a

GAO

United States General Accounting Office

Report to the Ranking Democratic 

Member, Subcommittee on Aviation, 

Committee on Transportation and 

Infrastructure, House of Representatives

January 2004 AVIATION SAFETY

More Research 

Needed on the Effects 

of Air Quality on 

Airliner Cabin 

Occupants

GAO-04-54
www.gao.gov/cgi-bin/getrpt?GAO-04-54.

To view the full product, including the scope 

and methodology, click on the link above. 

For more information, contact Gerald L. 

Dillingham at (202) 512-2834 or 

dillinghamg@gao.gov. 

Highlights of GAO-04-54, a report to the 

Ranking Democratic Member, 

Subcommittee on Aviation, Committee on 

Transportation and Infrastructure, House 

of Representatives 

January 2004

AVIATION SAFETY

More Research Needed on the Effects of 

Air Quality on Airliner Cabin Occupants 

Despite a number of studies of the air contaminants that airline passengers 

and flight attendants are potentially exposed to, little is known about their 

associated health effects. Reports on airliner cabin air quality published by 

the National Research Council in 1986 and 2001 concluded that more 

research was needed to determine the nature and extent of health effects on 

passengers and cabin crew. Although significant improvements have been 

made to aircraft ventilation systems, cabin occupants are still exposed to 

allergens and infectious agents, airflow rates that are lower than those in 

buildings, and air pressures and humidity levels that are lower than those 

normally present at or near sea level. 

The 2001 National Research Council report on airliner cabin air quality made 

10 recommendations, 9 of which directed the Federal Aviation 

Administration (FAA) to collect more data on the potential health effects of 

cabin air and to review the adequacy of its standards for cabin air quality. 

FAA has addressed these 9 recommendations to varying degrees as it 

attempts to balance the need for more research on cabin air with other 

research priorities (e.g., passenger safety). However, some in the aviation 

community, including some of the committee members who produced the 

report on cabin air, do not feel that FAA’s planned actions will address these 

recommendations adequately. For example, most members were concerned 

that FAA’s plan for implementing the report’s key recommendations on the 

need for more comprehensive research on the health effects of cabin air was 

too limited. FAA plans to address these recommendations in two parts—the 

first, which started in December 2003, and the second, which will start in 

December 2004 and end in late 2006 or early 2007. However, FAA lacks a 

comprehensive plan, including key milestones and funding needs. In 

addition, most committee members thought that FAA’s response to a 

recommendation for it to improve public access to information on the health 

risks of flying was inadequate. We also had difficulty accessing this 

information on FAA’s Web site. 

Several technologies are available today that could improve cabin air quality, 

(e.g., increasing cabin humidity and pressure or absorbing more cabin odors 

and gasses); however, opinions vary on whether FAA should require aircraft 

manufacturers and airlines to use these technologies. GAO found that one 

available technology, high-efficiency particulate air (HEPA) filtering, was 

strongly endorsed by cabin air quality and health experts as the best way to 

protect cabin occupants' health from viruses and bacteria in recirculated 

cabin air. While FAA does not require the use of these filters, GAO’s survey 

of major U.S. air carriers found that 85 percent of large commercial airliners 

in their fleets that recirculate cabin air and carry more than 100 passengers 

already use these filters. However, the use of HEPA filters in smaller 

commercial aircraft that carry fewer than 100 passengers is much lower. 

The cost to retrofit the smaller aircraft to accept the HEPA filter, if it were 

made mandatory, could be expensive. 

Over the years, the traveling public, 

flight attendants, and the medical 

community have raised questions 

about how airliner cabin air quality 

contributes to health effects, such 

as upper respiratory infections. 

Interest in cabin air quality grew in 

2003 when a small number of 

severe acute respiratory syndrome 

(SARS) infections may have 

occurred on board aircraft serving 

areas that were experiencing 

outbreaks of the disease. In 2001, a 

National Research Council report 

on airliner cabin air quality and 

associated health effects 

recommended that additional 

research be done on the potential 

health effects of cabin air. 

GAO reviewed what is known 

about the health effects of cabin 

air, the status of actions 

recommended in the 2001 National 

Research Council report, and 

whether available technologies 

should be required to improve 

cabin air quality. 

GAO recommends that FAA 

develop detailed plans for its 

research and surveillance program 

on cabin air quality, improve the 

public’s access to information on 

the health risks of flying, and 

assess the costs and benefits of 

requiring HEPA filters in 

commercial aircraft. 
Page i GAO-04-54 Airliner Cabin Air Quality

Contents

Letter 1

Results in Brief 3

Background 6

Despite a Number of Studies, Data Are Lacking About the Effects of 

Air Quality On Cabin Occupants 11

FAA has Taken Action to Address Council Recommendations On 

Cabin Air Quality, but These Efforts Could Be Improved 17

Some Technologies Exist for Improving Cabin Air Quality, but There 

Are Questions About Whether They Should be Required 32

Conclusions 39

Recommendations for Executive Action 40

Agency Comments 41

Appendixes

Appendix I: Objectives, Scope, and Methodology 43

Appendix II: Biographical Information on the National Research Council 

Committee 46

Appendix III: Transmission of Severe Acute Respiratory Syndrome (SARS) 

on Board Aircraft Is Rare and Associated with Proximity 49

Appendix IV: European CabinAir Study: Scope and Methodology 53

Appendix V: Surveillance and Research Programs 55

Surveillance Program 55

Research Program 56

Appendix VI: GAO Contacts and Staff Acknowledgments 58

GAO Contacts 58

Staff Acknowledgments 58

Selected Bibliography 59

Tables Table 1: Potential Air Quality Related Concerns on Aircraft Cited by 

the National Research Council in 2001 16

Table 2: Status of the National Research Council’s 2001 Report 

Recommendations on Airliner Cabin Air Quality 18

Table 3: Number of Large and Regional Aircraft of Top 28 Airlines 

That Do or Do Not Recycle Cabin Air 44
Contents

Page ii GAO-04-54 Airliner Cabin Air Quality

Figures Figure 1: Passenger Cabin of Commercial Airliner 8

Figure 2: Overview of How Air Is Supplied on a Commercial 

Airliner 10

Figure 3: A Typical HEPA Filter for Commercial Passenger 

Aircraft 33
Contents

Page iii GAO-04-54 Airliner Cabin Air Quality

Abbreviations

AFA Association of Flight Attendants

APFA Association of Professional Flight Attendants

APL Applied Physics Laboratory (Johns Hopkins University)

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning 

Engineers

AsMA Aerospace Medical Association

ATA Air Transport Association

ATR Avions de Transport Regional

BAe British Aerospace

BRE Building Research Establishment

CAA Civil Aviation Authority (United Kingdom)

CDC Centers for Disease Control and Prevention

CO carbon monoxide

CO2 carbon dioxide

DOT Department of Transportation

ECS Environmental Control System

EPA Environmental Protection Agency

FAA Federal Aviation Administration

FARS Federal Aviation Regulations

GAO General Accounting Office

HEPA high-efficiency particulate air

IAPA International Airline Passengers Association

IATA International Air Transport Association

JAA European Joint Aviation Authorities

NEJM New England Journal of Medicine

NIOSH National Institute for Occupational Safety and Health

NRC National Research Council

O3 ozone

RPM revenue passenger mile

SARS severe acute respiratory syndrome

TB tuberculosis

URI upper respiratory tract infection

WHO World Health Organization 
Contents

Page iv GAO-04-54 Airliner Cabin Air Quality

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Page 1 GAO-04-54 Airliner Cabin Air Quality

United States General Accounting Office

Washington, D.C. 20548

A

January 16, 2004 Letr

The Honorable Peter DeFazio

Ranking Democratic Member

Subcommittee on Aviation

Committee on Transportation and Infrastructure

House of Representatives

Dear Mr. DeFazio:

The quality of air in commercial airliner cabins has long been a concern of 

the traveling public, the medical community, and particularly flight 

attendants, who fly often. Air quality, in the context of airliner cabins, 

refers to the extent to which airflow, low humidity, and air pressure1

 and 

contaminants such as pollutants and infectious disease pathogens affect 

the healthfulness of the air. Air travelers, flight attendants, and the medical 

community have raised questions about the extent to which cabin air 

contributes to discomfort, such as dry eyes and nose, and to more serious 

health effects, such as upper respiratory infections. Interest in cabin air 

quality heightened in 2003, with reports that a small number of severe acute 

respiratory syndrome (SARS) infections may have occurred on board 

aircraft serving areas with SARS outbreaks.2

 In 2001, the National 

Research Council3 issued a report that assessed airborne contaminants in 

commercial aircraft, including an evaluation of their toxicity and 

associated health effects; addressed cabin pressure (oxygen supply) and 

ventilation; and recommended approaches to improving data on cabin air 

quality.4

1

Although airliners are pressurized, the air pressure in an aircraft cabin is lower than it is at 

sea level. Airliners are required to be pressurized to an altitude that is not higher than 8,000 

feet. This is about three-fourths the air pressure at sea level.

2

According to the World Health Organization (WHO), there is a very low risk of catching 

SARS through an airplane’s ventilation system. SARS is believed to be transmitted based on 

proximity to an infected individual. However, WHO reported that as of May 23, 2003, there 

were 29 probable cases of in-flight SARS transmissions on four flights. See appendix III for 

more information on SARS.

3

The National Research Council is the principal operating arm of the National Academy of 

Sciences and the National Academy of Engineering. 

4

National Research Council. The Airliner Cabin Environment and the Health of 

Passengers and Crew, National Academy Press (Washington, D.C.: Distributed 

electronically December 2001; bound report copyrighted 2002).
Page 2 GAO-04-54 Airliner Cabin Air Quality

Given this backdrop, you asked us to provide information on steps that the 

aviation community is taking to address concerns about cabin air quality. 

Specifically, you asked us to address the following questions: (1) What is 

known about the major potential health effects of air quality in commercial 

airliner cabins on passengers and flight attendants? (2) What actions has 

the National Research Council recommended to improve cabin air quality, 

and what is the status of those actions? (3) What technologies are available 

today to improve the air quality in commercial airliner cabins, and which, if 

any, should be required?

To address these questions we reviewed the December 2001 National 

Research Council report on airliner cabin air quality because it was the 

most current and comprehensive work of its kind in this area. The Council 

is the principal operating agency of the National Academy of Sciences, 

which was chartered by Congress to advise the federal government on 

scientific and technical matters. To produce the report, the Council 

convened a committee of experts in the fields of industrial hygiene, 

exposure assessment, toxicology, occupational and aerospace medicine, 

epidemiology, microbiology, aerospace and environmental engineering, air 

monitoring, ventilation and airflow modeling, and environmental 

chemistry. (App. II lists the members of the committee.) The committee 

examined the existing literature on this issue and made recommendations 

for potential approaches for improving cabin air quality. We also 

independently reviewed other studies on issues related to cabin air quality, 

paying particular attention to those issued after the publication of the 

National Research Council report.5

 We also gathered information from 

airlines and the governments of Australia, Canada, and the United Kingdom 

because of the research these countries have done on airliner cabin air 

quality. We also interviewed officials representing the World Health 

Organization (WHO), the Centers for Disease Control and Prevention 

(CDC), the Federal Aviation Administration (FAA), the National Institute 

for Occupational Safety and Health (NIOSH), the Aerospace Medical 

Association (AsMA), the Air Transport Association (ATA), the Association 

of Flight Attendants (AFA), the International Airline Passengers 

Association (IAPA), and aircraft and air filter manufacturers. We also 

interviewed several recognized experts on cabin air quality issues. In 

5

See the Selected Bibliography at the end of this report and, in particular, Hocking, Martin 

B., “Trends in Cabin Air Quality on Commercial Aircraft: Industry and Passenger 

Perspectives,” Reviews on Environmental Health 17, 1 (2002): 1-49; and Rayman, Russell 

B., “Cabin Air Quality,” Aviation, Space and Environmental Medicine 73 (2002): 211-215. 
Page 3 GAO-04-54 Airliner Cabin Air Quality

addition, we interviewed 11 of the 13 members6 of the National Research 

Council Committee on Air Quality in Passenger Cabins of Commercial 

Aircraft that produced the 2001 report to obtain their views on the status of 

the report’s recommendations and other cabin air quality issues, including 

leveraging expertise outside of FAA, such as the Environmental Protection 

Agency for its large body of research on indoor air quality and NIOSH for 

its role in conducting public health and air quality research. Finally, we 

contacted the 14 largest U.S. airlines that use Airbus, Boeing, or McDonnell

Douglas aircraft to determine the extent to which their aircraft fleets use 

high-efficiency particulate air (HEPA) filters7

 on recirculated cabin air. 

Twelve of these 14 airlines responded, allowing us to determine HEPA filter 

usage rates for approximately 90 percent of the aircraft in our study 

population. We also obtained information from an aviation publication and 

the manufacturers of regional jets (typically aircraft that seat 100 or fewer 

passengers) on the extent of HEPA filter usage in these aircraft. We 

conducted our work from April 2003 through December 2003 in 

accordance with generally accepted government auditing standards. See 

appendix I for additional information on our objectives, scope, and 

methodology.

Results in Brief Despite a number of studies of the air contaminants that passengers and 

flight attendants are potentially exposed to in airliner cabins and 

complaints by cabin occupants about health effects from poor cabin air 

quality, little is known about the extent of associated health effects. 

Reports published by the National Research Council in 1986 and 2001 on 

what was then known about airliner cabin air quality concluded that more 

research was needed to determine the nature and extent of health effects 

on passengers and cabin crew and that available air quality data are not 

adequate to address critical questions on aircraft cabin air quality and its 

possible effects on cabin occupant health. While aircraft manufacturers 

6

The NRC committee consisted of 13 members. We attempted to contact all 13 members. We 

interviewed 11, and 8 members responded to cabin air quality questions and the 

implementation status of their recommendations. Of the 11 committee members 

interviewed, 3 declined to address our questions, stating that they did not follow the 

progress of FAA’s implementation of the recommendations. For example, 1 member stated 

that as a toxicologist, he could not comment on the overall approach FAA is taking to 

address the NRC recommendations.

7

For purposes of this report, we use the Environmental Protection Agency’s definition of 

HEPA, which is a filtering efficiency of 99.97 percent. 
Page 4 GAO-04-54 Airliner Cabin Air Quality

have made significant improvements to aircraft ventilation systems, 

passengers and cabin crews are still exposed to a number of air 

contaminants, such as allergens and infectious agents. Passengers and 

crew are also subjected to airflow rates that are lower than those 

recommended for buildings and to air pressures and humidity levels that 

are lower than those normally present at or near sea level. This exposure 

can pose a health risk to passengers with certain medical conditions, such 

as lung, heart, and circulatory disorders. In addition, poor cabin air quality 

has been associated with such discomforts as eye and nasal passage 

irritation. 

The 2001 National Research Council report on airliner cabin air quality 

made 10 recommendations directed largely to the Federal Aviation 

Administration (FAA) to collect more information on the potential health 

effects of cabin air quality and to review the adequacy of its standards for 

air quality in commercial airliner cabins. To varying degrees, the agency has 

addressed the recommendations for which it is responsible. FAA is 

attempting to balance the need for additional research on the potential 

health effects of cabin air quality with other research priorities, such as 

improving passenger safety. However, some in the aviation community, 

including members of the Council committee who prepared the report, do 

not feel that FAA’s planned actions will adequately address all of its 

recommendations on cabin air quality. For example, several of the Council 

committee members were particularly concerned about FAA’s approach to 

implementing the committee’s principal recommendations that more 

comprehensive research on the health effects of cabin air quality is needed. 

In response to the committee’s recommendations in this area, FAA is 

leading the development of a surveillance and research program intended 

to relate perceptions of discomfort or health-related symptoms of flight 

attendants and passengers to possible causal factors, such as air 

contaminants, reduced air pressures and airflows, jet lag, low humidity, or 

inactivity. However, FAA has not yet developed a detailed plan with key 

milestones and funding estimates for conducting the planned surveillance 

and research program. In addition, of the 8 committee members who 

discussed the recommendations with us,8

 all said that FAA’s program was 

much more limited than the Committee had envisioned. For example, 2 of 

the 8 said that FAA’s program does not include an adequate number and 

cross-section of aircraft types and flights for accomplishing its objective. 

8

Of the 11 members interviewed, 8 agreed to address our questions concerning the 

committee recommendations (see app. I). 
Page 5 GAO-04-54 Airliner Cabin Air Quality

One committee member was also concerned that the program is too heavily 

tied to the aircraft industry to ensure objectivity and independence. In 

addition, another committee member believes that although FAA has a 

committee to oversee the selection of the contractor for the program, it has 

not assembled an advisory committee to review the research design and 

monitor the implementation of the program. In addition, 3 committee 

members are concerned that the research effort may not be adequately 

funded. Furthermore, 6 of the committee members felt that FAA’s 

approach for addressing its recommendation that increased efforts be 

made to provide cabin crew, passengers, and health professionals with 

information on health issues related to flying by creating links on the FAA 

Web site to relevant information from health organizations was inadequate 

because the links are difficult to navigate and need to be supplemented 

with other information dissemination methods, such as providing 

physicians with brochures to share with patients who are planning air 

travel. 

Several technologies are available today that could improve cabin air 

quality (e.g., by filtering or removing contaminants, increasing cabin 

humidity and raising cabin pressure, or absorbing more cabin odors and 

gasses), but opinions vary on whether FAA should require aircraft 

manufacturers and airlines to use these technologies. Aircraft 

manufacturers contend that unless future research proves otherwise, the 

ventilation systems in the aircraft that they have produced provide ample 

amounts of relatively clean air. Most aircraft currently in production have 

ventilation systems that recirculate cabin air. In addition, all of the new 

large commercial airliners in production that carry more than 100 

passengers and have ventilation systems that recirculate cabin air come 

equipped with high-efficiency particulate air (HEPA) filters, which are 

highly effective (99.97 percent) at capturing airborne contaminants, such as 

viruses, when properly fitted and maintained. According to our survey of 

major U.S. air carriers, 85 percent of commercial airliners in the current 

U.S. fleet that recirculate cabin air and carry more than 100 passengers use 

HEPA filters. However, we found that only a small portion of the smaller 

regional jets that recirculate cabin air are using these filters. According to 

the manufacturers, most of these aircraft have no provision for installing 

any type of filter for their recycled air and could not be retrofitted with 

HEPA filters without extensive modifications. Nevertheless, given the 

proven effectiveness of HEPA filters, some National Research Council 

committee members and health officials believe that FAA should require 

them on all aircraft with recirculation systems. GAO also found that HEPA 

filters are relatively low cost when their use does not require modifying the 
Page 6 GAO-04-54 Airliner Cabin Air Quality

existing ventilation system. In addition, airflow rates could be increased in 

some aircraft by adjusting settings on the ventilation system to reduce the 

effects of some airborne contaminants by diluting their concentration. 

However, this would be done at the expense of higher fuel consumption, 

increased engine emissions, and lower cabin humidity. Finally, both Boeing 

and Airbus—the world’s two largest airframe manufacturers—are 

considering using air quality improvement technologies (e.g., increasing 

cabin humidity) to improve passenger comfort on the long-range 

commercial aircraft that they are developing. 

To help ensure that FAA’s research and surveillance efforts on airliner cabin 

air quality answer critical outstanding questions about the nature and 

extent of potential health effects of cabin air quality on passengers and 

flight attendants, GAO recommends that the FAA Administrator (1) 

develop a detailed plan for the research and surveillance efforts, including 

key milestones and funding estimates; (2) appoint a committee of 

acknowledged experts in the fields of aircraft ventilation and public health, 

including representatives of EPA and NIOSH, to assist in planning and 

overseeing the research and surveillance efforts; (3) leverage the findings 

of international counterparts’ research on airliner cabin air quality to 

inform FAA’s surveillance and research efforts; and (4) report to Congress 

annually on the progress and findings of the research and surveillance 

efforts and funding needs.

In addition, to help improve the healthfulness of cabin air for passengers 

and cabin crews, GAO also recommends that the FAA Administrator assess 

the costs and benefits of requiring the use of HEPA filters on commercial 

aircraft with ventilation systems that recirculate cabin air. GAO also 

recommends that FAA should go farther in addressing the Council 

recommendation to increase efforts to provide the public with information 

on the health risks of flying by taking additional steps to improve its 

methods for disseminating this information, such as improving the ease 

with which the public can access this information on FAA’s Web site and 

systematically disseminating such information to physicians and their 

patients through various medical associations. 

Background Since people began traveling in pressurized, climate-controlled aircraft 

more than 40 years ago, questions have arisen about the quality of air inside 

aircraft cabins and its effect on the health of passengers and cabin crews. 

In addition, the number of people traveling by commercial aircraft has 

increased dramatically over the years, with more than 600 million 
Page 7 GAO-04-54 Airliner Cabin Air Quality

passengers flown by U.S. carriers in 2002 alone. Despite a downturn in air 

travel following the events of September 11, 2001, FAA expects demand to 

recover and then continue a long-term trend of 3.6 percent annual growth. 

As air travel has become more accessible, the flying public mirrors the 

general population more closely than in years past. Therefore, it includes 

more young and elderly passengers who can be more susceptible to 

potential health risks associated with air travel. This diverse group of 

passengers, as well as the cabin crew, experiences an environment in the 

aircraft cabin that in some ways is similar to that of homes and buildings 

but in other ways is distinctly different. The National Research Council (the 

Council)—the principal operating agency of the National Academy of 

Sciences—has issued two reports at the request of Congress on the air 

quality in aircraft cabins, one in 1986 and another in 2001.9

 The 2001 

Council report notes that the aircraft cabin is a unique environment in 

which the occupants are densely confined in a pressurized space. The 

report goes on to note that airline passengers encounter environmental 

factors that include low humidity, reduced air pressure, and potential 

exposure to air contaminants, including ozone, carbon monoxide, 

pesticides, various organic chemicals, and biological agents that can have 

serious health effects. The report concluded that there are still many 

unanswered questions about how these factors affect cabin occupants’ 

health and comfort and about the frequency and severity of incidents in 

which heated oils or hydraulic fluids release contaminants into the cabin 

ventilation system. Figure 1 shows the passenger cabin of a commercial 

aircraft. 

9

National Research Council, The Airliner Cabin Environment: Air Quality and Safety, 

National Academy Press (Washington, D.C.: 1986) and National Research Council, The 

Airliner Cabin Environment and the Health of Passengers and Crew, National Academy 

Press (Washington, D.C.: Distributed electronically December 2001; bound report 

copyrighted 2002).
Page 8 GAO-04-54 Airliner Cabin Air Quality

Figure 1: Passenger Cabin of Commercial Airliner

As depicted in figure 2, supplying air to modern jet airliner cabins is a 

complex process that varies somewhat among airplane models but has 

essential characteristics that are shared by most airliners. Basically, some 

of the outside air that enters the aircraft engines is diverted and processed 

for use in the cabin in order to achieve an air pressure and temperature 

closer to that experienced on the earth’s surface. FAA requires that air 

supplied to aircraft be designed to maintain a cabin pressure equivalent to 

that at an elevation of no more than 8,000 feet, which is similar to the 

elevation of Mexico City (7,500 ft.). Nevertheless, the air pressures inside 

aircraft cabins are much higher than the extremely low outside air 

pressures at normal cruising altitudes of 25,000 to 40,000 feet. After 

flowing through the engines, the air enters an intricate system of cooling 

devices and ducts and is distributed throughout the cabin and cockpit.

Source: Markus Wechselberger.
Page 9 GAO-04-54 Airliner Cabin Air Quality

Airlines that fly in areas where ozone levels are high10 are required to take 

steps to ensure that ozone levels do not exceed prescribed standards (e.g., 

by having a device that converts the ozone pollutant into oxygen before it 

enters the cabin and cockpit). The Council reported that unacceptable 

high ozone levels can occur in passenger cabins of commercial aircraft in 

the absence of effective controls. On most modern aircraft, an average of 

about 56 percent of the outside air supplied to the cabin is vented out of the 

aircraft through valves that help regulate cabin pressure. The remaining air 

is then recirculated through the cabin; this recirculation allows the engines 

to use less fuel for air supply and pressurization. In addition to less fuel 

and pressurization, recirculation also provides the benefit of higher 

airplane cabin humidity, improved airflow patterns, and minimized 

temperature gradients. On most large aircraft, the recirculated air typically

passes through filters that are designed to remove harmful particulates, 

such as viruses and bacteria.11 FAA requires that aircraft ventilation 

systems for aircraft designs certified after June 1996 be designed to supply 

at least 10 cubic feet per minute of outside air per person under standard 

operating conditions. This compares with the standard minimum rate of 15 

cubic feet per minute per person for buildings recommended by the 

American Society of Heating, Refrigerating and Air-Conditioning Engineers 

(ASHRAE).12 However, according to FAA officials, there is currently no 

standard for cabin ventilation rate, and it has yet to be determined if it is 

appropriate to compare building and aircraft ventilation rates because 

outside air at altitude is very clean, while air sources for buildings are often 

contaminated by pollution. Furthermore, in rare instances, oil leaks or 

other engine malfunctions can cause contaminants such as carbon 

monoxide to be released into the cabin ventilation system. The 2001 

Council report noted that questions about the frequency and significance of 

such incidents remain unanswered. In February 2002, FAA published a 

report that discussed many of the issues in the Council report, including an 

10The 2001 Council study reported that the effects of ozone vary with latitude, altitude, and 

season and that the concentration of ozone is much higher at cruise altitudes in high 

latitudes (greater than approximately 60°N) than at low latitudes (approximately 30°N), 

resulting in higher concentrations of ozone on polar flights.

11FAA does not require these filters; however, our survey of U.S. airlines found that 85 

percent of the large aircraft (those that carry 100 passengers or more) currently use HEPA 

filters. 

12The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 

advances the arts and sciences of heating, ventilation, air conditioning, refrigeration, and 

related human factors to serve the evolving needs of the public.
Page 10 GAO-04-54 Airliner Cabin Air Quality

estimate of 416 air contaminant events (or 2.2 events every 1,000,000 

aircraft hours) that may have taken place in commercial transports within 

the United States between January 1978 and December 1999.

Figure 2: Overview of How Air Is Supplied on a Commercial Airliner

(1) Outside air continuously enters the engine, where it is compressed.

(2) It then passes through a catalytic ozone converter (in some aircraft) to air-conditioning packs.
Page 11 GAO-04-54 Airliner Cabin Air Quality

(3) The air passes through cooling packs to a mixing manifold.

(4) Outside air entering the mixing manifold is mixed with recirculated air that has been cleaned with 

high-efficiency filters.

(5) The makeup of air in the mixing manifold is approximately 50 percent outside and 50 percent 

filtered, recirculated air.

(6) Air from the mixing manifold is then supplied to the cabin on a continuous basis from overhead 

outlets.

(7) As outside air enters the airplane, air is continuously exhausted from the airplane.

(8) Mixed outside and filtered recirculated air is provided to the flight deck from the mixing manifold.

FAA is responsible for setting design standards for aircraft ventilation 

systems. To fulfill its responsibilities, FAA requires that manufacturers 

design and build their large commercial airplanes to meet specific 

engineering standards, which limit the amounts of certain air quality 

contaminants (e.g., carbon monoxide, carbon dioxide, and ozone) that can 

be present in an airliner cabin. Manufacturers comply with these 

engineering standards in order to have FAA certify their airplanes as 

airworthy.13 However, while FAA monitors overall aircraft system 

operations, it does not require airlines to monitor cabin air quality during 

their operations to determine if air quality during routine flight operations 

is meeting the agency’s engineering standards. According to FAA, the 

certification requirements combined with the monitoring of overall aircraft 

system operations are sufficient. However, the 2001 Council report stated 

that because of a lack of data it was not able to answer questions about the 

extent to which aircraft ventilation systems are operated properly.

Despite a Number of 

Studies, Data Are 

Lacking About the 

Effects of Air Quality 

On Cabin Occupants

Passengers and flight attendants have had long-standing concerns about 

negative health effects from the quality of air in airliner cabins; however, 

research to date, including two reports by the Council, has not been able to 

definitively link the broad, nonspecific health complaints of passengers and 

flight attendants to possible causes, including cabin air quality. In its most 

recent report, the Council concluded that critical questions about the 

potential effect of cabin air quality on the health of cabin occupants remain 

13According to FAA officials, FAA regulations have always required limitations on certain 

contaminants (e.g., carbon monoxide and carbon dioxide). Later amendments added ozone 

and changed the ventilation requirements. However, these officials stressed that airplanes 

are certified to the regulations in effect at a certain time prior to their manufacture. Only 

the latest certified airplanes will have had to meet the latest amendment level for the 

regulations governing the cabin environment, such as a 1996 amendment which added the 

requirement that each occupant be provided with 0.55 pounds (equivalent to 10 cubic feet) 

of fresh air per minute under standard operating conditions. 
Page 12 GAO-04-54 Airliner Cabin Air Quality

unanswered because existing data are inadequate, and it recommended 

further research to narrow this knowledge gap. 

Passengers and flight attendants (cabin occupants) have long complained 

of acute and chronic health effects during and after flying. Many 

complaints made by cabin occupants are relatively minor, such as dry eyes 

and nose, or the onset of colds soon after flying, but others are much more 

serious. According to the Association of Flight Attendants, its members 

have reported such health problems as respiratory diseases, nausea, 

dizziness, muscle tremors, nervous system damage, and memory loss.14 

The association notes that these illnesses are consistent with exposure to 

carbon monoxide, pesticides, reduced oxygen levels, neurotoxins, and 

ozone gas, all of which can be present in the cabin itself or in cabin air 

supplies, depending on the flight. In addition, passengers with certain 

medical conditions can be at higher risk from the quality of cabin air than 

the general population due to air contaminants, lowered oxygen levels in 

the body (hypoxia), and changes in cabin pressure. Such medical 

conditions include limited lung capacity (e.g., asthma) and cardiovascular 

and circulatory disorders. Those who fly soon after surgery are particularly 

vulnerable to changes in cabin pressure. However, according to the 

Council report, many of the complaints made by cabin occupants are so 

broad and nonspecific that they could have many causes, and it is difficult 

to determine a specific illness or syndrome. 

Although numerous studies have been conducted on cabin air quality 

issues, there are insufficient data to determine the nature and extent of 

cabin air quality’s effect on cabin occupants. Council reports published in 

1986 and 2001 reviewed the literature on cabin air quality issues and 

concluded that the studies had not collected data in a systematic manner 

that would conclusively address many of the questions about potential 

exposures in aircraft cabins and their health effects. Both reports 

recommended actions for improving what is known about cabin air quality, 

including the need to collect better data on the potential effect of cabin air 

quality on passenger and cabin crew health. The 2001 report concluded 

that available data on air quality and its possible negative effects on cabin 

14ATA officials noted that these symptoms are also consistent with a host of other causes, 

such as lack of sleep (perhaps due to difficulty in adjusting to different time zones), 

dehydration (possibly from drinking too much caffeine or alcohol and not enough water 

during a long flight), the effect of changes in climate, or exposure to contaminants in other 

settings. 
Page 13 GAO-04-54 Airliner Cabin Air Quality

occupant health have left three critical outstanding questions unaddressed 

and that additional research is needed:

• Do current aircraft as operated comply with FAA design and operational 

limits for ventilation rate and for chemical contaminants, including 

ozone, carbon monoxide, and carbon dioxide, and are the existing air 

quality regulations adequate to protect health and ensure the comfort of 

passengers and cabin crew?

• What is the association, if any, between exposure to cabin air 

contaminants and reports or observations of adverse health effects in 

cabin crew and passengers?

• What are the frequency and severity of incidents when air contaminants 

enter the cabin due to nonroutine conditions such as oil leaks or other 

engine malfunctions?

Following the 1986 report, the Department of Transportation sponsored a 

study to evaluate the health risks posed by exposures to contaminants on 

randomly selected flights. In addition, various researchers conducted a 

number of studies of cabin air quality issues, including eight investigations 

of biological agents, such as viruses and bacteria, on commercial aircraft. 

However, these and other studies were not able to link the broad, 

nonspecific health complaints that passengers and cabin crew continued to 

make to possible causes, including cabin air quality. 

Recognizing the need for more data on the issue, Congress directed FAA, in 

AIR-21,15 to request that the Council perform another independent 

examination of cabin air quality. The Council’s report, issued in 2001, 

concluded that when operated properly, the environmental control 

system16 should provide an ample supply of air to pressurize the cabin, 

meet general comfort conditions, and dilute or reduce normally occurring 

odors, heat, and contaminants. However, the Council also found

15The Wendell H. Ford Aviation Investment and Reform Act for the 21st Century (AIR-21), 

Public Law 106-181, April 5, 2000.

16The environmental control system includes devices that pressurize the cabin in flight, 

control thermal conditions in the cabin, and ventilate the cabin with outside air to prevent a 

buildup of contaminants that might cause discomfort or present a health hazard.
Page 14 GAO-04-54 Airliner Cabin Air Quality

that the design standard for ventilation rates17 in aircraft required by FAA 

was less than one-half to two-thirds the rate recommended by ASHRAE for 

buildings. The Council noted that whether the building ventilation standard 

is appropriate for the aircraft cabin environment has not been 

established.18 Studies have shown that low ventilation rates in buildings 

have contributed to “sick building syndrome,” which causes fatigue, 

headache, and throat irritation. However, FAA officials told us that a sick 

building syndrome comparison is not applicable, in part because HEPA 

filtration results in much cleaner recirculated air than in a building 

environment.

The 2001 Council report also found that although the environmental 

control system in aircraft is designed to provide adequate air pressure and 

minimize the concentration of contaminants in the cabin, passengers and 

cabin crew are potentially exposed to air quality-related health risks. The 

Council was particularly concerned about two cabin air characteristics and 

suggested that they be given high priority for further investigation. The 

first is reduced oxygen partial pressure, which results from the lower air 

pressures present in aircraft cabins at cruise altitudes. Most healthy 

individuals are unaffected by reduced oxygen partial pressure, but those 

with health problems such as cardiopulmonary disease and infants can 

experience serious health effects from a lack of oxygen (e.g., respiratory 

stress). The other concern of the Council was elevated concentrations of 

ozone, which can occur at high cruise altitudes over certain areas of earth, 

such as the Arctic. The Council reported that unacceptably high ozone 

levels could occur in passenger cabins of commercial aircraft in the 

absence of effective controls. FAA allows aircraft operators to maintain 

cabin ozone concentrations at or below prescribed limits through flight 

planning that avoids areas with ozone concentrations exceeding those 

limits or the installation of devices that convert ozone to oxygen. However, 

FAA does not have a process in place to ensure that ozone converters are 

17The ventilation rate is the flow of outside air supplied to the cabin for ventilation and it 

does not normally include recirculated air even though recirculated air may be used for 

cabin ventilation.

18According to FAA officials, a comparison of ventilation rates for buildings and aircraft is 

not valid and that “sick building syndrome” should not be applied to aircraft. Furthermore, 

both FAA and Boeing officials told us that the new ASHRAE standards for buildings create 

two sets of building standards for ventilation—one for high density buildings and another 

for low density buildings. Boeing officials said that under this standard, high density 

buildings would have lower airflow rates per occupant, and that high density buildings are 

most comparable to airplanes with high density occupancy.
Page 15 GAO-04-54 Airliner Cabin Air Quality

installed in all aircraft that fly routes where ozone may pose a risk or that 

converters in service are operating properly. 

The Council also had what it termed moderate concern about several other 

potential air quality-related exposures on aircraft, but it noted that there 

were little data available on the frequency at which they occur. For 

example, according to the Council, infectious agents, such as viruses and 

bacteria, were likely present on aircraft, and high occupant densities could 

increase the risk of transmittal. The Council observed, however, that air 

recirculation did not increase the risk of transmittal, especially in systems 

using HEPA filters. Likewise, the Council noted that airborne allergens, 

such as cat dander, could pose problems for passengers with sensitivities. 

In addition, when aircraft are on the ground, according to the Council, 

passengers can be exposed to contaminants from engine exhaust, such as 

carbon monoxide and other outdoor air pollutants, including ozone and 

particulate matter, when they are pulled into the aircraft through the 

ventilation system. Also of some concern to the Council were incidents 

when lubricating and hydraulic fluids seep into the aircraft ventilation 

system during engine and other system malfunctions. Although such 

occurrences are rare, and the actual exposure to contaminants resulting 

from them is unknown, lubricating and hydraulic fluids contain substances 

that can pose neurological health risks to passengers and cabin crew if they 

are present in sufficient concentrations and for a sufficient length of time. 

Finally, the Council was somewhat concerned about exposures to the 

pesticide spraying that takes place on some international flights,19 which 

can cause skin rashes and other health effects. Table 1 summarizes 

information presented by the Council on the potential air quality-related 

exposures on aircraft.

19Disinsection is the process of spraying the aircraft cabin with insecticide to prevent the 

conduction of insects such as mosquitoes from one country to another. The spraying is 

often done while passengers and crewmembers are still on board. The United States 

terminated this practice in 1979 because of health concerns and doubts about the 

effectiveness of the spraying. Over the years, a number of countries have changed their 

policies regarding the spraying of pesticides. The Department of Transportation is studying 

alternative technological methodologies, including air curtains to prevent airborne insects 

from flying into the aircraft cabin.
Page 16 GAO-04-54 Airliner Cabin Air Quality

Table 1: Potential Air Quality Related Concerns on Aircraft Cited by the National Research Council in 2001

Source: National Research Council. 

Since the issuance of the 2001 Council report, some limited studies have 

examined specific air quality issues, such as infectious disease 

transmission, but they have raised as many questions as they have 

answered. For example, according to a revised 2003 WHO report on 

tuberculosis (TB) and air travel, as of August 2003, no case of active TB has 

Characteristic Potential health impacts Exposure frequency Availability of information

High concern

Cabin pressure Serious health effects may occur in 

infants and those with cardiorespiratory diseases from lack of 

oxygen. Temporary discomfort or 

pain from gas expansion in middle 

ears or sinuses.

Reduced cabin pressure 

occurs on nearly all flights.

Reliable measurements are 

available; health effects in some 

sensitive groups are uncertain.

Ozone Airway irritation and reduced lung 

function. 

Elevated concentrations are 

expected primarily on aircraft 

without ozone converters.

Few systematic measurements made 

since 1986 Council report.

Moderate concern

Airborne allergens Irritated eyes and nose, sinusitis, 

acute increases of asthma, or 

anaphylaxis.

Not known. Only self-reported data are available. 

Carbon monoxide Headaches and lightheadedness 

occur at low concentrations, more 

serious health effects result from 

higher concentrations. 

High concentrations could 

occur during air-quality 

incidents. Frequency of 

incidents is highly uncertain but 

is believed to be low.

Reliable measurements are available 

for normal operating conditions, but 

no data are available for incidents.

Hydraulic fluids Mild to severe health effects can 

result from exposure to these fluids. 

Frequency of incidents in which 

these fluids enter the cabin is 

uncertain but is expected to be 

relatively low.

No quantitative data are available. 

Little information is available on 

health effects related to smoke, 

mists, or odors in aircraft cabins.

Pesticides Skin rashes can result from skin or 

inhalation exposure.

Exposure likely on some 

international flights.

Only self-reported data are available. 

Low concern

Carbon dioxide Indicator of ventilation adequacy. 

Elevated concentrations associated 

with increased perceptions of poor 

air quality.

Concentrations are generally 

below FAA regulatory limits.

Reliable measurements are available 

only for normal operating conditions.

Nuisance odors Annoyance and mucous membrane 

irritation can occur.

Can be present on any flight. Reliable information is available from 

surveys of cabin occupants.

Relative humidity Temporary drying of skin, eyes, and 

mucous membranes can occur at 

relative low humidity (10 to 20%).

Relative low humidity occurs on 

most flights.

Reliable and accurate measurements 

in aircraft are available. 
Page 17 GAO-04-54 Airliner Cabin Air Quality

been identified as resulting from exposure while on a commercial aircraft.20

The report did note, however, that there is some evidence that transmission 

of TB may occur during long flights (i.e., more than 8 hours) from an 

infectious source (passenger or crew) to other passengers or 

crewmembers. In 2002, the American Medical Association21 did not find 

any evidence that aircraft cabin air recirculation increases the risk for 

upper respiratory tract infection (URI) symptoms in passengers traveling 

aboard commercial jets. However, passengers had higher incidents of URI 

infections than the general public within a week after completing their 

trips. One of the study’s authors noted that the research indicated that 

while flying increases the risk of getting colds or other infections, an 

aircraft’s ventilation system may not be a key factor. A 2003 study 

appearing in the New England Journal of Medicine found that SARS 

transmissions may occur on flights carrying people in the symptomatic 

stages of the disease. (See app. II for more details on this study.22)

FAA has Taken Action 

to Address Council 

Recommendations On 

Cabin Air Quality, but 

These Efforts Could Be 

Improved 

The December 2001 Council report on airliner cabin air quality made 10 

recommendations about air quality standards for the cabins of commercial 

airliners and the need for more information concerning the health effects of 

cabin air. Nine of these recommendations were directed to FAA, and it has 

implemented them to varying degrees. The Council report’s 10 

recommendations focused on five aspects of cabin air quality and its 

environment: (1) the establishment of cabin air quality surveillance and 

research programs, (2) FAA’s oversight of the operation of aircraft 

ventilation systems, (3) exposures on aircraft due to the transport of small 

animals in aircraft cabins, (4) distribution of health related information, 

and (5) recommended procedures as a result of a ventilation system 

shutdown. Although one recommendation asked Congress to designate a 

lead federal agency for conducting airliner cabin air quality research, most

of the recommendations were directed at or involved FAA. Table 2 

describes each of the Council report recommendations and FAA’s response. 

20World Health Organization, Tuberculosis and Air Travel: Guidelines for Prevention and 

Control (Geneva, Switzerland: Aug. 27, 2003).

21Zitter, Jessica, Peter Mazonson, Dave Miller, Stephen Hulley, and John Balmes, “Aircraft 

Cabin Air Recirculation and Symptoms of the Common Cold,” Journal of the American 

Medical Association 288 (2002): 483-486.

22Olsen, Sonja J. et al., “Transmission of the Severe Acute Respiratory Syndrome on 

Aircraft,” The New England Journal of Medicine 349; 25 (2003): 2416-2422.
Page 18 GAO-04-54 Airliner Cabin Air Quality

Table 2: Status of the National Research Council’s 2001 Report Recommendations on Airliner Cabin Air Quality

Council Report Recommendations FAA’s Response

Cabin Air Quality Surveillance and Research Programs

Surveillance program

To be consistent with FAA’s mission to promote aviation safety, an air quality and 

health-surveillance program should be established. The objectives and approaches 

of this program are summarized in appendix V of this report. The health and air 

quality components should be coordinated so that the data are collected in a 

manner that allows analysis of the suggested relationship between health effects or 

complaints and cabin air quality. 

FAA is addressing this recommendation 

through a joint research effort combining the 

resources of FAA and the American Society 

of Heating, Refrigerating and AirConditioning Engineers (ASHRAE).

Research program

To answer specific questions about cabin air quality, a research program should be 

established. See appendix V of this report for a summary of research questions, 

objectives, and research program approach. 

FAA is addressing this recommendation 

through a joint research effort combining the 

resources of FAA and ASHRAE.

Research program lead agency

The Council committee recommends that Congress designate a lead federal 

agency and provide sufficient funds to conduct or direct the research program 

recommendation (see above), which is aimed at filling major knowledge gaps 

identified in this report. An independent advisory committee with appropriate 

scientific, medical, and engineering expertise should be formed to oversee the 

research program to ensure that its objectives are met and the results publicly 

disseminated.

Congress has designated FAA as the lead 

agency to direct the cabin air quality 

research program, but, according to FAA 

officials, has not appropriated sufficient 

funds to support it.

FAA Oversight of Aircraft Ventilation Systems

Air quality regulations

FAA should rigorously demonstrate in public reports the adequacy of current and 

proposed Federal Aviation Regulations (FARs) related to cabin air quality and 

should provide quantitative evidence and rationales to support sections of the 

regulations that establish air quality-related design and operational standards for 

aircraft (standards for carbon monoxide, carbon dioxide, ozone, ventilation, and 

cabin pressure). If a specific standard is found to be inadequate to protect the 

health and ensure the comfort of passengers and crew, FAA should revise it. For 

ventilation, the committee recommends that an operational standard consistent with 

the design standard be established.

Necessary data to implement this 

recommendation will be available upon 

completion of the ASHRAE study in late 

2006 or early 2007.

Regulations for ozone

FAA should take effective measures to ensure that the current FAR for ozone

(average concentrations not to exceed 0.1 ppm above 27,000 ft; and peak 

concentrations not to exceed 0.25 ppm above 32,000 ft.) is met on all flights, 

regardless of altitude. These measures should include a requirement that either 

ozone converters be installed, used, and maintained on all aircraft capable of flying 

at or above those altitudes, or strict operating limits be set with regard to altitudes 

and routes for aircraft without converters to ensure that the ozone concentrations 

are not exceeded in reasonable worst-case scenarios. To ensure compliance with 

the ozone requirements, FAA should conduct monitoring to verify that the ozone

controls are operating properly (see also surveillance program recommendation).

Necessary data to implement this 

recommendation will be available upon 

completion of the ASHRAE study.
Page 19 GAO-04-54 Airliner Cabin Air Quality

Sources: National Research Council and GAO analysis of FAA documents.

Note: Federal Aviation Regulations are legal requirements and rules for the aviation industry set by 

the Federal Aviation Administration.

FAA formed the Airliner Cabin Environment Report Response Team to 

review the findings of the NRC report on airliner cabin air quality and 

Air cleaning equipment

FAA should investigate and publicly report on the need for and feasibility of installing 

air cleaning equipment for removing particles and vapors from the air supplied by 

the environmental control system (ECS) on all aircraft to prevent or minimize the 

introduction of contaminants into the passenger cabin during ground operation, 

normal flight, and air quality incidents. 

Necessary data to implement this 

recommendation will be available upon 

completion of the ASHRAE study.

Carbon monoxide monitoring

FAA should require a carbon monoxide monitor in the air supply ducts to passenger 

cabins and establish standard operating procedures for responding to elevated 

carbon monoxide concentrations. 

Necessary data to implement this 

recommendation will be available upon 

completion of the ASHRAE study.

Exposures on Aircraft, Health Information, and Ventilation Shutdown Procedures

Allergens

Because of the potential for serious health effects related to exposures of sensitive 

people to allergens, the need to prohibit transport of small animals in aircraft cabins 

should be investigated, and cabin crews should be trained to recognize and 

respond to severe, potentially life-threatening responses (e.g., anaphylaxis, severe 

asthma attacks) that hypersensitive people might experience because of exposure 

to airborne allergens. 

FAA issued an advisory circular providing 

guidance regarding air carrier passenger 

handling procedures for allergen-sensitive 

people, but did not prohibit the transport of 

animals on aircraft, particularly service 

animals. Agency officials do not think that a 

prohibition on animals in the cabin would be 

effective in minimizing animal allergens 

because they believe that these allergens 

are brought on board aircraft primarily on 

the clothes of passengers. 

Health information

Increased efforts should be made to provide cabin crew, passengers, and health 

professionals with information on health issues related to air travel. To that end, 

FAA and the airlines should work with such organizations as the American Medical 

Association and the Aerospace Medical Association to improve health 

professionals’ awareness of the need to advise patients on the potential risks of 

flying, including risks associated with decreased cabin pressure, flying with active 

infections, increased susceptibility to infection, or hypersensitivity.

The FAA’s Office of Aerospace Medicine 

made health information and 

recommendations available to passengers 

and crews through its Web site and linked 

the site to other health-related 

organizations. The agency also developed 

a brochure on the potential risk of 

developing a condition known as deep vein 

thrombosis (DVT), in which blood clots can 

develop deep in the veins of the legs after 

extended periods of inactivity. This brochure 

has been distributed to aviation medical 

examiners and cited in the Federal Air 

Surgeon’s Bulletin.

Ventilation shutdown

The committee reiterates the recommendation of the 1986 Council report that a 

regulation be established to require removal of passengers from an aircraft within 

30 minutes after a ventilation failure or shutdown on the ground and ensure the 

maintenance of full ventilation whenever on-board or ground-based air conditioning 

is available. 

FAA concurred with the objective of the 

recommendation and advised air carriers, 

through advisory circulars, to deplane 

passengers as long as operational safety is 

not compromised. 

(Continued From Previous Page)

Council Report Recommendations FAA’s Response
Page 20 GAO-04-54 Airliner Cabin Air Quality

published a planned response in February 2002. However, many of the 

actions included in this plan were contingent on the formation of an 

aviation rulemaking advisory committee, on which the agency has deferred 

action. FAA subsequently updated its plans, as reflected above. 

We reviewed FAA’s approach for addressing the recommendations and 

found that the agency has made progress on implementing some of them, 

including those relating to making information available on potential health 

issues related to cabin air quality and the risks posed to sensitive people by 

allergens from small animals transported in aircraft cabins; however action 

on others is pending. For example, recommendations to improve FAA 

oversight of aircraft ventilation systems are pending until completion of the 

ASHRAE study in late 2006 or early 2007. In implementing the Council 

report recommendations, FAA is attempting to balance the need to conduct 

additional research on the healthfulness of cabin air quality with other 

research priorities, such as improving passenger safety. Our prior work on 

airliner cabin safety and health has underscored the importance of setting 

risk-based research priorities, in part by establishing cost and effectiveness 

estimates to allow direct comparisons among competing research 

priorities. In commenting on this prior work, FAA cautioned that if too 

much emphasis is placed on cost/benefit analyses, potentially valuable 

research may not be undertaken.23 We concur in that caution. Similarly, we 

found that many members of the Council committee on airliner cabin air 

quality question FAA’s approach to implementing some of the 

recommendations it made, particularly those related to the committee’s 

principal finding that more comprehensive research on the health effects of 

cabin air quality is needed. Specifically, some in the aviation community 

have raised concerns that FAA’s planned actions for implementing the 

Council recommendations on cabin air quality, including its research and 

surveillance efforts, will not be adequate to answer long-standing questions 

about the nature and extent of potential health effects posed by cabin air. 

Council Recommendations 

Calling for Cabin Air Quality 

Surveillance and Research 

Programs

To address the need for more information on the health effects of cabin air 

quality, the 2001 Council report made three recommendations regarding the 

establishment of cabin air quality surveillance and research programs. 

FAA, in coordination with ASHRAE, has begun to develop a program to 

monitor air quality on some flights and correlate this information with 

23U.S. General Accounting Office, Aviation Safety: Advancements Being Pursued to 

Improve Airliner Cabin Safety and Health, GAO-04-33 (Washington, D.C.: October 3, 2003).
Page 21 GAO-04-54 Airliner Cabin Air Quality

health data collected from passengers and cabin crews. Although this 

effort can provide a foundation for future research, members of the 

committee that produced the report are concerned that its scope is too 

limited to adequately answer long-standing questions concerning the 

association between cabin air quality and health effects.

Council Concluded That 

Surveillance and Research 

Programs Needed to Answer 

Outstanding Questions 

Concerning Cabin Air Quality

According to a committee member, the Council report’s most important 

recommendations are those pertaining to the establishment of cabin air 

quality surveillance and research programs. The report concluded that 

available air quality data are not adequate to address three critical 

questions on aircraft cabin air quality and its possible effects on cabin 

occupant health: 

• Do current aircraft, as operated, comply with FAA design and 

operational limits for ventilation rate and for chemical contaminants, 

including ozone, carbon monoxide, and carbon dioxide, and are the 

existing air quality regulations adequate to protect the health and ensure 

the comfort of passengers and the cabin crew?

• What is the association, if any, between exposure to cabin air 

contaminants and reports or observations of adverse health effects in 

cabin crew and passengers?

• What are the frequency and severity of incidents when air contaminants 

enter the cabin due to nonroutine conditions such as oil leaks or other 

engine malfunctions?

To answer these questions, the Council report recommended a dual 

approach that includes a routine surveillance program and a more focused 

research program. The report said that the surveillance program should 

continuously monitor and record chemical contaminants, cabin pressure, 

temperature, and relative humidity in a representative number of flights 

over a period of 1 to 2 years. Thereafter, the program should continue to 

monitor flights to ensure accurate characterization of air quality as existing 

aircraft equipment ages or is upgraded. In addition to air quality 

monitoring, the report said the surveillance program should also include 

the systematic collection, analysis, and reporting of health data, with the 

cabin crew as the primary study group. The report said a detailed research 

program to investigate specific questions about the possible association 

between air contaminants and reported health effects should supplement 

the surveillance program. Among the subjects suggested for research are 
Page 22 GAO-04-54 Airliner Cabin Air Quality

the factors that affect ozone concentration in cabin air and the adequacy of 

outside air ventilation flow rates.

FAA Has Taken the Lead in 

Developing Surveillance and 

Research Programs

In order to implement the surveillance and research programs, the report 

recommended that Congress designate a lead federal agency and provide 

sufficient funding to conduct or direct the research program to fill the 

major knowledge gaps. It also called for an independent advisory 

committee with appropriate scientific, medical, and engineering expertise 

to oversee the programs to ensure that the research program’s objectives 

are met. In response, as a part of FAA’s reauthorization, Congress 

designated FAA as the lead federal agency.24 Prior to this, FAA acted in this 

capacity and allocated limited funding for this effort, although, according 

to FAA officials, Congress provided no additional funding through fiscal 

year 2003 for air quality surveillance and research; however, pending 

legislation for fiscal year 2004 would provide $2.5 million for this effort. In 

addition, on March 4, 2003, FAA announced the creation of a voluntary 

program for air carriers, called the Aviation Safety and Health Partnership 

Program. Through this program, the agency intends to enter into 

partnership agreements with participating air carriers, which will, at a 

minimum, make data on their employees’ injuries and illnesses available to 

FAA for collection and analysis. According to FAA officials, this program 

has a reporting system and database available to capture air quality 

incidents. 

In taking the lead for implementing the recommendations for surveillance 

and research programs, FAA has undertaken a joint effort with ASHRAE. 

According to FAA, this joint effort will build on a previous study conducted 

for FAA by NIOSH, which identified and characterized potential health 

issues, including respiratory effects, related to the aircraft cabin

24Vision 100—Century of Aviation Reauthorization Act,’’ passed by Congress in November 

2003, requires that FAA, at a minimum: 1) conduct surveillance to monitor ozone in the 

cabin on a representative number of flights and aircraft to determine compliance with 

existing regulations for ozone, 2) collect pesticide exposure data to determine exposures of 

passengers and crew, 3) analyze samples of residue from aircraft ventilation ducts and 

filters after air quality incidents to identify potential exposure of contaminants to 

passengers and crew, 4) analyze cabin air pressure and altitude, and 5) establish an air

quality incident reporting system. The FAA administrator is to report the findings to 

Congress no later than 30 months after the date of the act’s enactment.
Page 23 GAO-04-54 Airliner Cabin Air Quality

environment, but did not link the health issues to cabin conditions.25 The 

joint effort includes a surveillance and research initiative whose principal 

aim is to relate perceptions of discomfort or health-related symptoms that 

flight attendants and passengers have had to possible causal factors, 

including cabin and outside air quality and other factors, such as reduced 

air pressure, jet lag, inactivity, humidity, flight attendant duty schedule and 

fatigue, disruptions to circadian rhythm,26 stress, and noise. While FAA’s 

fiscal year 2004 appropriation in the research and development budget 

includes $2.5 million for cabin air research—including identifying bacterial 

and pesticide contamination and monitoring air quality incidents—it is 

unclear which of the cabin air quality projects outlined in the FAA 

reauthorization bill will be funded.27 Additionally, ASHRAE officials stated 

that the surveillance and research initiative would support ASHRAE’s 

ongoing efforts to develop air quality standards for commercial aircraft. 

According to FAA, the surveillance and research program is to be carried 

out in two parts; the first started in December 2003 and the second will 

start in December 2004 and end in late 2006 or early 2007. In part I, air 

quality data will be collected on four to six flights on a minimum of two 

different types of aircraft, and the data will then be compared with health 

information gathered from surveys of passengers and crew on the flights. 

According to FAA and ASHRAE, the protocol and procedures developed in 

part I of the study will be the basis for conducting on-ground and in-flight 

monitoring in part II of the initiative. In part II, air quality monitoring will 

be conducted on different models of commercial jet airplanes representing 

a large section of the world fleet and will include a minimum number of

25NIOSH conducted the study over 2 years on 33 commercial flights on 10 different types of 

airplanes owned by four air carriers. NIOSH initially surveyed female flight attendants on 

reproductive health, but the survey was later expanded to include respiratory effects. The 

study did not include direct linkage to measurement of cabin environment conditions. The 

survey respondents flew on a wide variety of aircraft in which the cabin environment was 

not sampled.

26Circadian rhythm is the body’s internal resting or wakefulness schedule over the course of 

a day. Outside influences, such as jet lag, can disrupt the circadian rhythm temporarily.

27FAA’s fiscal year 2004 facilities and equipment budget includes $8.5 million to develop and 

demonstrate a chemical/biological detection and mitigation capability and decontamination 

procedures for aircraft occupants and for returning the aircraft to service. 
Page 24 GAO-04-54 Airliner Cabin Air Quality

flights that has not yet been determined.28 However, according to FAA 

officials, the level of funding that will be available for part II is uncertain. 

FAA and ASHRAE have assembled a committee which is responsible for 

selecting a contractor to conduct the monitoring and health surveillance in 

part I and overseeing the contractor’s performance. The committee 

consists of aircraft, health, and air quality experts, including five members 

of the Council committee, as well as representatives from FAA, the 

Association of Professional Flight Attendants, and the Boeing Commercial 

Airplane Group. In September 2003, the committee chose a contractor for 

part I, and work began in December 2003. FAA and ASHRAE have not yet 

selected a contractor for part II, although the estimated completion date 

for the entire program is late 2006 or early 2007. 

ASHRAE officials stated that to date FAA, Boeing, and two major U.S. 

airlines are supporting this effort. FAA has provided $50,000 of the 

estimated $250,000 it will cost to conduct air quality surveillance on two 

aircraft. Boeing is the major source for the balance of the funding for the 

surveillance program. FAA had previously reported that it was seeking a 

$500,000 contract with the Johns Hopkins University Applied Physics 

Laboratory (APL) to develop devices to monitor the aircraft cabin 

environment as part of the research and surveillance program. However, 

the contract was not finalized because APL determined that the project 

would cost significantly more than $500,000 and FAA reprogrammed the 

funds. FAA said that it has not yet funded part II, while ASHRAE officials 

noted that they are planning to solicit the part I contributors again for part 

II once part I is under way.

Despite FAA’s efforts to date, we found that the agency has not developed a 

detailed plan for the research and surveillance program, including key 

milestones and funding estimates, in keeping with generally accepted 

practices for oversight and independence. In addition, the agency has not 

created an independent panel of experts in the areas of aircraft ventilation, 

air quality, and public health to help plan and oversee this effort. 

Furthermore, FAA’s plans do not explicitly include leveraging the findings 

of international research on cabin air quality. 

28The minimum number of flights to be included will depend on the recommendations of 

part I and on the availability of research funds and will be specified in the solicitation for 

part II to be released by ASHRAE in the future.
Page 25 GAO-04-54 Airliner Cabin Air Quality

Committee Members Concerned 

about Scope, Independence, and 

Funding of FAA Surveillance and 

Research Program

Members of the committee that produced the 2001 Council report are 

concerned that the FAA/ASHRAE surveillance and research program, as 

designed, will fall short of answering the long-standing questions about the 

effect of cabin air quality on passenger and cabin crew health and comfort. 

We contacted the 13 members of the committee, and 8 agreed to comment 

on FAA’s response to their recommendations on cabin air quality 

surveillance and research. We refer to these 8 individuals from here 

forward as commenting committee members. Although 5 of 8 commenting 

committee members said that the initiative should shed some light on cabin 

air quality’s effects on health, all said that it was much more limited than 

the committee had envisioned. Two of the 8 commenting committee 

members thought that the air quality and health surveillance initiative 

should be a continuous undertaking in which air quality and health 

information is taken from a representative sample of commercial aircraft 

and flight routes. They also said that it appears the FAA and ASHRAE 

program will not include a broad enough cross-section of aircraft and 

flights to determine the full range of air quality problems and relate them to 

health effects. Two commenting committee members said that part I of the 

FAA and ASHRAE program will extensively monitor cabin air quality on 

two aircraft types; however, part I will not provide information that is 

generalizable to the U.S. commercial airliner fleet. According to Boeing 

officials involved in this study, part I research is designed to validate test 

equipment and study protocols and is not designed to be generalized to the 

airliner fleet. One committee member said that although more aircraft are 

to be included in part II, it is doubtful that enough information will be 

collected to adequately answer the key questions the agency’s research and 

surveillance program was designed to address. According to Boeing 

officials, part II includes plans for information collection to address the key 

question of the agency surveillance and research program, provided 

sufficient funds are available. Another commenting committee member 

said that the FAA and ASHRAE program would also yield little or no 

information on air quality incidents that occur when cabin air is 

contaminated by oil or hydraulic fuel leaks. According to the member, 

these incidents are rare and can be monitored only if simple, inexpensive 

equipment (e.g., devices that can “grab” samples) is available to cabin crew 

on a large number of flights to use in the event that an incident occurs. 

FAA officials said that issues of sampling adequacy and specimen handling 

could complicate the grab sample approach. These officials also noted that 

a voluntary injury and illness reporting system that it has in place could 

capture air quality incidents if it were made mandatory.
Page 26 GAO-04-54 Airliner Cabin Air Quality

Seven of the eight commenting committee members also noted that FAA 

has not adequately addressed the Council report’s recommendations 

regarding cabin air surveillance and research programs. FAA has indicated 

that its program responds to the report’s recommendations calling for 

surveillance and research efforts. However, these committee members 

believe that the program focuses only on surveillance and does not include 

in-depth research of air quality issues as outlined in the committee’s 

recommendation calling for a separate comprehensive research program. 

One of the commenting committee members said that a cabin air quality 

study currently under way in Europe contains many of the elements that 

the committee had hoped to see in the U.S. surveillance and research 

efforts. As part of the ongoing surveillance and research study, the 

European cabin air study29 is currently coordinated by Building Research 

Establishment, Ltd. (BRE).30 The study focuses on three major goals: (1) 

advancing the industry’s understanding of what is known about air quality 

issues by assessing the current level of air quality found in aircraft cabins; 

(2) identifying the technology (i.e., environmental control systems 

including filtration and air distribution) that is available to improve cabin 

air quality; and (3) assessing and determining potential improvements to 

existing standards and performance specifications for the cabin 

environment. (The scope and methodology for Europe’s cabin air study is 

found in appendix IV). The cabin air study partnered (to various degrees) 

with 16 organizations, including Boeing, Airbus Deutschland, Honeywell 

(manufacturer of environmental control systems), Pall Aerospace (filter 

manufacturer), British Airways, United Kingdom’s Civil Aviation Authority 

(CAA), European Joint Aviation Authorities (JAA), and other organizations 

representing Austria, France, Germany, Greece, Norway, Poland, and 

Sweden. The European cabin air study began on January 2001 with an

29The European cabin air study is known as CabinAir. 

30Building Research Establishment, Ltd. (BRE) is a high-level research-based consultancy 

organization, owned by a not-for-profit entity headquartered in the United Kingdom. BRE 

provides the aviation industry with expert advice on cabin environment issues and, 

particularly, on air quality in passenger aircraft.
Page 27 GAO-04-54 Airliner Cabin Air Quality

estimated cost of $8 million and is expected to disclose its findings in 

2004.31

Of the eight commenting committee members, three addressed the funding 

of the FAA and ASHRAE surveillance and research programs. These 

members said that the amount of funding available for U.S. efforts might be 

insufficient to conduct surveillance and research programs of the scope 

they envisioned in their recommendations. For example, one of the 

committee members stated that to conduct a surveillance and research 

program of the scope the Council had in mind, Congress would have to 

provide funding levels comparable to that of the European cabin air study. 

One commenting committee member, National Institute for Occupational 

Safety and Health (NIOSH) officials, and airline flight attendant 

representatives we interviewed expressed concern that the extensive 

involvement of aircraft manufacturers and airlines in the design and 

implementation of the FAA and ASHRAE program could threaten the 

independence of the effort. However, with the exception of the flight 

attendant representatives,32 they agreed that any surveillance and research 

programs require participation by these groups. Nonetheless, they point to 

the fact that much of the available funding for the initiative ($200,000 of the 

$250,000) is coming from the aviation industry, which has a stake in the 

outcome, and that this might give the impression that the study lacks the 

necessary objectivity. The commenting committee member suggested that 

the research money provided by the aviation industry be placed in a special 

fund that would be managed by FAA or an independent research group. 

According to ATA officials, due to a lack of public funding on a scale 

comparable to what has been provided for Europe’s cabin air study, the 

financial support and cooperation of aircraft manufacturers and airlines is 

essential if FAA is to conduct this research. In addition, Boeing officials 

stressed that the project funding is currently controlled by ASHRAE and 

the project oversight committee is led by the chairman of the Council 

study.

31In addition to Europe’s cabin air study (CabinAir), Australia has addressed cabin air quality 

issues through the creation of a Reference Group on Cabin Air Quality. The Reference 

Group is responsible for following the progress of and analyzing the outcomes of 

international research and development. The Reference Group comprises government 

agencies, industry representatives, employee/union representatives, and representatives of 

aircraft and engine manufacturers.

32The flight attendant groups have actively lobbied for independent research that is not 

funded and controlled by companies that have a financial interest in the outcome. 
Page 28 GAO-04-54 Airliner Cabin Air Quality

Five of the commenting committee members also discussed the status of 

their recommendation concerning the need for Congress to designate a 

lead federal agency and advisory committee for the air quality research 

effort. Although Congress designated FAA as the lead agency in November 

2003, FAA had already assumed responsibility for implementing the 

research and surveillance-related recommendations. In commenting on the 

Council recommendation to designate a lead federal agency, several 

members said they thought that the lead agency should be one that is 

experienced in conducting scientific research on air quality and 

environmental health issues. Some noted that the Environmental 

Protection Agency (EPA) has supported a large body of research into air 

quality issues, and another pointed out that NIOSH has performed studies 

of air quality in buildings and the workplace. Several commenting 

members indicated that although it is FAA’s mission to promote aviation 

safety, they had reservations about whether the agency was well suited to 

oversee a large air quality research program on its own. Several members 

thought that, as an alternative, FAA might be part of a cooperative federal 

effort to perform airliner cabin air quality research. In addition, another 

committee member believes that although FAA has a committee to oversee 

the selection of the contractor for the program, it has not assembled an 

advisory committee to review the research design and monitor the 

implementation of the program.

Council’s Recommendations 

Concerning FAA Oversight 

of Aircraft Ventilation 

Systems

Four of the Council recommendations pertain to FAA’s oversight of the 

operation of aircraft ventilation systems. These recommendations call for 

FAA to (1) demonstrate in public reports the adequacy of its regulations 

related to cabin air quality and establish operational standards for 

ventilation systems, (2) ensure that standards for ozone levels are met on 

all flights, (3) investigate the need for and feasibility of installing equipment 

to clean the air supplied to aircraft ventilation systems, and 4) require 

carbon monoxide monitors in air supply ducts to passenger cabins and 

establish procedures for dealing with elevated carbon monoxide 

concentrations. According to FAA officials, the agency originally planned 

to have an aviation rulemaking advisory committee assess whether current 

standards were appropriate for ensuring that aircraft ventilation systems 

adequately prevent contamination of cabin air. However, FAA decided to 

defer this action until data is available from the surveillance and research 

study, as well as the European cabin air study. Additionally, FAA believes 

that data from this study will aid in the reconsideration of air quality 

standards for commercial aircraft. However, most of the commenting 
Page 29 GAO-04-54 Airliner Cabin Air Quality

committee members questioned the need for delay in addressing some of 

the recommendations. 

Four of the eight commenting committee members said that they 

recommended that FAA demonstrate, in public records, the rationale for 

the established design standards for carbon monoxide (CO), carbon 

dioxide (CO2), ozone (O3), ventilation, and cabin pressure because FAA 

was unable to explain the reasoning for these standards. For example, FAA 

has not documented the reasons for setting the ventilation rate standard for 

aircraft cabins of new aircraft types at .55 pounds of outside air per minute 

per occupant. The American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE)33 recommends that ventilation rates 

inside a building environment be at least 1.1 pounds of outside air per 

minute per occupant, which is about 50 percent more than the current FAA 

requirement for aircraft. In addition, FAA has not documented the reasons 

for requiring a design for cabin air pressure altitude of not more than 8,000 

feet air pressure, which is about three-fourths of the air pressure found at 

sea level. Members of the research community, including the Aerospace 

Medical Association (AsMA) and CAA, state that the loss of air pressure 

and oxygen may pose serious health risks for infants whose lungs have not 

fully developed and for older adults who may have upper respiratory 

problems. 

In response to the committee members’ comments, FAA provided us the 

following explanations for the design standards in question. The 

ventilation rate standard was based on a regulatory value established 

decades ago, which has been shown to be acceptable, and ASHRAE has 

formed a subcommittee to develop a standard specifically for airplanes. 

The limit for carbon monoxide concentration of 1 part in 20,000 parts air 

(0.005 percent) was adopted from the Occupational Safety and Health 

Administration (OSHA) and ASHRAE standards. The limit of maximum 

allowable carbon dioxide concentration in occupied areas of transport 

category airplanes was reduced to 0.5 percent in part due to a

recommendation from the National Academy of Sciences to review the 

carbon dioxide limit in airplane cabins; it provides a cabin carbon dioxide 

concentration level representative of that recommended by some 

33ASHRAE writes standards and guidelines in its fields of expertise to guide industry in the 

delivery of goods and services to the public. Currently, it has some 87 active standards and 

guideline project committees, addressing such broad areas as indoor air quality, thermal 

comfort, energy conservation in buildings, reduction of refrigerant emissions, and the 

designation and safety classification of refrigerants.
Page 30 GAO-04-54 Airliner Cabin Air Quality

authorities for buildings. The ozone limits were based on studies 

conducted by the FAA Civil Aerospace Medical Institute and are 

comparable to standards adopted by the Environmental Protection Agency 

and the Occupational Safety and Health Administration. The cabin 

pressure altitude standard was based on the accepted industry practice of 

maintaining the health and safety of occupants while considering the 

structural limitations of the aircraft.

A commenting committee member also expressed concern that FAA 

certifies aircraft ventilation systems that are designed to meet certain 

standards, such as those for ventilation rates, but it does not require that 

systems operate in accordance with these standards. The practical effect is 

that aircraft are not monitored to determine if they meet the design 

standards. According to another commenting committee member, FAA did 

not need data from the planned research project to provide a rationale for 

ventilation system standards, or to require that ventilation systems operate 

according to standards. Some committee members also said that FAA 

could begin to take steps to ensure that ozone standards are met on all 

flights regardless of altitude and require monitors for dangerous carbon 

monoxide vapors in air supply ducts to passenger cabins before the 

completion of the planned research study. FAA officials said that although 

it does not conduct recurrent system design compliance checks, the agency 

uses various reporting systems to monitor aircraft system performance and 

takes appropriate mandatory action when an unsafe condition is found. 

Council Recommendation 

Concerning Airborne 

Allergens

Because of the potential for serious health effects for people sensitive to 

allergens, the 2001 Council report also recommended that FAA investigate 

the need to prohibit the transport of small animals in aircraft cabins and 

provide training to cabin crews to deal with allergic reactions. However, 

FAA does not think that prohibiting animals in the cabin would be effective 

because it believes that most animal allergens are brought onboard aircraft 

on the clothes of passengers rather than by the animals themselves. 

Instead, the agency issued an advisory circular highlighting the effective 

procedures that passengers can use when carrying animals and guidance 

on how to train crewmembers to recognize and respond to in-flight medical 

events that result from exposure to allergens. Additionally, FAA will 

enhance its Internet site to provide general information related to FAA and 

air carrier policy concerning the transport of animals in aircraft cabins. 

Commenting committee members generally supported FAA’s approach to 

this recommendation. 
Page 31 GAO-04-54 Airliner Cabin Air Quality

Council Recommendation 

Concerning Health 

Information

In response to the Council report recommendation calling for FAA to 

increase efforts to provide cabin crew, passengers, and health 

professionals with information on health issues related to air travel, FAA 

modified the general information section of its Web site; however, we found 

that the traveler health information is not easy to access. FAA created 

hyperlinks to other Web sites, such as those of the Aerospace Medical 

Association and Centers for Disease Control and Prevention, which include 

information on potential health risks of flying, particularly for healthchallenged individuals. However, we found it difficult to locate the section 

of the FAA Web site that deals with traveler health information and when 

we did, it required several steps to reach the hyperlinks. Some commenting 

committee members also noted how difficult it is to access health-related 

information on the FAA Web site. In addition to citing the need for FAA to 

increase the accessibility of health-related information on its Web site, six 

of the eight committee members also mentioned that FAA should take 

further steps to make health information available to the flying public. 

Suggestions included having airlines include health related information on 

their Web sites and establishing a program to provide flying-related heath 

risk information to physicians that they could then share with their patients 

(e.g., through brochures).

Council Recommendation 

Concerning Aircraft 

Ventilation System 

Shutdown

FAA responded to the 2001 Council report recommendation that it 

establish a regulation to require removal of passengers from an aircraft 

within 30 minutes after a ventilation failure or shutdown on the ground by 

issuing an advisory circular to airlines. Some commenting committee 

members viewed this action as insufficient. This recommendation 

reiterated one made in the 1986 Council report, which FAA did not act on. 

The committees that produced both the 1986 and 2001 reports noted that 

environmental conditions in an aircraft cabin respond quickly to changes in 

ventilation system operation. The committees felt that the ventilation 

system should not be shut down for a long period when the aircraft is 

occupied, except in the case of an emergency, because excessive 

contaminant concentrations and uncomfortably high temperatures can 

occur quickly. Several commenting committee members told us that they 

felt strongly that FAA should require passenger removal in the event of 

ventilation system shutdown of more than 30 minutes and that advising 

airlines that this should be done was insufficient to accomplish the 

committee’s objective. FAA, on the other hand, said that airlines pay close 

attention to advisories. The agency decided against issuing a regulation 

because there are situations when an evacuation within 30 minutes is not 
Page 32 GAO-04-54 Airliner Cabin Air Quality

possible due to operational necessity, such as when a ventilation system 

breakdown occurs on a taxiway far from a gate.

Some Technologies 

Exist for Improving 

Cabin Air Quality, but 

There Are Questions 

About Whether They 

Should be Required

Several technologies exist today that could improve cabin air quality, but 

opinions vary on whether requiring the use of improved technologies in 

commercial airliner cabins is warranted. We found one of these 

technologies, HEPA filters, is strongly endorsed by cabin air quality and 

health experts as providing the best possible protection against one cabin 

air problem—the presence of particulates, bacteria, and viruses in 

recirculated air. While FAA does not currently require HEPA filters, some 

health experts believe these filters should be required, given their 

demonstrated effectiveness in cleansing cabin air. Figure 3 illustrates a 

typical HEPA filter for commercial passenger aircraft.
Page 33 GAO-04-54 Airliner Cabin Air Quality

Figure 3: A Typical HEPA Filter for Commercial Passenger Aircraft

According to many in the aviation community, several technologies are 

available today, and more are in the planning stages, that could improve the 

air quality in commercial airliner cabins. However, some in the aviation 

industry question whether requiring their use is warranted. Filtering 

particulates, bacteria, viruses, and gaseous pollutants and removing ozone 

can improve the healthfulness of cabin air, and increasing cabin humidity 

and absorbing more cabin odors and gasses can increase the comfort of 

passengers and cabin crews. While aircraft manufacturers acknowledge 

that a few technologies are available today that could further improve air 

quality and comfort in airliner cabins and that more are possible in the 

future, they believe that unless future research proves otherwise, the 

ventilation systems in the aircraft they have produced provide ample 
Page 34 GAO-04-54 Airliner Cabin Air Quality

amounts of relatively clean air. One technology with proven effectiveness is 

HEPA filtering of recycled cabin air. All new large commercial airliners in 

production with ventilation systems that recirculate cabin air come 

equipped with these filters, which, when properly fitted and maintained, 

are effective at capturing airborne contaminants such as viruses that enter 

the re-circulation system. However, some regional jets, which have fewer 

than 100 seats, are not equipped with filters, and some older large aircraft 

still use less efficient filters. FAA does not require the filtration of 

recirculated air, but health experts and members of the committee that 

produced the 2001 report on cabin air quality believe that given their 

proven effectiveness, HEPA filters should be required for all aircraft that 

recirculate cabin air. In addition, airflow rates could be increased in some 

aircraft by adjusting settings on the ventilation system, thereby dissipating 

the effects of some contaminants. However, this would be done at the 

expense of higher fuel consumption, increased engine emissions, and lower 

cabin humidity.

High Efficiency Particulate 

Filters Are an Effective 

Technology for Cleaning 

Recirculated Air

HEPA filters are a readily available and affordable technology for providing 

the best possible protection against one cabin air problem—the presence 

of particulates, bacteria, and viruses in recirculated air. However, HEPA 

filters will not filter gaseous contaminants. These filters have become 

widely available for aircraft since the late 1990s. According to EPA, HEPA 

filters can remove nearly all particulate contaminants, such as airborne 

particles and infectious agents including bacteria and viruses, from the 

recirculated air that passes through them.34 A manufacturer of HEPA 

filters, as well as health authorities such as CDC, NIOSH, and WHO, believe 

that HEPA filters are highly effective in preventing the transmission of 

bacteria and viruses through aircraft ventilation systems. However, they 

emphasize that HEPA filters clean only the air that is recirculated through 

aircraft ventilation systems, so transmissions from an infected person to 

others nearby are still possible. 

HEPA filters are available for most large commercial airliners in the U.S. 

fleet, but some aircraft with recirculation systems are equipped with less 

effective filters. However, not all commercial aircraft recirculate air 

through their ventilation systems. For example, some smaller jets, such as 

34The Environmental Protection Agency states that HEPA filters are to be 99.97 percent 

efficient for the removal of Particulate Matter (PM) that is greater than or equal to 0.3 

micrometer (mm) in diameter.
Page 35 GAO-04-54 Airliner Cabin Air Quality

the Boeing 717 and Bombardier CRJ-200s, which typically fly shorter 

routes, as well as older models of some longer-range aircraft, such as the 

Boeing 737-200 and the DC-10, provide 100 percent outside air to the 

passenger cabins instead of recirculating air and, therefore, would not need 

HEPA filters. Nevertheless, most commercial airliners in use today 

recirculate between 30 and 55 percent of the air provided to the passenger 

cabin. Officials from Boeing and Airbus, the world’s two largest 

manufacturers of commercial aircraft, told us that all their aircraft with 

recirculation systems currently in production are equipped with HEPA 

filters. The ventilation systems in many older commercial aircraft were 

designed to use the less effective filters available at the time, and some of 

these aircraft still use these types of filters. However, according to Boeing 

and Airbus officials, HEPA filters can be used on these older aircraft with 

little or no retrofitting required.35 According to a filter manufacturer, a 

HEPA filter costs about twice as much (e.g., $400 to $600 for the smaller 

narrow-body aircraft) as the non-HEPA models that are less effective in 

trapping particulates. Some regional jets, such as the Embraer ERJ-145 

recirculate air but are not equipped with filters. 

In fact, FAA does not require the filtration of recirculated air on aircraft. 

However, when manufacturers voluntarily equip their aircraft models that 

recirculate cabin air with HEPA or other filters when they are certified for 

flight by FAA, as most do, the aircraft are required to continue operating 

with the filters. The schedule for changing the filters is also included in the 

FAA certification process. Airlines typically change HEPA filters after 4,000 

to 12,000 hours of service to maintain good airflow and in accordance with 

manufacturers’ recommendations.

Little information has previously been available on the extent of HEPA 

filter usage in commercial aircraft ventilation systems, though the Council 

report and many in the health community have pointed to the importance 

of HEPA filters in preventing the spread of bacteria, viruses, and other 

contaminants in aircraft cabins. As noted earlier in this report, the 2001 

Council report recommended that FAA investigate and publicly report on 

the need for installing equipment to clean the air supplied to aircraft cabin 

ventilation systems. In the report, the committee did not determine how 

many larger aircraft were equipped with HEPA filters, and regional jets 

were not within the scope of its study. However, the report concluded that 

HEPA filters are highly effective in removing all airborne pathogens and 

35Installing HEPA filters on the A300 would require some modification.
Page 36 GAO-04-54 Airliner Cabin Air Quality

other particulate matter that pass through them. The report further stated 

that the use of recirculated air in aircraft cabins when combined with 

effective HEPA filtration does not contribute to the spread of infectious 

agents. Members of the research community, including those from NIOSH, 

as well as the Association of Flight Attendants, have noted that given the 

proven effectiveness of HEPA filters in capturing contaminants such as 

infectious viruses and bacteria, FAA should require their use on all aircraft 

with recirculation systems.

To determine the extent of HEPA filter usage in the United Stares, we 

surveyed the largest 14 airlines36 in the United States that had Airbus, 

Boeing, or McDonnell Douglas aircraft that recirculate cabin air, and we 

received responses from 12 airlines. Of the 3,038 aircraft for which we 

were able to obtain survey results, 15 percent (454 aircraft)37 did not use 

HEPA filters. All of the aircraft that did not use HEPA filters were older 

out-of-production models that used less effective filters. One airline has 

plans to retrofit a small number of these aircraft with HEPA filters.

We were also able to obtain some information on HEPA filter usage in the 

U.S. regional aircraft fleet by contacting the manufacturers of these 

aircraft. We found that 69 percent of these regional aircraft recycle cabin 

air (1,087 of 1,584), and only a handful of these aircraft are equipped with 

HEPA filters. The manufacturer of a new regional jet model38 offers HEPA 

filters as an option. Information we obtained from two airlines that had 29 

of these aircraft indicated that about half (14 of 29) were equipped with 

HEPA filters. 

36We used revenue passenger miles (RPM) as reported in Aviation Daily for May 2003 to 

identify the largest U.S. carriers. This list identified the largest 28 airlines, 14 of which had 

the larger aircraft that recirculate cabin air. The other 14 airlines only had smaller regional 

aircraft or larger aircraft that did not recycle cabin air. An RPM is a standard unit of 

passenger demand for air transport, defined as one fare-paying passenger transported one 

mile. We obtained the model information for these carriers from data published in Air 

Transport World (July 2003).

37We obtained information on 3,038 larger aircraft that recycled cabin air, 454 of which did 

not have a HEPA filter. We were not able to obtain survey results for another 384 aircraft. 

Of these 384, 56 (15 percent) of the aircraft were older models that most airlines had not 

retrofitted with HEPA filters. Our study included 3,770 larger aircraft, of which 348 did not 

recycle cabin air.

38HEPA filters are available for the CRJ700 manufactured by Bombardier.
Page 37 GAO-04-54 Airliner Cabin Air Quality

We also found that 90 percent of the regional aircraft (973 of 1,087 aircraft) 

that recycled cabin air would require modifications to be retrofitted with 

HEPA filters. Most of these aircraft (73 percent) had no provision for 

installing filters in their air ducts.

Consideration has also been given to filtering outside air entering an 

aircraft’s ventilation system. Outside air at cruise altitudes is mainly free of 

pollutants, except for ozone. However, in the event of an engine or 

hydraulic system malfunction, outside air can become contaminated before 

it enters the ventilation system. In addition, when an aircraft is at the gate 

or taxiing, the available outside air contains pollutants normally present 

around the airport, including exhaust from other aircraft on the runway. 

For these reasons, the 2001 Council report recommended that FAA 

investigate the need for and feasibility of installing air-cleaning equipment 

for removing particles and vapors from the air supplied to the ventilation 

system. As previously noted, FAA has put off consideration of this 

recommendation until the completion of FAA’s and ASHRAE’s air quality 

research and surveillance program in 2006 or 2007. One manufacturer did 

begin installing outside air filtering equipment on one of its models in 1992. 

British Aerospace began equipping its BAe 146 aircraft (now out of 

production) with outside air filters as part of an effort to reduce cabin 

odors. Other manufacturers, including Boeing and Airbus, contend that 

outside air filtration is not necessary unless U.S. and European research 

indicates a problem with the quality of air entering aircraft ventilation 

systems. 

Technology is Available to 

Remove Ozone from the Air 

Brought in from Outside the 

Aircraft 

Technologies are currently available for removing ozone from outside air. 

Ozone is present in the air at high altitudes on some routes, particularly 

those over the polar regions, and FAA requires that the airlines that fly 

these routes take measures to maintain cabin ozone levels at or below 

prescribed limits (e.g., using devices that convert ozone to oxygen). 

According to ATA officials, nearly all commercial aircraft that fly on these 

routes are so equipped. However, the Council report said that although 

FAA requires that ozone concentrations in aircraft cabins be maintained 

within specified limits, surveillance programs with accurate and reliable 

equipment are needed to ensure compliance and that the ozone converter 

equipment works properly. One study attributed elevated ozone levels that 

exceeded FAA limits to temporary ozone plumes that can appear 

unexpectedly. In November 2000, the British House of Lords, in a study of
Page 38 GAO-04-54 Airliner Cabin Air Quality

health issues in aircraft cabins,39 made a recommendation that airlines fit 

their aircraft that fly on routes where these plumes occur with ozone 

converters to minimize potential health problems. The Council report also 

identified the need for FAA to take effective measures to ensure that ozone 

does not exceed levels specified in FAA regulations, regardless of altitude. 

As noted earlier, FAA plans to monitor ozone levels in selected aircraft as 

part of its surveillance and research program. However, some committee 

members told us that the effort will be too limited to enable FAA to 

determine if ozone is present on aircraft not fitted with converters or 

whether ozone converters are working properly.

Increasing Ventilation Rates 

in Aircraft Cabins Poses 

Challenges

Increasing ventilation rates on aircraft to levels approximating those 

currently required in buildings would pose technological challenges, and 

aircraft manufacturers believe such increases are not necessary. Raising 

ventilation rates would reduce the effects of some airborne contaminants 

by diluting their concentration.

According to Boeing and Airbus officials, airflow rates on their aircraft 

could be slightly increased by adjusting settings on the ventilation systems, 

but such adjustments would increase fuel consumption and result in higher 

operating costs. According to Boeing officials, to achieve the same airflow 

rates recommended for buildings, aircraft ventilation systems, and possibly 

the aircraft themselves, would have to undergo expensive modifications. 

Boeing and Airbus believe that unless the U.S. and European research and 

surveillance initiatives prove otherwise, ventilation rates in commercial 

aircraft are sufficient to sustain passenger and cabin crew comfort and 

health. 

Boeing and Airbus officials told us that they are always seeking to improve 

the aircraft they build, but they believe that the ventilation systems in the 

aircraft they produce provide a healthy and relatively comfortable 

environment for passengers and cabin crew. Nevertheless, Boeing is 

considering increasing the air pressure and humidity levels on the 7E7, its 

proposed long-range, high-altitude aircraft. Airbus will also offer an 

improved air ventilation system on its new large aircraft, the A380. Because 

of the competitive nature of the aircraft manufacturing industry, few details 

are available on the 7E7 and A380 ventilation systems. Boeing and Airbus 

39The House of Lords, Select Committee on Science and Technology, Air Travel and Health, 

5th Report HL.
Page 39 GAO-04-54 Airliner Cabin Air Quality

officials noted that if current research and surveillance efforts indicate 

problems with any aspects of the ventilation systems in their aircraft, they 

would work toward developing the necessary technologies to deal with 

these problems.

Conclusions The combined research efforts of FAA and ASHRAE on cabin air quality 

will provide a foundation of knowledge, according to some members of the 

committee that produced the 2001 Council report on cabin air quality. 

However, as currently designed and funded, these efforts may not answer 

many long-standing questions about the effect of air quality on cabin 

occupants’ health and comfort. FAA is attempting to balance the need to 

conduct additional research on the healthfulness of cabin air quality with 

other research priorities, such as improving passenger safety. Our prior 

work on airliner cabin safety and health has underscored the importance of 

setting risk-based research priorities, in part by establishing cost and 

effectiveness estimates to allow direct comparisons among competing 

research priorities. In commenting on this prior work, FAA cautioned that 

if too much emphasis is placed on cost/benefit analyses, potentially 

valuable research may not be undertaken. We concur in that caution. 

However, information on the nature and extent of health effects from cabin 

air is needed in order to identify potential health threats so that it can be 

determined if action is warranted to improve cabin air quality and to target 

research and development accordingly. Moreover, committee members 

recommended more study of these issues, and others in the industry have 

concerns about FAA’s surveillance and research program as currently 

conceived. Committee members were particularly concerned about FAA’s 

decision to delay action on ensuring that air quality regulations are 

adequate or being met on all flights. In addition, the agency’s current plan 

to monitor cabin air quality on only two aircraft types during part I of its 

program will not provide FAA with information that is generalizable to the 

U.S. commercial airliner fleet. Thus, key questions that the agency’s 

research and surveillance program were designed to address will remain 

unanswered if part II of FAA’s program is not properly designed and 

adequately funded. Such information is also needed to guide the 

development of new technologies. Given the importance of this research 

and surveillance effort, the program needs to be well designed, properly 

funded, coordinated with international cabin air quality research efforts 

such as those ongoing in Europe and Australia, and conducted in 

accordance with accepted standards for independence and oversight. The 

Council in its 2001 report recommended that Congress designate a federal 

agency to conduct or direct the cabin air quality research program and 
Page 40 GAO-04-54 Airliner Cabin Air Quality

recent legislation assigned FAA as the lead federal agency for this effort. 

FAA has begun a surveillance and research program on its own. 

Furthermore, FAA has not taken steps to ensure that HEPA filters, which 

are a proven technology for eliminating some contaminants such as viruses 

and bacteria from recirculated cabin air, are used as widely as possible on 

commercial aircraft. FAA does not currently require the use of filters on 

recirculated air. Nevertheless, we found that a number of aircraft 

manufacturers and airlines voluntarily install them and that the vast 

majority of larger commercial aircraft are equipped with HEPA filters. 

However, we also found that only a few smaller regional jets that 

recirculate cabin air have HEPA or any other type of filters. FAA has 

decided to delay addressing the 2001 Council report recommendation 

calling for the agency to investigate the need for air cleaning equipment on 

aircraft ventilation systems until it completes its cabin air quality 

surveillance and research program in 2006 or 2007. FAA needs to 

determine the costs and benefits of requiring HEPA filters on commercial 

aircraft that recirculate air. 

Finally, although FAA has made some progress in implementing the 

Council’s recommendation regarding the need to increase the availability of 

information on health issues related to air travel, more needs to be done. 

Creating links on the FAA Web site to pertinent information on the CDC 

and WHO Web sites is a good start, but navigating the FAA’s Web site to 

reach these links is difficult. In addition to improving the user friendliness 

of the FAA Web site links, some commenting committee members 

suggested that FAA should consider other methods for disseminating 

information on the health risks of flying, such as providing brochures for 

physicians to use when discussing these issues with patients. 

Recommendations for 

Executive Action

To help ensure that FAA’s research and surveillance efforts on airliner cabin 

air quality answer critical outstanding questions about the nature and 

extent of potential health effects of cabin air quality on passengers and 

flight attendants, GAO recommends that the Secretary of Transportation 

direct the FAA Administrator to

• develop a detailed plan for the research and surveillance efforts, 

including key milestones and funding estimates, in accordance with 

generally accepted practices for oversight and independence; 
Page 41 GAO-04-54 Airliner Cabin Air Quality

• appoint a committee of acknowledged experts in the fields of aircraft 

ventilation and public health, including representatives of EPA and 

NIOSH, to assist in planning and overseeing the research and 

surveillance efforts recommended by the National Research Council in 

2001;

• leverage the findings of international research on airliner cabin air 

quality to inform FAA’s surveillance and research efforts; and

• report to Congress annually on the progress and findings of the research 

and surveillance efforts and funding needs.

In order to help improve the healthfulness of cabin air for commercial 

aircraft passengers and cabin crews, the FAA Administrator should assess 

the costs and benefits of requiring the use of HEPA filters on commercial 

aircraft with ventilation systems that recirculate cabin air. If FAA chooses 

to require the use of HEPA filters, it should also ensure that the regulation 

covers the maintenance requirements for these filters. 

In addition, to increase access to information on the health risks related to 

air travel, the FAA Administrator should direct the staff responsible for the 

FAA Web site to improve the links to other Web sites containing this 

information. The Administrator should also consult with medical 

associations and health organizations, such as CDC, on other ways to 

increase the dissemination of this information.

Agency Comments We provided copies of a draft of this report to the Department of 

Transportation for review and comment. FAA generally agreed with the 

report’s contents and its recommendations. The agency provided us with 

oral comments, primarily technical clarifications, which we have 

incorporated as appropriate.

As agreed with your office, unless you publicly announce the contents of 

this report earlier, we plan no further distribution until 30 days from the 

report date. At that time, we will send copies of this report to interested 

congressional committees, the Secretary of Transportation, and the 

Administrator, FAA. We will also make copies available to others upon 
Page 42 GAO-04-54 Airliner Cabin Air Quality

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

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

Please call me at (202) 512-2834 if you or your staff have any questions 

concerning this report. Major contributors to this report are listed in 

appendix VI.

Sincerely yours,

Gerald L. Dillingham

Director, Civil Aviation Issues
Page 43 GAO-04-54 Airliner Cabin Air Quality

Appendix I

Objectives, Scope, and Methodology AAppenednxidexiIs

The Ranking Democratic Member of the Subcommittee on Aviation, House 

Committee on Transportation and Infrastructure, asked us to provide 

information on steps that the aviation community is taking to address 

concerns about cabin air quality. Specifically, our research focused on the 

following questions: (1) What is known about the major potential health 

effects of air quality in commercial airliner cabins on passengers and flight 

attendants? (2) What actions has the National Research Council 

recommended to improve cabin air quality, and what is the status of those 

actions? (3) What technologies are available today to improve the air 

quality in commercial airliner cabins, and which, if any, should be required?

To answer the first question, we reviewed the December 2001 National 

Research Council report on aircraft cabin air quality, which was the most 

current and comprehensive examination of the existing literature on this 

issue and made recommendations for potential approaches for improving 

cabin air quality. We also independently reviewed many of the studies on 

issues related to cabin air quality, paying particular attention to those 

issued after the publication of the 2001 Council report.1

 We also gathered 

information from the governments of Australia, Canada, and the United 

Kingdom and airlines. We also interviewed officials representing the 

Federal Aviation Administration (FAA), the World Health Organization 

(WHO), the Centers for Disease Control and Prevention (CDC), the 

National Institute for Occupational Safety and Health (NIOSH), the 

Aerospace Medical Association (AsMA), the Air Transport Association 

(ATA), the Association of Flight Attendants (AFA), the International Airline 

Passengers Association (IAPA), aircraft and air filter manufacturers, as 

well as experts on cabin air quality issues, including members of the 

committee that produced the 2001 Council report on cabin air quality.

To address the second question, we interviewed Council committee 

members about their views on how FAA was addressing the 

recommendations they made in their report. Before conducting the 

interviews, we provided the committee members with information from 

FAA on its plans for addressing the Council’s recommendation. We then 

asked them for their views on the approach for addressing each of the 

recommendations. We conducted interviews with 11 of the 13 committee 

1

See the Selected Bibliography at the end of this report and, in particular, Hocking, 

Martin B., “Trends in Cabin Air Quality on Commercial Aircraft: Industry and Passenger 

Perspectives,” Reviews on Environmental Health 17, 1 (2002): 1-49; and Rayman, 

Russell B., “Cabin Air Quality,” Aviation, Space and Environmental Medicine 73 

(2002): 211-215. 
Appendix I

Objectives, Scope, and Methodology

Page 44 GAO-04-54 Airliner Cabin Air Quality

members; we were unable to contact 2 members. Of the 11 members we 

interviewed, 8 agreed to provide their views on at least some of the 

recommendations. Three members declined to address any of the 

recommendations, saying that they were outside their fields of expertise 

and that they had not followed the progress of FAA’s implementation of the 

recommendations.

To address the third question, we interviewed representatives of aircraft 

manufacturers, filter manufacturers, FAA officials, and experts on aircraft 

ventilation systems, including members of the committee. To determine 

HEPA filter usage, we first identified the 28 airlines that account for 99.94 

percent of the revenue passenger miles (RPM) flown by U.S. airlines as 

reported in Aviation Daily for May 2003.2

 Fourteen of these airlines had 

aircraft that recirculate cabin air. The other 14 only had smaller regional 

aircraft or larger aircraft that did not recirculate cabin air. After selecting 

the 28 airlines, we obtained information from Air Transport World

(Airclaims 2002 data, July 2003 edition) on the number of aircraft they 

operate by model type. We then obtained information from the aircraft 

manufacturers that allowed us to categorize the 5,354 aircraft in the 28 

airlines by whether or not they recycle air (see table 3). 

Table 3: Number of Large and Regional Aircraft of Top 28 Airlines That Do or Do Not 

Recycle Cabin Air

Source: GAO. 

Larger aircraft included the commercial aircraft manufactured by Airbus, 

Boeing, and McDonnell Douglas. Regional aircraft included Avions de 

Transport Regional (ATR), British Aerospace (BAe), Bombardier, Dornier, 

Embraer, Fokker, Jetstream, and Saab models.

2

A revenue passenger mile is a standard unit of passenger demand for air transport, defined 

as one fare-paying passenger transported one mile.

Aircraft size Cabin air recycled

Cabin air not 

recycled Total

Larger aircraft 3,422 348 3,770

Regional aircraft 1,087 497 1,584

Total 4,509 845 5,354
Appendix I

Objectives, Scope, and Methodology

Page 45 GAO-04-54 Airliner Cabin Air Quality

Our primary focus with the larger aircraft was to determine the HEPA filter 

usage for the 3,422 larger aircraft that recycled cabin air. To obtain this 

information, we surveyed the 14 airlines that had aircraft in this category 

and obtained responses from 12 (covering 3,038 of the 3,422 aircraft in this 

category). Our survey form, which we administered by e-mail, asked the 

airlines to provide the following information: the number of active aircraft 

by model type as of June 30, 2003; the number of active aircraft with HEPA 

filters; the number of active aircraft without HEPA filters; the reasons why 

HEPA filters are not used; and, if applicable, the types of filters used if 

other than HEPA filters. 

Our primary focus with the regional aircraft was to determine what 

percentage of these aircraft recycled air, and, for those aircraft that did 

recycle air, what percentage would require major modifications to be 

retrofitted with a HEPA filter. We were able to make this determination on 

the basis of information provided by the manufacturers. Because only a 

small portion of the regional aircraft that recycle air are capable of being 

fitted with HEPA filters, we did not survey the 13 airlines that had only 

regional aircraft. In the cases where returned surveys also included 

information on regional aircraft that could use HEPA filters with little or no 

retrofitting, we found that only a small portion were doing so.
Page 46 GAO-04-54 Airliner Cabin Air Quality

Appendix II

Biographical Information on the National 

Research Council Committee ApendxiI

Dr. Morton Lippman

Professor of environmental medicine and director of the Center for 

Particulate Matter Health Effects Research and of the Human Exposure 

and Health Effects Research Program at New York University School of 

Medicine.

Dr. Harriet A. Burge

Associate professor of environmental microbiology at the Harvard School 

of Public Health. Dr. Burge’s current area of research is on the role of 

environmental exposures in the development of asthma and evaluating 

exposure to fungi, dust mite, cockroach, and cat allergens in three separate 

epidemiology studies assessing risk factors for the development of asthma.

Dr. Byron Jones

Associate dean for Research and Graduate Programs and director of the 

Engineering Experiment Station at the College of Engineering, Kansas 

State University. Dr. Jones’s research interests are in heat and mass 

transfer, human thermal systems simulation, and thermal measurements 

and instrumentation.

Dr. Janet M. Macher

Air pollution research specialist with the Division of Environmental and 

Occupational Disease Control of the California Department of Health 

Services. Her research has focused on the evaluation of methods to collect 

and identify airborne biological material and on engineering measures to 

control airborne infectious and hypersensitivity diseases.

Dr. Michael S. Morgan

Professor in the Department of Environmental Health, Industrial Hygiene 

and Safety Program of the University of Washington and director of the 

Northwest Center for Occupational Health and Safety. His research is 

focused on human response to inhalation of air contaminants, including the 

products of combustion and volatile solvents, and has encompassed both 

ambient air contaminants and occupational environmental health hazards.

Dr. William W. Nazaroff

Professor of environmental engineering in the Department of Civil and 

Environmental Engineering of the University of California, Berkeley. His 

main research interest is indoor air quality, with emphasis on pollutantsurface interactions, transport/mixing phenomena, aerosols, 

environmental tobacco smoke, source characterization, exposure 

assessment, and control techniques.
Appendix II

Biographical Information on the National 

Research Council Committee

Page 47 GAO-04-54 Airliner Cabin Air Quality

Dr. Russell B. Rayman

Executive director of the Aerospace Medical Association in Alexandria, 

Virginia, retired from the U.S. Air Force in 1989 with the rank of colonel 

after a military medical career.

Dr. John D. Spengler

The Akira Yamaguchi Professor of Environmental Health and Human 

Habitation and director of the Environmental Science and Engineering 

Program at the Harvard School of Public Health. Dr. Spengler’s research is 

focused on assessment of population exposures to environmental 

contaminants that occur in homes, offices, schools, and during transit, as 

well as in the outdoor environment.

Dr. Ira B. Tager

Professor of epidemiology in the Division of Public Health, Biology, and 

Epidemiology at the University of California, Berkeley, and is codirector 

and principal investigator for the Center for Family and Community Health. 

Dr. Tager’s research includes the development of exposure assessment 

instruments for studies of health effects of chronic ambient ozone 

exposure in childhood and adolescence, the effects of ozone exposure on 

pulmonary function, and the effects of oxidant and particulate air pollution 

on cardio-respiratory morbidity and mortality and morbidity from asthma 

in children.

Dr. Christiaan Van Netten

Associate professor in the Department of Health Care and Epidemiology at 

the University of British Columbia and head of the Division of Occupational 

and Environmental Health. Dr. Van Netten’s research interests include 

environmental toxicology and the use of electrodiagnostics to monitor 

worker exposure to agents that affect the peripheral nervous system.

Dr. Bernard Weiss

Professor of environmental medicine and pediatrics at the University of 

Rochester School of Medicine and Dentistry. His special interest and 

publications lie primarily in areas that involve chemical influences on 

behavior, including the neurobehavioral toxicology of metals such as lead, 

mercury, and manganese.
Appendix II

Biographical Information on the National 

Research Council Committee

Page 48 GAO-04-54 Airliner Cabin Air Quality

Dr. Charles J. Weschler

Adjunct professor in the Department of Environmental and Community 

Medicine at the University of Medicine and Dentistry of New Jersey, Robert 

Wood Johnson Medical School/Rutgers. His research interests, among 

others, include chemical interactions among indoor pollutants and the 

chemistry of the outdoor environment as it impacts the indoor 

environment.

Dr. Hanspeter Witschi

Professor of toxicology and associate director of the Institute for 

Toxicology and Environmental Health at the University of California, Davis. 

Dr. Witschi’s research interests include experimental toxicology, 

biochemical pathology, and the interaction of drugs and toxic agents with 

organ function at the cellular level.

Source: National Research Council.
Page 49 GAO-04-54 Airliner Cabin Air Quality

Appendix III

Transmission of Severe Acute Respiratory 

Syndrome (SARS) on Board Aircraft Is Rare 

and Associated with Proximity ApendxiI

Aboard aircraft, cabin occupants are confined in close quarters for 

extended periods and can be exposed to infectious diseases carried by 

other occupants. Because air travel is rapid, people can complete their 

journeys before the symptoms of a disease begin. Consequently, there has 

been much concern regarding the in-flight transmission of contagious 

diseases, particularly tuberculosis and, more recently, severe acute 

respiratory syndrome (SARS). As part of our review of airliner cabin air 

quality, we tracked the status of SARS and air travel. 

SARS is a serious respiratory illness that has affected persons in Asia, 

North America, and Europe. According to the World Health Organization 

(WHO), as of September 26, 2003, there were an estimated 8,098 probable 

cases reported in 27 countries, including 29 cases in the United States. 

There have been 774 deaths worldwide, none of which have occurred in the 

United States. The Centers for Disease Control and Prevention (CDC) 

believes SARS is caused by a previously unrecognized coronavirus.1

 The 

symptoms of SARS can include a fever, chills, headache, other body aches, 

and a dry cough.

SARS appears to be transmitted by close personal contact, which includes 

touching the eyes, nose, or mouth after touching the skin of infected 

individuals or objects that have been contaminated with infectious droplets 

released by an infected individual while coughing or sneezing. People with 

SARS pose the highest risk of transmission to household members and 

health care personnel in close contact. Most cases of SARS involved people 

who cared for or lived with someone with SARS or had direct contact with 

objects contaminated with infectious droplets. Information to date 

suggests that people are most likely to be infectious when they have 

symptoms such as fever or cough. However, it is not known how long 

before or after their symptoms begin that people with SARS might be able 

to transmit the disease to others. Most of the U.S. cases of SARS have 

occurred among travelers returning to the United States from other parts of 

the world affected by SARS, such as China. According to WHO, as of 

September 26, 2003, the latest probable case of SARS reported in the 

United States was on July 13, 2003. However, there is no evidence that 

SARS is spreading in the United States. WHO has reported that although 

1

A coronavirus is so named because it looks like a corona or halo when viewed under an 

electron microscope. Two human coronaviruses cause about 30 percent of common colds. 

Coronavirses have been found to infect cattle, pigs, horses, turkeys, chickens, cats, dogs, 

rats, and mice. 
Appendix III

Transmission of Severe Acute Respiratory 

Syndrome (SARS) on Board Aircraft Is Rare 

and Associated with Proximity

Page 50 GAO-04-54 Airliner Cabin Air Quality

the global outbreak of SARS has been contained, considerable uncertainty 

surrounds the question of whether SARS might recur, perhaps according to 

a seasonal pattern. Several respiratory illnesses occur much less 

frequently when temperature and humidity are high and then return when 

the weather turns cooler. WHO has also requested all countries to remain 

vigilant for the recurrence of SARS and to maintain their capacity to detect 

and respond to the reemergence of SARS, should it occur. The CDC has 

conducted broadcasts over the Internet for healthcare providers on 

preparing for the return of SARS.

WHO has reported that as of May 23, 2003, there have been 29 probable 

cases of in-flight SARS transmissions on four flights worldwide. Out of the 

29 cases, 24 were on one flight, and 4 of the 29 cases were flight attendants. 

WHO has stated that since then there have been no reported cases of inflight SARS transmissions. The WHO Director of Communicable Diseases 

stated there is a very low risk of catching SARS on an airplane through the 

airplane’s ventilation system. He noted that nearly all of the in-flight 

transmissions occurred between passengers who were sitting near each 

other. This official also stated that airport screening procedures have been 

effective in keeping individuals displaying SARS symptoms from boarding 

aircraft. In October 2003, WHO issued a report in which it did not find 

evidence that SARS is an airborne disease. This report further stated that at 

all outbreak sites the main route of transmission was direct contact, via the 

eyes, nose, and mouth, with infectious respiratory droplets. 

In December 2003, the New England Journal of Medicine published the 

results of a study on the transmission of SARS on three flights that 

transported at least one person who had SARS.2

 The study found that on 

one flight carrying four people with SARS symptoms, one other person at 

most developed the disease, and no illness was documented on another 

flight transporting a person with presymptomatic SARS. However, on a 

third flight carrying a symptomatic person, 22 probable cases of SARS3

occurred among the other 119 passengers. According to the study, for the 

2

Olsen, Sonja J. et al., “Transmission of the Severe Acute Respiratory Syndrome on Aircraft,” 

The New England Journal of Medicine 349; 25 (2003): 2416-2422.

3

According to the study, laboratory confirmed SARS developed in 16 persons, 2 others were 

given diagnosis of probable SARS and four were reported to have SARS but could not be 

interviewed by the study team. WHO reported that as of May 23, 2003, 24 probable SARS 

transmissions occurred on this flight. The study does not indicate the reason for the 

discrepancy.
Appendix III

Transmission of Severe Acute Respiratory 

Syndrome (SARS) on Board Aircraft Is Rare 

and Associated with Proximity

Page 51 GAO-04-54 Airliner Cabin Air Quality

22 people with illness, the mean time from the flight to the onset of 

symptoms was four days, and there were no recognized exposures to 

persons with SARS before or after the flight. The study found that illness in 

passengers was related to the physical proximity to the person with SARS 

on the flight. Illness was reported in 8 of the 23 passengers seated in the 

three rows in front of the person with SARS, as compared to 10 of the 88 

passengers seated elsewhere on the aircraft. The study noted however, 

that 90 percent of the passengers who became ill on the flight were seated 

more than 36 inches from the person with SARS, which had been the cutoff 

used to define the spread of SARS droplets in other investigations. The 

study authors speculated that “airborne, small particle, or other remote 

transmission may be more straightforward explanations for the observed 

distribution of cases.” The study concluded that SARS transmissions may 

occur on flights carrying people in the symptomatic stages of the disease 

and that measures to reduce the risk of transmission are warranted.

In November of 2003, more than 50 leading SARS researchers from 15 

countries concluded that a safe and effective vaccine would be an 

important complement to existing SARS control strategies. Most of the 

experts agreed, however, that a SARS vaccine will not be available in time, 

should an epidemic reoccur in the near future. A WHO official stated that 

the licensing and commercialization of a SARS vaccine could probably not 

be realized in 2004.

According to the International Air Transport Association (IATA), 

passengers are not at risk from being infected with the SARS virus from the 

cabin crew, who must be medically fit, without SARS symptoms, and 

physically capable to fly and fulfill their duties. CDC has stated that there is 

currently no evidence that a person can be infected with SARS from 

handling baggage or goods, because the primary means of infection is close 

personal contact. CDC has also stated the transmission of SARS has been 

associated with close contact with people with SARS symptoms, such as 

passengers on an aircraft. 

The CDC has issued travel alerts and advisories for travel to areas affected 

by SARS. A travel advisory recommends that nonessential travel be 

deferred; in contrast, a travel alert informs travelers of the health concern 

and provides advice about specific precautions. The CDC recommends that 

if SARS is suspected in an outpatient setting, healthcare providers should 

provide and place a surgical mask over the person’s nose and mouth. The 

CDC further recommends that if this is not feasible, the person with SARS 

should be asked to cover his/her mouth with a disposable tissue when 
Appendix III

Transmission of Severe Acute Respiratory 

Syndrome (SARS) on Board Aircraft Is Rare 

and Associated with Proximity

Page 52 GAO-04-54 Airliner Cabin Air Quality

coughing, sneezing, or talking. WHO has urged airport officials in countries 

affected with SARS outbreaks to take precautionary screening measures, 

such as asking passengers if they have had contact with anyone who has 

had the disease. U.S. airlines that fly to Asia report that they are following 

CDC and WHO guidelines. FAA has links to the CDC and WHO guidelines 

on its Web site. U.S. airlines that do not fly internationally are not 

modifying their procedures because they see no SARS risk to cabin

occupants. According to ATA officials, U.S. airlines that do not fly 

internationally were not advised by CDC to modify procedures because 

there was no evidence of community transmission of SARS in the United 

States. However, all ATA-member airlines cooperated fully with CDC in 

instances where there was a possible person with SARS who might have 

transferred from an international to a domestic flight. 
Page 53 GAO-04-54 Airliner Cabin Air Quality

Appendix IV

European CabinAir Study: Scope and 

Methodology ApendxiIV

In 2001, Building Research Establishment, Ltd. (BRE)1 initiated a study on 

cabin air quality that was estimated to cost $8 million. The following link 

provides the official description of the effort as posted on BRE’s Internet 

site: http://projects.bre.co.uk/envdiv/cabinair/work_programme.html

To further the industry’s understanding of what is known about air quality 

issues by assessing the current level of air quality found in aircraft cabins, 

BRE will monitor four generic aircraft types in flight and assess cabin air 

quality and ventilation system performance, including the effects of 

passenger density and flight duration. A total of 50 such flights are planned. 

The findings will identify current best practice and will be used to improve 

understanding of (1) what constitutes good cabin air; (2) the impact on the 

safety, health, and comfort of passengers and cabin crew; and (3) the 

effects on operating costs, fuel energy use, and the external environment.

To identify the technology (i.e., environmental control systems including 

filtration and air distribution) that is available to improve cabin air quality, 

BRE will develop new designs to address various air quality issues, 

including the control of carbon dioxide, humidification, outside air supply, 

and the recirculation and filtration of air. Operating costs and energy 

consumption will be analyzed in relation to environmental impacts. New 

designs must be suitable for retrofitting to existing aircraft, either as 

complete environmental control systems or as subsystems within existing 

units. The overall intention is to make environmental control systems 

flexible and easy to operate. For example, improved systems might enable 

the crew to match the system to the passenger load factor, reduce bleed air, 

or provide additional comfort in different areas of the cabin.

BRE will seek to improve the performance of filtration systems and then 

develop new technologies and systems. It will assess existing filtration 

systems and consider how the installation process and activities such as 

maintenance, lifting, and cleaning affect performance. A technology 

demonstrator rig will be developed to test new filtration systems. New and 

enhanced features will be developed to mitigate such problems as the 

recirculation of pollutants, bacteria, and viruses. Other major factors 

1

Building Research Establishment, Ltd. (BRE) is a high-level research-based consultancy 

organization, owned by a not-for-profit entity headquartered in the United Kingdom. BRE 

provides the aviation industry with expert advice on cabin environment issues and 

particularly on air quality in passenger aircraft.
Appendix IV

European CabinAir Study: Scope and 

Methodology

Page 54 GAO-04-54 Airliner Cabin Air Quality

include the compatibility of the filtration systems with the overall 

environmental control system, operational costs, and energy consumption. 

The effectiveness of current air distribution systems will be gauged through 

in-flight monitoring. New design strategies and technologies, such as 

personal controls, will be developed with the goal of maximizing the 

effectiveness of cabin ventilation. The study will also look at ways of 

making the distribution system more easily integrated with aircraft design.

To assess and determine potential improvements to existing standards and 

performance specifications for the cabin environment, BRE will assess 

existing standards. Potential improvements to existing standards and 

specifications will be determined. Checks will be carried out to ensure the 

feasibility of the performance specifications and costs and to identify any 

environmental implications. New performance indexes and comfort 

criteria will also be defined, and BRE will develop a model to be tested.
Page 55 GAO-04-54 Airliner Cabin Air Quality

Appendix V

Surveillance and Research Programs ApendxiV

Key recommendations of the Council report were to establish surveillance 

and research programs to determine effects of cabin air quality on aircraft 

occupants’ health and comfort.

Surveillance Program The following is a detailed description of these programs as stated in the 

Council report.

Surveillance program 

objectives

• To determine aircraft compliance with existing Federal Aviation 

Regulations (FARS) for air quality.

• To characterize accurately air quality and establish temporal trends of 

air-quality characteristics in a broad sample of representative aircraft.

• To estimate the frequency of nonroutine operations in which serious 

degradation of cabin air quality occurs.

• To systematically document health effects or complaints of passengers 

and crew related to routine conditions of flight or air-quality incidents; 

to be effective, this effort must be conducted and coordinated in 

conjunction with air-quality monitoring.

Surveillance program 

approach

• Continuously monitor and record ozone, carbon monoxide, and carbon 

dioxide, fine particles, cabin pressure, temperature, and relative 

humidity.

• Sample a representative number of flights over a period of 1 to 2 years.

• Continue to monitor flights to ensure accurate characterization of air 

quality as new aircraft come online and aircraft equipment ages or is 

upgraded.
Appendix V

Surveillance and Research Programs

Page 56 GAO-04-54 Airliner Cabin Air Quality

• Conduct a program for the systematic collection, analysis, and reporting 

of health data with the cabin crew as the primary study group.1

Research Program The following is a detailed description of the research program, including 

long-standing questions regarding air quality, objectives, and program 

approach.

Outstanding air qualityrelated questions to be 

addressed by the research 

program

• How is the ozone concentration in the cabin environment affected by 

various factors (e.g., ambient concentrations, reaction with surfaces, the 

presence and effectiveness of catalytic converters) and what is the 

relationship between cabin ozone concentrations and health effects on 

cabin occupants?

• What is the effect of cabin pressure altitude on susceptible cabin 

occupants, including infants, pregnant women, and people with 

cardiovascular disease?

• Does the environmental control system (ECS) provide sufficient 

quantity and distribution of outside air to meet the FAA regulatory 

requirements, and to what extent is cabin ventilation associated with 

complaints from passengers and cabin crew? Can it be verified that 

infectious disease agents are transmitted primarily between people who 

are in close contact? Does recirculating cabin air increase cabin 

occupants’ risk of exposure?

• What is the toxicity of the constituents or degradation products of 

engine lubricating oils, hydraulic fluids, and de-icing fluids, and is there 

a relationship between exposures to them and reported health effects 

on cabin crew? How are these oils, fluids, and degradation products 

distributed from the engines into the ECS and throughout the cabin 

environment?

1

On March 4, 2003, FAA announced the creation of a voluntary program for air carriers, 

called the Aviation Safety and Health Partnership Program. Through this program, the 

agency intends to enter into partnership agreements with participating air carriers, which 

will, at a minimum, make data on their employees’ injuries and illnesses available to FAA for 

collection and analysis. 
Appendix V

Surveillance and Research Programs

Page 57 GAO-04-54 Airliner Cabin Air Quality

• What are the magnitudes of exposures to pesticides in aircraft cabins, 

and what is the relationship between the exposures and reported 

symptoms?

• What is the contribution of low relative humidity to the perception of 

dryness, and do other factors cause or contribute to the irritation 

associated with the dry cabin environment during flight?

Research program 

objectives 

• To investigate possible association between specific air quality 

characteristics and health effects or complaints.

• To evaluate the physical and chemical factors affecting specific air 

quality characteristics in aircraft cabins.

• To determine whether FARS for air quality are adequate to protect 

health and ensure the comfort of passengers and crew.

• To determine exposure to selected contaminants (e.g., constituents of 

engine oils and hydraulic fluids, their degradation products, and 

pesticides) and establish their potential toxicity more fully.

Research program approach • Use continuous monitoring data from surveillance program when 

possible.

• Monitor additional air quality characteristics on selected flights as 

necessary (e.g., integrated particulate-matter sampling to assess 

exposure to selected contaminants).

• Identify and monitor “problem” aircraft and review maintenance and 

repair records to evaluate issues associated with air quality incidents.

• Collect selected health data (e.g., pulse-oximetry data to assess arterial 

oxygen saturation of passengers and crew).

• Conduct laboratory and other ground-based studies to characterize air 

distribution and circulation and contaminant generation, transport, and 

degradation in the cabin and the ECS.
Page 58 GAO-04-54 Airliner Cabin Air Quality

Appendix VI

GAO Contacts and Staff Acknowledgments ApendxiVI

GAO Contacts Gerald L. Dillingham, (202) 512-2834

Beverly L. Norwood, (202) 512-2834

Staff 

Acknowledgments

In addition to the individuals named above, Kevin Bailey, Jim Geibel, David 

Ireland, Bert Japikse, Stanley Kostyla, Edward Laughlin, Donna Leiss, and 

Maria Romero made key contributions to this report.
Page 59 GAO-04-54 Airliner Cabin Air Quality

Selected Bibliography

American Society of Heating, Refrigerating and Air-Conditioning Engineers. 

Standard 62-2001, Ventilation for Acceptable Indoor Air Quality. Atlanta, 

GA: 2001.

Barnas, Gary P. Altitude Sickness: Preventing Acute Mountain Sickness. 

Milwaukee, WI: Medical College of Wisconsin, June 4, 1997. 

http://healthlink.mcw.edu/article/907195877.html (accessed June 19, 2003).

California Department of Health Services, Occupational Illness Among 

Flight Attendants Due to Aircraft Disinsection, California Department of 

Health Services, http://www.dhs.ca.gov/ohb/OHSEP/disinsection.pdf

(accessed Nov. 10, 2003).

Centers for Disease Control. Updated Interim Domestic Infection Control 

Guidance in the Health-Care and Community Setting for Patients with 

Suspected SARS, Centers for Disease Control, 

http://www.cdc.gov/ncidod/sars/infectioncontrol.htm (accessed May 13, 

2003).

Environmental Protection Agency. Air Pollution Technology Fact Sheet on 

High Efficiency Particulate and Ultra low Penetration Air Filters.

Research Triangle Park, NC: July 15, 2003.

Environmental Protection Agency. Indoor Air Facts Number 4 (revised): 

Sick Building Syndrome. Washington, D.C.: February 10, 2003.

Federal Aviation Administration. Report to the Administrator on the 

National Research Council Report “The Airliner Cabin Environment and 

the Health of Passengers and Crew.” Washington, D.C.: February 6, 2002. 

Gratz, Norman G., Robert Steffen, William Cocksedge. “Why Aircraft 

Disinsection?” Bulletin of the World Health Organization 78 (8) (2000): 

995-1004. 

Hocking, Martin B. “Indoor Air Quality: Recommendations Relevant to 

Aircraft Passenger Cabins.” American Industrial Hygiene Association 

Journal 59 (1998): 446-454. 

Hocking, Martin B. “Trends in Cabin Air Quality on Commercial Aircraft: 

Industry and Passenger Perspectives.” Reviews on Environmental Health

17, 1 (2002): 1-49. 
Selected Bibliography

Page 60 GAO-04-54 Airliner Cabin Air Quality

Maresh, Carl M., Lawrence E. Armstrong, Stravos A. Kavouras, George J. 

Allen, Douglas J. Casa, Michael Whittlesey, and Kent E. LaGrasse. 

“Physiological and Psychological Effects Associated with High Carbon 

Dioxide Levels in Healthy Men.” Aviation, Space, and Environmental 

Medicine 68, 1 (1997): 41-45.

MedicineNet.com. Definitions of Bacteria, Virus, and Coronavirus, 

MedicineNet.com, http://www.medterms.com/script/main/art.asp? 

ArticleKey=13954 and http://www.medicinenet.com/script/main/art.asp? 

li=MNI&ArticleKey=5997&pf=3 (accessed May 12, 2003) and 

http://www.medterms.com/script/main/art.asp?ArticleKey=22789

(accessed October 14, 2003).

Military Specification. MIL-E-5007D, General Specifications for Aircraft 

Turbojet and Turbofan Engines. 1973.

Nagda, Niren L., Harry E. Rector, Zhidong Li, David R. Space. “Aircraft 

Cabin Air Quality: A Critical Review of Past Monitoring Studies,” Air 

Quality and Comfort in Airliner Cabins, ASTM STP 1393, N. L. Nagda, 

Ed., American Society for Testing and Materials (2000): 215-239. 

National Research Council. The Airliner Cabin Environment: Air Quality 

and Safety. National Academy Press. Washington, D.C.: 1986.

National Research Council. The Airliner Cabin Environment and the 

Health of Passengers and Crew. National Academy Press. Washington, 

D.C.: Distributed electronically December 2001; bound report copyrighted 

2002.

Olsen, Sonja J. et al. “Trasmission of Severe Acute Respiratory Syndrome 

on Aircraft.” The New England Journal of Medicine 349; 25 (2003): 2416-

2422.

Parliament of the Commonwealth of Australia. Rural and Regional Affairs 

and Transport References Committee. Australian Senate Air Safety and 

Cabin Quality in the BAe 146 Aircraft. Canberra: 2000. 

Rayman, Russell B. “Cabin Air Quality.” Aviation, Space and 

Environmental Medicine 73 (2002): 211-215. 
Selected Bibliography

Page 61 GAO-04-54 Airliner Cabin Air Quality

Society of Automotive Engineers. ARP 4418, Procedure for Sampling and 

Measurement of Engine Generated Contaminants in Bleed Air Supplies 

from Aircraft Engines Under Normal Operating Conditions. Warrendale, 

PA: 1995.

Society of Automotive Engineers. ARP 1270, Aircraft Cabin 

Pressurization Control Criteria. Warrendale, PA: 2000.

The House of Lords, Select Committee on Science and Technology. Air 

Travel and Health,5th Report HL Paper 121-I. Session 1999-2000. London: 

2000. 

U.S. Department of Transportation, Office of the Inspector General. 

Further Delays in Implementing Occupational Safety and Health 

Standards for Flight Attendants Are Likely. AV-2001-102. Washington, 

D.C.: September 26, 2001.

U.S. General Accounting Office. SARS Outbreak: Improvements to Public 

Health Capacity Are Needed for Responding to Bioterrorism and 

Emerging Infectious Diseases. GAO-03-769T. Washington, D.C.: May 7, 

2003.

U.S. General Accounting Office. Serve Acute Respiratory Syndrome: 

Established Infectious Disease Control Measures Helped Contain Spread, 

But a Large Scale Resurgence May Pose Challenges. GAO-03-1058T. 

Washington, D.C.: July 30, 2003.

U.S. General Accounting Office. Aviation Safety: Advancements Being 

Pursued to Improve Airliner Cabin Safety and Health. GAO-04-33. 

Washington, D.C.: October 3, 2003.

World Health Organization. International Travel and Health, World Health 

Organization, http://www.who.int/ith/chapter02_01.html (accessed July 24, 

2003).

World Health Organization. Tuberculosis and Air Travel: Guidelines for 

Prevention and Control World Health Organization, 

http://www.who.int/gtb/publications/aircraft/ (accessed Oct. 1, 2003). 

Zitter, Jessica, Peter Mazonson, Dave Miller, Stephen Hulley, and John 

Balmes. “Aircraft Cabin Air Recirculation and Symptoms of the Common 

Cold.” Journal of the American Medical Association 288 (2002): 483-486.

(540060)
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