This is the accessible text file for GAO report number GAO-02-710 
entitled 'National Airspace System: FAA's Approach to Its New 
Communications System Appears Prudent, but Challenges Remain' which was 
released on July 15, 2002.

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Report to Congressional Requesters:

July 2002

GAO:

GAO-02-710

Contents:

Letter:

Results in Brief:

FAAs Planned Improvements Would Likely Expand the Life of Its Existing 

Communications System but Would Not Meet Aviation Needs Beyond 2009:

To Help Ensure NEXCOM Will Meet Future Communications Needs, FAA Has 

Collaborated with the Aviation Industry to Assess Alternative 

Technologies:

FAA Needs to Resolve Three Key Issues Before It Can Make a Final 

Decision on the Technology for NEXCOM:

Conclusions:

Recommendation:

Agency Comments:

Scope and Methodology:

Appendix I:

GAO Contacts and Staff Acknowledgments:

GAO Contacts:

Staff Acknowledgments:

Tables:

Table 1: FAAs Plans Provide for Additional Channel Assignments for 

Voice Communications:

Table 2: Alternative Technologies and Reasons for Their Rejection:

Table 3: Major Milestones for Certifying VDL-3s Radio Equipment:

Figures:

Figure 1: Increasing Channel Capacity through Channel Splitting, 1966 

through 1999, and the Proposed Future Use of VDL-3:

Figure 2: Relationship between the Demand for Assigning Channels for 

Voice Communications and Increases in Air Traffic, 1977 through 2016:

Figure 3: FAAs Channel Assignments for Voice Communications, Actual, 

and Projected, 1974 through 2009:

Figure 4: Effect of a Projected 2-Percent Annual Increase in Air 

Traffic on FAAs Ability to Make New Channel Assignments for Voice 

Communications, 2000 through 2015:

Figure 5: FAAs Planned Approach to Implement VDL-3:

Figure 6: FAAs Schedule to Implement Voice and Data Digital 

Communications:

Abbreviations:

ACARS: Aircraft Communications Addressing and Reporting System:

FAA: Federal Aviation Administration:

GHz: gigahertz:

ICAO: International Civil Aviation Organization:

kHz: kilohertz:

MHz: megahertz:

NARC: NEXCOM Aviation Rulemaking Committee:

NASA: National Aeronautics and Space Administration:

NEXCOM:	Next Generation Air/Ground Communications:

VHF: very high frequency:

VDL-2: Very High Frequency Digital Link Mode 2:

VDL-3: Very High Frequency Digital Link Mode 3:

VDL-4: Very High Frequency Digital Link Mode 4:

United States General Accounting Office:

Washington, DC 20548:

July 15, 2002:

The Honorable John L. Mica

Chairman

The Honorable William O. Lipinski

Ranking Democratic Member

Subcommittee on Aviation

Committee on Transportation and

 Infrastructure

House of Representatives:

The Federal Aviation Administration (FAA) uses radios to provide air-

ground voice and data communications for pilots and air traffic 

controllers to safely coordinate all flight operations--ground 

movements of aircraft at airports, take-offs and landings, and 

separation distances between aircraft as they cruise at high altitudes. 

However, the anticipated growth in air traffic, coupled with FAAs 

efforts to reduce air traffic delays and introduce new air traffic 

services, will create a demand for additional channels for voice 

communications that FAAs current system cannot provide. FAA is 

implementing a new communications system to respond to this challenge 

and also seeking to enhance its existing ability to transmit data to 

provide more information to pilots, reduce errors in voice 

communications, and better balance controllers workload. Moreover, FAA 

expects that its new system should be less susceptible to interference 

from such sources as power lines and radio and television stations and 

also improve security against unauthorized users. FAA is developing 

products to use with its future integrated voice and data 

communications system. FAA refers to the initiative to acquire this 

system as Next Generation Air/Ground Communications (NEXCOM) and 

estimates that its long-term funding commitment for this initiative 

could reach $4 billion through fiscal year 2023.

Because voice and data communications are critical to air traffic 

management, you asked us to determine (1) to what extent the existing 

voice and data communications system used by FAA can effectively meet 

its expected future needs, (2) what FAA has done to help ensure that 

the technology it wants to use for NEXCOM will meet its future needs, 

and (3) what major issues FAA needs to resolve before it can make a 

final decision on the technology it wants to use for NEXCOM. To address 

these objectives, among other things, we interviewed and analyzed data 

and documentation from FAA program officials, experts in communications 

from the Department of Defense and the National Aeronautics and Space 

Administration, representatives of national and international aviation 

groups, and officials representing FAAs controller and maintenance 

workforces. We did not verify the data FAA provided or the results of 

FAAs analysis.

Results in Brief:

FAA and the aviation industry agree that the existing communications 

system, even with enhancements, cannot meet aviations expanding need 

for communications. FAA has identified 23 measures to improve its 

existing voice communications system, which the agency and industry 

believe will add several years to its useful life. However, they 

believe that it will not meet aviations future voice communications 

needs beyond 2009, even with these improvements. Because FAAs current 

system does not provide the capability for data link communications, 

the agency is currently leasing this service from a commercial vendor. 

However, even with planned improvements to this leased service, it will 

not meet FAAs projected needs for sharing data between FAA facilities 

and with aircraft operators. As FAA relies more on data communications, 

in part to help alleviate voice congestion, this service cannot meet 

the need to prioritize those messages that must be delivered 

expeditiously.

To help ensure that the technology it wants to use for NEXCOM will meet 

its future needs, FAA completed a comparative analysis of numerous 

technologies, in collaboration with the aviation industry, to assess 

each ones ability to meet technical requirements, minimize program 

risk, and meet the agencys schedule. As a result of this analysis, in 

March 1998, FAA selected Very High Frequency Digital Link Mode 3 (VDL-

3) as the technology it wanted to use for its future communications 

needs. Although five other technologies, such as FAAs current voice 

communications system coupled with a commercially available data link 

communications system, offered some potential to satisfy a broad range 

of future needs, each was rejected during the evaluation process. FAA 

plans to implement its preferred technology for NEXCOM by using a 

phased approach to help ensure that this technology can continue to 

meet its future needs. In September 2001, an aviation industry panel 

conditionally approved FAAs preferred technology.

However, before making a final decision to select the technology for 

NEXCOM, FAA will need to effectively address three major issues: 

whether the preferred technology is technically sound and will operate 

as intended, if the preferred technology and the equipment it requires 

can be certified as safe for use in the National Airspace System, and 

whether it is cost effective for users and the agency. To evaluate the 

technical and operational merits of the technology it wants to use, FAA 

has scheduled a series of three system demonstrations to be completed 

between October 2002 and October 2004. Using the preferred technology, 

these tests will, among other things, demonstrate the integration of 

voice and data communications and that the new equipment required for 

NEXCOM is compatible with existing equipment. Moreover, these tests 

will also demonstrate if this integrated system can be certified as 

safe for aircraft operations. Because FAA plans to require aviation 

users to buy new radios and other equipment to use with the technology 

it selects for NEXCOM, FAA has begun to analyze the cost and benefits 

of the technology it wants to use. Under FAAs current plans, the 

agency is assuming a 30-year useful life for the NEXCOM technology it 

wants to use. However, emerging technologies might shorten the useful 

life and thus reduce the overall benefits. To help ensure that FAAs 

final selection for NEXCOM is the most cost effective for the agency 

and aviation users, we are recommending that, as part of its cost 

benefit analysis before committing to a technology, FAA assess the 

potential impact of emerging technologies in light of its requirements.

In commenting on a draft of this report, the Product Team Lead for Air/

Ground Voice Communications and officials from Spectrum Policy and 

Management, FAA, indicated that they generally agreed with the facts 

and recommendation. These officials and those from the National 

Aeronautics and Space Administration provided a number of clarifying 

comments, which we have incorporated where appropriate.

Background:

Air traffic controllers monitor and direct traffic in a designated 

volume of airspace called a sector. Each sector requires a separate 

channel assignment for controllers to communicate with aircraft flying 

in that sector. As the amount of air traffic grows, the need for 

additional sectors and channel assignments also increases. FAAs 

present air-ground communications system operates in a worldwide, very 

high frequency (VHF) band reserved for safety communications within the 

118 to 137 megahertz (MHz) range.[Footnote 1] Within this range of 

frequencies, FAA currently has 524 channels available for air traffic 

services. During the past four decades, FAA has primarily been able to 

meet the increased need for more channel capacity within this band by 

periodically reducing the space between channels (a process known as 

channel splitting). For example, in 1966, reducing the space between 

channels from 100 kHz to 50 kHz doubled the number of channels. The 

last channel split in 1977, from 50 kHz to 25 kHz, again doubled the 

number of channels available. Each time FAA reduced this space, owners 

of aircraft needed to purchase new radios to receive the benefits of 

the increased number of channels. FAA can use or assign its 524 

channels several times around the country (as long as channel 

assignments are separated geographically to preclude frequency 

interference). Through channel reuse, FAA can make up to 14,000 channel 

assignments nationwide. While aviation literature often refers to 

channel and channel assignments as frequency and frequency assignments, 

throughout this report, we use the terms channel and channel 

assignments.

Because the growth in air traffic during the past decade has created a 

need for more communications channels since the 1977 split, FAA has 

been increasingly concerned that the demand for channels would exceed 

their availability, which would cause frequency congestion. FAA first 

explored this issue at length at a 1990 International Civil Aviation 

Organization (ICAO) conference,[Footnote 2] at which the ICAO member 

countries addressed increasing congestion in the air traffic control 

communications band and the especially acute problem in the U. S. and 

Western Europe. Over the next 5 years, ICAO evaluated different 

solutions that were proposed by the conferences participants. While 

the Western European countries proposed further channel splitting to 

increase capacity, FAA proposed a totally new air-ground communications 

system. FAAs proposed technology, known as VDL-3, would be based on a 

new integrated digital voice and data communications technology, which 

would assign segments of a channel to users in milliseconds of time, 

thereby allowing both voice and data to travel over the same channels 

using one of the available time slots. Under the current system, each 

channel is used exclusively and continuously for voice, so the air 

traffic controller can communicate at all times with the aircraft. This 

new technology could provide up to a fourfold increase in capacity 

without channel splitting, thus meeting the demand for new voice 

channels. VDL-3 digitizes a persons voice and sends it as encoded bits 

of information, which is reassembled by the receiver. Moreover, this 

technology could provide real-time data link on-board communications of 

air traffic control messages and events.

Although ICAO adopted FAAs proposed digital air-ground communications 

system VDL-3 in 1995 as its model for worldwide implementation, it also 

approved standards allowing Western Europe, which was then experiencing 

severe frequency congestion, to further reduce the spacing between 

channels from 25 kHz to 8.33 kHz. While this action tripled the number 

of channels available for assignment, it also resulted in the need for 

aircraft flying in Western Europe to install new radios that are 

capable of communicating over the 8.33 kHz channels. ICAO intended that 

this reduction would be an interim measure until 2004, when FAA 

estimated that the technology it had proposed would be operational. 

However, FAA did not pursue developing VDL-3 in 1995, in part, because 

its existing communications system still had available capacity to meet 

near-term communications needs, and because the agencys need to 

modernize its air traffic control system became an urgent priority. In 

1998, FAA resumed developing VDL-3; however, the agency is not expected 

to implement this technology until 2009. Figure 1 depicts how channel 

splitting has increased channel capacity since 1966 and how FAAs 

proposed use of VDL-3 will further increase channel capacity.

Figure 1: Increasing Channel Capacity through Channel 

Splitting, 1966 through 1999, and the Proposed Future Use of VDL-3:

[See PDF for image]

Note: The distance between the vertical lines and horizontal lines--in 

the case of VDL-3--represents the space between assigned channels.

Source: GAOs presentation of information provided by FAA.

[End of figure]

FAAs Planned Improvements Would Likely Expand the Life of Its Existing 

Communications System but Would Not Meet Aviation Needs Beyond 2009:

FAA has identified 23 measures to improve its existing voice 

communications system. While FAA and the U. S. aviation industry 

generally believe that implementing all these measures would add 

several years to the useful life of the existing system, they believe 

it would not meet aviations future voice communications needs beyond 

2009. Because increases in air traffic create the need for more channel 

assignments, the events of September 11, which have resulted in slower 

than expected increases, might delay by a year or two when FAA starts 

to encounter problems systemwide in providing new channel assignments. 

Agency and industry representatives agree that it is not possible to 

precisely predict when the existing system with its planned 

improvements will no longer meet aviations needs. As a result, FAA 

plans to annually assess whether this system will be capable of meeting 

the projected need for more channel assignments for at least 5 years 

into the future. FAA plans to release the first of these annual 

assessments in September 2002.

While the focus of FAAs efforts has been to meet aviations need for 

voice communications through 2009, FAA recognizes that its data 

communications needs are evolving. The agency expects to increase its 

use of data communications to help alleviate voice congestion and to 

help controllers and pilots accurately exchange more information. 

Because FAAs current system cannot do this, it has been leasing data 

link services from ARINC.[Footnote 3] However, even with the planned 

improvements, this service will not be able to meet FAAs projected 

need for more data communications. As FAA relies more on data 

communications, this leased system will not be able to meet the 

agencys need to prioritize those messages that must be delivered 

expeditiously. Recognizing that accurately projecting the growth in 

aviations need for data link communications beyond 15 years would be 

difficult, FAA is designing a system to provide a sevenfold increase in 

capacity to meet future needs.

FAA Does Not Have Enough Channels to Meet Aviations Projected Need for 

Voice Communications:

During the 1990s, several of FAAs studies found that, historically, 

increases in air traffic were closely related to the growing need to 

assign more channels for voice communications (see fig. 2).

Figure 2: Relationship between the Demand for Assigning 

Channels for Voice Communications and Increases in Air Traffic, 1977 

through 2016:

[See PDF for image]

Source: GAOs presentation of FAAs data.

[End of figure]

In its most recent study about the growing need for more channel 

assignments for voice communications,[Footnote 4] FAA found that this 

need had grown annually, on average, about 4 percent (about 300 new 

channel assignments) since 1974 (see fig. 3). This growth paralleled 

the increase in domestic air travel during that time frame. Despite the 

recent downturn in air traffic resulting from a recession and the 

September 11 terrorist attacks, FAA expects it to resume its historical 

4-percent annual growth within a year or two. Currently, FAAs voice 

communications system is limited to a maximum of 14,000 channel 

assignments. Because increases in air traffic require more new channel 

assignments, FAA expects that providing them in some metropolitan areas 

will become increasingly difficult. If the system is left unchanged, 

FAA has concluded that, as early as 2005, it could no longer fully 

support aviations need for voice communications and that in such high 

traffic metropolitan areas as New York, Chicago, and Los Angeles the 

need for additional assignments could be evident sooner.

Figure 3: FAAs Channel Assignments for Voice Communications, 

Actual, and Projected, 1974 through 2009:

[See PDF for image]

Note: The Y-axis and graph line have been enlarged to show detail.

Source: GAOs presentation of FAAs data.

[End of figure]

Because FAA has delayed NEXCOMs implementation until 2009, the 

agencys 23 planned improvement measures are designed to add 

approximately 2,600 additional channel assignments for voice 

communications. (See table 1.) FAA has classified these initiatives, 

which involve a variety of technical, regulatory, and administrative 

changes, according to how soon it expects to implement them. However, 

FAA recognizes that there is no guarantee that all of these measures 

can be implemented because some of them largely depend on gaining 

agreement from other entities, such as other federal agencies and the 

aviation community, and some may involve international coordination. 

FAA also recognizes that the exact degree of improvement resulting from 

the totality of these measures cannot be precisely projected and actual 

test results could show less gain than anticipated. Many of these 

initiatives involve reallocating channels being used for purposes other 

than air traffic services and increasing FAAs flexibility to use 

already assigned channels. For example, FAA is reviewing its policy for 

assigning channels to such special events as air shows to determine if 

fewer channels could be assigned to them so that channels could be used 

for other purposes.

Table 1: FAAs Plans Provide for Additional Channel Assignments for 

Voice Communications:

Year: 2003; Improvement measures: 15: Additional channel 

assignments: 1,041.

Year: 2005; Improvement measures: 7; Additional channel 

assignments: 1,574. 

Year: 2009; Improvement measures: 1; Additional channel assignments: 
[A].

Year: Total; Improvement measures: 23; Additional channel 

assignments: 2,615.

[A] FAA is still studying the gains that this measure should achieve.

Source: GAOs analysis of FAAs data.

[End of table]

While it is not possible to predict exactly when FAAs existing voice 

communications system will run out of available channel assignments, 

agency and aviation representatives concur that, without the 23 

improvement measures, the system will be strained to provide enough 

channel assignments. According to a MITRE Corporation study completed 

in 2000,[Footnote 5] even if the need for more channel assignments for 

voice communications were to grow at 2 percent per year (instead of 

FAAs projected growth of 4 percent per year), by 2005 or sooner, it 

would be difficult for FAA to meet the need for air traffic 

communications in major metropolitan areas. MITRE also projected that 

the shortage of available channel assignments would become a nationwide 

problem by 2015 or sooner.[Footnote 6] In 2000, FAA first encountered a 

shortage problem when it had to reassign a channel from one location to 

another that FAA viewed as a higher priority in the Cleveland area. 

Figure 4 shows MITREs analysis of how the projected demand for more 

voice communications capacity will intensify if FAA does nothing to 

improve this system.

Figure 4: Effect of a Projected 2-Percent Annual Increase in 

Air Traffic on FAAs Ability to Make New Channel Assignments for Voice 

Communications, 2000 through 2015:

[See PDF for image]

Note: Each circle represents where the demand for voice communications 

capacity will inhibit FAAs ability to meet new air traffic needs.

Source: GAOs presentation of MITREs analysis.

[End of figure]

FAA Does Not Have Enough Channels to Meet Aviations Projected Need for 

Data Communications:

Currently, FAA is leasing ARINCs Aircraft Communications Addressing 

and Reporting System (ACARS) to provide data link communications that 

are not time critical, such as forwarding clearances to pilots prior to 

takeoff.[Footnote 7] Because this analog system is also reaching its 

capacity to handle data link communications, FAA plans to use ARINCs 

new digital data communications system, known as Very High Frequency 

Digital Link Mode 2 (VDL-2) until 2009.[Footnote 8] By then, FAA 

expects to use its VDL-3 system, which is being developed to integrate 

voice and data communications, to meet aviations needs for about 1,800 

channel assignments for data communications over the next 15 years and 

to prioritize messages that must be delivered expeditiously, which VDL-

2 cannot provide. Because FAA believes that aviations need for data 

communications cannot be realistically projected beyond 15 years, it is 

designing a system to provide a sevenfold increase in capacity for data 

communications, thereby providing what it believes is an excess 

capacity that should meet aviations future needs.

To Help Ensure NEXCOM Will Meet Future Communications Needs, FAA Has 

Collaborated with the Aviation Industry to Assess Alternative 

Technologies:

In consultation with stakeholders from the aviation industry, FAA 

selected VDL-3 as the preferred solution to meet its future 

communications needs. During the 1990s, FAA collaborated with its 

stakeholders to analyze many different communications systems, as well 

as variations of them, as potential candidates to replace its existing 

communications system. As a result of these studies, FAA eliminated 

several designs because they did not meet some of the fundamental needs 

established for NEXCOM. For example, FAA found that Europes Very High 

Frequency Digital Link Mode 4 (VDL-4) technology was too early in 

development to assess and that it would not provide voice 

communications, FAAs most pressing need. Moreover, a vendor of VDL-4 

recently told us that this technology still needed additional 

development to meet FAAs communications needs and that the 

international community had not yet validated it as a standard for air 

traffic control communications, which could take at least an additional 

3 years. In March 1998, FAA rated VDL-3 as the best of the six possible 

technologies to meet its future communications needs and the most 

likely to meet its schedule with the least risk. FAA found that VDL-3, 

the international model for aviation communications, could:

* provide up to a maximum fourfold increase in channel capacity, but 

the increase is estimated to be three to fourfold because of initial 

deployment scenarios;

* transmit voice and data communications without interference;

* increase the level of security;

* provide voice and data communications to all users with minimal 

equipment replacement;

* require no additional channel splitting, thereby reducing the need 

for engineering changes; and:

* reduce the number of ground radios required by FAA because each radio 

could accommodate up to four channels within the existing 25 kHz 

channel spacing.

Although FAA and its stakeholders thought that each of the five other 

technologies had some potential to satisfy a broad range of their 

future needs, each was rejected during the 1998 evaluation process. 

(See table 2.):

Table 2: Alternative Technologies and Reasons for Their Rejection:

Alternative: 25 kHz and VDL-2; Description: FAAs current analog voice 

communications technology and a separate digital data technology that 

ARINC is developing for aviation; Reason for rejection: Would not 

provide the needed additional channels for voice communications because 

the channels would need to be reassigned to communicate data.

Alternative: 8.33 kHz and VDL-2; Description: A system providing 

additional channel capacity by reducing the space between channels by 

using FAAs current analog voice communications technology and a 

separate digital data technology that ARINC is developing for aviation; 

Reason for rejection: --Could only double the number of voice channels; 

--Could not resolve existing radio interference and loss of 

communications issues and; --Would likely require a significant 

increase in the number of ground radios.

Alternative: Cellular telecommunications; Description: A commercially 

available digital technology that would need to be enhanced for air 

traffic control; Reason for rejection: Significant technical challenges 

would preclude meeting FAAs need to deploy an initial operational 

system by 2005.

Alternative: Geostationary satellites; Description: A system whose 

satellites maintain fixed positions at 22,000 miles above the earth; 

Reason for rejection: Significant technical challenges would preclude 

meeting FAAs need to deploy an initial operational system by 2005.

Alternative: Low-earth orbit or medium-earth orbit satellites; 

Description: A system whose satellites can range from 200 to 500 miles 

above the earth or a system from a few hundred to a few thousand miles 

above the earth; Reason for rejection: Significant technical challenges 

would preclude meeting FAAs need to deploy an initial operational 

system by 2005.

Source: GAOs presentation of FAAs data.

[End of table]

Academia and other experts have concluded that FAAs rationale for 

rejecting alternative technologies in 1998 remains valid today. 

Specifically, the technical challenges facing these technologies have 

not been sufficiently resolved to allow FAA to deploy an initial 

operating system by 2005. For example, while satellite technology is 

used to provide voice and data communications across the oceans and in 

remote regions, it is expensive, it does not support the need for 

direct aircraft-to-aircraft communications, and does not meet 

international standards for air traffic control communications. 

Representatives from the National Aeronautics and Space Administration 

(NASA) told us that emerging technologies that could meet FAAs need 

for voice and data communications could be developed and available by 

2015. However, in further discussion with these representatives, they 

indicated that while such technologies might be mature enough to 

provide communications services, it may require additional time for 

them to meet all of the requirements associated with air traffic 

control safety systems. NASA officials commented that FAA initiated its 

plans for its new communications system at the outset of the emerging 

wireless technology explosion and was not able to assess and integrate 

any of these emerging technologies into the NEXCOM architecture. 

However, they noted that the telecommunications field is changing 

rapidly, and FAA and the aviation industry will need to continually 

assess their requirements and keep abreast of emerging technologies 

that could better meet their future communications needs.

FAAs planned approach for NEXCOM is to implement VDL-3 in three 

segments, as shown in figure 5. Currently, FAAs senior management has 

only approved investments for the first segment.

Figure 5: FAAs Planned Approach to Implement VDL-3:

[See PDF for image]

Note: In segment 1, FAA plans to start deploying radios that can 

operate in both the current analog and future digital modes because 

voice communications will continue in the analog mode until 2009 when 

FAA plans to start providing digital voice communications.

Source: GAOs presentation of FAAs plans.

[End of figure]

If FAA cannot demonstrate that VDL-3 can successfully integrate both 

voice and data in a cost-effective manner, FAA plans to implement a 

backup approach to meet the need for more channel capacity. FAAs 

backup follows the Western European approach as follows:

* For analog voice communications, reduce the 25 kHz space between 

channels to 8.33 kHz.

* For digital data communications, rely on a commercial vendor that is 

developing a technology to support aviations need for data, known as 

VDL-2.

However, this approach remains a backup because it doubles, not 

quadruples, voice channel capacity. Furthermore, it does not resolve 

the issues of radio interference and loss of communications that now 

confront FAA, nor does it meet all of the requirements for air traffic 

control data link communications.

FAA Needs to Resolve Three Key Issues Before It Can Make a Final 

Decision on the Technology for NEXCOM:

Before selecting VDL-3 as the technology for NEXCOM, FAA needs to 

demonstrate the technical and operational merits of VDL-3, certify VDL-

3 as a safety critical system, and prove its cost-effectiveness to 

the aviation industry. To help address these issues, the FAA 

Administrator formed the NEXCOM Aviation Rulemaking Committee (NARC) in 

2000.[Footnote 9] The NARC, composed of representatives from the 

aviation industry and other groups, submitted its final report in 

September 2001, which included recommendations to expedite the 

resolution of technical and operational issues involving NEXCOM.

To demonstrate VDL-3s technical and operational merits, FAA has 

scheduled a series of three tests of this technology, beginning in 

October 2002 and ending in October 2004. The first test is designed to 

demonstrate the quality of voice communications and the integration of 

voice and data communications. A key component of the second test is to 

demonstrate that new digital ground radios can work with new digital 

aircraft equipment and other equipment in FAAs air traffic control 

system.[Footnote 10] Finally, in the third test, FAA plans to validate 

that VDL-3 can be certified as safe for aircraft operations. Moreover, 

to make VDL-3 fully operational will require FAA and users to undertake 

a phased installation of tens of thousands of new pieces of equipment. 

In addition to FAA and users installing radios with new transmitters 

and receivers, FAA would need to install new voice switches and 

workstations. FAA also needs to ensure that all the new equipment 

required for NEXCOM will be compatible with FAAs existing equipment, 

especially the numerous types of voice switches as well as the local 

and wide area networks. Therefore, FAA estimates that it will take 5 

years following the successful conclusion of its demonstration tests 

for it to install the new ground equipment, while the airlines install 

new aircraft equipment. Figure 6 shows FAAs schedule to implement both 

voice and data digital communications.

Figure 6: FAAs Schedule to Implement Voice and Data Digital 

Communications:

[See PDF for image]

Note: FAA has yet to determine what services it will receive on VDL-2 

after it implements VDL-3.

Source: FAA.

[End of figure]

Because communications are critical to ensuring safe aircraft 

operations, FAA is developing a process to certify that VDL-3 and the 

new equipment it requires could be used in the National Airspace 

System. In April 2002, FAAs teams responsible for developing and 

certifying VDL-3 drafted a memorandum of understanding that describes 

their respective responsibilities. They agreed to maintain effective 

communications among them as well as with the manufacturers developing 

VDL-3 equipment. (See table 3 for the schedule for certifying the 

radios that will be used with VDL-3.) To FAAs credit, the agency is 

proactively seeking certification before making a final decision on 

VDL-3.

Table 3: Major Milestones for Certifying VDL-3s Radio Equipment:

Date: September 2002; Milestone: Sign a final memorandum of 

understanding..

Date: August 2003; Milestone: Publish guidelines for manufacturing FAA-

approved digital radios..

Date: August 2004; Milestone: Certify that the radios selected for 

NEXCOM meet aviations needs before the final October 2004 

demonstration..

Source: GAOs presentation of information provided by FAA.

[End of table]

The issue of cost effectiveness was raised by the NARC because it 

wanted FAA to fully analyze the airlines transition to digital radios 

before the agency requires their use. Convincing enough users to 

purchase VDL-3 radios might be difficult because some air carriers had 

recently bought 8.33 kHz radios for operation in Europe, and they would 

not be eager to purchase additional equipment. As part of its cost-

benefit analysis, FAA is assuming a 30-year life cycle for NEXCOM; 

however, changing requirements coupled with the rapidly changing 

developments in telecommunications technology could reduce this life 

cycle. Without analyzing the costs and benefits under different 

confidence levels for other potential life cycles for NEXCOM while 

considering the impact of changing requirements and the effects of 

emerging technologies, FAA might find it more difficult to enlist the 

continued support of the aviation community for NEXCOM. FAA plans to 

begin analyzing the cost-effectiveness of NEXCOM in mid-2002, publish a 

notice of proposed rulemaking by January 2004, complete its cost-

benefit analysis by mid-2004, and publish its final rulemaking by June 

2005. FAA officials agreed that it is important to continually evaluate 

the requirements of the future system and whether emerging technologies 

could reduce VDL-3s cost-effectiveness prior to making the final 

selection. Throughout its rulemaking process, program officials 

stressed that they plan to continue involving all key FAA organizations 

and the aviation industry.

Conclusions:

FAAs approach for selecting its NEXCOM technology appears prudent. The 

FAA officials managing NEXCOM have worked with the aviation industry 

and involved other key FAA organizations to help ensure that the 

technical and operational, safety, and cost-effectiveness issues are 

resolved in a timely manner. However, FAA is only in the early stages 

of resolving these three issues, and the programs continued success 

hinges on FAAs maintaining close collaboration with major 

stakeholders. FAAs follow-through on the development of a 

comprehensive cost-benefit analysis, which considers how changing 

requirements and emerging technologies could affect the cost 

effectiveness of VDL-3, will be key to this success. Otherwise, the 

aviation community might not continue to support FAA in developing 

NEXCOM, as they now do.

Recommendation:

To make the most informed decision in selecting the technology for 

NEXCOM and continue to receive the support from the aviation community, 

we recommend that the Secretary of Transportation direct the FAA 

Administrator to assess whether the requirements for voice and data 

communications have changed and the potential impact of emerging 

technologies on VDL-3s useful life as part of its cost-effectiveness 

analysis of NEXCOM.

Agency Comments:

We provided the Department of Transportation, the Department of 

Defense, and the National Aeronautics and Space Administration with a 

draft of this report for review and comment. The Department of Defense 

provided no comments. The Product Team Lead for Air/Ground Voice 

Communications and officials from Spectrum Policy and Management, FAA, 

indicated that they generally agreed with the facts and recommendation. 

These officials, along with those from the National Aeronautics and 

Space Administration, provided a number of clarifying comments, which 

we have incorporated where appropriate.

Scope and Methodology:

To determine the extent to which FAAs existing communications system 

can effectively meet its future needs, we interviewed officials from 

FAAs NEXCOM program office, the agencys spectrum management office, 

union officials representing the air traffic controller and maintenance 

technician workforces, representatives of the MITRE Corporation, and 

members of the NARC, an advisory committee formed by FAA to help ensure 

that NEXCOM meets the aviation industrys needs. We reviewed 

documentation on the current status of FAAs existing air-ground 

communications system as well as documentation on potential measures 

FAA plans to take to increase the channel capacity of its existing 

system.

To determine what FAA did to help ensure that its preferred technology 

for NEXCOM will meet aviations future needs, we interviewed officials 

from FAAs NEXCOM program office; officials from the Department of 

Defense, the National Aeronautics and Space Administration, and 

Eurocontrol;[Footnote 11] an expert in satellite communications from 

the University of Maryland; and contractors who offer VDL-2 and VDL-4 

communications services. We reviewed documentation indicating to what 

extent varying technologies could meet FAAs time frames for 

implementing NEXCOM. We also reviewed documentation indicating how well 

varying technologies could meet FAAs specifications for NEXCOM. We did 

not perform an independent verification of the capabilities of these 

technologies. Additionally, we reviewed studies performed by FAA in 

collaboration with the U.S. aviation industry to assess alternative 

technologies for NEXCOM that led the U.S. aviation community to endorse 

FAAs decision to select VDL-3 as its preferred technology for NEXCOM.

To identify issues FAA needs to resolve before it can make a final 

selection for NEXCOMs technology, we interviewed officials from FAAs 

NEXCOM program office as well as members of the NARC. We also reviewed 

NEXCOM program office documentation that prioritizes the programs 

risks, assesses their potential impact on the programs cost and 

schedule, and describes the status of FAAs efforts to mitigate those 

risks. In addition, we reviewed the NARCs September 2001 report that 

made recommendations to FAA for modernizing its air-ground 

communications system. We conducted our review from September 2001 

through May 2002, in accordance with generally accepted government 

auditing standards.

We are sending copies of this report to interested Members of Congress; 

the Secretary of Transportation; the Secretary of Defense; the 

Administrator, National Aeronautics and Space Administration, and the 

Administrator, FAA. We will also make copies available to others upon 

request. In addition, the report will be available at no charge on the 

GAO Web site at http://www.gao.gov.

If you or your staff have any questions about this report, please 

contact me at (202) 512-3650. I can also be reached by E-mail at 

dillinghamg@gao.gov. Key contributors are listed in appendix I.

Gerald L. Dillingham, Ph.D.

Director, Physical Infrastructure:

Signed by Gerald L. Dillingham:

GAO Contacts:

Appendix I: GAO Contacts and Staff Acknowledgments:

Gerald L. Dillingham (202) 512-3650

Belva M. Martin (202) 512-4285:

Staff Acknowledgments:

In addition to those individuals named above, Nabajyoti Barkakati, 

Geraldine C. Beard, Jeanine M. Brady, Peter G. Maristch, and Madhav S. 

Panwar made key contributions to this report.

FOOTNOTES

[1] Frequency is the number of waves traveling by a given point per 

unit of time, in cycles per second, or hertz. Radio frequency is 

usually measured in thousands of hertz or kilohertz (kHz), millions of 

hertz or megahertz (MHz), and billions of hertz or gigahertz (GHz). 

Because the range of consecutive frequencies makes up a band, the 

greater the range of frequencies, the greater the bandwidth. In 

addition to using this bandwidth for air traffic services, FAA uses it 

for such other services as flight-testing and air shows. Other 

organizations, such as the Department of Defense and commercial 

airlines, also use it for flight-testing and airline operations. 

[2] ICAO is a specialized agency of the United Nations that sets 

international standards and regulations necessary for the safety, 

security, and efficiency in all fields of civil aviation.

[3] ARINC coordinates radio frequencies for the airlines and is a 

leader in providing air-ground communications worldwide.

[4] FAAs Radio Spectrum Plan for 2001-2010, which was issued on 

September 30, 2001, does not reflect the impact of the terrorist 

attacks of September 11.

[5] MITRE provides air traffic control, air traffic management, and 

airport systems engineering support to FAA and civil aviation 

authorities around the world.

[6] Due, in part, to the events of September 11, 2001, concerns also 

exist about the adequacy of radio spectrum resources to enable public 

safety agencies to communicate with one another. 

[7] ACARS is an analog data link communications system designed 

primarily for airlines use.

[8] Analog radios rely on signals that use electric currents with 

continuously variable voltages to reproduce data being transmitted. 

Because an analog system transmits data by using variable voltages, 

removing noise and wave distortions is very difficult. For this reason, 

analog signals cannot perform high-quality data transmission. Because 

digital radios rely on signals that use binary digits (0 and 1) to 

transmit data, there is little interference. The resulting high-quality 

transmission of data at high speeds is crucial for communications that 

use computers because they use digital signals to process information.

[9] The NARC was composed of representatives from various 

organizations, including the National Business Aviation Association; 

American, Southwest, Northwest, and United Airlines; the Airline Pilots 

Association; the Aircraft Owners and Pilots Association; the Department 

of Defense; the National Air Traffic Controllers Association; 

Professional Airways Systems Specialists; MITRE; the General Aviation 

Manufacturers Association; and the Air Transport Association. FAA 

chartered the NARC to review its previous work on cost, benefits, and 

transition assumptions and to recommend appropriate actions. Moreover, 

since some members of the U.S. aviation community knew that Western 

Europe had chosen a different technology to meet its more pressing need 

for additional channels for voice communications, they requested that 

the NARC review both the U. S. and European systems.

[10] In July 2001, FAA awarded a contract for ground radios that can 

operate in either the current analog mode or the future digital mode. 

Likewise the radios being developed for aircraft will operate in both 

modes, which will make them compatible with radios being used by the 

Western European communications system.

[11] Eurocontrol is Europes organization for managing air traffic.

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