Allowable Carbon Dioxide Concentration in Transport Category Airplane Cabins

SUMMARY: This amendment revises the standards for maximum allowable

carbon dioxide (CO2) concentration in occupied areas of transport

category airplanes by reducing the maximum allowable concentration from

3 percent to 0.5 percent. This action is in response to a

recommendation from the National Academy of Sciences to review the

CO2 limit in airplane cabins, and provides a cabin CO2

concentration level representative of that recommended by some

authorities for buildings.

EFFECTIVE DATE: January 2, 1997.

FOR FURTHER INFORMATION CONTACT: Kristin L. Larson, FAA, Flight Test

and Systems Branch, ANM-111, Transport Airplane Directorate, Aircraft

Certification Service, 1601 Lind Avenue SW., Renton, Washington 98055-

4056; telephone (206) 227-1760, facsimile (206) 227-1100.

SUPPLEMENTARY INFORMATION:

Background

This amendment is based on Notice of Proposed Rulemaking No. 94-14,

published in the Federal Register on May 2, 1994 (59 FR 22718). As

discussed in that notice, this action reduces the maximum allowable

carbon dioxide concentration level from 3 percent to 0.5 percent.

In October 1984, the Department of Transportation was directed by

Congress (Public Law 98-466) to commission the National Academy of

Sciences (NAS) to conduct an independent study on the cabin air quality

in transport category airplanes. The NAS formed the Committee on

Airliner Cabin Air Quality to study all safety aspects of airliner

cabin air quality, and submitted its report, ``The Airliner Cabin

Environment--Air Quality And Safety,'' to the FAA on August 12, 1986.

One of the recommendations in the report relates to the allowable

carbon dioxide (CO2) concentration in the airplane cabin. This

action is a result of that recommendation. For the purposes of this

rule, the term ``cabin'' is meant to include the passenger cabin, the

flight deck, lower lobe galleys, crew rest areas, and any other areas

occupied by passengers or crew members in a transport category

airplane.

Discussion

Carbon dioxide is the product of normal human metabolism, which is

the predominant source in airplane cabins. The CO2 concentration

in the cabin depends on the ventilation rate, the number of people

present, and their individual rates of CO2 production, which

varies with activity and (to a smaller degree) with diet and health.

Carbon dioxide is also generated by sublimation of dry ice used to cool

food in the galleys, and to preserve certain cargo carried in the cargo

compartments. The carbon dioxide concentration level is frequently used

as an indication of general air quality. At concentrations above a

given level, complaints of poor air quality or ``stuffiness'' begin to

appear.

The maximum CO2 limit of Sec. 25.831(b)(2) of the Federal

Aviation Regulations (FAR) is 3 percent by volume, sea level

equivalent. This 3 percent limit was incorporated into Sec. 4b.371 of

the Civil Air Regulations (CAR) by Amendment 4b6 on March 5, 1952. This

limit was carried over into 14 CFR part 25 when this part was codified

in 1965. This high limit was established to allow for increases in the

carbon dioxide levels in the crew compartment to ensure that, in

airplanes with built-in carbon dioxide fire extinguishing systems, safe

carbon dioxide concentration levels would not be exceeded in the

occupied areas when combating fires in cargo compartments.

The American Conference of Governmental Industrial Hygienists

(ACGIH) has adopted a short-term exposure limit (STEL) for CO2 of

30,000 parts per million (3 percent). The 3 percent limit specified in

part 25 may therefore be satisfactory as a short-term limit, but is

inappropriate for a steady-state condition. However, the NAS Committee

notes in their report that this 3 percent limit is much higher than the

limits adopted by the air conditioning industry for buildings and other

types of interior environments, and recommends that the limit specified

in part 25 be revised to more closely match the currently acceptable

limits. The FAA concurs.

In contrast to the 3 percent limit specified in part 25, the

American Society of Heating, Refrigerating, and Air-Conditioning

Engineers (ASHRAE), in their Standard 62-1989, recommends an outside

air ventilation rate of 15 cubic feet per minute for vehicles. Based on

the ASHRAE calculations, this equates to a CO2 limit of 1,000

parts per million (PPM), or 0.1 percent, if the occupants have a low

physical activity level. As most of the airplane occupants are

passengers who are not active, this is a reasonable parallel. ASHRAE

standards such as the 0.1 percent CO2 limit are frequently quoted

in magazine and newspaper articles when reporting on airliner cabin air

quality.

As CO2 concentration in the air increases, there is an

increase in both the rate and the depth of breathing, reaching twice

the normal rate at 3 percent concentration. At 3 percent concentration,

there is some discomfort; at higher concentrations, headache, malaise,

and, occasionally, fatigue occur, and the air is reported by those

affected as being stale. People can function for long periods of time

at levels of CO2 as high as 1 percent (as in nuclear submarines),

but it is generally felt by ASHRAE that 0.1 percent is a better limit.

This value, however, is based on the dissipation of smoke and odors and

not on health considerations. As noted above, according to ASHRAE

Standard 62-1989, a steady-state CO2 concentration of 0.1 percent

would require a fresh-air ventilation rate of 15 cubic feet per minute

(cfm) per person. In the previous edition of the standard (62-1981),

ASHRAE recommended a limit of 0.5 percent for office buildings and

other occupied spaces, but suggested that 0.25 percent would provide an

additional safety factor. The ASHRAE standard is intended to be used as

a comfort standard rather than a health and safety standard. ASHRAE has

recognized that the 0.1 percent CO2 concentration limit may not be

appropriate for airliner cabins, and has formed an aviation

subcommittee, the charter of which is to develop a transport airplane

cabin air quality standard. While this subcommittee is not an FAA

advisory committee, industry often uses ASHRAE standards in designing

systems. The subcommittee will sponsor research studies to determine

the quality of the ambient air and quantify the correlation between

measurable contaminants and passenger perception of air quality. As

noted above, ASHRAE standards were intended to be used for buildings

rather than vehicles such as airplanes, and they consider it

appropriate to establish a new standard for airplanes at this time.

The Occupational Safety and Health Administration (OSHA), in

Sec. 1910.1000 of part 1910 (CFR 29), sets an interim (transitional)

limit for CO2 at 5,000 ppm or 0.5 percent, with a final rule limit

of

[[Page 63953]]

10,000 ppm or 1 percent, effective December 31, 1993. The increase to 1

percent is apparently in deference to operators of commercial bakeries

and breweries, both of which generate a significant amount of CO2

in their processes. The FAA does not believe it is appropriate to base

the allowable CO2 concentration in transport category airplanes on

the needs of specific manufacturing processes. Other commercial

enterprises have no difficulty in meeting the existing OSHA limit of

0.5 percent.

The American Conference of Governmental Industrial Hygienists, in

its ``Documentation of the Threshold Limit Values and Biological

Exposure Indices--Sixth Edition,'' also recommends 0.5 percent as a

limit, but ACGIH recommends this value as a time-weighted average limit

for repeated daily exposure by workers. The FAA is adopting this value

as a limit. A concentration limit of 0.5 percent is considered to be

appropriate because there are no documented safety or health benefits

associated with the establishment of a lower value.

Copies of the pertinent documents from ASHRAE, OSHA, and ACGIH have

been placed in the public docket for this rulemaking.

Cabin ventilation provides air for dilution of airborne

contaminants, and supplies oxygen for passengers and crew. Oxygen

requirements for sedentary adults can be met with a fresh-air

ventilation rate of only 0.24 cubic feet per minute (CFM) per person.

Ventilation rates for current transport category airplanes vary from a

low of approximately 7 cfm per person (with one or more air

conditioning packs turned off for economy), to over 20 cfm per person

(which includes up to 50 percent filtered, recirculated air). Thus,

even at the lowest ventilation rates available on current airplanes,

there is no significant reduction in the percentage of oxygen, or

increase in the amount of water vapor in the cabin due to respiration.

However, the design parameters for the ventilation systems are driven

by operation on the ground during hot days. Contamination of air with

CO2 varies inversely with the ventilation rate, because CO2

production by sedentary people is nearly constant.

In order to bring the maximum allowable carbon dioxide

concentration into concert with accepted modern limits, this rule

adopts a new maximum allowable carbon dioxide concentration of 0.5

percent. According to ASHRAE, for sedentary people this concentration

can be maintained by a fresh air flow rate of 2.25 cfm per person,

which is lower than that currently measured in transport category

airplanes.

Section 25.831(b)(2) currently reads, ``Carbon dioxide in excess of

three percent . . . is considered hazardous in the case of

crewmembers.'' The health and comfort considerations discussed earlier

are equally valid for passengers. Therefore, the FAA has removed the

reference to crewmembers. In addition, Sec. 25.831(b)(2) also specifies

that, ``Higher concentrations of carbon dioxide may be allowed in crew

compartments if appropriate protective breathing equipment is

available.'' This sentence was incorporated when the 3 percent limit

was established in CAR 4b.371 in 1952. As noted above, the origins of

the 3 percent limit are unclear, but it is likely that the limit was

set at this high level to account for the discharge of CO2 fire

extinguishers in the flight deck, cabin, or cargo compartment. This

thesis is supported by the mention of protective breathing in the

existing rule. However, most CO2 extinguishers have been replaced

by Halon or other types of fire extinguishers. Further, the rule is not

intended to cover the short-duration rise in CO2 concentration

that would accompany discharge of a fire extinguisher. Therefore, that

sentence in Sec. 25.831(b)(2) is removed because it is no longer

considered necessary or appropriate.

Section 25.831(b)(1) specifies a limit for carbon monoxide (CO)

concentration of 1 part in 20,000 parts air (0.005 percent). This limit

is the same as currently recommended by ASHRAE and the Occupational

Safety and Health Administration (OSHA), and therefore this action does

not change this limit.

Discussion of Comments

Comments were received from foreign and domestic airplane

manufacturers through their respective trade associations, foreign

airworthiness authorities, trade organizations representing flight

attendants and US and Canadian pilots, one US operator, an organization

representing airline passengers, and several individuals.

Two commenters support the proposed change as it appears in the

notice. Five commenters wrote to register dissatisfaction with the air

quality on airplanes, mentioning both comfort for passengers and

illnesses believed to be associated with inadequate fresh air flow. One

commenter urges the FAA to ``make the changes necessary so that we can

fly in reasonable health.'' Another commenter is of the opinion that

``very poor recirculation of air in planes is costing a lot of money in

medical terms, not to mention suffering.'' Two commenters state that

the FAA should perform tests on existing airplanes. The FAA infers from

these comments that the commenters are in favor of revising the

requirements to ensure acceptable air quality. Studies conducted by the

FAA and others do not indicate that there is a health hazard associated

with cabin air quality. As none of these commenters suggest specific

changes to the proposal, there are no changes to the final rule in

response to the comments.

One commenter misread the proposal as to the allowable

concentration currently in the regulations and that proposed in the

notice. This commenter states that the standards for cabin air quality

should be better than the standard set for buildings, because the

population density is higher in an airplane, and in an office building

people may exit periodically. While the commenter made no specific

recommendations, the FAA infers that the commenter advocates lower

limits than proposed in the notice. The FAA does not concur that these

factors justify a requirement for a lower carbon dioxide concentration.

The existing standards are all based on a ventilation rate per

occupant. To meet the same requirements with a higher population

density, a greater volume of fresh air ventilation is required. It is

not clear how this concern can be addressed by the airline industry or

the FAA when the studies conducted indicate that the air quality in

airplanes does not present a hazard to the health of the travelers.

Two commenters state that the proposed 0.5 percent carbon dioxide

concentration limit is too high. One commenter suggests that the FAA

``set a limit of 800 parts per million (ppm), the same level proposed

by the Occupational Safety and Health Administration for indoor air

quality,'' which is 0.08 percent. Another commenter recommends that the

FAA adopt an airplane cabin carbon dioxide maximum concentration of 0.1

percent. Both commenters express concerns about the effect of higher

carbon dioxide levels and increased recirculation on the spread of

disease and on people with respiratory difficulties. One commenter

notes that concentrations above 0.1 percent may result in complications

for persons with an existing respiratory difficulty, noting that 12.4

million Americans have asthma.

Another commenter states that flight attendants who are repeatedly

exposed to carbon dioxide levels above 0.1 percent develop a tolerance,

while passengers do not. Another commenter states that flight

attendants are at a greater risk because of this same

[[Page 63954]]

repeated exposure. The FAA does not concur with these views. The

documented studies contained in the docket for this rule indicate that

the air quality currently present in the airliner cabins is comparable

to that found in other indoor environments. The OSHA recommendation

proposed in the Federal Register on April 5, 1994 (59 FR 16035), which

has not been adopted at this time, addresses the carbon dioxide

concentration as a comfort factor to be used in determining the need to

verify proper operation of heating and ventilating equipment. Further,

this proposal addresses non-industrial work environments and

specifically excludes vehicles. A copy of the OSHA proposed amendment

has been included in the docket for this rulemaking. There is no

evidence that concentrations up to 0.5 percent present any health

hazard in terms of general health or the spread of disease. In the

economic evaluation conducted by the FAA, the higher costs associated

with requiring a carbon dioxide concentration limit below 0.5 percent

do not present a favorable cost/benefit ratio and cannot be justified.

Further, there appears to be no specific concentration level, even at

levels down to 0.1 percent, at which at least some passengers might not

be affected. This rule, which will be contained in the airworthiness

requirements of part 25, is intended to provide safe flight and landing

for transport category airplanes. Because carbon dioxide in

concentrations below 0.5 percent do not have adverse safety effects,

the FAA has determined that a concentration limit of 0.5 percent

provides a reasonable balance between cost and benefit, and provides a

significant improvement over the existing allowable concentration.

Several commenters note that the OSHA and ACGIH standards are for

an average concentration over a specific time period. ACGIH, for

instance, recommends 5,000 ppm (0.5 percent) as a time-weighted average

for a normal 8-hour workday or a 40-hour workweek. They note in their

1991 report that Australia, Germany, Sweden, and the United Kingdom all

recommend a time-weighted value of 0.5 percent for carbon dioxide

concentration. OSHA's limits also reflect the average airborne exposure

in any 8-hour work shift of a 40-hour workweek. The FAA infers that the

commenters advocate providing both a time weighted and a short term

concentration limit. The FAA does not concur that the carbon dioxide

level should be averaged over the entire flight for several reasons.

Many flights exceed eight hours in duration, and the occupants are not

able to leave the airplane as are workers in an office. Also, there are

added stresses involved in being in an airplane cabin. The cabin

pressure altitude is significantly above sea level, usually at 6,000 to

8,000 feet. The relative humidity is lower than is usually found in

ground-based environments. There are unquantified stresses associated

with being in a crowded airplane cabin. Many people experience anxiety

from the mere fact that they are aloft. While most of these factors

cannot be controlled, the FAA has determined that the present part 25

limit on carbon dioxide concentration does not reflect industry

standards and should be reduced accordingly.

One commenter suggests that the average concentration should be

limited to 0.5 percent, but ``a limit of 3 percent by volume (sea level

concentration) may be allowed for short term durations.'' The commenter

points out that the 3 percent limit for short term durations

corresponds to the short term exposure limit (STEL) adopted by the

ACGIH, and having two limits should be similar to the two limits on

cabin ozone concentration specified in Sec. 25.832. Again, the FAA does

not concur. The adverse health and safety effects of ozone are defined

in available literature and Sec. 25.832 of the FAR addresses that

concern. There appears to be no reason to phrase the two requirements

similarly.

The FAA has determined, however, that some short term excursions to

values higher than 0.5 percent at some locations in the airplane may

occur during normal, inflight operations when airplane pressurization

and air conditioning systems are controlling the environment in the

cabin. One commenter notes that the area in close proximity to the

galley may experience higher carbon dioxide levels because meals are

often cooled by dry ice, which releases gaseous carbon dioxide. Another

commenter states that cabin air can be contaminated on the ground by

exhaust ingestion or self ingestion during certain wind conditions. The

FAA does not agree that this presents a problem. In one survey,

conducted by the Harvard University School of Public Health, carbon

dioxide levels were measured during boarding and deboarding operations.

The typical levels reported were 2,000 to 2,550 ppm, or 0.2 to 0.25

percent, well below the 0.5 percent proposed by the FAA. However, the

FAA does concur that it is not appropriate for the certification

standards to apply to operations on the ground when the airplane

systems are not operating (e.g., at the gate or during ``push-back'').

The final rule is changed to reflect this determination.

The same commenter expresses concern that the use of carbon dioxide

hand-held fire extinguishers in the cabin could result in local

concentrations exceeding 0.5 percent, noting that the present Halon

extinguishers might be replaced by carbon dioxide devices now that

production of Halon is banned, and suggests a higher short-term

exposure limit. The FAA does not concur that this is a justification

for a higher limit. The use of carbon dioxide fire extinguishers is not

envisioned, although there are no prohibitions against their use in

airplanes. When Halon is no longer available, the replacement

extinguishers will be required to be safe in the concentrations

predicted for use in occupied areas. Further, the use of fire

extinguishers in the cabin is, by its nature, an emergency situation.

This is not, in the context of the previous paragraph, normal in-flight

operations. Therefore, there appears to be no need for the higher limit

on carbon dioxide.

Two commenters state that the utilization of building criteria for

establishing carbon dioxide concentration limits for airplane cabins is

not appropriate. Both commenters add that the statement in the proposal

that concentrations above 0.5 percent are hazardous is not justifiable.

The FAA concurs with the general statement that carbon dioxide

concentrations above 0.5 percent may not be hazardous for most people.

Many standards in use today allow higher concentrations. As noted by

one commenter, the World Health Organization considers 12,000 ppm (1.2

percent) to be a safe level. In any case, the final rule has been

changed and no longer contains the word ``hazardous.'' Both of these

commenters note that the rule, as proposed, would limit carbon dioxide

concentrations in lower lobe galleys, accessible cargo compartments

where animals are carried, cockpits, and other occupied areas. They

express concern that local carbon dioxide concentrations in the galley

areas where food is cooled with dry ice might exceed 0.5 percent. The

FAA concurs in part with these comments. The ventilation requirements

associated with this rule change are intended to address areas that are

normally occupied. Cargo compartments accessible in flight, whether in

all cargo or ``combi'' airplanes with main deck cargo compartments, are

not ``normally occupied.'' The final rule has been changed to reflect

this determination.

One commenter disagrees with the statement in the preamble of the

proposed rule that ``This low ventilation rate is also sufficient to

dissipate the water vapor * * *,'' noting that water

[[Page 63955]]

buildup in insulation blankets is significant with present airplane

fresh air inflow rates, especially in hot day ground conditions. The

FAA concurs and the statement has been removed from the preamble. In

stating this view, the commenter did not recommend any changes in the

rule.

One commenter states that the term ``sea level equivalent'' should

be clarified. The commenter suggests that the clarification include

technical and/or medical rationale, including referenced sources, and

provide an explanation of the methodology by which this value is to be

calculated. If this rationale is not provided, the commenter states

that the FAA should delete the phrase. The FAA does not concur that the

term ``sea level equivalent'' is not defined, although the definition

appears in reference to another gas. In FAA Advisory Circular 120-38,

``Transport Category Airplanes Cabin Ozone Concentrations,'' sea level

equivalent is defined as ``* * * concentration in ppmv referenced to

standard conditions of 25 deg. C and 760 millimeters of mercury

pressure.'' Based on this definition, and calculations provided in the

AC, the maximum measured concentration, sea level equivalent, for a

cabin altitude of 8,000 feet would be 0.5 percent multiplied by 0.74

(the ratio of air pressure at 8,000 feet to air pressure at sea level),

or 0.37 percent. Values of this ratio for other cabin altitudes are

provided in the AC. As the term sea level equivalent is defined, the

rule is adopted as proposed.

The same commenter also notes that the statement in the preamble

that control of carbon dioxide buildup due to respiration is the factor

that dictates the design parameters for ventilation systems is

incorrect. Operation on the ground during high ambient temperatures

generally dictates the ventilation system design parameters. The FAA

concurs and the preamble has been changed accordingly.

One commenter recommends that the new standards for carbon dioxide

concentration not be applied to all-cargo airplanes. The commenter

notes that measured carbon dioxide levels on the flight decks of these

airplanes are well below both the current standard and that proposed in

Notice 94-14. The commenter goes on to state that lowering the limit on

carbon dioxide is a comfort issue, and would place a burden on the

manufacturers of transport category airplanes that is not commensurate

with any safety benefit that might result. The FAA does not concur. As

noted elsewhere in this preamble, the FAA has determined that the

existing concentration limit of 3 percent for carbon dioxide is not

appropriate because many passengers and crewmembers are adversely

affected at that level. The lower levels adopted by this amendment will

provide a standard that, when met, will ensure that passengers and

crewmembers, including those on all-cargo airplanes, will not be

subjected to levels of carbon dioxide that would reduce their ability

to perform their assigned duties. There are no costs associated with

lowering the limit as proposed.

With the exception of the changes noted above, this final rule is

adopted as proposed in Notice 94-14.

Regulatory Evaluation

Changes to Federal regulations must undergo several economic

analyses. First, Executive Order 12866 directs Federal agencies to

promulgate new regulations or modify existing regulations only if the

potential benefits to society justify its costs. Second, the Regulatory

Flexibility Act of 1980 requires agencies to analyze the economic

impact of regulatory changes on small entities. Finally, the Office of

Management and Budget directs agencies to assess the effects of

regulatory changes on international trade. In conducting these

assessments, the FAA has determined that this rule: (1) will generate

benefits exceeding its costs and is not ``significant'' as defined in

Executive Order 12866; (2) is not ``significant'' as defined in DOT's

Policies and Procedures; (3) will not have a significant impact on a

substantial number of small entities; and (4) will not constitute a

barrier to international trade. These analyses, available in the

docket, are summarized below, following FAA's disposition of comments

on the economic aspects of the NPRM.

Response to Comments

One commenter calculates that it would cost about $0.076 per person

per hour to provide 100 percent fresh air in the cabin of a typical

300-seat widebody airplane. The FAA disagrees with this commenter and

estimates that the cost of 100 percent fresh air would be $0.095 per

person per hour.

Another commenter states that the FAA did not account for the

potential costs of applying the rule to all occupiable sections of the

airplane because it evaluated only the passenger cabin area and ignored

the flight deck and lower lobe galleys. The FAA concurs in part with

this comment. The carbon dioxide concentration requirements are

intended to apply to areas that are normally occupied. The final rule

has been changed to reflect this intent. Thus, the commenter's

statement does not alter the FAA's economic analysis.

Another commenter states that the FAA did not evaluate the

possibility that ground-air contamination (ingestion of other

airplanes' exhausts) may temporarily push the CO2 level above the

0.5 percent limit. The FAA does not agree that this presents a problem.

In one survey, conducted by the Harvard University School of Public

Health, CO2 levels were measured during boarding and deboarding

operations. The typical levels reported were 0.2 percent to 0.25

percent, well below the 0.5 percent in this rule. However, the FAA does

concur that it is not appropriate for the certification standards to

apply to ground operations when the airplane systems are not

functioning. As a result, the final rule has been changed to reflect

this determination. Consequently, there is no economic impact as a

result of this remote possibility.

Two commenters state that if live animal cargo areas are included

under the definition of ``inhabited'' areas, there would be

considerable potential costs. The FAA partly concurs with these

comments in that cargo compartments accessible in flight, whether in

all cargo or ``combi'' airplanes with main deck cargo compartments, are

not normally occupied and the final rule has been changed to reflect

this determination. As a result, there is no economic impact from

excluding live animal cargo areas from this rule.

Costs

Airplane cabin CO2 levels can be reliably calculated from the

number of passengers and the ventilation rate. In addition, engineering

analyses have determined the amount of fuel used to provide a unit

ventilation rate. These functional relationships allow the calculation

of the costs to maintain a given cabin CO2 level. The FAA

estimates that the 3 percent CO2 limit under the current rule

costs about 0.27 cents per person per hour while the new 0.5 percent

limit will cost about 1.7 cents per person per hour. Thus, the amended

limit constitutes a 1.43 cent increase per person per hour, or about

$4,475 per (newly certificated) airplane per year.

In point of fact, however, the ventilation rates in current

transport category airplanes currently maintain cabin CO2 levels

below 0.5 percent. As the FAA expects that the minimum ventilation

rates of future aircraft designs will also maintain CO2 levels

below 0.5 percent in order to control

[[Page 63956]]

odors, temperature, water vapor, etc., no actual incremental costs or

benefits will result from the rule change. However, codification of

this limit will ensure that future designs maintain the 0.5 percent

level.

Benefits

Although outdoor air contains CO2 at the 0.03 percent level,

CO2 may produce respiratory center stimulation, mild narcotic

effects, and asphyxiation under high levels and high exposure duration.

At concentrations of 2 to 3 percent, CO2 can produce headaches,

breathing difficulty, and increases in blood pressure and pulse. By

comparison, no ill-effects have been observed at the 0.5 percent level.

Cost-Benefit Comparison

From a strict cost-benefit evaluation of the rule change itself,

isolated from actual practice, the FAA concludes that it would cost

about 1.43 cents per person per hour to increase the ventilation to

reduce cabin CO2 levels from 3 percent to 0.5 percent. By

comparison, this reduction eliminates the cabin CO2 levels known

to produce headaches, breathing difficulty, and increases in blood

pressure and pulse. While no precise economic value has been assigned

to the benefit from avoiding these ill effects, the FAA has determined

that they are worth more than 1.43 cents per person per hour.

Regulatory Flexibility Determination

The Regulatory Flexibility Act of 1980 (RFA) was enacted by

Congress to ensure that small entities are not unnecessarily or

disproportionately burdened by Government regulations. The RFA requires

a Regulatory Flexibility Analysis if a proposed or final rule would

have a significant economic impact, either detrimental or beneficial,

on a substantial number of small entities. FAA Order 2100.14A,

Regulatory Flexibility Criteria and Guidance, prescribes standards for

complying with RFA review requirements in FAA rulemaking actions. The

Order defines ``small entities'' in terms of size, ``significant

economic impact'' in terms of annualized costs, and ``substantial

number'' as eleven or more and which is more than one-third of the

small entities subject to the proposed or final rule.

The final rule would affect manufacturers of transport category

airplanes produced under future new airplane type certificates. For

manufacturers, Order 2100.14A defines a small entity as one with 75 or

fewer employees. Since no part 25 airplane manufacturer has 75 or fewer

employees, the rule would not have a significant economic impact on a

substantial number of small entities.

International Trade Impact Assessment

As the certification rules apply to both foreign and domestic

manufacturers that market airplanes in the United States, neither group

will receive a competitive advantage. As no incremental compliance

costs are expected, there will be no competitive trade disadvantage or

advantage for U.S. manufacturers in foreign markets or for foreign

manufacturers in the United States.

Federalism Implications

The regulations adopted herein will not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the various levels of government. Therefore, in

accordance with Executive Order 12612, it is determined that this final

rule will not have sufficient federalism implications to warrant the

preparation of a Federalism Assessment.

International Civil Aviation Organization (ICAO) and Joint Aviation

Regulations

In keeping with U.S. obligations under the Convention on

International Civil Aviation , it is FAA policy to comply with ICAO

Standards and Recommended Practices to the maximum extent practicable.

The FAA has determined that this rule does not conflict with any

international agreement of the United States.

Paperwork Reduction Act

In accordance with the Paperwork Reduction Act of 1990 (44 U.S.C.

3501 et seq.), there are no reporting or recordkeeping requirements

associated with this rule.

Conclusion

Because the revised standards for maximum allowable carbon dioxide

concentration are not expected to result in a substantial economic cost

or have a significant adverse effect on competition, the FAA has

determined that this final rule is not significant under Executive

Order 12866. In addition, the FAA has determined that this action is

not significant as defined in Department of Transportation Regulatory

Policies and Procedures (44 FR 11034, February 26, 1979). Since no

actual incremental costs are expected to be incurred to comply with the

requirements of this rule, the FAA certifies, under the criteria of the

Regulatory Flexibility Act, that this regulation will not have a

significant economic impact, positive or negative, on a substantial

number of small entities. A copy of the regulatory evaluation prepared

for this final rule has been placed in the public docket. A copy may be

obtained from the person identified under the caption, FOR FURTHER

INFORMATION CONTACT.

List of Subjects in 14 CFR Part 25

Aircraft, Aviation safety, Reporting and recordkeeping

requirements.

Adoption of the Amendment

In consideration of the foregoing, the Federal Aviation

Administration (FAA) amends 14 CFR part 25 of the Federal Aviation

Regulations (FAR) as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

1. The authority citation for part 25 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.

2. Section 25.831 is amended by revising paragraph (b)(2) to read

as follows:

Sec. 25.831 Ventilation.

* * * * *

(b) * * *

(2) Carbon dioxide concentration during flight must be shown not to

exceed 0.5 percent by volume (sea level equivalent) in compartments

normally occupied by passengers or crewmembers.

* * * * *

Issued in Washington, D.C., on November 21, 1996.

Linda Hall Daschle,

Acting Administrator.

[FR Doc. 96-30525 Filed 11-29-96; 8:45 am]

BILLING CODE 4910-13-P