its true position.  Integrity is the ability to provide timely
warnings when the GPS/WAAS is providing erroneous information and
thus should not be used for navigation.  Availability is the
probability that at any given time GPS/WAAS will meet the accuracy
and integrity requirements for a specific phase of flight.\4

WAAS is a system comprising a network of ground stations and
geostationary (GEO) communications satellites. 

  -- Reference stations (up to 54 sites) on the ground will serve as
     the primary data collection sites for WAAS.  These stations
     receive data from GPS and GEO satellites. 

  -- Master stations (up to 8 sites) on the ground will process data
     from the reference stations to determine and verify corrections
     for each GPS satellite.  These stations also validate the
     transmitted corrections. 

  -- Ground earth stations (up to 8 sites) will, among other things,
     receive WAAS message data from the master stations, and transmit
     and validate the message to the GEO satellites. 

  -- GEO satellites will transmit wide-area accuracy corrections and
     integrity messages to aircraft and also serve as additional
     sources of signals similar to GPS signals. 

  -- The ground communications system will transmit information among
     the reference stations, master stations, and ground stations. 

For pilots to use GPS/WAAS for navigation, their aircraft must be
equipped with receivers that process the information carried by the
GPS and GEO signals.  The receivers will enable the pilots to
determine the time and their aircrafts' three-dimensional position
(latitude, longitude, and altitude). 


--------------------
\1 FAA currently categorizes landing systems according to their
ability to safely guide an aircraft to a runway.  A Category I
precision landing system provides safe vertical guidance to an
aircraft as it descends to a height of not less than 200 feet with
runway visibility of at least 1,800 feet. 

\2 A "sole means" navigation system must, for a given operation or
phase of flight, allow the aircraft to meet all navigation system
performance requirements, without having another navigation system on
board the aircraft. 

\3 See National Airspace System:  Questions Concerning FAA's Wide
Area Augmentation System (GAO/RCED-97-219R, Aug.  7, 1997).  Past GAO
reports and testimonies on the augmentation of GPS are listed at the
end of this document. 

\4 Continuity and service volume are also considered major
requirements.  However, because they are derived from the accuracy,
integrity, and availability requirements, we did not focus on them
separately in our analysis.  Continuity is the probability that the
GPS/WAAS signal will meet accuracy and integrity requirements
continuously for a specified period.  Service volume is the area of
coverage for which the GPS/WAAS signal will meet availability
requirements. 


   CONCERNS EXIST ABOUT WHETHER
   WAAS CAN SATISFY PERFORMANCE
   REQUIREMENTS WITHIN BUDGET AND
   ON SCHEDULE
---------------------------------------------------------- Chapter 0:2

While system developers and outside experts have confidence that WAAS
can achieve most key performance requirements within current cost and
schedule estimates, four concerns are worth noting:\5 (1) the ability
of WAAS to provide the level of service for precision approaches
provided by existing ground-based systems; (2) the ability of
computers to process the large quantities of GPS/WAAS data within a
few seconds; (3) the vulnerability of GPS/WAAS signals to
interference; and (4) the need for additional satellites to achieve
the availability requirement. 

Regarding the first concern, it is uncertain whether WAAS can meet
the requirement that the GPS/WAAS signal be available for precision
approaches all but about 11 hours per year.  Under current
definitions based on ground-based navigation technology, a Category I
system provides a level of service that allows aircraft to descend to
an altitude (height) of not less than 200 feet when visibility is at
least 1,800 feet.  If WAAS cannot meet this requirement, FAA may
incur additional costs to install local area augmentation systems at
more airports than expected.\6

The agency may also change the procedures by which pilots can make
precision approaches.  One procedural option under consideration is
that FAA would require pilots to visually recognize additional
approach markings before completing a landing.  A decision is
expected on any needed procedural changes by late 1998. 

A second concern is the integrity requirement that calls for the
system to sound an alarm within 5.2 seconds when it receives
hazardously misleading information, such as a correction that is
wrong and would result in an aircraft operator being placed in a
dangerous situation.  The large volume of data that must be processed
within a few seconds to meet this requirement is beyond the
capabilities of computer data processors that are commercially
available.  However, FAA is testing newly developed processors and is
confident that they will meet the agency's needs. 

A third concern exists about the possibility that the GPS/WAAS signal
could prove vulnerable to unintentional or intentional radiofrequency
interference that could affect the signal's availability or accuracy
and, ultimately, flight safety.  These vulnerabilities are common to
ground- and satellite-based navigation aids.  Because GPS broadcasts
its signal at a very low power level, its signal is somewhat more
vulnerable to interference.  FAA expects to complete a vulnerability
assessment for WAAS in October 1997.  Once the assessment is
completed, countermeasures, if needed, would be identified.  Because
of the sensitivity of this issue, we cannot go into details in this
public hearing.  FAA has stated that it will offer a private briefing
for the Subcommittee. 

A fourth concern is whether FAA may have to add more GEO satellites
to meet the availability requirement.  FAA requires that GPS/WAAS be
available virtually 100 percent of the time--all but about 5 minutes
a year--for the phases of flight leading up to precision approaches. 
Although FAA originally thought it could meet this requirement by
using four geostationary communications satellites, the agency may
need five or six.  If so, FAA could continue using one or two of the
GEO satellites currently in space or obtain others.  FAA intends to
decide on the need for additional satellites by late 2000.  Even with
the added satellites, there may be isolated areas of air space, such
as the far northern and western areas of Alaska, where the
requirements may not be met.  In such areas, according to FAA
officials, FAA intends to use ground-based systems or local area
augmentation systems to provide a level of service that is at least
equal to what is provided today. 

The addition of one or two GEO satellites would increase the program
cost beyond the current estimate of $2.4 billion.  FAA expects that
adding one or two GEO satellites would cost between $71 million and
$192 million over the WAAS life cycle (2001-2016).\7

FAA faces a very tight time frame for putting the GEO satellites in
space.  FAA intends to work with the Defense Department to begin the
acquisition process this month, but it typically takes 4 years to
acquire, launch, and check out a GEO satellite.  Given FAA's October
2001 milestone for the delivery of the full WAAS, any delays in
putting the GEO satellites in space could cause the WAAS program's
schedule to slip. 


--------------------
\5 See app.  I for additional information on achievability of
requirements. 

\6 Local area augmentation systems enhance GPS to provide precision
approaches under the most stringent conditions. 

\7 Program costs are presented in then-year dollars. 


   FULL COST SAVINGS FROM WAAS
   TIED TO FAA'S DECOMMISSIONING
   OF GROUND-BASED SYSTEM
---------------------------------------------------------- Chapter 0:3

To get the full cost savings from WAAS, FAA will need to decommission
its ground-based network of navigation aids, which now costs the
agency $166 million annually to maintain.  FAA's plan presumes that
both its current ground-based system and the new satellite-based
system will be in place from the time that the full, Phase 3 WAAS is
commissioned until the decommissioning of the ground-based network is
completed in 2010.\8 FAA's plan recognizes that a critical factor in
the transition will be the widespread installation by commercial and
general aviation operators of GPS/WAAS avionics aboard their
aircraft. 

FAA believes that the safety and economic benefits of GPS/WAAS will
motivate aircraft operators to install GPS/WAAS avionics in the 5- to
6-year period after the services become available in 2001.  The
safety improvements include the vertical guidance WAAS will give
aircraft during approach and landing at airports where no precision
approach capability currently exists.  This guidance enables aircraft
to follow a smooth glide path safely to the runway.  Other benefits
include the cost savings that aircraft operators could realize by
using one type of navigation equipment in the cockpit for all phases
of flight and by flying more direct, fuel-efficient routes.  FAA also
expects that when it begins decommissioning ground-based navigation
aids, aircraft that are not equipped with GPS/WAAS avionics will have
to fly less direct routes and will have limits on the precision
approach options available to them.  As a result, there will be added
incentives for aircraft operators to switch to satellite technology. 

Nevertheless, FAA's plans could be impeded if the WAAS program's
schedule slips or if safety and economic benefits are not sufficient
to cause the aviation industry to switch quickly to satellite
technology.  As already discussed, the primary concern about whether
the WAAS requirements can be achieved on time is the potential for
delays in putting the communications satellites in space. 

Economic considerations, however, could cause commercial and general
aviation aircraft operators to switch to GPS/WAAS avionics more
slowly than FAA envisioned in its Transition Plan.  According to the
U.S.  GPS Industry Council, the typical GPS receiver used by large
commercial aircraft costs between $20,000 and $50,000, and the
typical GPS receiver used by smaller general aviation aircraft
capable of flying when visibility is limited costs between $5,000 and
$15,000.  Database changes needed to keep the receivers up to date
now cost $70 to $100 a month.  Expenses for installing the equipment
and training the pilots to use it would be additional. 

Airlines already recognize the value of GPS/WAAS for determining the
position of aircraft flying over the oceans, where no ground-based
navigation aids exist, and have been installing GPS receivers for
that purpose.  For flights over the continental United States, the
airlines' interest is not so clear cut.  Responding to our questions,
the organization representing the airlines, the Air Transport
Association, wrote that

     "Airspace users must have a compelling reason to change from
     their current ground-based avionics to space-based avionics. 
     Simply stating that the technology is better is not enough. 
     There must be real operational benefits for changing or the
     equipment will have to [be] mandated.  Otherwise, avionics
     change will be extremely slow."

The organization representing general aviation, the Aircraft Owners
and Pilots Association, has argued that the present cost of GPS/WAAS
avionics, including the cost of maintaining a current database, is
not affordable for all segments of the general aviation community. 
Representatives of the Association told us that FAA's plan for
decommissioning by 2010 would be realistic if (1) FAA provides routes
that are more direct, (2) more inexpensive avionics are available,
(3) FAA places a high priority on certifying approach procedures
where none currently exist, (4) inexpensive database updates for GPS
receivers can be obtained electronically from FAA, and (5) FAA does
not require aircraft operators to incur the added expense of carrying
redundant (dual) GPS/WAAS receivers. 

FAA is currently working with industry to resolve these concerns. 
Even if the Association's concerns are satisfied, however, FAA could
still face a slower-than-expected conversion to GPS/WAAS avionics if
individual aircraft operators do not conclude that the benefits of
installing the new navigation equipment outweigh their costs.  FAA
would then have to make a difficult choice--either slow down its
decommissioning of ground-based navigation aids or, in effect,
require conversion by proceeding with decommissioning as planned. 


--------------------
\8 FAA's Plan for Transition to GPS-Based Navigation and Landing
Guidance (July 1996). 


   COST INCREASES AND DELAYS IN
   DECOMMISSIONING REDUCE NET
   BENEFITS OF WAAS, BUT BENEFITS
   STILL EXCEED COSTS
---------------------------------------------------------- Chapter 0:4

In making investment decisions, FAA conducts benefit-cost analyses to
determine if the benefits to be derived from acquiring new equipment
outweigh the costs.  In the case of WAAS, the benefits to the
government include the cost savings from reduced maintenance of the
existing, ground-based network of navigation aids and the avoidance
of capital expenditures for replacing those aids.  The benefits to
aircraft operators--the users of the system--include the reduction in
accident-related costs (from death, injury, and property damage)
because WAAS landing signals would be available at airports that
currently lack precision landing capability.  Operators could also
realize "direct route" savings that result from the shorter flight
times on restructured, more direct routes that aircraft can fly using
GPS/WAAS.  The costs include the life cycle costs for WAAS facilities
and equipment as well as operations and maintenance. 

Despite differing assumptions used in calculating benefit-cost
ratios, FAA's analyses dating back to 1994 have always found WAAS to
be a cost-beneficial investment--that is, the benefits clearly
exceeded the costs, resulting in benefit-cost ratios in excess of
1.\9

The most recent 1997 analysis found (1) a 5.2 ratio of benefits to
costs when passenger time savings were included in the direct route
benefits and all aircraft would gain a savings of 1 minute per flight
from shorter routes, and (2) a 2.2 ratio when passenger time savings
were excluded and 30 percent of all aircraft would gain a savings of
1 minute per flight.\10 When these two cases were evaluated in dollar
terms, the net benefits of WAAS were $5.3 billion and $1.5 billion,
respectively.\11 (See app.  II for details on FAA's benefit-cost
analyses for the WAAS program in 1994, 1996, and 1997.)

To understand the impact of the potential cost increases and
decommissioning delays previously discussed, we requested that FAA's
support contractor perform alternative runs of the benefit-cost
analysis.\12 FAA's 1997 analysis served as the base case for
comparison purposes.  One pessimistic scenario that we requested made
the following alternative assumptions from the base case:  (1) the
development cost of the primary WAAS contract would increase by 15
percent, (2) the leasing costs for communications satellites would
increase by 50 percent, and (3) the decommissioning of the
ground-based navigation aids would be delayed by 5 years. 

Using these assumptions, the contractor's analysis found that the
benefit-cost ratio would be 4.6 when passenger time savings were
included and all aircraft gained savings from shorter flights and 1.7
when passenger time savings were excluded and 30 percent of all
aircraft gained savings from shorter flights.  In dollar terms, net
benefits declined substantially--about $490 million--when going from
the base case to the pessimistic scenario.  When scenarios were run
using the three assumptions in turn, the analysis showed that the
decommissioning delay of 5 years caused about $370 million of the
decline in net benefits.  The cost increases for contract development
and satellite leasing contributed the remainder.  We also asked for a
run with a more pessimistic scenario in which the contract
development and satellite leasing costs would increase by the same
amount but ground-based navigation aids would never be
decommissioned.  In this case, the decline in net benefits totaled
about $700 million. 

Ultimately, even when pessimistic assumptions were used, the analysis
found that the benefits of the WAAS program still clearly outweighed
its costs.  However, delays in decommissioning or the retention of
ground-based navigation aids would cause substantial decreases in the
net benefits of the WAAS program. 


--------------------
\9 Although WAAS will benefit nonaviation users, these benefits were
not included in FAA's analysis.  If these additional benefits were
included, the benefit-cost ratio would increase. 

\10 Cost-Benefit Analysis of the Wide Area Augmentation System
(draft), July 1997. 

\11 As an alternative to the benefit-cost ratio, where the present
value of benefits are divided by the present value of costs, analysts
sometimes calculate the present value of net benefits.  This value is
equal to the present value of benefits minus the present value of
costs.  When using alternative assumptions for calculating benefits
and costs, the present value of net benefits can be a useful tool for
making comparisons. 

\12 While we did not perform an extensive review of the contractor's
model used to calculate benefit-cost ratios, the model appeared to be
reasonably constructed.  For example, future benefits and costs were
discounted appropriately. 


   AGENCY COMMENTS
---------------------------------------------------------- Chapter 0:5

We received comments on a draft of this testimony from officials of
the Department of Transportation and FAA, including FAA's Deputy
Program Manager of the GPS Integrated Product Team and the WAAS
Program Manager.  These officials expressed general agreement with
the findings of the testimony, considered it well-balanced, and
provided clarifying and technical suggestions, which we incorporated
as appropriate. 


-------------------------------------------------------- Chapter 0:5.1

Mr.  Chairman, this concludes our statement.  I would be happy to
answer any questions that you or other Members of the Subcommittee
may have. 


ACHIEVABILITY OF WAAS PERFORMANCE
REQUIREMENTS
=========================================================== Appendix I

Phase 3 WAAS requirements     Remarks
----------------------------  ----------------------------
Availability: Probability that the system will provide an
accurate and c navigation signal for each pha
----------------------------------------------------------
En route through              FAA may need to add one or
nonprecision approach:        two GEO satellites to the
99.999% availability (i.e.,   four it planned to procure.
unavailable less than 5       Also, FAA is investigating
minutes a year)               the optimal placement of GEO
                              satellites in orbit. But in
                              isolated areas such as the
                              far northern and western
                              areas of Alaska the
                              requirement may not be met.

Precision approach: 99.9%     FAA may field up to 54
available (i.e., unavailable  ground stations, and Canada
11 hours a year)              and Mexico may field up to
                              21. Between late 1998 and
                              mid-1999, FAA will determine
                              how many ground stations are
                              needed based on system test
                              results. FAA may be required
                              to make changes to approach
                              procedures to meet this
                              requirement.


Accuracy: Percentage of time that an aircraft's GPS
position is wit distance of the aircraft's tru
----------------------------------------------------------
En route through              No major concerns have been
nonprecision approach:        raised by system developers
Within 100 meters 95% of the  or outside parties about
time--During periods when     these requirements because
this standard cannot be met   the existing GPS already
(up to a cumulative 72        guarantees this level of
minutes a day), system        performance. Feasibility
safety will be guaranteed by  testing at FAA's National
a proposed 2-mile horizontal  Satellite Test Bed (NSTB)
protection limit.             has validated that these
                              requirements have been met.
Within 500 meters 99.999% of  FAA will revalidate whether
the time--During periods      the WAAS software and
when this standard cannot be  hardware will achieve these
met (up to a cumulative 6     requirements.
seconds a day), system
safety will be guaranteed by
a proposed 2-mile horizontal
protection limit.

Precision approach: Within    No major concerns have been
7.6 meters 95% of the time-   raised by system developers
-During periods when this     or outside parties about
standard cannot be met (up    this requirement. FAA's NSTB
to a cumulative 72 minutes a  has achieved this level of
day), system safety will be   accuracy. During WAAS
guaranteed by a proposed 63-  software and hardware
foot horizontal and vertical  testing, FAA will validate
protection limit.             that this requirement can be
                              met.


Integrity: Ability of the system to provide users with
timely warn erroneous information
----------------------------------------------------------

Probability that the system will not detect hazardously
misleading informa
----------------------------------------------------------
En route through              No major concerns have been
nonprecision approach: 1      raised by system developers
chance in 10 million during   and outside parties about
1 hour of system operation    these requirements. FAA
                              plans to acquire safety-
Precision approach: 1 chance  certified equipment and
in 400 million per approach   software, and during
(an approach is the final 2-  hardware and software
1/2 minutes of flight)        testing also plans to
                              collect and analyze data to
                              provide increased assurance
                              that the requirements will
                              be met.


Maximum number of seconds elapsed before an alarm sounds
----------------------------------------------------------
En route through              The feasibility of meeting
nonprecision approach: 8      the 5.2-second requirement
seconds                       (and, therefore, the 8-
                              second requirement) has been
Precision approach: 5.2       demonstrated at FAA's NSTB.
seconds                       But as WAAS processes more
                              data, its ability to meet
                              the requirement may decline.
                              FAA's present analysis shows
                              that the requirement is
                              being marginally satisfied.
                              FAA is looking at faster
                              processing equipment to
                              accommodate the expected
                              increase in data.


Continuity: Probability that service will continue to be
available for a period
----------------------------------------------------------
En route through              FAA may need to add one or
nonprecision approach: 1      two GEO satellites to the
chance in 100 million per     four it planned to procure
hour of flight operations     or it may have to relax the
that the accuracy             requirement. Experts believe
requirement will not be met   relaxing the requirement may
                              be possible, but FAA has to
                              determine the impact on
                              safety if, in the event of a
                              catastrophic loss of both
                              GPS and WAAS, air traffic
                              controllers might have to
                              rely on radar to separate
                              and direct aircraft.

En route through              No major concerns have been
nonprecision approach: 1      raised by system developers
chance in 100,000 per hour    or outside parties because
of flight operations that     existing aircraft systems
the integrity requirement     have demonstrated this
will not be met               ability. During testing, FAA
                              will review contractor data
                              to validate that the
                              integrity requirement can be
                              met.

Precision approach: Per       No major concerns have been
approach, 1 chance in         raised by system developers
550,000 that the accuracy     or outside parties about
and integrity requirements    this requirement on the
will not be met (an approach  basis of the preliminary
is the final 2-1/2 minutes    analysis. But because of the
of flight)                    volume of data needed to
                              validate compliance with
                              this requirement, FAA is
                              gathering additional data
                              and exploring alternative
                              methods for validating that
                              the requirement can be met.


Service volume: The air space in which all other
performance requirements
----------------------------------------------------------
En route through              FAA may need to add one or
nonprecision approach: The    two GEO satellites to the
continental United States,    four it planned to procure.
Alaska, Hawaii, the           Also, FAA is investigating
Caribbean, the Gulf of        the optimal placement of GEO
Mexico, and major portions    satellites in orbit. But in
of the Atlantic and the       isolated areas such as
Pacific                       eastern Canada and oceanic
                              airspace the requirement may
                              not be met.

Precision approach: The       FAA may field up to 54
continental United States,    ground stations, and Canada
Alaska, Hawaii, and Puerto    and Mexico may field up to
Rico                          21. Between late 1998 and
                              mid-1999, FAA will determine
                              how many ground stations are
                              needed based on system test
                              results. FAA may be required
                              to make changes to approach
                              procedures to meet this
                              requirement.
----------------------------------------------------------

RESULTS OF FAA'S BENEFIT-COST
ANALYSES, 1994, 1996, AND 1997
========================================================== Appendix II

The results of FAA's benefit-cost analyses of the WAAS program in
1994, 1996, and 1997 are summarized in table II-1.  On the benefit
side, benefits to the government accrue from the reduced maintenance
of the existing, ground-based network of navigation aids and the
avoidance of capital expenditures for replacing these aids.  Benefits
to users--the aircraft operators--fall into five categories: 

  -- Efficiency benefits derive from having precision landing
     capability at airports where it does not now exist. 

  -- Avionics cost savings reflect how GPS/WAAS will enable users to
     reduce the proliferation of avionics equipment in their
     cockpits. 

  -- Fuel savings reflect the use of less fuel to fly aircraft that
     carry less avionics equipment. 

  -- Safety benefits stem from the reduction in accident-related
     costs (death, injury, and property damage) because of the
     availability of WAAS landing signals at airports that presently
     lack a precision landing capability. 

  -- Direct route savings result from the shorter flight times
     associated with restructured, more direct routes that aircraft
     can fly. 



                               Table II-1
                
                FAA's Analysis of Benefits and Costs for
                   WAAS Project, 1994, 1996, and 1997

                         (Dollars in millions)

                                                          1997    1997
                                          1994    1996    High     Low
--------------------------------------  ------  ------  ------  ------
Benefits
----------------------------------------------------------------------
Government                               1,385     943     754     754

User
----------------------------------------------------------------------
Efficiency                               1,051     768     286     148
Avionics                                 1,312   1,109     546     546
Fuel                                        98      95      13      13
Safety                                     560   1,384     624     624
Direct Route                                     5,489   4,299     637
======================================================================
Total                                    4,406   9,789   6,521   2,722

Costs
----------------------------------------------------------------------
R&D, F&E                                                   540     540
O&M                                                        720     720
======================================================================
Total                                    1,081   1,051   1,260   1,260
Benefit-Cost Ratio                         4.1     9.3     5.2     2.2
----------------------------------------------------------------------
Source:  Federal Aviation Administration. 

FAA's 1997 benefit-cost analysis took a more conservative approach
than previous versions of the model in estimating the benefit-cost
ratio.  That is, compared with the previous analyses, the assumptions
underlying the current study increased the expected costs of WAAS and
simultaneously reduced the expected benefits, which resulted in a
lower benefit-cost ratio than found in the previous versions of the
study.  The higher total costs in the 1997 version were largely due
to the inclusion of the costs of decommissioning land-based
navigation systems that were not included in any earlier versions of
the study.  On the benefit side, several changes in key assumptions
led to reduced expected benefits including (1) a shorter life cycle
for the project, (2) a reduction in the assumed "saved" costs from
phasing out ground-based navigation systems,\13 (3) a reduction in
estimated safety benefits based on the use of the more recent
accident data,\14 and (4) a reduction in the expected flight time
savings resulting from more direct routes. 

RELATED GAO PRODUCTS

National Airspace System:  Questions Concerning FAA's Wide Area
Augmentation System (GAO/RCED-97-219R, Aug.  7, 1997). 

Air Traffic Control:  Improved Cost Information Needed to Make
Billion Dollar Modernization Investment Decisions (GAO/AIMD-97-20,
Jan.  22, 1997). 

Global Positioning System Augmentations (GAO/RCED-96-74R, Feb.  6,
1996). 

National Airspace System:  Assessment of FAA's Efforts to Augment the
Global Positioning System (GAO/T-RCED-95-219, June 8, 1995). 

Air Traffic Control:  Status of FAA's Modernization Program
(GAO/RCED-95-175FS, May 26, 1995). 

Aviation Research:  Perspectives on FAA's Efforts to Develop New
Technology (GAO/T-RCED-95-193, May 16, 1995). 

National Airspace System:  Comprehensive FAA Plan for Global
Positioning System Is Needed (GAO/RCED-95-26, May 10, 1995). 

Global Positioning Technology:  Opportunities for Greater Federal
Agency Joint Development and Use (GAO/RCED-94-280, Sept.  28, 1994). 

Airspace System:  Emerging Technologies May Offer Alternatives to the
Instrument Landing System (GAO/RCED-93-33, Nov.  13, 1992). 


--------------------
\13 Specifically, the analyst assumed that old equipment would have
been replaced at a slower rate so that savings from not having to
replace that equipment were reduced. 

\14 In previous versions of the study, older data on accident rates
were used.  Since rates of accidents have been declining with time,
use of the most recent data reduced the expected safety benefits from
WAAS. 


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