oversight

National Airspace System: Observations on the Wide Area Augmentation System

Published by the Government Accountability Office on 1997-10-01.

Below is a raw (and likely hideous) rendition of the original report. (PDF)

                          United States General Accounting Office

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


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



    Page 1                                                      GAO/T-RCED-98-12
                 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.


                 In the 1980s, FAA began considering how a satellite-based navigation
Background       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



                 Page 2                                                       GAO/T-RCED-98-12
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



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.


Page 3                                                                             GAO/T-RCED-98-12
                           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).


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


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



                           Page 4                                                                     GAO/T-RCED-98-12
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


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



Page 5                                                                      GAO/T-RCED-98-12
                      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.


                      To get the full cost savings from WAAS, FAA will need to decommission its
Full Cost Savings     ground-based network of navigation aids, which now costs the agency
From WAAS Tied to     $166 million annually to maintain. FAA’s plan presumes that both its
FAA’s                 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    decommissioning of the ground-based network is completed in 2010.8 FAA’s
Ground-Based System   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.

                      7
                       Program costs are presented in then-year dollars.
                      8
                       FAA’s Plan for Transition to GPS-Based Navigation and Landing Guidance (July 1996).



                      Page 6                                                                         GAO/T-RCED-98-12
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.




Page 7                                                                   GAO/T-RCED-98-12
                        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.


                        In making investment decisions, FAA conducts benefit-cost analyses to
Cost Increases and      determine if the benefits to be derived from acquiring new equipment
Delays in               outweigh the costs. In the case of WAAS, the benefits to the government
Decommissioning         include the cost savings from reduced maintenance of the existing,
                        ground-based network of navigation aids and the avoidance of capital
Reduce Net Benefits     expenditures for replacing those aids. The benefits to aircraft
of WAAS, but Benefits   operators—the users of the system—include the reduction in
                        accident-related costs (from death, injury, and property damage) because
Still Exceed Costs      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




                        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.



                        Page 8                                                                               GAO/T-RCED-98-12
$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.


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.



Page 9                                                                             GAO/T-RCED-98-12
                  We received comments on a draft of this testimony from officials of the
Agency Comments   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.


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




                  Page 10                                                   GAO/T-RCED-98-12
Page 11   GAO/T-RCED-98-12
Appendix I

Achievability of WAAS Performance
Requirements


              Phase 3 WAAS requirements                      Remarks
              Availability: Probability that the system will provide an accurate and continuous
              navigation signal for each phase of flight
              En route through nonprecision approach: FAA may need to add one or two GEO
              99.999% availability (i.e., unavailable less satellites to the four it planned to procure.
              than 5 minutes a year)                       Also, FAA is investigating 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% available (i.e.,     FAA may field up to 54 ground stations,
              unavailable 11 hours a year)                   and Canada 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 within a given
              distance of the aircraft’s true position
              En route through nonprecision approach:        No major concerns have been raised by
              Within 100 meters 95% of the time—During       system developers or outside parties
              periods when this standard cannot be met       about these requirements because the
              (up to a cumulative 72 minutes a day),         existing GPS already guarantees this level
              system safety will be guaranteed by a          of performance. Feasibility testing at FAA’s
              proposed 2-mile horizontal protection limit.   National Satellite Test Bed (NSTB) has
                                                             validated that these requirements have
              Within 500 meters 99.999% of the               been met. FAA will revalidate whether the
              time—During periods when this standard         WAAS software and hardware will achieve
              cannot be met (up to a cumulative 6            these requirements.
              seconds a day), system safety will be
              guaranteed by a proposed 2-mile horizontal
              protection limit.
              Precision approach: Within 7.6 meters          No major concerns have been raised by
              95% of the time—During periods when this       system developers or outside parties
              standard cannot be met (up to a cumulative     about this requirement. FAA’s NSTB has
              72 minutes a day), system safety will be       achieved this level of accuracy. During
              guaranteed by a proposed 63-foot               WAAS software and hardware testing, FAA
              horizontal and vertical protection limit.      will validate that this requirement can be
                                                             met.
                                                                                             (continued)




              Page 12                                                                 GAO/T-RCED-98-12
Appendix I
Achievability of WAAS Performance
Requirements




Phase 3 WAAS requirements                        Remarks
Integrity: Ability of the system to provide users with timely warnings about
erroneous information
Probability that the system will not detect hazardously misleading information
En route through nonprecision approach: No major concerns have been raised by
1 chance in 10 million during 1 hour of  system developers and outside parties
system operation                         about these requirements. FAA plans to
                                         acquire safety-certified equipment and
Precision approach: 1 chance in 400      software, and during hardware and
million per approach (an approach is the software testing also plans to collect and
final 2-1/2 minutes of flight)           analyze data to provide increased
                                         assurance that the requirements will be
                                         met.
Maximum number of seconds elapsed before an alarm sounds
En route through nonprecision approach: The feasibility of meeting the 5.2-second
8 seconds                               requirement (and, therefore, the 8-second
                                        requirement) has been demonstrated at
Precision approach: 5.2 seconds         FAA’s NSTB. 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 specified
period
En route through nonprecision approach:          FAA may need to add one or two GEO
1 chance in 100 million per hour of flight       satellites to the four it planned to procure
operations that the accuracy requirement         or it may have to relax the requirement.
will not be met                                  Experts believe 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 nonprecision approach:          No major concerns have been raised by
1 chance in 100,000 per hour of flight           system developers or outside parties
operations that the integrity requirement will   because existing aircraft systems have
not be met                                       demonstrated this ability. During testing,
                                                 FAA will review contractor data to validate
                                                 that the integrity requirement can be met.
Precision approach: Per approach, 1              No major concerns have been raised by
chance in 550,000 that the accuracy and          system developers or outside parties
integrity requirements will not be met (an       about this requirement on the basis of the
approach is the final 2-1/2 minutes of flight)   preliminary analysis. But because of the
                                                 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.
                                                                                   (continued)


Page 13                                                                    GAO/T-RCED-98-12
Appendix I
Achievability of WAAS Performance
Requirements




Phase 3 WAAS requirements                    Remarks
Service volume: The air space in which all other performance requirements must be
met
En route through nonprecision approach:      FAA may need to add one or two GEO
The continental United States, Alaska,       satellites to the four it planned to procure.
Hawaii, the Caribbean, the Gulf of Mexico,   Also, FAA is investigating the optimal
and major portions of the Atlantic and the   placement of GEO satellites in orbit. But in
Pacific                                      isolated areas such as eastern Canada
                                             and oceanic airspace the requirement may
                                             not be met.
Precision approach: The continental United FAA may field up to 54 ground stations,
States, Alaska, Hawaii, and Puerto Rico    and Canada 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.




Page 14                                                               GAO/T-RCED-98-12
Appendix II

Results of FAA’s Benefit-Cost Analyses,
1994, 1996, and 1997

                                             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,            Dollars in millions
1996, and 1997                                                                                            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.




                                             Page 15                                                     GAO/T-RCED-98-12
Appendix II
Results of FAA’s Benefit-Cost Analyses,
1994, 1996, and 1997




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.




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.



Page 16                                                                         GAO/T-RCED-98-12
Page 17   GAO/T-RCED-98-12
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Page 19   GAO/T-RCED-98-12
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(341525)      Page 20                                                      GAO/T-RCED-98-12
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