a

GAO

United States General Accounting Office

Report to Congressional Requesters

July 2002 NATIONAL 

AIRSPACE SYSTEM

FAA’s Approach to Its 

New Communications 

System Appears 

Prudent, but 

Challenges Remain

GAO-02-710
Page i GAO-02-710 FAA's New Communications System

Letter 1

Results in Brief 2

Background 3

FAA’s Planned Improvements Would Likely Expand the Life of Its

Existing Communications System but Would Not Meet Aviation

Needs Beyond 2009 7

To Help Ensure NEXCOM Will Meet Future Communications

Needs, FAA Has Collaborated with the Aviation Industry to

Assess Alternative Technologies 13

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

Decision on the Technology for NEXCOM 17

Conclusions 19

Recommendation 20

Agency Comments 20

Scope and Methodology 20

Appendix I GAO Contacts and Staff Acknowledgments 23

GAO Contacts 23

Staff Acknowledgments 23

Tables

Table 1: FAA’s Plans Provide for Additional Channel Assignments

for Voice Communications 11

Table 2: Alternative Technologies and Reasons for Their Rejection 14

Table 3: Major Milestones for Certifying VDL-3’s Radio Equipment 19

Figures

Figure 1: Increasing Channel Capacity through Channel Splitting,

1966 through 1999, and the Proposed Future Use of VDL-3 6

Figure 2: Relationship between the Demand for Assigning Channels

for Voice Communications and Increases in Air Traffic,

1977 through 2016 8

Figure 3: FAA’s Channel Assignments for Voice Communications,

Actual, and Projected, 1974 through 2009 10

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

Traffic on FAA’s Ability to Make New Channel

Assignments for Voice Communications, 2000 through

2015 12

Contents
Page ii GAO-02-710 FAA's New Communications System

Figure 5: FAA’s Planned Approach to Implement VDL-3 16

Figure 6: FAA’s Schedule to Implement Voice and Data Digital

Communications 18

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
Page 1 GAO-02-710 FAA's New Communications System

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 airground 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 FAA’s efforts to reduce air traffic delays and

introduce new air traffic services, will create a demand for additional

channels for voice communications that FAA’s 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

United States General Accounting Office

Washington, DC 20548
Page 2 GAO-02-710 FAA's New Communications System

Administration, representatives of national and international aviation

groups, and officials representing FAA’s controller and maintenance

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

FAA’s analysis.

FAA and the aviation industry agree that the existing communications

system, even with enhancements, cannot meet aviation’s 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 aviation’s future voice communications needs beyond

2009, even with these improvements. Because FAA’s 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 FAA’s

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

one’s ability to meet technical requirements, minimize program risk, and

meet the agency’s 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 FAA’s 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 FAA’s

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

Results in Brief
Page 3 GAO-02-710 FAA's New Communications System

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 FAA’s 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 FAA’s 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.

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. FAA’s present air-ground

communications system operates in a worldwide, very high frequency

(VHF) band reserved for safety communications within the 118 to 137

Background
Page 4 GAO-02-710 FAA's New Communications System

megahertz (MHz) range.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,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

conference’s participants. While the Western European countries

proposed further channel splitting to increase capacity, FAA proposed a

totally new air-ground communications system. FAA’s proposed

technology, known as VDL-3, would be based on a new integrated digital

 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.
Page 5 GAO-02-710 FAA's New Communications System

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 person’s 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 FAA’s 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

agency’s 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

FAA’s proposed use of VDL-3 will further increase channel capacity.
Page 6 GAO-02-710 FAA's New Communications System

Figure 1: Increasing Channel Capacity through Channel Splitting, 1966 through 1999, and the Proposed Future Use of VDL-3

Note: The distance between the vertical lines and horizontal lines—in the case of VDL-3—represents

the space between assigned channels.

Source: GAO’s presentation of information provided by FAA.
Page 7 GAO-02-710 FAA's New Communications System

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 aviation’s 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 aviation’s 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 FAA’s efforts has been to meet aviation’s 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

FAA’s current system cannot do this, it has been leasing data link services

from ARINC.3

 However, even with the planned improvements, this service

will not be able to meet FAA’s projected need for more data

communications. As FAA relies more on data communications, this leased

system will not be able to meet the agency’s need to prioritize those

messages that must be delivered expeditiously. Recognizing that

accurately projecting the growth in aviation’s 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.

 3

ARINC coordinates radio frequencies for the airlines and is a leader in providing airground communications worldwide.

FAA’s Planned

Improvements Would

Likely Expand the

Life of Its Existing

Communications

System but Would Not

Meet Aviation Needs

Beyond 2009
Page 8 GAO-02-710 FAA's New Communications System

During the 1990s, several of FAA’s 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

Source: GAO’s presentation of FAA’s data.

FAA Does Not Have

Enough Channels to Meet

Aviation’s Projected Need

for Voice Communications
Page 9 GAO-02-710 FAA's New Communications System

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

assignments for voice communications,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, FAA’s 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 aviation’s 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.

 4

FAA’s 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.
Page 10 GAO-02-710 FAA's New Communications System

Figure 3: FAA’s Channel Assignments for Voice Communications, Actual, and Projected, 1974 through 2009

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

Source: GAO’s presentation of FAA’s data.

Because FAA has delayed NEXCOM’s implementation until 2009, the

agency’s 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
Page 11 GAO-02-710 FAA's New Communications System

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 FAA’s 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: FAA’s Plans Provide for Additional Channel Assignments for Voice

Communications

Year

Improvement

measures

Additional channel

assignments

2003 15 1,041

2005 7 1,574

2009 1 a

Total 23 2,615

a

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

Source: GAO’s analysis of FAA’s data.

While it is not possible to predict exactly when FAA’s 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 2000,5

 even if the need for more channel assignments for voice

communications were to grow at 2 percent per year (instead of FAA’s

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.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 MITRE’s analysis of

 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.
Page 12 GAO-02-710 FAA's New Communications System

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 FAA’s Ability to Make New Channel Assignments

for Voice Communications, 2000 through 2015

Note: Each circle represents where the demand for voice communications capacity will inhibit FAA’s

ability to meet new air traffic needs.

Source: GAO’s presentation of MITRE’s analysis.
Page 13 GAO-02-710 FAA's New Communications System

Currently, FAA is leasing ARINC’s 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.7

 Because this analog system is also reaching its capacity to handle

data link communications, FAA plans to use ARINC’s new digital data

communications system, known as Very High Frequency Digital Link Mode

2 (VDL-2) until 2009.8

 By then, FAA expects to use its VDL-3 system, which

is being developed to integrate voice and data communications, to meet

aviation’s 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 aviation’s 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 aviation’s

future needs.

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 Europe’s 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, FAA’s most pressing need.

Moreover, a vendor of VDL-4 recently told us that this technology still

needed additional development to meet FAA’s 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

 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.

FAA Does Not Have

Enough Channels to Meet

Aviation’s Projected Need

for Data Communications

To Help Ensure

NEXCOM Will Meet

Future

Communications

Needs, FAA Has

Collaborated with the

Aviation Industry to

Assess Alternative

Technologies
Page 14 GAO-02-710 FAA's New Communications System

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 Description Reason for rejection

25 kHz and VDL-2 FAA’s current analog voice communications

technology and a separate digital data

technology that ARINC is developing for

aviation

Would not provide the needed additional channels

for voice communications because the channels

would need to be reassigned to communicate data

8.33 kHz and VDL-2 A system providing additional channel capacity

by reducing the space between channels by

using FAA’s current analog voice

communications technology and a separate

digital data technology that ARINC is

developing for aviation

—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

Cellular telecommunications A commercially available digital technology that

would need to be enhanced for air traffic control

Significant technical challenges would preclude

meeting FAA’s need to deploy an initial operational

system by 2005

Geostationary satellites A system whose satellites maintain fixed

positions at 22,000 miles above the earth

Significant technical challenges would preclude

meeting FAA’s need to deploy an initial operational

system by 2005

Low-earth orbit or mediumearth orbit satellitesA 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

Significant technical challenges would preclude

meeting FAA’s need to deploy an initial operational

system by 2005

Source: GAO’s presentation of FAA’s data.
Page 15 GAO-02-710 FAA's New Communications System

Academia and other experts have concluded that FAA’s 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 FAA’s 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.

FAA’s planned approach for NEXCOM is to implement VDL-3 in three

segments, as shown in figure 5. Currently, FAA’s senior management has

only approved investments for the first segment.
Page 16 GAO-02-710 FAA's New Communications System

Figure 5: FAA’s Planned Approach to Implement VDL-3

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: GAO’s presentation of FAA’s plans.

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. FAA’s

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 aviation’s 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.
Page 17 GAO-02-710 FAA's New Communications System

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 2000.9

 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-3’s 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 FAA’s air traffic control system.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

FAA’s 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

 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.

10In 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.

FAA Needs to Resolve

Three Key Issues

Before It Can Make a

Final Decision on the

Technology for

NEXCOM
Page 18 GAO-02-710 FAA's New Communications System

airlines install new aircraft equipment. Figure 6 shows FAA’s schedule to

implement both voice and data digital communications.

Figure 6: FAA’s Schedule to Implement Voice and Data Digital Communications

Note: FAA has yet to determine what services it will receive on VDL-2 after it implements VDL-3.

Source: FAA.

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,

FAA’s 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 FAA’s credit, the agency is proactively seeking certification

before making a final decision on VDL-3.
Page 19 GAO-02-710 FAA's New Communications System

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

Date Milestone

September 2002 Sign a final memorandum of understanding.

August 2003 Publish guidelines for manufacturing FAA-approved digital

radios.

August 2004 Certify that the radios selected for NEXCOM meet aviation’s

needs before the final October 2004 demonstration.

Source: GAO’s presentation of information provided by FAA.

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 costeffectiveness of NEXCOM in mid-2002, publish a notice of proposed

rulemaking by January 2004, complete its cost-benefit analysis by mid2004, 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-3’s costeffectiveness 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.

FAA’s 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 program’s continued success hinges

on FAA’s maintaining close collaboration with major stakeholders. FAA’s

follow-through on the development of a comprehensive cost-benefit

analysis, which considers how changing requirements and emerging

Conclusions
Page 20 GAO-02-710 FAA's New Communications System

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.

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-3’s useful life as part of its cost-effectiveness analysis

of NEXCOM.

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.

To determine the extent to which FAA’s existing communications system

can effectively meet its future needs, we interviewed officials from FAA’s

NEXCOM program office, the agency’s 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 industry’s needs. We reviewed

documentation on the current status of FAA’s 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 aviation’s future needs, we interviewed officials

from FAA’s NEXCOM program office; officials from the Department of

Defense, the National Aeronautics and Space Administration, and

Recommendation

Agency Comments

Scope and

Methodology
Page 21 GAO-02-710 FAA's New Communications System

Eurocontrol;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 FAA’s time frames for implementing NEXCOM.

We also reviewed documentation indicating how well varying technologies

could meet FAA’s 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 FAA’s 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 NEXCOM’s technology, we interviewed officials from FAA’s

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

reviewed NEXCOM program office documentation that prioritizes the

program’s risks, assesses their potential impact on the program’s cost and

schedule, and describes the status of FAA’s efforts to mitigate those risks.

In addition, we reviewed the NARC’s 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.

 11Eurocontrol is Europe’s organization for managing air traffic.
Page 22 GAO-02-710 FAA's New Communications System

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
Appendix I: GAO Contacts and Staff

Acknowledgments

Page 23 GAO-02-710 FAA's New Communications System

Gerald L. Dillingham (202) 512-3650

Belva M. Martin (202) 512-4285

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.

Appendix I: GAO Contacts and Staff

Acknowledgments

GAO Contacts

Staff

Acknowledgments

(540012)
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