28684 Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 26070, Amendment No. 25–87]

RIN 2120–AB18

Standards for Approval for High

Altitude Operation of Subsonic

Transport Airplanes

AGENCY: Federal Aviation

Administration (FAA), DOT.

ACTION: Final rule.

SUMMARY: This amendment to the

Federal Aviation Regulations (FAR)

specifies airplane and equipment

airworthiness standards for subsonic

transport airplanes to be operated up to

an altitude of 51,000 feet. This action is

prompted by an increase in the number

of applications received to raise the

maximum certificated operating altitude

for transport category airplanes, and is

intended to ensure an acceptable level

of safety for airplanes operated at high

altitudes.

EFFECTIVE DATE: July 5, 1996.

FOR FURTHER INFORMATION CONTACT:

Robert C. McCracken, Flight Test and

Systems Branch, ANM–111, Transport

Airplane Directorate, Aircraft

Certification Service, 1601 Lind Avenue

Southwest, Renton, Washington 98055–

4056; telephone (206) 227–2118.

SUPPLEMENTARY INFORMATION:

Background

This amendment is based on Notice of

Proposed Rulemaking (NPRM) No. 89–

31, which was published in the Federal

Register on November 22, 1989 (54 FR

48538). The notice proposed to upgrade

airplane and equipment airworthiness

standards for subsonic transport

airplanes to be operated up to an

altitude of 51,000 feet, and it was based

on special conditions that have been

used for type certification for many

years.

Current policy for FAA rulemaking

projects is to endeavor to achieve

harmonization with the Joint

Airworthiness Authorities (JAA) and

other airworthiness authorities through

the Aviation Rulemaking Advisory

Committee (ARAC) and its

harmonization working groups.

Although this rulemaking project has

not been the subject of a harmonization

working group activity, because it was

initiated prior to the time harmonization

became a high priority with the FAA

and JAA, comments received from the

JAA members were addressed in this

amendment.

As noted in Notice 89–31, the higher

operational altitudes made feasible by

the advent of turbojet transport

airplanes introduced certain risks with

respect to crew and passenger breathing

that were not experienced with earlier

propeller-driven airplanes. Accordingly,

certification standards were developed

in the early 1950s to permit safe

operation of early turbojet transport

airplanes up to certain maximum

operating altitudes—typically 41,000 or

42,000 feet. Subsequent to the type

certification of the early turbojet

transport airplanes, applicants

requested approval to operate certain

later airplanes at higher altitudes. These

were in most cases small ‘‘executive’’

transport airplanes, and the requested

altitudes ranged up to 51,000 feet.

The operation of these airplanes at

altitudes above 40,000 feet usually

involved a number of novel or unusual

design features that were not addressed

by the airworthiness requirements in the

current regulations. In order to ensure a

level of safety equivalent to that

established by part 25 of the FAR,

§§ 21.16 and 21.101 of part 21 require

that additional standards be developed

in the form of special conditions and

that compliance with the special

conditions be demonstrated.

The regulatory changes adopted by

this amendment codify and consolidate

the different high-altitude criteria that

have been made applicable by special

conditions to previously certificated

subsonic transport airplanes. In

addition, the changes acknowledge a

human physiological limit of 34,000 feet

(see Glossary), the level above which

persons not using supplementary

oxygen are in serious peril. To assure

compatibility or equivalency with other

provisions of part 25, which were

amended after many of the special

conditions discussed herein were

implemented, these changes are written

so that terminology relating to the

probability of certain failures is

consistent with those other provisions.

Generally, the intent of those provisions

is to recognize that the degree of hazard

of any given failure is inversely related

to the probability of occurrence of that

failure. Failures that are considered to

be catastrophic must be shown to be

extremely improbable, and hazardous

failures must be shown to be improbable

(see Glossary). Examples of these terms

are found in §§ 25.671, 25.672, and

25.1309.

It must be noted that widespread

operation of transport category airplanes

at altitudes greater than 51,000 feet is

not currently envisioned. A major factor

in an approval for operation up to

51,000 feet is an emergency descent

during a decompression, which must be

shown to result in a maximum cabin

altitude of no more than 40,000 feet.

Accordingly, the changes adopted in

this amendment have been developed to

provide adequate standards for safe

operation of such airplanes up to 51,000

feet. Should an applicant seek approval

to operate a transport category airplane

above that altitude, additional standards

may be needed for safe operation. If so,

appropriate special conditions would be

adoptive to require compliance with

those standards.

The changes in this amendment

involve ventilation, cabin cooling,

pressurization and pressure vessel

integrity, and oxygen equipment. The

following paragraphs describe the

changes, and the reasons for the

changes, in the regulations incorporated

with the adoption of this amendment.

The comments received in response to

Notice 89–31, the disposition of the

comments, and, when applicable, the

effect of the comments on the changes,

are discussed immediately following

this section.

1. Ventilation (Airflow and

Contamination)

Prior to this amendment, § 25.831(a)

required each passenger and crew

compartment to be ventilated and each

crew compartment to have enough fresh

air to enable crewmembers to perform

their duties without undue discomfort

or fatigue. For the crew compartment, a

minimum of 10 cubic feet of fresh air

per minute per crewmember was

required. Section 25.1309 (specifically

§§ 25.1309(b)(2) and 25.1309(d)(3))

requires that the effects on occupants of

any failures of required systems be

analyzed, but § 25.1309 is a general rule

and does not specifically address

minimum airflow requirements.

The executive transport special

conditions that have been applied in the

past supplemented § 25.831(a) by

specifying that the minimum fresh

airflow of 10 cubic feet per minute (cfm)

per crewmember was to be provided to

each occupant during normal operation.

The special conditions also required

that each occupant be furnished with

enough uncontaminated air to provide

reasonable comfort during normal

operating conditions and also after any

probable failure of any system that

would adversely affect the cabin

ventilation air. This rule amends

§ 25.831 to include the additional

airflow requirements contained in

previous special conditions, stipulating

that the ventilation system must be

designed to provide 10 cfm (converted

to pounds of air) for each occupant.
Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations 28685

Some airplanes now incorporate

ventilation systems in which fresh air is

augmented with conditioned and

recirculated air. Section 25.831(a) as

amended permits a ventilation system

that uses a mixture of the minimum

amount of fresh air and any desired

quantity of recirculated air that is

shown to be uncontaminated by odors,

particulates, or gases. In this regard, the

minimum amount of fresh air is

specified by weight rather than by

volume in order to provide a parameter

independent of altitude. Ten cubic feet

of standard air at a typical cabin altitude

of 8,000 feet and typical cabin

temperature of 75°F. weighs

approximately 0.55 pounds. This rule

amends § 25.831 to include the

additional airflow requirements as

noted above. This standard is equivalent

to the present requirement for

crewmembers.

2. Cabin Cooling

During the Supersonic Transport

(SST) review in the 1960s, it was noted

that certain pressurization system

failures, whether considered by

themselves or in combination with the

use of hot ram air for emergency

pressurization, could lead to cabin

temperatures exceeding human

tolerance. The FAA therefore concluded

that any failure or combination of

failures that could lead to temperature

exposures that would cause undue

discomfort must be shown to be

improbable (see Glossary). Minor

corrective actions (e.g., selection of

alternate equipment or procedures)

would be allowed if necessary for

probable failures. The FAA also

concluded that any failure or

combination of failures that could lead

to intolerable temperature exposures

must be extremely improbable. Major

corrective actions (e.g., emergency

descent, configuration changes) would

be allowed for an improbable failure

condition. Temperature limits were

incorporated into the special conditions

imposed on executive transport

airplanes when approved for high

altitude operation. The SST and

executive transport special conditions

contained two graphs which explained

the requirements for the probable and

improbable cases. In formulating this

amendment, the FAA has determined

that the public interest is served by

adopting the time-temperature limits

associated with improbable failure

conditions, and they are adopted as a

new § 25.831(g). This amendment does

not allow the time of exposure at any

given temperature to exceed the values

given in the associated graph.

3. Pressurization and Pressure Vessel

Integrity

Section 25.365(d), increases the

fuselage pressure relief valve safety

factor of 1.33 by 25 percent to 1.67,

codifying the standard that was

originally contained in the SST special

conditions. This increased structural

safety factor was also included in the

executive transport special conditions to

reduce the likelihood of structural

failure and to limit the size of the

opening if a failure occurs. It is included

in this amendment for this reason.

The FAA had considered proposing

both pressurization standards similar to

those previously required by the special

conditions for executive transport and

separate standards similar to those

required for large transport airplanes.

The separate standards were thought to

be necessary because of the inherent

differences in pressurized volume of the

two types of transports, and the belief

that a larger airplane may decompress

more slowly than a smaller airplane.

Upon further review, this approach was

deemed impractical because certain

larger transport airplanes have

decompression characteristics more

analogous to smaller transport airplanes

and vice versa. Therefore, this

amendment applies the same standard

to all transport airplanes.

It should be noted that the special

conditions required consideration of

specific failures, which are addressed

later in this discussion. Subsequent to

the issuance of the special conditions,

reliability, probability, and damage

tolerance concepts addressing other

failures and methods of analysis were

incorporated into part 25. This

amendment allows the use of these

additional methods of analysis and

failure considerations.

The earlier executive transport special

conditions required a pressure demand

mask (see Glossary). Later special

conditions included, pursuant to the

recommendations of the FAA Civil

Aeromedical Institute (CAMI), a

requirement for a pressure demand

mask with a mask-mounted regulator

(see Glossary). The requirement for the

use of the same type of equipment is

adopted by this amendment.

The objective of the amended

§ 25.841(a) (pressurization) when

applied in conjunction with amended

§ 25.1447(c) (oxygen equipment) is to

provide airworthiness standards that

allow subsonic airplanes to operate at

their maximum achievable altitudes.

This is the highest altitude for which an

applicant chooses to demonstrate that,

after decompression caused by a single

failure or combination of failures that

are not shown to be extremely

improbable: (1) the flightcrew will

remain alert and be able to fly the

airplane; (2) the cabin occupants will be

protected from the effects of hypoxia;

and (3) in the event that some occupants

do not receive supplemental oxygen,

they nevertheless will be protected

against permanent physiological

damage.

Section 25.841(a)(1) as amended is

equivalent to the existing § 25.841(a)

with the exception of editorial changes

and elimination of the words

‘‘reasonably’’ and ‘‘or malfunctions.’’

The ‘‘probable’’ failure criteria are the

same as those contained in § 25.1309.

The term ‘‘failure conditions’’ has been

added to this section to clarify that

failure combinations that lead to a

probable depressurization event must

also be considered.

Section 25.841(a)(2) as amended

limits exposure of the airplane

occupants, after decompression, to a

cabin altitude no greater than 40,000

feet. This requirement is unchanged

from that previously established in part

25 for certification of transport category

airplanes using diluter demand

(flightcrew) and continuous flow

(passenger) oxygen equipment (see

Glossary).

Section 25.841(a)(2) as amended is a

combination of the later executive

transport high altitude special

conditions and § 25.1309, i.e., the

degree of the hazard must be inversely

related to the probability of the failure

condition. The amended § 25.841(a)(2)

was developed from the

recommendations of CAMI and is based

on the concept of ‘‘Time of Safe

Unconsciousness’’ documented by

James G. Gaume (see Reference 1). The

use of continuous-flow oxygen masks by

passengers following rapid

decompression to cabin altitudes above

34,000 feet may fail to provide

protection from hypoxia, as noted in the

discussion under Paragraph 4.

‘‘OXYGEN EQUIPMENT,’’ below.

Additionally, some passengers might be

exposed to high cabin altitudes

following decompression without the

use of oxygen. A few passengers may

lose consciousness at 34,000 feet cabin

altitude, and more may lose

consciousness at greater altitudes even

with the use of continuous-flow oxygen

equipment. Exposure to cabin altitudes

in excess of 25,000 feet for more than 2

minutes without supplemental oxygen

may cause permanent physiological

(brain) damage. Therefore, in order to

demonstrate compliance with this rule,

approved emergency descent

procedures and a cabin altitude analysis

must be prepared to ensure that these
28686 Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations

altitude limits are not exceeded

following a decompression failure that

is not shown to be extremely

improbable.

Section 25.841(a)(3) as amended

describes the failure conditions that

must be considered in evaluating cabin

decompression. Possible modes of

failure to be evaluated include

malfunctions and damage from external

sources such as tire burst, wheel failure,

uncontained engine failure, engine fan,

compressor or turbine multi-blade

failure, and loss of antennas. Sections

25.1309 and 25.571, and associated

advisory material, provide guidance in

determining the sources of failure.

System failures (both latent and active),

combinations of system failures, system

failures combined with pressure vessel

leaks, system failures causing engine

shutdown, uncontained engine failures

causing structural and system damage,

and structural failures without system

failures must all be evaluated. Typical

systems include engine bleed air

systems, air conditioning systems,

power sources, outflow valves and

control systems. Failures which expose

the occupants to cabin altitudes in

excess of either 25,000 feet for more

than 2 minutes or 40,000 feet for any

amount of time must be shown to be

extremely improbable.

The executive transport airplane

special conditions required evaluation

of uncontained engine failure (including

fan, compressor and turbine blades, and

rotor disc) and complete loss of thrust

from all engines. The FAA policy has

been to presume that these failures will

occur and permit the use of analytical

methods to assess the damage. Multiple

engine failures have occurred because of

secondary effects from uncontained

engine failure and from operational

errors. Multiple fan blade, rotor, and

other uncontained engine failures have

occurred during cruise conditions and

have caused cabin decompression. The

service history of airplane

decompressions resulting from

uncontained engine failure has been

acceptable. Flight levels for most

transport airplanes have been at an

altitude where oxygen equipment is

capable of providing adequate

protection. Uncontained engine failure

is most likely to occur during takeoff

and climb; however, approximately 20

percent of the known bursts have

occurred in cruise mode, not including

those caused by bird strikes. The

possibility of an uncontained engine

failure in cruise mode cannot be

ignored, and the damage resulting in

depressurization must be assessed.

Structural failures in large transport

airplanes which would result in

decompression are generally considered

to include a loss of a typical skin panel

bound by a crack stopper pattern, a door

seal, window, or windshield, unless the

design is such that loss of the

windshield is shown to be extremely

improbable when operating at the

higher altitudes. Structural failures in

executive transport airplanes leading to

decompression, discussed in the various

special conditions, included the

following:

1. Any single failure in the

pressurization system combined with

the occurrence of a leak produced by the

complete loss of a door seal element, or

a fuselage leak through an opening

having an area 2.0 times the area which

produces the maximum permissible

fuselage leak rate approved for normal

operation in accordance with

§ 25.841(a).

2. The maximum pressure vessel

opening resulting from an initially

detectable crack propagating for a

period encompassing four normal

inspection intervals. Mid-panel cracks

and cracks through skin-stringer and

skin-frame combinations must be

evaluated.

3. Pressure vessel openings resulting

from tire burst, uncontained engine

failure, loss of antennas, or stall warning

vanes, or any probable equipment

failure. The effects of such damage

while operating under maximum cabin

pressure differential must be evaluated.

Subsequent to the initial development

and issuance of high altitude special

conditions, § 25.571 was amended by

Amendments 25–45 (1978) and 25–52

(1980) to require damage-tolerance and

fatigue evaluation of airplane primary

structure. Section 25.571 requires

showing that a catastrophic failure due

to fatigue, corrosion, or accidental

damage will not occur throughout the

operational life of the airplane (§ 25.571

(a)). The effects that are required to be

considered under § 25.571 are not

limited to depressurization. Compliance

with § 25.571 requires the development

of inspection intervals and procedures

for the detection of crack lengths

associated with the decompression of

critical vent areas. Any event that would

expose the occupants to cabin pressure

altitudes in excess of the limits

established under this amendment must

be shown to be extremely improbable.

In demonstrating compliance with

proposed § 25.841, the crew would

presumably perform an emergency

descent in accordance with an approval

emergency procedure. The time

required for the crew to recognize a

decompression emergency and don their

oxygen masks has been established by

tests to be 17 seconds. This 17-second

delay is imposed between the cabin

altitude warning and the beginning of

action for descent. The critical failure

case (probable system failure) must be

demonstrated by system failure tests at

the maximum airplanes altitude. For

improbable failure, the cabin altitude

can be established by analysis, and

verified, if necessary, by tests at a much

lower altitude, with the results

extrapolated to the higher altitude.

4. Oxygen Equipment

Both diluter demand and pressure

demand oxygen equipment have proven

satisfactory for cabin pressure altitudes

of 40,000 feet or less when the person

using the oxygen equipment is exposed

gradually to increased altitudes.

However, the FAA was concerned that

rapid decompression to cabin pressure

altitudes that exceed 34,000 feet could

temporarily negate the protective

qualities of such equipment, unless the

mask and oxygen are being used prior

to the decompression, leading to

moderate to severe decreases in

flightcrew performance. To prevent

such performance decrements, Notice

89–31 proposed that the use of 100

percent oxygen be required by this

amendment for flightcrews operating at

airplane altitudes which may expose

them to cabin altitudes exceeding

34,000 feet following a pressurization

failure. As discussed below, in response

to public comment, this requirement has

been removed pending further study by

the FAA.

Prior to this amendment,

§ 25,1447(c)(3) required that each

washroom be equipped with two oxygen

outlets and two units of dispensing

equipment. The term washroom has

been replaced in other sections of part

25. This reference is deleted for

consistency, and the existing provisions

of § 25,1447(c)(3) are incorporated into

a revised § 25.1447(c)(1). The amended

regulation does not specify demand

equipment under § 25.1447(c)(2),

because § 25.1447(c)(3)(i) as amended

allows the option of using either diluter

demand or pressure demand equipment

for airplanes to be operated above an

altitude of 25,000 feet, and

§ 25,1447(c)(3)(ii) as amended requires

pressure demand equipment for

airplanes where decompression may

expose the flightcrew to cabin altitudes

in excess of 34,000 feet.

Discussion of Comments

Comments were received from foreign

and domestic airplane manufacturers,

foreign government agencies, various

trade organizations representing

employee groups, and individuals. The

majority of the commenters support the
Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations 28687

proposals but many suggest changes.

Many commenters recommend editorial,

organizational, and clarifying comments

which would result in clearer language.

Several commenters recommend

removing the proposed change to

§ 25.365(d) that would require a safety

factor of 1.67 times the structural design

pressure differential loads

corresponding to the maximum relief

valve setting for airplanes to be

approved for operation above 45,000

feet. One commenter notes that the

pressure vessel structural design is

based on fatigue loads and their effect

on crack propagation. Another

commenter expresses the opinion that,

as the justification for the margin

increase is concerned with damage

tolerance rather than static strength, the

FAA should attack the problem through

damage tolerance requirements rather

than static strength. This commenter

also states that the damage tolerance

requirements, even at altitudes below

40,000 feet, lead to stress levels

sufficiently low so that the 1.67

requirement is ‘‘likely to be complied

with.’’ A third commenter recommends

changing the wording to remove the

1.67 factor, substituting a requirement

that thermal effects on structural

components and materials must be

accounted for. The FAA does not concur

that the higher factor is not necessary

for airplanes operating at altitudes

above 45,000 feet. A rapid

decompression at altitudes above 45,000

feet could be catastrophic to the

passengers. Therefore, this event must

be extremely improbable; i.e., it is not

expected to occur during the lifetime of

an entire fleet of airplanes. Service

history, however, shows that

decompressions at higher altitudes are

not extremely remote events even for

airplanes assessed to the damage

tolerance criteria. Loss of cabin pressure

at lower altitudes has not been

catastrophic to the passengers from

environmental effects due to the higher

ambient pressures and relatively short

time for emergency descent. Although

application of damage tolerance

techniques will reduce the incidence of

pressure vessel failures in service, there

is no reason to expect that current

methodology will preclude all future

failures. To address these concerns, the

FAA has determined that requiring the

higher safety factor of 1.67 will reduce

the probability of structural failures

which could result in depressurization.

The static factor of 1.67 is not

appropriate to account for thermal

effects because not all parts are

subjected to the same temperature and

also materials may not be affected to the

same degree. The current § 25.603(c)

already requires that the effects of

temperature be accounted for in

determining material properties. Section

25.365 is, therefore, amended as

proposed.

Two commenters note that the

probability terminology regarding

proposed §§ 25.831 (c), (d), and (g) is

not consistent with that found in

regulatory and advisory material

associated with § 25.1309. The FAA

concurs with these comments. The

terminology in the amendment is

changed to address failure conditions

rather than failures or failure

combinations as proposed.

One commenter recommends

allowing the fresh air requirements

proposed to be required under

§ 25.831(a) to remain a crewmember

requirement only. The FAA does not

concur with this recommendation. It has

been determined that this level of

airflow is required for several reasons.

Members of the flightcrew performing

their functions in the passenger cabin

are not sedentary and must perform

their duties without undue discomfort

or fatigue. In addition, fresh airflow has

been determined to be necessary to

provide adequate smoke clearance in

the event of smoke accumulation due to

a system failure or fire. However, it is

clear that the additional airflow is not

required at all times and under all

operating conditions. Therefore, the

wording in the final rule has been

changed to state that the ventilation

system must be designed to provide the

fresh airflow. This also addresses

concerns regarding the low fresh airflow

capability that occurs during descent at

low power levels.

Two commenters note that the fresh

air requirement should be 0.55 pounds

of fresh air per minute per occupant

rather than the 0.6 pounds proposed in

the notice. The FAA ‘‘rounded off’’ the

value for mass flow from 0.55 to 0.6

pounds of fresh air per second when

proposing the rule. Recognizing that this

constitutes an increase in the level of

safety not originally intended by the

FAA, and noting that the added fresh air

must be supplied at some specific cost,

the final rule is changed to require that

the airplane ventilation system be

designed to provide 0.55 pounds of

fresh air per minute per occupant.

Another commenter recommends that

the FAA use 0.5 pounds per minute per

occupant rather than 0.6, noting that the

Civil Aviation Authorities (CAA) and

other airworthiness authorities use 0.5

pounds per minute. The FAA has

determined that the 10 cubic feet per

minute, converted to 0.55 pounds per

minute as noted above, provides an

acceptable minimum airflow. The

commenter provides no data to support

the recommendation. The rule is issued

with the change noted above.

The same commenter notes that the

notice does not contain clear

requirements for airflow following

failures. The commenter further notes

that the JAA provides guidance in ACJ

25.831(e) regarding this matter. The

FAA has not determined that a need

exists to define the ventilation

requirements following failures. The

ventilation rates following various

failures conditions were not addressed

either in previously issued special

conditions or Notice 89–31. In addition,

the commenter did not provide any data

in support of his proposal other than

that it exists in advisory material in

other airworthiness standards.

One commenter states that 0.6 pounds

of fresh air per occupant is impractical

and unjustified for commuter airplanes

because available engines do not

provide sufficient bleed flow to meet the

new requirement. The FAA does not

concur that this proposal is impractical

or unjustified. This rule will not apply

to existing airplanes. When new

airplanes are designed and certificated,

propulsion systems are available that

can provide adequate bleed air to meet

these requirements. The FAA has

determined that health and safety

considerations justify the new

requirements for airplanes operating at

all altitudes.

Further, the commenter states that the

changes proposed for §§ 25.831 (c) and

(d) will require an increase in reliability

requirements that is not justifiable for

airplanes certificated for altitudes below

40,000 feet. This commenter believes

that the existing wording, ‘‘reasonably

probable,’’ is not equivalent to the

proposed wording, ‘‘not extremely

improbable.’’ The FAA concurs with the

commenter, and has determined that

these changes are not needed. Therefore,

because these were the only proposed

changes to §§ 25.831 (c) and (d), the

final rule has been revised to remove the

changes to these sections.

Two commenters recommend either

removing or defining the word

‘‘uncontaminated’’ as used in the

proposed § 25.831(a), noting that the

term is too vague, and might well be

impossible to meet in, for instance, the

case where the airplane is operating in

an environment which itself contains

contaminants, as might be the case near

some airports in congested areas, the

FAA does not concur with the

comment. Descriptive wording is often

used when the desire is to present

objective design standards. The intent in

this case is to ensure that the system
28688 Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations

designer will consider the need to

provide an environment conducive to

crew and passenger comfort. The FAA

has prepared and plans to release

advisory material to provide more

detailed guidance for use in finding

compliance with this rule.

One commenter recommends

removing both the proposed and the

existing §§ 25.831 (c) and (d), stating

that the sections are ambiguous and that

the requirement that the systems

perform their intended functions under

all foreseeable (normal and failure)

conditions is addressed in § 25.1309.

The FAA does not concur. As noted

above, descriptive terminology is used

to present design standards when

specific requirements would be too

inflexible and restrictive. Further,

§ 25.1309 is not intended to be the sole

regulation for use in determining

acceptability of system design when

failure conditions exist. The FAA has

found that individual rules are desirable

when addressing specific functions,

such as those governing ventilation

requirements, in order to ensure

adequate consideration of the specific

issues identified.

One commenter suggest changing the

wording of the proposed § 25.831(d)

from ‘‘If the accumulation of hazardous

quantities of smoke * * *,’’ noting that

in-service experience has shown that

accumulation of smoke is reasonably

likely. The FAA concurs that the

accumulation of smoke in cockpits has

occurred on numerous occasions, and is

not an extremely improbable event.

However, future designs may embody

features that render smoke

accumulation extremely improbable.

Should a manufacturer be able to show

such reliability, smoke evacuation

should not be required to be

demonstrated.

Two commenters note that protection

from smoke in the cockpit cannot be

ensured, even while wearing and using

the crewmember oxygen equipment

stipulated in the proposed

§ 25.1447(c)(3), unless an ‘‘emergency

pressure (1 to 3 inches of water) is

provided to ensure positive mask

pressure and flow into goggles.’’ The

FAA recognized that a positive pressure

differential between the inside of the

mask and ambient is desirable. Many

existing regulators have a ‘‘test’’ or

‘‘emergency’’ position to provide the

pressure differential noted above.

However, the FAA does not concur that

this approach needs to be required by

regulation, and has not proposed such a

change. For the purposes of this

rulemaking, the preamble of Notice 89–

31 merely notes that one of the

advantages of the pressure demand

mask is that, if either the 100 percent or

the full positive pressure (sometimes

called ‘‘test’’) setting is selected,

protection from smoke within the

cockpit would be provided. While the

degree of protection is not identified,

selection of either of these settings does

eliminate the ambient air which is

inspired with diluter demand masks,

thus reducing the risk of smoke or

fumes being inhaled by the wearer.

Three parties offer comments on the

proposed new § 25.831(g). One

commenter recommends continuing the

time/temperature curve proposed for

this section beyond 90 minutes, and

recommends referring to the curve in

the FAA SST ‘‘white book,’’

TENTATIVE AIRWORTHINESS

STANDARDS FOR SUPERSONIC

TRANSPORTS. Copies of the

appropriate pages from that document

have been added to the docket for this

rulemaking action. The FAA infers that

the commenter believes the curve

should be extended to 200 plus minutes

because that is the extent of the graph

in the white book. The FAA does not

concur with this comment. The curve in

the white book actually ends at 90

minutes for a temperature of 90 degrees

Fahrenheit (90 °F), although the actual

graph grid extends to over 200 minutes.

The FAA, in responding to comments

on previously issued special conditions

for high altitude operations, modified

the SST time/temperature curve by

increasing the allowable maximum

temperature from 90 degrees to 100

degrees Fahrenheit to accommodate

aircraft while operating in high ambient

temperature conditions. It was noted

that it would be difficult to meet the

temperature maximums while operating

on the ground with outside

temperatures above 100 degrees. The

end point on the proposed curve

indicates that the exposure time to a

temperature of 100 degrees Fahrenheit

(100 °F) shall not exceed 90 minutes.

The FAA has determined that the limits

established by this curve are appropriate

for improbable failure conditions. In

addition, there were no other comments

addressing the proposed time/

temperature limits. Considering the

above, the curve in the final rule is

retained as proposed.

A second commenter states that this

amendment is not justified for airplanes

operating below 40,000 feet. The FAA

infers that the commenter is

recommending removing this proposal.

The FAA does not concur that this

change is unjustified. Excessive

temperatures in the crew and passenger

compartments can present a hazard to

continued safe flight and landing for

any airplane. Therefore, although this

hazard is not regarded as sufficient to

warrant retroactive application of these

requirements to existing designs, these

improvements in design standards are

appropriate and cost effective for future

designs. While this change was

proposed primarily to codify existing

special conditions for high altitude

operation, it is also appropriate for

airplanes certificated for operation at

lower maximum altitudes. A third

commenter recommends changing the

proposed rule to clarify that the

amended rule is directed at airplanes

which utilize high temperature air to

maintain pressurization following

failure conditions. While the FAA

concurs that the requirement, which

originated in existing special

conditions, was directed primarily at

such airplanes, the amended rule is

intended to apply to any failure

condition that can result in excessively

high temperatures. For the above

reasons, § 25.831(g) is added as

proposed.

One commenter recommends leaving

the phrase ‘‘Pressurized cabins and

compartments to be occupied * * *’’ in

§ 25.841(a) rather than changing it to

‘‘Pressurized cabins and any other

occupied compartments * * *’’ as

proposed. The commenter notes that

this change is not addressed in the

preamble to the proposal, and expresses

concern that the change in wording

might result in a change in

interpretation. The FAA does not

concur with this comment. This change

in wording does not change the meaning

of the Section, and, in the opinion of the

FAA, is clearer.

One commenter recommends adding

a section to the proposed § 25.841(a)(3)

to note that ‘‘Turbine engine

installations failures must be assessed

according to the specific requirements

of § 25.903(d) * * *’’ The FAA does not

concur with this recommendation. It is

not clear how adding this detail would

clarify the requirements for assessing

the damage resulting from an contained

engine failure. Further clarification is

considered to be appropriate for

advisory material, and the FAA

addresses uncontained engine failure in

the advisory circular which was

proposed concurrent with Notice 89–31.

One commenter states that the

proposed § 25.841(a)(1) calls for ‘‘an

unjustified reliability increase relating

to the pressurization system.’’ The FAA

infers that the commenter is requesting

that the rule continue to address only

those failures which are ‘‘reasonably

probable.’’ The FAA does not concur.

As noted earlier, reasonably probable

has been interpreted by the FAA to

include both the probable and
Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations 28689

improbable categories. For this reason,

the new wording does not constitute an

increase in the required reliability.

The same commenter states that the

proposed § 25.841(a)(2) will be in

conflict with the proposed

§ 25.841(a)(1). The FAA does not agree.

Section 25.841(a)(1) addresses

acceptable cabin pressure altitudes

following probable failure conditions,

while § 25.841(a)(2) addresses cabin

altitudes following failure conditions

not shown to be extremely improbable,

i.e., probable and improbable failure

conditions.

One commeter expresses the concern

that the adoption of the proposed

§ 25.841(a)(2)(i), which limits exposure

to cabin pressure altitudes exceeding

25,000 feet to a maximum of 2 minutes

for failure conditions not shown to be

extremely improbable, will result in

‘‘severe restrictions on flight routes as

well as maximum certification altitude.’’

The commeter states that the proposed

§§ 25.841(a)(2) and (a)(3) are proposed

to address concerns regarding

‘‘extremely rapid decompressions which

may occur with small volume, high

altitude (to 51,000 feet) executive

transport airplanes,’’ and recommends

that the FAA remove these sections

from the final rule. The FAA does not

concur. While it is true that one of the

reasons for formulating this rule change

was to codify the certification

requirements previously issued as

special conditions for small volume

transport category airplanes requesting

approval for high altitude operation, the

FAA has reviewed the service history of

rapid depressurizations on all transport

category airplanes including those with

large pressurized volumes. Such events,

while rare, do occur in service. The

effects of exposure to altitudes above

25,000 feet for more than 2 minutes, or

to an altitude above 40,000 feet for any

period of time, are discussed in the

preamble of the notice. If an applicant

can show that failure conditions leading

to excellence of these cabin altitudes are

extremely improbable, there is no

impact on operating altitude. As to

having a significant effect on operating

altitudes, this requirement does not

affect airplanes already certificated, so

there would be no ‘‘more extensive

requirements on the current commercial

fleet.’’ This commenter also

recommends changing ‘‘any probable

failure or failure combinations’’ to ‘‘any

probable failure or probable failure

combination.’’ As noted earlier, the FAA

is changing the wording for both

§§ 25.831 and 25.841 to ‘‘failure

conditions,’’ which covers failures and

combinations of failures, and more

closely parallels § 25.1309 terminology.

One commenter recommends revising

§ 25.841(a)(1) to show that ‘‘In case of

dispatch with equipment inoperative

per an approved Minimum Equipment

List (MEL), only reasonably probable

failures or reasonably probable failure

malfunctions need be considered,’’

when addressing the 15,000 feet

maximum cabin altitude requirement of

this section. The commenter notes that

dispatch under an approved MEL with

one of two air conditioning packs

inoperative has been a safe practice. The

FAA does not concur with this

recommendation. The certification rules

in part 25 do not address MEL dispatch.

In the case of dispatch with one pack

inoperative, the practice followed in

recent certification projects has been to

limit the operating altitude of an

airplane dispatching under these

conditions to that which has been

demonstrated in that configuration

considering the effect of potential

failures. The FAA intends that this

practice be continued under this rule.

One commenter suggests adding a

new § 25.841(a)(2)(iii) reading

‘‘Compliance with paragraph (i) is not

required for cabin altitude versus time

profiles where exposure above ten

thousand feet does not exceed 10

minutes.’’ The commenter notes that

operating rules (§ 121.333(a)) assume

that the airplane descends from the

maximum altitude to 10,000 feet in ten

minutes, and that permanent ill effects

from hypoxia under present operating

rules have been rare. Further, recent

special conditions for the Beech Model

400A and British Aerospace Model BAe

Model 125–1000A airplane contains

cabin altitude versus time curves which

support the ‘‘ten minutes above 10,000

feet’’ criteria. The FAA does not concur

with the commenter’s suggestion. The

cabin altitude limitations stipulated in

the special conditions were interim

standards applicable to those airplanes

only. Physiological data from CAMI

have resulted in the FAA establishing

the requirements for cabin altitudes as

they are stated in the proposal.

Adopting the commenter’s proposal

could result in an applicant being

allowed to demonstrate compliance

while showing exposures to cabin

altitudes up to 40,000 feet for extended

periods while still meeting the

standards, which would be

unacceptable. The FAA has determined

that preventing the occupants from

being exposed to cabin altitudes greater

than 25,000 feet for more than 2 minutes

or 40,000 feet for any duration will

provide an acceptable level of safety at

an acceptable cost.

This commenter also suggests adding

a new § 25.841(a)(2)(iv) to allow the

occupants to be exposed to cabin

altitudes greater than 25,000 feet or

10,000 feet (if (iii) were adopted) when

minimum flight altitudes make literal

compliance with these sections

impractical. The commenter is

concerned that literal compliance with

§ 25.841(b) would result in prohibition

of flight over the Himalayas or Andes,

or in certain areas where minimum

altitudes are stipulated. The FAA does

not share this concern. The proposed

rule requires design features to prevent

the exposure of occupants to the high

cabin altitudes in the presence of failure

conditions. The ability to operate in

areas where operational constraints

dictate minimum flight altitudes is a

function of operating rules and

appropriate flight planning in terms of

supplemental oxygen, etc. The

certification rules do not address these

considerations.

The same commenter recommends

changing § 25.841(a)(3) to more

precisely define the manner in which

various causes of a decompression are

treated, and suggests subparagraphs

treating uncontained engine failure,

fuselage structural failure, discrete

source failure, and system failure

separately. The FAA does not agree that

these details are appropriate for

inclusion in the certification rule. The

FAA plans to provide guidance material

regarding the manner in which the

various failure cases may be addressed.

One commenter supports the

rulemaking but states that ‘‘Existing

crew and passenger emergency oxygen

systems in civil aircraft do not have

sufficient pressure breathing capability

to protect the individual for the required

length of time for controlled descent to

below 33,000 feet where, I believe,

existing oxygen systems may function

adequately for life support.’’ The FAA

infers from this comment that the

commenter desires that this proposal

contain new requirements for oxygen

systems. The FAA does not agree with

this commenter concerning equipment

used by the flightcrew. The FAA has

determined that the oxygen dispensing

equipment required by this rule will

provide adequate protection when the

exposure envelopes are observed. The

FAA shares the commenter’s concern

with respect to the passenger oxygen

equipment. While the passenger

equipment is certificated to operate to a

pressure altitude of 40,000 feet, the

physiological effects of decompression

on the passengers may prevent the

equipment from being effective in all

cases. The alternatives would be to

require the passengers to breathe 100

percent oxygen at the altitudes of

concern or to prohibit operation at the
28690 Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations

higher altitudes. Breathing 100 percent

oxygen by all passengers is considered

to be an unacceptable solution from an

operational standpoint, and the

exposure envelopes adopted for this

rule have been selected to mitigate the

limitations of the passenger oxygen

system. It is considered that developing

new oxygen equipment standards to be

included with this rule is unwarranted.

The FAA has determined that operation

at the altitudes addressed in this rule

can be accomplished with an acceptable

level of safety, and this rule has

established cost effective means of

attaining that goal.

One commenter suggests that the

requirement in § 25.1447(c)(1) for

automatic presentation of oxygen

dispensing units if certification for

operation above 30,000 feet is requested

refer to 31,000 feet, as 30,000 feet

(FL300) is not an authorized cruising

altitude. The FAA agrees that this is not

a cruising altitude. However, the FAA

does not concur that it is inappropriate

to stipulate a requirement for operation

above 30,000 feet. Further, this

requirement is unchanged from the

existing rule.

A second commenter recommends

amending § 25.1447(c)(1) by removing

the requirement for supplemental

oxygen for passengers if the cabin

altitude limits in Notice 89–31 are

adopted. The commenter states that it is

not realistic to expect all passengers to

utilize the oxygen system, and infers

that if the limits proposed are adopted,

the risk to healthy passengers is

minimal. The FAA does not concur with

this comment. If the FAA were to follow

the commenter’s logic, i.e., not to

require passenger oxygen systems, the

exposure envelope would limit the

cabin altitude to 15,000 feet. Historical

events and decompression tests indicate

that supplemental oxygen is needed

even when the cabin pressure altitudes

required by this rule are observed.

Further, this requirement is unchanged

from the existing rule. No other

comments were received on the

proposed §§ 25.1447 (c)(1) and (c)(2)

and they are adopted as proposed.

One commenter states that

§ 25.1447(c)(3) requires pressure

demand masks for operation above

25,000 feet but the justification in the

preamble of the notice states that diluter

demand masks are acceptable up to

34,000 feet. The FAA does not agree

with this comment. Section

25.1447(c)(3)(i) requires a diluter

demand or pressure demand (pressure

demand mask with a diluter demand

pressure breathing regulator) type mask

for airplanes to be operated above

25,000 feet. The pressure demand

(pressure demand mask with a diluter

demand pressure breathing regulator)

type with a mask-mounted regulator is

required for airplanes operated at

altitudes where decompressions that are

not extremely improbable may expose

the flightcrew to cabin pressure

altitudes above 34,000 feet.

One commenter recommends that the

pressure breathing requirements of

§§ 25.1447(c)(3)(i) and (ii) be detailed in

the form of mask pressure versus cabin

altitude curves. The commenter suggests

that the current pressure breathing

equipment specified under Technical

Standard Order TSO–C89 may not be

acceptable for cabin altitudes up to

45,000 feet. The commenter provides no

rationale in support of his

recommendation. The FAA does not

concur. The type of data recommended

by the commenter is appropriate to TSO

requirements, and the revision to those

documents is beyond the scope of this

notice. Further, one of the purposes of

this rulemaking is to provide protection

by preventing exposure of the occupants

to cabin altitudes above 40,000 feet.

Masks and regulators are currently in

use that meet the requirements in the

curves submitted by the commenter for

conditions up to that altitude.

One commenter notes that a pressure

demand mask with a mask-mounted

regulator may have different oxygen

delivery percentage requirements under

TSO–C89 depending on the altitude for

which it is certificated. The commenter

suggests that the rule clarify the mask

and regulator requirements by

stipulating the altitude to which the

mask and regulator are approved under

the TSO. The FAA does not concur with

this suggestion. By specifying the type

of oxygen equipment for the crew, and

the manner of its use, the FAA has

determined that the flightcrew will

retain the ability to safely operate the

airplane during a decompression.

One commenter suggests withdrawing

the proposed § 25.1447(c)(3)(ii) because

the equipment standards defined in

TSO–C89 ‘‘provide the necessary

oxygen up to 40,000 feet, and are

considered safe.’’ The FAA does not

concur. There is no requirement that the

equipment used in transport category

airplanes be approved under a TSO. As

discussed in the notice, operation at

altitudes which can, in the event of a

rapid decompression, result in

incapacitation or a physiological hazard

to the occupants requires oxygen

equipment to meet the specific

environments that may be encountered.

It is recognized that equipment with

TSO authorization is available that will

provide the required protection at a

reasonable cost. The intent of this

rulemaking is to identify a minimum

equipment standard that is known to

provide this protection, and that

equipment is called out in the amended

sections.

Another commenter suggests

amending § 25.1443 by addition of a

curve of ‘‘cabin pressure altitude versus

minimum required oxygen mass flow’’

for cabin altitudes from 0 to 51,000 feet

which would replace the generic mass

flow requirement which appears in

§ 25.1441. The FAA does not concur

with this comment. A revision to

§ 25.1443 as suggested by the

commenter would not increase the level

of safety. Existing rules related to

oxygen mass flow provide an adequate

level of safety. If such material were to

be added, this level of detail would be

more appropriate in a Technical

Standard Order or the advisory material

that has been proposed to accompany

this rulemaking action.

One commenter recommends deleting

§ 25.1447(c)(3)(ii) both as it now exists

and as proposed. The existing section is

deleted for the reasons noted in the

preamble to Notice 89–31. The

commenter believes that the section as

proposed, which stipulates the use of ‘‘a

pressure demand (pressure demand

mask with a diluter demand pressure

breathing regulator) type with a maskmounted regulator,’’ is unduly

restrictive by requiring a mask-mounted

regulator, and dictates a design solution.

Additionally, the commenter states that

§§ 25.1441(d) and 25.1443(b) and

Technical Standard Order TSO–C89

address oxygen equipment, thereby

obviating the need for the proposed

section. Another commenter

recommends that the FAA define the

required oxygen equipment (diluter

demand and pressure demand masks) in

terms of performance rather than by

stipulating a specific equipment type.

The FAA does not concur with these

comments. The specific descriptions for

the oxygen equipment that is proposed

in these amendments has been

determined by the FAA to be necessary

to provide protection for the flightcrew

in cases where the cabin altitude will

exceed the specified levels. Neither of

the FAR sections nor the TSO data

provide adequate assurance of that

protection. The FAA believes that this

detailed stipulation is necessary to

ensure the protection and to provide

standardization in interpretation of the

new requirements. However, the FAA

intends to allow sufficient latitude for

system designers to develop safer and/

or less expensive approaches to specific

requirements. For this reason,

§ 25.1447(c)(3)(ii) is changed to allow

other means of protection for flight
Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations 28691

crewmembers if the proposed

equipment affords the same protection.

One commenter states that existing

panel-mounted diluter-demand

regulators have proven satisfactory. This

party suggests that the pressure-demand

mask with a mask-mounted regulator be

mandatory for newly certificated

airplanes only. The FAA agrees that

panel mounted regulators have proven

satisfactory, but the FAA has

determined that in a high altitude rapid

decompression, the protection afforded

by a mask mounted regulator is superior

to that found in panel mounted

regulators. As noted in the preamble of

the notice, the time delay in providing

100 percent oxygen to the flight

crewmember, which results from the air

in the hoses of the oxygen equipment,

can significantly negate the hypoxic

protection of such equipment. Further,

this amendment constitutes a revision to

part 25, and is not applicable to the

existing fleet. It is, however, the FAA’s

position that every effort be made to

provide a level of safety equal to the

latest certification standards for existing

airplanes that are updated by amended

or supplemental type certification. The

FAA’s policy regarding establishment of

the type certification basis for derivative

airplanes is described in Action Notice

A 8110.23, dated September 26, 1990. A

copy of this document has been placed

in the Rules Docket. Following issuance

of these amendments, the concepts

contained herein would be applicable to

airplanes which incorporate changes in

the oxygen systems or increases in

approved operating altitudes, in

accordance with § 21.101. For high

altitude approvals, this has been

accomplished in the past through

special conditions which contain

provisions essentially the same as those

embodied in these amendments.

Several comments express concerns

regarding long term use of 100 percent

oxygen by fightcrews. One of these

parties suggests that the crew member

use normally diluted oxygen with the

regulator set at the ‘‘normal’’ position.

Another states that 100 percent oxygen

should not be permitted unless adequate

safeguards have been established. A

third party states that 100 percent

oxygen should be used only for short

periods as an emergency measure due to

a health hazard. One commenter

recommends deleting the proposed

§ 25.1447(c)(4) and retaining

§ 121.333(c)(2), which requires at least

one pilot to wear and use an oxygen

mask at altitudes of 41,000 feet and

greater. Another commenter believes

that wearing an oxygen mask at lower

altitudes ‘‘is not necessary nor is it

useful.’’ One commenter notes that

breathing 100 percent oxygen will dry

out the lungs, can lead to narcosis, and

states that the long term effects are not

clearly understood. Another commenter

recommends deleting the proposal to

require the wearing of masks and revert

to the requirements in the operating

rules. Another commenter states that

large volume transports decompress

slowly giving crews more time to don

oxygen masks, and current large

transports are certificated to 45,000 feet

without requiring the flightcrew to be

using oxygen. The FAA infers that the

commenter believes that this proposal

should not apply to ‘‘large’’ transport

airplanes. The FAA does not concur

with this viewpoint. The physical size

of the airplane is not germane; the

important parameter is the postdecompression cabin altitude and its

effect on occupants. One commenter

notes that the requirement for

prebreathing 100 percent oxygen would

necessitate additional oxygen supplies

at added cost. Finally, one commenter

questions whether breathing 100

percent rather than 40 percent oxygen

provides better protection in terms of

blood oxygen saturation level. This

commenter provides data showing that

prebreathing 30 to 40 percent oxygen

provides adequate protection against the

effects of hypoxia following rapid

decompression. The data show that the

blood oxygen saturation level following

the decompression is not significantly

depressed even if the crew member is

breathing 30 percent oxygen, as long as

the oxygen supplied to the crew

member goes to 100% immediately.

After considering all the negative

comments received and reviewing

existing data regarding high altitude

decompressions, the FAA has

determined that it is appropriate to

withdraw this proposal. The proposed

§ 25.1447(c)(4), requiring that one flight

crewmember be wearing an oxygen

mask and breathing 100 percent oxygen

when operating at altitudes where the

cabin altitude can reach 34,000 feet in

the event of a decompression, has been

withdrawn.

One commenter states that, regarding

the proposed § 25.1447(c)(5), portable

oxygen equipment would only be ‘‘at

hand’’ if the crew members were sitting

by the oxygen equipment or were

actually using it, and recommends

striking the work ‘‘immediately’’ from

the proposal. The FAA does not believe

this change is necessary or warranted.

This requirement is retained from the

existing § 25.1447(c)(4), and is

considered met in existing airplanes by

having portable oxygen equipment

located adjacent to the crew member

seat with additional units located at

specific locations in the passenger

cabin. The FAA anticipates that

industry will continue to provide this

protection in the same manner as it has

done in existing airplanes, with no

change in the rule or in FAA policy

regarding showing compliance.

Two commenters point out that the

nomenclature used in the glossary of the

notice misidentified the type of

passenger oxygen equipment used in

airplanes with altitudes above 35,000

feet. One commenter recommends

changing the definition in the Glossary

for ‘‘Continuous Flow Oxygen Systems’’

to note that the type of equipment used

is a mask with a ‘‘reservoir’’ bag rather

than a ‘‘rebreather’’ bag. The FAA

concurs with these comments, and the

glossary is changed to reflect the

terminology used in current descriptive

literature.

One commenter notes that, while

special conditions have been issued

covering various airplanes requesting

approval for high altitude operations,

this proposal impacts all airplanes

seeking certification under part 25 of the

FAR, including those with maximum

flight altitudes less than 41,000 feet.

These proposals constitute increased

standards for those airplanes. The FAA

concurs with this statement. This

rulemaking addresses the physiological

limitations of occupants of transport

category airplanes which can experience

depressurization to cabin altitudes

greater than 34,000 feet. However, the

commenter does not recommend any

specific changes in the proposals.

The JAA notes that future rulemaking

relative to the Joint Airworthiness

Regulations (JAR) will require

retroactive application for each new

amendment, and asks if the FAA is

considering similar action. As noted

earlier, application of new amendments

to the FAR are made applicable to type

certification programs in accordance

with § 21.101 of the FAR. There are no

plans to require retroactive application

of new amendments to the existing fleet,

as suggested by the JAA. The JAA also

suggests considering a number of added

concerns regarding operations at high

altitudes, such as the effects of icing on

airspeed and pressure probes, changes

in static stability criteria for high mach/

high altitude operation, and health

hazards related to cosmic radiation

during high altitude cruise. A second

commenter recommends that the

proposal be revised to address standards

related to the exposure of crewmembers

to cosmic radiation when operating at

altitudes up to 51,000 feet. The effects

of icing (ice crystals) on airspeed and

pressure probes and stability criteria
28692 Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations

were not considered in the special

conditions issued prior to this

rulemaking, and no data was submitted

by the commenter to support its

position. No action is contemplated by

the FAA regarding these comments. The

effects of cosmic radiation are not

addressed in this proposal, and no data

were submitted by either commenter in

support of their suggestions. The FAA is

aware of the concerns expressed by the

commenters and may consider further

rulemaking to address those concerns.

One commenter suggests requiring

initial and periodic training including

altitude chamber and pressure breathing

instruction for pilots of airplanes

affected by this rulemaking. As the

certification rules in part 25 do not

address specific training requirements,

this proposal is outside the scope of this

rulemaking. However, this proposal will

be discussed with the FAA organization

responsible for crew training.

One commenter notes that the FAA

should require improvements in

pressure demand masks to improve

comfort, and suggests that research and

development in comfort and human

factors is needed. The FAA believes that

there is oxygen equipment available that

meets the requirements of this rule and

also provides an acceptable level of

comfort. The small executive jet

airplanes approved under existing

special conditions are so equipped. If

further improvements are needed, the

marketplace will drive the development

and availability of these products.

One commenter suggests that the FAA

has failed to consider the relatively

small transport category airplanes

intended for commuter airline

operation. The example noted is a

16,000 pound airplane intended to carry

25 passengers, operating at altitudes of

25,000 to 30,000 feet. The commenter

states that the manufacturer will apply

for certification to the highest expected

operating altitude and the amendments

of this proposal will apply. The specific

comments related to these concerns are

addressed elsewhere in this document,

but the commenter apparently believes

that these applicants should not have

these requirements imposed on their

airplanes. The position adopted by the

FAA with this rulemaking action is that

any airplane operating at flight altitudes

where decompression can result in a

hazard to the occupants must be

designed to provide protection.

One commenter recommends leaving

the regulations as they now exist for

large airplanes operating up to 45,000

feet and directing the proposed rules to

the smaller airplanes operating at higher

altitudes. This party states that large

airplanes certified under the existing

rules provide an acceptable level of

safety, and the proposed rules will

result in ‘‘undue restrictions or

unvalidated costly additional effort.’’

Another commenter expresses a similar

opinion, and comments that adoption of

these standards will have a significant

economic impact due to requiring

retrofit of many existing airplanes. The

FAA does not share these views. The

protection afforded the occupants

should be the same for any transport

category airplane, regardless of volume.

Larger airplanes have shown

decompression characteristics similar to

the small airplanes. If the applicant can

demonstrate that the cabin altitude does

not exceed prescribed limits, many of

the provisions of this amendment do not

apply. In any case, these rules are not

retroactive to existing airplanes as a

result of this rulemaking, and only new

or modified airplanes are required to

meet the new requirements. Another

commenter makes the point that there

have been recent decompression events

involving large airplanes wherein the

decompression ‘‘is surely as explosive

as any to be realized on a smaller Lear

Jet . . .,’’ and agrees with the proposals.

Another commenter believes that

existing supplemental oxygen systems

are acceptable, and if the requirements

in Notice 89–31 are adopted, there are

strong arguments for elimination of the

passenger oxygen system. The FAA does

not concur with these statements. While

it is recognized that not all passengers

will be able to don their oxygen

equipment, the protection afforded by

the systems currently installed provides

acceptable protection from the effects of

hypoxia at an acceptable cost for the

majority of the occupants from the

effects of hypoxia. Even when the

decompression event is slower or the

cabin altitude is limited, and the oxygen

masks are not absolutely essential for

survival, some protection is afforded to

all the passengers when the cabin

altitude exceeds safe limits. The

operating rules also require the

installation of this equipment.

One commenter states that the

economic analysis reflects an operating

cost increase of $19 million per year,

implying that the rule would have to

save 19 lives per year to be reasonable.

The same commenter recommends

revising the Regulatory Flexibility

Determination because small entities

may operate affected airplanes and may

incur increased operating costs. In each

case, the commenter appears to be

referring to FAA’s economic analysis of

proposed § 25.1447(c)(4). As noted

earlier, Notice 89–31 proposed that

§ 25.1447(c)(4) require that one flight

crewmember wear an oxygen mask and

breathe 100 percent oxygen when

operating at altitudes where the cabin

altitude can reach 34,000 feet in the

event of a decompression. In response to

public comments and cost

considerations, the FAA has withdrawn

this proposal and will subject it to

further study. In regard to the

commenter’s recommendation regarding

small entities, the magnitude of the

costs and the number of affected small

entities, rather than simply the

incidence of costs, are the criteria by

which a rule is judged to have a

significant economic impact on small

entities. A regulatory flexibility

determination of the final rule is

presented in the next section of this

document.

The same commenter also states that

the Regulatory Evaluation does not take

into consideration evolving FAA policy

of applying the latest FAR amendments

when determining the certification basis

for amended type certifications. The

FAA agrees and has added this policy

to this final regulatory evaluation,

without affecting the justification of the

rule. It is FAA’s policy that every effort

be made to provide a level of safety

equal to the latest certification standards

for existing airplanes that are updated

by amended or supplemental type

certificates. Amendments to the FAR

may be made applicable to derivative

airplanes in accordance with § 21.101 if

it is determined that the new or

redesigned system is not adequately

addressed in the regulations

incorporated by reference to the type

design.

The commenter also identifies a

statement in the NPRM Regulatory

Evaluation that incorrectly assumes that

new airplanes will not have engines

mounted in positions which could

damage the fuselage. The commenter

appears to be misinterpreting FAA’s

language. The statement being referred

to by the commenter is one pertaining

only to small volume transport

airplanes. The FAA agrees that most

other transport category airplanes will

have wing-mounted engines located

such that fragments from an engine

burst could affect the fuselage and

pressure vessel.

References

Reference 1. ‘‘Factors Influencing the Time

of Safe Unconsciousness (TSU) for

Commercial Jet Passengers Following Cabin

Decompression’’ by James G. Gaume,

Aerospace Medicine, April 1970.

Reference 2. Aerospace Information Report

(AIR) No. 822 and 825B (Physiology Section);

SAE Committee A–10.

Copies of pertinent portions of these

documents have been placed in the
Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations 28693

Rules Docket and are available for

public inspection.

Glossary

Physiology Altitude Limits. The

response of human beings to increased

altitude varies with the individual.

People that smoke or are in poor health

will be affected at a much lower altitude

than people who are young and in good

physical condition. Without

supplementary oxygen, most people

will begin to experience a reduction in

night vision or general visual acuity at

approximately 5,000 feet altitude. At an

altitude of approximately 10,000 feet, a

person will begin to display measurable

deterioration in mental abilities and

physical dexterity after a period of

several hours. At 18,000 feet, the mental

deterioration may result in

unconsciousness, and the time of useful

consciousness (TUC) is generally about

15 minutes. At 25,000 feet, the TUC for

most people is about 3–10 minutes. At

altitudes above 25,000 feet, the TUC

decreases very rapidly, becoming only a

few seconds at 40,000 feet. If a person

is breathing 100 percent oxygen,

however, the partial pressure of oxygen

in the lungs at 34,000 feet altitude is the

same as that for a person breathing air

at sea level. At 40,000 feet, a person

breathing 100 percent oxygen will have

the same partial pressure of oxygen in

the lungs as a person breathing air at

10,000 feet. Therefore, 34,000 feet is the

highest altitude at which a person

would be provided complete protection

from the effects of hypoxia, and 40,000

feet is the highest altitude at which 100

percent oxygen will provide reasonable

protection for the time period needed to

descend to a safe altitude.

Hypoxia. Hypoxia is a condition

caused by insufficient oxygen. It results

from the reduced oxygen partial

pressure in the inspired air caused by

the decrease in barometric pressure with

increasing altitude.

Diluter Demand Oxygen System. A

flightcrew oxygen system consisting of a

close-fitting mask with a regulator that

supplies a flow of oxygen proportional

to cabin altitude. Regulators are usually

designed to provide zero percent oxygen

and 100 percent cabin air at cabin

altitudes of 8,000 feet or less, with the

ratio changing to 100 percent oxygen

and zero percent cabin air at

approximately 34,000 feet cabin

altitude. Oxygen is supplied only when

the user inhales, reducing, the amount

of oxygen that is required.

Pressure Demand Oxygen System.

Similar to diluter demand equipment,

except that oxygen is automatically

supplied to the mask under pressure at

cabin altitudes above approxmately

34,000 feet. This pressurized supply of

oxygen provides some additional

protection against hypoxia at altitudes

up to 39,000 feet.

Pressure Demand Mask With MaskMounted Regulator. A pressure demand

mask with the regulator attached

directly to the mask, rather than

mounted on the instrument panel or

other area within the flight deck. The

mask-mounted regulator eliminates the

problem of a long hose which must be

purged of air before oxygen is delivered

to the mask.

Continuous Flow Oxygen System. The

oxygen system typically provided to

passengers. The passenger mask most

commonly used in transport category

airplanes is equipped with a reservoir

bag, which is replenished by a

continuous flow of oxygen. This design

incorporates a check valve between the

reservoir bag and the face mask to

prevent introduction of exhaled gasses

into the bag and assure 100% oxygen in

the reservoir. Dilution is accomplished

at the later phases in inspiration by a

loaded ambient air valve which

introduces ambient air following

depletion of the oxygen in the reservoir

bag.

Probable Failures. Probable failures

may be expected to occur several times

during the operational life of each

airplane. The probability of occurrence

is on the order of 1 × 10¥5 or greater

(Advisory Circular 25.1309–1A). The

consequences of the failure or the

required corrective action may not

significantly impact the safety of the

airplane or the ability of the crew to

cope with adverse operating conditions.

Systems that operate within this

category are referred to as nonessential

systems.

Improbable Failures. Improbable

failures are not expected to occur during

the total operational life of a random

single airplane of a particular type, but

may occur during the total operational

life of all airplanes of a particular type.

The probability of occurrence is on the

order of 1 × 10¥5 or less. The

consequences of the failure or the

required corrective action must not

prevent the continued safe flight and

landing of the airplane. Systems that

operate within this category are referred

to as essential systems.

Extremely Improbable Failures.

Extremely improbable failures are so

unlikely that they need not be

considered to ever occur, unless

engineering judgement would require

their consideration. The probability of

occurrence is on the order of 1 × 10¥9

or less. This category includes failures

or combinations of failures that would

prevent the continued safe flight and

landing of the airplane. Systems that

operate within this category are referred

to as critical systems.

Regulatory Evaluation Summary

Proposed changes to Federal

regulations must undergo economic

analyses. First, Executive Order 12866

directs that each Federal agency shall

propose or adopt a regulation only upon

a reasoned determination that the

benefits of the intended regulation

justify its costs. Section, the Regulatory

Flexibility Act of 1980 requires agencies

to analyze the economic effect of

regulatory changes on small entities.

Third, the Office of Management and

Budget directs agencies to assess the

effects of regulatory changes on

international trade. In conducting these

analyses, the FAA has determined that

this rule: (1) will generate benefits that

justify its costs; (2) is not a ‘‘significant

regulatory action’’ as defined in the

Executive Order and is not ‘‘significant’’

as defined in DOT’s Regulatory Policies

and Procedures; (3) will not have a

significant economic 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.

Regulatory Evaluation Summary

The rule may impose relatively

incremental costs in that applicant

manufacturers will be required to

demonstrate compliance and operators

may experience increased operating

costs. The FAA has determined that

these potential incremental costs will be

exceeded by the safety and efficiency

benefits of the rule.

A. Ventilation and Cabin Cooling—

§ 25.831 (a), (c), (d), and (g)

The FAA has determined that health

and safety considerations justify the

airflow design requirements of

§ 28.831(a) for all transport category

airplanes. First, cabin crewmembers

must be able to perform their duties

without undue discomfort or fatigue.

Secondly, benefits may be realized from

the assured availability of the additional

airflow when it is required. Third, fresh

airflow is necessary to provide adequate

smoke clearance in the event of smoke

accumulation in the passenger cabin, an

event which has occurred on several

occasions. Fourth, administrative

benefits will be realized because

codified regulations are more efficient

than special conditions. Finally, it is

noted that other airworthiness

authorities have comparable ventilation

standards.
28694 Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations

The airflow design requirements in

revised § 25.831(a) are not expected to

result in significant cost changes.

Incremental design and manufacturing

costs will be negligible because most

current airplane models were designed

with the additional airflow capability

and, even in the absence of this rule,

future airplane models would likely

continue to be so designed. Incremental

operating costs are expected to be

nominal because the rule isn’t an

operating requirement and because the

additional airflow is not required at all

times and under all operating

conditions. Furthermore, to the extent

that the amendment codifies special

conditions that would have continued

to be applied to future high altitude

airplane certifications, it will not cause

changes in costs.

The new § 25.831(g) supplements the

requirements found in § 25.1309 by

limiting exposure times to excessive

temperatures in the crew and passenger

compartments which can present a

hazard to continued safe flight and

landing, and the limits are appropriate

for all transport category airplanes,

regardless of certificated maximum

flight altitude.

B. Pressurization and Pressure Vessel

Integrity—§§ 25.365(d) and 25.841(a)

The higher structural safety factor in

revised § 25.365(d) is necessary for

airplanes operating above 45,000 feet

because a rapid decompression could be

catastrophic to occupants. Therefore,

the FAA finds that this event should be

extremely improbable; i.e., not expected

to occur during the lifetime of an entire

fleet of airplanes. Service history shows

that decompressions at high altitudes

are not extremely remote events even for

airplanes assessed to damage tolerance

criteria. Loss of cabin pressure at lower

altitudes has not been catastrophic due

to higher ambient pressures and

relatively short emergency descent time.

The higher structural safety factor was

included in the SST and executive

transport category airplane special

conditions to reduce the likelihood of

structural failure and to limit the size of

the opening if a failure occurs. The

amendment will have a negligible cost.

Revised § 25.841(a) will provide

airworthiness standards that allow

subsonic airplanes to operate at the

highest altitude for which the applicant

manufacturer chooses to demonstrate

that, after decompression caused by a

single failure or combination of failures

that are not shown to be extremely

improbable: (1) the flightcrew will

remain alert and be able to fly the

airplane; (2) the cabin occupants will be

protected from the effects of hypoxia;

and (3) in the event that some occupants

do not receive supplemental oxygen,

they nevertheless will be protected

against physiological injury.

Revised § 25.841(a)(1) is equivalent to

existing § 25.841(a) except for editorial

changes, elimination of the words

‘‘reasonably’’ and ‘‘or malfunctions,’’

and addition of the term ‘‘failure

conditions.’’ Revised § 25.841(a)(2),

which limits exposure of occupants

after decompression to a cabin altitude

not greater than 40,000, is unchanged

from previously established standards

for airplanes using diluter demand

(flightcrew) and continuous flow

(passenger) oxygen equipment. It

combines the executive transport

category high altitude special conditions

and § 25.1309, i.e., the degree of the

hazard must be inversely related to the

probability of the failure condition.

The FAA has determined that the

amendment will provide an acceptable

level of safety at an acceptable cost. To

demonstrate compliance with revised

§ 25.841, an approved emergency

descent procedure and a cabin altitude

analysis must be prepared and the crew

would perform an emergency descent in

accordance with the approved

procedure. For probable system failures,

the critical failure case (probable system

failure) system failure tests must be

conducted at the maximum airplane

altitude. For improbable failures, the

cabin altitude could be established by

analysis and verified by tests at a lower

altitude with the results extrapolated to

the higher altitude. To the extent that

the rule codifies special conditions that

would have continued to be applied to

future high altitude airplane type

certifications, it will have no

incremental economic effects. There

will also be administrative benefits in

that codified regulations are more

efficient than special conditions.

C. Oxygen Equipment—§ 25.1447(c)

The FAA has determined that

operation in accordance with the

revised oxygen equipment standards

will provide an acceptable level of

safety. By specifying the type of oxygen

equipment for the crew and the manner

of its use, there will be assurance that

the flightcrew will retain its ability to

safely operate the airplane during a

decompression. Panel-mounted

regulators have proven satisfactory, but

the FAA has determined that in a high

altitude rapid decompression, the

protection afforded by a mask-mounted

regulator is superior to that of panelmounted regulators. The FAA intends to

allow sufficient latitude for system

designers to develop safer and/or less

expensive approaches to specific

requirements. For this reason,

§ 25.1447(c)(3)(ii) will allow other

means of protection for flight

crewmembers if they afford the same

protection.

To the extent that the changes codify

special conditions that would have

continued to be applied to future high

altitude airplane type certifications, the

amendments will have no incremental

economic effect other than the

administrative benefits of codified

regulations relative to special

conditions.

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, in which

alternatives are considered and

evaluated if a rule is expected to have

‘‘a significant economic impact 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

thresholds, ‘‘significant economic

impact’’ in terms of annualized cost

thresholds, and ‘‘substantial number’’ as

a number which is not less than eleven

and which is more than one-third of the

small subject to the proposed or final

rule.

The rule will affect manufacturers and

operators of transport category airplanes

produced under future new, and some

amended and supplemental, airplane

type certifications. For manufacturers,

Order 2100.14A specifies a size

threshold for classification as a small

entity as 75 or fewer employees. Since

no part 25 airplane manufacturer has 75

or fewer employees, the rule will not

have a significant economic impact on

a substantial number of small airplane

manufacturers. The size threshold for

classification as a small operator is the

ownership (but not necessarily the

operation) of nine or fewer aircraft. The

annualized cost thresholds constituting

‘‘significant economic impact’’ for

operators of aircraft-for-hire, when

expressed in 1994 dollars, are $120,000

for scheduled operators whose fleets

consist entirely of aircraft with seating

capacities of over 60, $69,000 for other

scheduled operators, and $4,900 for

unscheduled operators. The annualized

incremental costs of this rule amortized

over a maximum nine-airplane fleet are

expected to be less than these

annualized cost thresholds. The FAA
Federal Register / Vol. 61, No. 109, Wednesday, June 5, 1996 / Rules and Regulations 28695

has therefore determined that the rule

will not have a significant economic

impact on a substantial number of small

operators.

International Trade Impact Assessment

The rule will have little or no effect

on the sale of U.S. airplanes in foreign

markets and the sale of foreign airplanes

into the U.S.

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 Compatibility

The FAA has reviewed corresponding

International Civil Aviation

Organization regulations and Joint

Airworthiness Authorities regulations,

where they exist, and has identified no

differences in these amendments and

the foreign regulations.

Paperwork Reduction Act

In accordance with the Paperwork

Reduction Act of 1980 (Pub. L. 96–511),

there are no requirements for

information collection associated with

this rule.

Conclusion

Because amending the airplane and

equipment airworthiness standards for

subsonic transport airplanes for

operation to an altitude of 51,000 feet is

not expected to result in substantial

costs, the FAA has determined that this

final rule is not major as defined in

Executive Order 12866. For the same

reason and because this is an issue

which has not prompted a great deal of

public concern, this final rule is not

considered to be significant as defined

in Department of Transportation

Regulatory Policies and Procedures (44

FR 11034; February 26, 1979). In

addition, since there are no small

entities affected by this rulemaking, it is

certified, under the criteria of the

Regulatory Flexibility Act, that this final

rule, a promulgation, will not have a

significant economic impact, positive or

negative, on a substantial number of

small entities. A copy of the final

regulatory evaluation prepared for this

project may be examined in the public

docket or obtained from the person

identified under the caption FOR

FURTHER INFORMATION CONTACT.

List of Subjects in 14 CFR Part 25

Air transportation, Aircraft, Aviation

safety, Safety.

The Amendment

Accordingly, the FAA amends part 25

of the Federal Aviation Regulations

(FAR) (14 CFR part 25) 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. By amending § 25.365, by revising

paragraph (d), to read as follows:

§ 25.365 Pressurized compartment loads.

* * * * *

(d) The airplane structure must be

designed to be able to withstand the

pressure differential loads

corresponding to the maximum relief

valve setting multiplied by a factor of

1.33 for airplanes to be approved for

operation to 45,000 feet or by a factor of

1.67 for airplanes to be approved for

operation above 45,000 feet, omitting

other loads.

* * * * *

3. By amending § 25.831 by revising

paragraph (a) and by adding a new

paragraph (g) to read as follows:

§ 25.831 Ventilation.

(a) Under normal operating conditions

and in the event of any probable failure

conditions of any system which would

adversely affect the ventilating air, the

ventilation system must be designed to

provide a sufficient amount of

uncontaminated air to enable the

crewmembers to perform their duties

without undue discomfort or fatigue and

to provide reasonable passenger

comfort. For normal operating

conditions, the ventilation system must

be designed to provide each occupant

with an airflow containing at least 0.55

pounds of fresh air per minute.

* * * * *

(g) The exposure time at any given

temperature must not exceed the values

shown in the following graph after any

improbable failure condition.

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4. By amending § 25.841 by revising

paragraph (a) to read as follows:

§ 25.841 Pressurized cabins.

(a) Pressurized cabins and

compartments to be occupied must be

equipped to provide a cabin pressure

altitude of not more than 8,000 feet at

the maximum operating altitude of the

airplane under normal operating

conditions.

(1) If certification for operation above

25,000 feet is requested, the airplane

must be designed so that occupants will

not be exposed to cabin pressure

altitudes in excess of 15,000 feet after

any probable failure condition in the

pressurization system.

(2) The airplane must be designed so

that occupants will not be exposed to a

cabin pressure altitude that exceeds the

following after decompression from any

failure condition not shown to be

extremely improbable:

(i) Twenty-five thousand (25,000) feet

for more than 2 minutes; or

(ii) Forty thousand (40,000) feet for

any duration.

(3) Fuselage structure, engine and

system failures are to be considered in

evaluating the cabin decompression.

* * * * *

5. By amending § 25.1447, by revising

paragraphs (c) (1) through (4), to read as

follows:

§ 25.1447 Equipment standards for oxygen

dispensing units.

* * * * *

(c) * * *

(1) There must be an oxygen

dispensing unit connected to oxygen

supply terminals immediately available

to each occupant, wherever seated, and

at least two oxygen dispensing units

connected to oxygen terminals in each

lavatory. The total number of dispensing

units and outlets in the cabin must

exceed the number of seats by at least

10 percent. The extra units must be as

uniformly distributed throughout the

cabin as practicable. If certification for

operation above 30,000 feet is requested,

the dispensing units providing the

required oxygen flow must be

automatically presented to the

occupants before the cabin pressure

altitude exceeds 15,000 feet. The crew

must be provided with a manual means

of making the dispensing units

immediately available in the event of

failure of the automatic system.

(2) Each flight crewmember on flight

deck duty must be provided with a

quick-donning type oxygen dispensing

unit connected to an oxygen supply

terminal. This dispensing unit must be

immediately available to the flight

crewmember when seated at his station,

and installed so that it:

(i) Can be placed on the face from its

ready position, properly secured, sealed,

and supplying oxygen upon demand,

with one hand, within five seconds and

without disturbing eyeglasses or causing

delay in proceeding with emergency

duties; and

(ii) Allows, while in place, the

performance of normal communication

functions.

(3) The oxygen dispensing equipment

for the flight crewmembers must be:

(i) The diluter demand or pressure

demand (pressure demand mask with a

diluter demand pressure breathing

regulator) type, or other approved

oxygen equipment shown to provide the

same degree of protection, for airplanes

to be operated above 25,000 feet.

(ii) The pressure demand (pressure

demand mask with a diluter demand

pressure breathing regulator) type with

mask-mounted regulator, or other

approved oxygen equipment shown to

provide the same degree of protection,

for airplanes operated at altitudes where

decompressions that are not extremely

improbable may expose the flightcrew

to cabin pressure altitudes in excess of

34,000 feet.

(4) Portable oxygen equipment must

be immediately available for each cabin

attendant.

Issued in Washington, DC, on May 29,

1996.

David R. Hinson,

Administrator.

[FR Doc. 96–13947 Filed 6–4–96; 8:45 am]

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