27396 Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 28617; Amendment No. 25–104]

RIN 2120–AF79

Revision of Hydraulic Systems

Airworthiness Standards To

Harmonize With European

Airworthiness Standards for Transport

Category Airplanes

AGENCY: Federal Aviation

Administration (FAA), DOT.

ACTION: Final rule.

SUMMARY: This amendment revises the

hydraulic systems design and test

requirements of the airworthiness

standards for transport category

airplanes. The amendment adds

appropriate existing Joint Aviation

Requirements (JAR) standards to

achieve harmonization; moves some of

the existing regulatory text to a new

advisory circular (AC) 25.1435–1;

consolidates and/or separates certain

subparagraphs for clarity; and revises

airplane static proof pressure test

requirements to allow a complete

functional (dynamic) airplane test at the

hydraulic system relief pressure. These

revisions were developed in cooperation

with the Joint Aviation Authorities

(JAA) of Europe, Transport Canada, and

the U.S. and European aviation industry

through the Aviation Rulemaking

Advisory Committee (ARAC). These

changes benefit the public interest by

standardizing certain requirements,

concepts, and procedures contained in

the airworthiness standards without

reducing, but potentially enhancing, the

current level of safety.

DATE: Effective June 15, 2001.

FOR FURTHER INFORMATION CONTACT:

Mahinder K. Wahi, Propulsion/

Mechanical Systems Branch, ANM–112,

Transport Airplane Directorate, Aircraft

Certification Service, FAA, 1601 Lind

Avenue SW., Renton, WA 98055–4056;

telephone (425) 227–2142; facsimile

(425) 227–1320.

SUPPLEMENTARY INFORMATION:

Availability of Final Rules

You can get an electronic copy using

the Internet by taking the following

steps:

(1) Go to the search function of the

Department of Transportation’s

electronic Docket Management System

(DMS) Web page (http://dms.dot.gov/

search).

(2) On the search page type in the last

four digits of the Docket number shown

at the beginning of the notice. Click on

‘‘search.’’

(3) On the next page, which contains

the Docket summary information for the

Docket you selected, click on the final

rule.

You can also get an electronic copy

using the Internet through FAA’s web

page at http://www.faa.gov/avr/arm/

nprm/nprm.htm or the Federal

Register’s web page at http://

www.access.gpo/gov/su_docs/aces/

aces140.html.

You can also get a copy by submitting

a request to the Federal Aviation

Administration, Office of Rulemaking,

ARM–1, 800 Independence Avenue,

SW., Washington, DC 20591, or by

calling (202) 267–9680. Make sure to

identify the amendment number or

docket number of this final rule.

Small Business Regulatory Enforcement

Fairness Act

The Small Business Regulatory

Enforcement Fairness Act (SBREFA) of

1996 requires the FAA to comply with

small entity requests for information or

advice about compliance with statutes

and regulations within its jurisdiction.

Therefore, any small entity that has a

question regarding this document may

contact their local FAA official, or the

person listed under FOR FURTHER

INFORMATION CONTACT. You can find out

more about SBREFA on the Internet at

our site, http://www.gov/avr/arm/

sbrefa.htm. For more information on

SBREFA, e-mail us at 9-AWASBREF@faa.gov.

Background

This amendment is based on notice of

proposed rulemaking (NPRM) Notice

No. 96–6, which was published in the

Federal Register on July 3, 1996 (61 FR

35056). The related background leading

to Notice No. 96–6 is as follows:

In 1988, the FAA, in cooperation with

the JAA and other organizations

representing the American and

European aerospace industries, began a

process to harmonize the airworthiness

requirements of the United States and

the airworthiness requirements of

Europe, especially in the areas of Flight

Test and Structures.

In 1992, the FAA harmonization effort

was undertaken by the Aviation

Rulemaking Advisory Committee

(ARAC). A working group of industry

and government hydraulic systems

specialists of Europe, the United States,

and Canada was chartered by notice in

the Federal Register (57 FR 58843,

December 12, 1992) to harmonize

requirements and the associated test

conditions for hydraulic systems,

installed in transport category airplanes

(§ 25.1435). The harmonization task was

completed by the working group and

recommendations were submitted to

FAA by letter dated November 6, 1995.

The FAA concurred with the

recommendations and proposed them in

Notice No. 96–6. A Notice of availability

of proposed AC 25.1435–1 and request

for comments was also published in the

Federal Register on July 3, 1996 (61 FR

35062). In August 1996, the JAA issued

its Notice of Proposed Amendment

(NPA) 25F–273: ‘‘Hydraulic Systems’’

which included the proposed advisory

material AMJ 25.1435. The amendments

proposed in NPA 25F–273 and the

advisory material proposed in AMJ

25.1435 were substantively the same as

the amendments proposed in Notice No.

96–6 and the advisory material in

proposed AC 25.1435–1.

As a result, although the FAA (and

JAA) has received two sets of comments

from the public, in response to the

proposed rule and the proposed AC, the

comments are interlinked and addressed

jointly. Therefore, the FAA has

considered both sets of comments in

preparing the final rule contained

herein and the new AC. The

announcement of the FAA’s issuance of

the new AC will be published in the

Federal Register once it is available to

the public. Interested persons have been

given an opportunity to participate in

this rulemaking, and due consideration

has been given to all matters presented.

Comments received are discussed

below.

Discussion of Comments

Eight commenters responded to the

request for comments contained in

Notice No. 96–6, the notice of

availability of proposed AC 25.1435–1

and the corresponding JAA document

NPA 25F–273 and AMJ 25.1435.

Comments were received from foreign

airplane manufacturers, foreign

airworthiness authorities, and both

foreign and domestic industry

organizations. The majority of the

commenters agree with the proposal and

recommend its adoption. However,

some commenters disagree with the

proposal while providing alternative

proposals that appear to merit further

consideration by the ARAC. Therefore

the FAA tasked the ARAC Hydraulic

Systems Harmonization Working Group

(HWG) by notice in the Federal Register

(62 FR 38187, July 16, 1997) to consider

the comments and provide

recommendations for the disposition of

the comments along with any

recommendations for changes to the

proposal. The disposition of the

comments that follows is based on the

agreement reached by the HWG. Several

Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations 27397

of the comments address multiple issues

and some of the issues were addressed

by many commenters. As a result, the

FAA responses to the comments are

organized by individual comment under

each proposal, i.e., proposals 1 through

12.

Proposal 1, § 25.1435(a)(1). One

commenter states that the structure of

the punctuation in the first sentence

appears to allow leakage under proof

pressure, providing that such leakage

does not prevent the element from

performing its intended function. The

proper intent should be to prohibit any

leakage under proof pressure. The

commenter suggests to revise the

regulatory text of the first sentence as

follows: ‘‘(1) Withstand the proof

pressure without leakage and without

permanent deformation that would

prevent it from performing its intended

function, and withstand the ultimate

pressure without rupture.’’ The FAA

agrees that some clarification of the rule

text is necessary. The FAA does not

however agree with the commenter’s

suggested text because under proof

pressure, some external seal leakage is

allowed as long as the element’s ability

to perform its intended function

remains unaffected once the design

operating pressure (DOP) is restored.

Accordingly, the final rule text of the

first sentence and the associated

advisory circular text have been revised

to read:

Rule text: ‘‘(a) Element design. Each

element of the hydraulic system must be

designed to:

(1) Withstand the proof pressure

without permanent deformation that

would prevent it from performing its

intended functions, and the ultimate

pressure without rupture.’’

Advisory circular text: The following

text has been added to Paragraph

4a(1)(d), Ref. § 25.1435(a)(1), of the AC:

‘‘At proof pressure, seal leakage not

exceeding the allowed maximum inservice leak rate is permitted. Each

element should be able to perform its

intended function when the DOP is

restored.’’ For consistency, in Paragraph

4a(2), Ref. § 25.1435(a)(2), of the AC, the

following text will be added: ‘‘At limit

load, seal leakage not exceeding the

allowed maximum in-service rate is

permitted.’’

Another commenter recommends that

consideration be given to address

system ‘‘return pressures’’ in addition to

the ‘‘design, proof, and ultimate

pressures’’ in the table presented as part

of § 25.1435(a)(1). The FAA did

consider the return pressures but

decided that since the factors specified

in the table apply to both high/supply

pressures and low/return pressures, it

was unnecessary to specify two sets of

factors.

A third commenter recommends that

the advisory material should include

guidance for determination of the DOP

for elements in the low pressure side of

the system. The FAA concurs and has

added the following definition in the

AC, Paragraph 4a(1)(b), Ref.

§ 25.1435(a)(1): ‘‘The DOP for low

pressure elements (e.g., return, casedrain, suction, reservoirs) is the

maximum pressure expected to occur

during normal user system operating

modes. Included are transient pressures

that may occur during separate or

simultaneous operation of user systems

such as slats, flaps, landing gears, thrust

reversers, flight controls, and power

transfer units. Short term transient

pressures, commonly referred to as

pressure spikes, that may occur during

the selection and operation of user

systems (e.g., those pressure transients

due to the opening and closing of

selector/control valves) may be

excluded, provided the fatigue effect of

such transients is addressed in

accordance with Paragraph 4a(4) of this

AC.’’

A fourth commenter proposes to

replace the term DOP with the term

‘‘nominal pressure’’ claiming that this

terminology was consistent with MILstandards and the commenter’s own

country’s practices where operating

pressure of 3000 psi corresponds to the

nominal pressure. The FAA notes that

consideration was given by the working

group to use the term ‘‘nominal

pressure’’ but no agreement could be

reached on its definition because the

term ‘‘nominal’’ could involve

tolerances, fluctuations, and other

interpretations; the term ‘‘DOP’’ is more

specific.

This commenter also proposes that

the same safety factor be used for all

elements, i.e., not less than 1.5 for proof

pressure and not less than 3.0 for burst

pressure. The FAA does not agree.

Existing U.S. and European industry

standards/practices were used to arrive

at these factors and to harmonize with

current JAR 25, Appendix ‘‘J’’

(Appendix ‘‘K’’ effective May 27, 1994)

requirements. The commenter’s

suggestion would simplify the

requirements but does not reflect the

acceptable industry standards.

For the above reasons, the proposed

§ 25.1435(a)(1) has been modified by

deleting reference to ‘‘without leakage’’

and text added in the advisory circular

regarding leakage and a definition of the

DOP for elements in the low pressure

side of the system.

Proposals 2 and 3, §§ 25.1435(a)(2),

(3). One commenter states that in spite

of the guidance material, there is still

room for misunderstanding the meaning

of structural loads in the context of

hydraulic system elements. The

commenter states that the intent is that

the designer must consider those loads

arising when the airplane responds to

the relevant critical loading conditions

of subpart C, in which case it would

improve clarity to say so. Also, the

strength analysis of hydraulic system

elements must not stop at consideration

of inertia, dynamic and aerodynamic

loads, but must also include

consideration of strains imposed by the

deformation (bending, twist, etc.) of the

structure to which the elements are

attached. Furthermore, thermal stresses

are likely to be important at the normal

operating temperature of the hydraulic

system. To address these factors, the

commenter proposes the following

amendment:

‘‘§ 25.1435(a)(2)—Withstand, without

deformation that would prevent it from

performing its intended functions, the

design operating pressure in

combination with the loads and

structural deflections arising from the

critical limit loading conditions of

subpart C. Where appropriate, thermal

effects must also be taken into account.

§ 25.1435(a)(3)—Withstand, without

rupture, the design operating pressure

multiplied by a factor of 1.5, in

combination with the ultimate loads

and ultimate structural deflections

arising from the critical loading

conditions of subpart C. Where

appropriate, thermal effects must also be

taken into account.’’

The commenter also suggests that the

third sentence of Paragraph 4a(2) of the

proposed AC be modified to read: ‘‘The

loading conditions to be considered

include, but are not limited to flight and

ground maneuvers, and gust and

turbulence conditions. The loads arising

in these conditions should be combined

with the maximum hydraulic pressures,

including dynamic transients, that

could occur simultaneously. Where

appropriate, thermal effects should also

be accounted for in the strength

justification.’’

The FAA has considered these

comments. The commenter’s suggested

amendments to §§ 25.1435(a)(2) and

(a)(3) are inherent in the regulations as

stated in the original document and do

not have to be itemized in the rule.

Therefore, it was determined that it

would be more appropriate that the

texts for §§ 25.1435(a)(2) and (a)(3)

should remain as proposed in the NPRM

but that the associated advisory material

should be improved, as suggested by the

commenter, to more adequately reflect

the intent of the proposed requirements.

27398 Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations

The AC, Paragraph 4a(2), is therefore

amended to read as follows:

‘‘(2) (Ref. § 25.1435(a)(2)) Limit

structural loads are defined in

§ 25.301(a). The loading conditions of

Part 25, Subpart C to be considered

include, but are not limited to flight and

ground maneuvers, and gust and

turbulence conditions. The loads arising

in these conditions should be combined

with the maximum hydraulic pressures,

including transients, that could occur

simultaneously. Where appropriate,

thermal effects should also be accounted

for in the strength justification. For

hydraulic actuators equipped with

hydraulic or mechanical locking

features, such as flight control actuators

and power steering actuators, the

actuators and other loaded elements

should be designed for the most severe

combination of internal and external

loads that may occur in use. For

hydraulic actuators that are free to move

with external loads, i.e., do not have

locking features, the structural loads are

the same as those produced by the

hydraulic actuators. At limit load, seal

leakage not exceeding the allowed

maximum in-service leak rate is

permitted.’’ For consistency, the

statement ‘‘Where appropriate, thermal

effects should be accounted for in the

strength justification’’ will also be

added at the end of Paragraph 4a(3) of

the AC.

The same commenter further adds

‘‘The final sentence in Paragraph 4a(3)

of the proposed AC specifically allows

operational/functional failure under

(when subjected to) ultimate load

conditions. However, the use of the

word ‘‘under’’ in this context could give

rise to confusion as to whether

operational/functional failure is allowed

‘‘below’’ ultimate load. If so, this would

be inconsistent with the safety

objectives set by the structural

requirements that prohibit failure at any

load level up to and including ultimate.

If a hydraulic component is essential for

continued safe flight then it must not be

allowed to fail, or lose operational

functionality, at or below, ultimate load

conditions. For example, the hydraulic

system powering an elevator would be

critical for recovery from the design

maneuvering condition, and must not be

allowed to fail below the ultimate loads

associated with this condition. To

improve clarity and remove confusion,

the wording should be changed to state

positively that operational/functional

failure is not allowed at any load level

up to and including ultimate.’’ The FAA

agrees with the commenter that no

structural failure (rupture) may occur up

to ultimate load. However, the

commenter seems to be suggesting that

operational/functional failures should

not be allowed up to ultimate loads. The

FAA disagrees. Section 25.1435(a)(3) of

the regulation requires that elements of

the hydraulic system not rupture

(structural failure) up to ultimate loads.

Section 25.1435(a)(2) requires

operational/functional integrity only up

to limit load. Paragraphs 4a(2) and (3) of

the AC properly capture this

relationship and no change is necessary.

Another commenter suggests that time

limits for proof and burst pressure tests

be included in the regulation, not just in

the AC. The FAA does not agree. The

recommended time limits in the

proposed AC, paragraph 4(a)(1)(e), are

an industry standard and one method,

but not the only method, of

demonstrating compliance and therefore

not appropriate for inclusion in the

regulation. The commenter also states

that the definitions of pressures and/or

pressures and times given in the

proposed AC do not appear to match the

current JAA criteria and wondered

whether they had been fully

harmonized. The FAA notes that the

proposed pressures and times have been

fully harmonized although they may

differ from the current JAA criteria

(Appendix J to JAR 25). The regulatory

agencies have agreed to use the criteria

proposed in the AC.

A third commenter states that the

proposed advisory material for

§ 25.1435(a)(3) was simply rephrasing of

the regulation and not a means of

compliance as expected; a more detailed

clarification in the AC of the methods of

implementing this requirement was

desirable. The FAA notes that the first

statement in the AC references

regulations relevant to the requirement,

however the remainder is advisory and

gives details of the methods of pass/fail

of a test of the requirement but allows

flexibility for the applicant to propose

any method acceptable to the FAA.

In light of the above discussion,

§§ 25.1435(a)(2) and (a)(3) are adopted

as proposed with clarifying text added

in the AC to account for thermal effects

in strength justification and to allow

some leakage at limit load.

Proposal 4, § 25.1435(a)(4). One

commenter states that in order to

provide sufficient safeguard against the

possibility of a premature failure in the

operational life of an airplane, it will be

necessary to consider the effects of

material fatigue variability on life.

Conventionally, this would be done

through application of an appropriate

scatter factor to the result of the fatigue

analysis or fatigue test (See JAR ACJ

25.571(a)(3)). To ensure that the effects

of variability are properly taken into

account in the interpretation of the

fatigue analysis and test data required

by this paragraph, the commenter

proposed the following:

‘‘§ 25.1435(a)(4)—Withstand, without

failure, the fatigue effects of repeated

loads of variable magnitude expected

during its service life, including

pressure cycles, pressure transients,

externally induced loads, structural

deformations and, where appropriate,

thermal effects. Appropriate safe-life

scatter factors must be applied.’’

The FAA understands the concerns

expressed here, but does not agree with

the linkage to § 25.571, which applies to

safe-life components, e.g., landing gear,

and not to hydraulic components.

However, the intent of this comment is

already addressed in AC Paragraph

4c(1), Ref. § 25.1435(c)(1).

The same commenter adds, ‘‘The term

‘‘cyclical loads’’ in Paragraph 4a(4) of

the proposed AC, is usually associated

with a periodic force. It would be better

to use the term ‘‘load cycles.’’ This

paragraph would be an appropriate

place to give guidance on the need to

cover scatter in fatigue properties—JAR

ACJ 25.571(a) has some relevant

guidance material.’’ The FAA agrees

with the use of the term ‘‘load cycles’’

and the advisory text has been modified

accordingly. The FAA does not agree

that any advisory material is needed for

scatter factors or the relevance to

§ 25.571, as discussed earlier.

Another commenter states that it is

not understood how the current JAR

25.1435(a)(6) requirement—means of

providing flexibility—comes into the

new § 25.1435(a)(4) requirement. The

FAA notes that it is not the new

§ 25.1435(a)(4) but rather the new

§ 25.1435(a)(5) that addresses the

current JAR 25.1435(a)(6) requirement

and NPRM Proposal 5 clearly stated

that. The new § 25.1435(a)(5) addresses

the environmental factors, including the

vibrational & acceleration effects of the

elemental installation as discussed in

the associated advisory material. The

commenter also suggested including in

the advisory material, a

recommendation for the scatter factor to

be used when conducting the fatigue

testing (for example 4.0 for non-critical

parts, 6.0 for critical parts). The FAA

notes that as stated in Paragraph 4c(1)

of the AC, the manufacturer may select

design factors identified in accepted

manufacturing, national, military, or

industry standards provided that it can

be established that they are suitable for

the intended application. It is not

appropriate to give scatter factors since

they are more suitable for safe life

components, e.g., landing gear and not

hydraulic system components.

Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations 27399

This same commenter also wonders

whether there should be an allowance

for the fact that a component might be

fitted on more than one airplane in its

lifetime, and hence the fatigue cycles

could well be considerably more than

predicted for a part which is assumed to

be on the airplane for its entire life; it

would be very useful to have a

consistent policy for this issue. The

FAA notes that the requirements of

§§ 25.671 and 25.1309 specify that the

failure of no single element shall

jeopardize the continued safe flight and

landing of the airplane. Section

25.1435(a)(4) specifies the design

requirements of the element and its

failure consequences that should be

understood and addressed by the

designer. The existing requirements

adequately cover the overall safety of an

airplane at the time of certification and

part 25 regulations are not intended to

deal with parts tracking. Furthermore,

reliability of hydraulic systems is based

on redundancy of the design

architecture rather than safe-life of

components.

Yet another commenter suggests that

Society of Automotive Engineers (SAE)

document ARP 1383 ‘‘Impulse Testing

of Hydraulic Actuators, Valves, Pressure

Containers, and Similar Fluid System

Components’’ be included as a reference

in the AC. The FAA notes that ARP

4752 ‘‘Aerospace-Design and

Installation of Commercial Transport

Aircraft Hydraulic Systems’’ listed in

the advisory circular in turn refers to

ARP 1383. All of the relevant SAE

documents are referenced in ARP 4752

and are too numerous to be individually

listed in the AC.

For the reasons stated, § 25.1435(a)(4)

is adopted as proposed.

Proposal 5, § 25.1435(a)(5). One

commenter recommends that the

advisory material state that thermal

effects be particularly considered for

accumulators which are isolated from

the hydraulic system by non-return

valves. The FAA notes that

§ 25.1435(a)(5) addresses the

environmental factors that are to be

considered when designing the element

and that in the AC, temperature effects

are specifically stated as one of the

variables to be addressed. For the stated

reasons, § 25.1435(a)(5) is adopted as

proposed.

Proposal 6, § 25.1435(b)(1). One

commenter expresses a concern that the

requirements of (b)(1)(i) could be open

for interpretation by different

airworthiness authorities, particularly

with respect to fluid level quantity

indication. The commenter further

states that there were occasions when

the warning/indication philosophy that

had been agreed to with one

airworthiness authority had not been

agreed to by other authorities and this

therefore led to redesign and/or other

additional costs. The FAA notes that the

commenter’s concern of eliminating

differences in interpretations is the

basic reason for harmonization effort.

The intent of the harmonized rule is to

specify what type of indication is

required from the point of view of what

the pilot can use, without specifying the

design of the indication. Adoption of a

harmonized rule and guidance material

will enhance the likelihood of similar

interpretations during the certification

process. But neither the rule nor the

guidance material can assure precision

in interpretation and application absent

detailed listings of acceptable methods

for particular applications. Since the

rule and guidance material are intended

to establish performance based

standards, useful for future applications

and developments, as well as current

certifications, it is impossible, and

undesirable to provide the detail that

would assure uniformity. The FAA has

determined that the currently agreed

upon language is as likely to produce

uniform interpretations as any other

language which can prudently be

adopted.

Another commenter states that

‘‘moving from prescriptive to general

indication requirements is considered to

be sensible, but to be truly meaningful,

the requirement should be stated more

objectively. Section 25.1435(b)(1)(ii) is

close to being an objective requirement

but § 25.1435(b)(1)(i) is not. In fact it is

not apparent what indication might be

required by § 25.1435(b)(1)(i) that would

not be required by § 25.1435(b)(1)(ii).’’

The FAA does not agree. Changing the

existing requirement of JAR

25.1435(a)(2), which refers to the

provision of indications of system

pressure and fluid quantity, to

§ 25.1435(b)(1) which is less

prescriptive in that it requires the

provision of indications of only the

appropriate parameters, establishes an

objective statement of the requirement.

The FAA has determined that, to ensure

continued safe flight and landing, each

hydraulic system that either (1)

performs an essential function or (2)

that requires corrective action by the

flightcrew following a malfunction

(irrespective of whether it performs an

essential function), must be associated

with the appropriate flight-crew

indications. The associated AC clarifies

that the ‘‘appropriate indications’’ are

not limited other than that they should

be appropriate. As discussed in the

response to the preceding comment, the

FAA believes the current language is as

close to a performance based standard

as is possible, while avoiding dictating

design and allowing flexibility in future

design development.

The second commenter also points

out that ‘‘in Paragraph 4b of the

proposed AC, the statement ‘These

requirements are unique to hydraulic

systems’ is questioned.’’ The FAA

agrees with the commenter.

Accordingly, the first sentence ‘‘These

requirements are unique to hydraulic

systems, and may compliment

§ 25.1309’’ has been deleted and the

second sentence has been modified to

read ‘‘Design features that should be

considered for elimination of

undesirable conditions and effects are:’’

The first commenter also points out

that the NPRM cited this requirement as

§ 25.1435(a)(1) when it should have

been § 25.1435(b)(1). The FAA concurs

that the preamble of the proposed rule

had a typographical error but not the

proposed rule text.

For the stated reasons, § 25.1435(b)(1)

is adopted as proposed with clarifying

changes made in the AC text including

deleting reference to § 25.1309.

Proposals 7, 8, and 9,

§§ 25.1435(b)(2), (3), and (4). No

comments were received. Sections

25.1435(b)(2), (3), and (4) are therefore

adopted as proposed.

Proposal 10, § 25.1435(b)(5). One

commenter states that the means to

identify the hydraulic fluid may not

always be practical—particularly for

small components such as in line nonreturn valves. The FAA notes that the

intent of the requirement is not that

every component be so identified but

rather that suitable placarding be

provided as practical so that servicing of

the hydraulic system(s) is done with the

specified fluid. As pointed out by

another commenter, typical/acceptable

marking locations for the hydraulic

fluid used are hydraulic actuators, refill

points, reservoirs, and applicable

servicing documents. The second

commenter recommends specifying

these typical locations in the AC. The

FAA concurs and appropriate wording

has been included in Paragraph 4b(5),

Ref. § 25.1435(b)(5), of the AC.

A third commenter suggests that FAA

consider clarifying the language in

proposed § 25.1435(b)(5) to address the

situation of fluid mixtures. The FAA

infers that the commenter is referring to

Paragraph 4b(5) of the AC which states:

‘‘If more than one approved fluid is

specified, the term suitable hydraulic

fluid is intended to include acceptable

mixtures.’’ The FAA notes that

acceptable fluids and/or mixtures are

those listed in the airplane

27400 Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations

manufacturer’s maintenance manuals as

approved for that airplane model. These

maintenance manual provisions,

coupled with the proposed AC

language, seem to provide adequate

clarity. For the stated reasons,

§ 25.1435(b)(5) is adopted as proposed.

Proposal 11, § 25.1435(c). One

commenter states that as written, this

section continues the practice of

including some means of compliance

within the main code rather than in the

advisory material. The commenter

believes § 25.1309(d) currently contains

the same anomaly, but understands that

the decision has been taken in the

§ 25.1309 Working Group to rectify this

by moving § 25.1309(d) into the

advisory material. The commenter

recommends that the same thing could

be done here. The FAA partially accepts

this comment, and is amending the

opening paragraph by deleting the

words ‘‘To demonstrate compliance

with § 25.1435 and support compliance

with § 25.1309.’’ The paragraph would

commence ‘‘Tests must be conducted

....’’ and would otherwise remain

unchanged from the original proposal.

Except for qualifying statements that

bring immediate clarification to the

primary regulatory statements, the

remainder of the paragraph is

considered regulatory and not advisory.

Section 25.1435(c) has been revised

accordingly.

Proposal 11, §§ 25.1435(c)(1) and (c)(2).

One commenter states ‘‘Although it is

considered that an endurance test of a

complete airplane hydraulic system is a

very useful test, there are circumstances

where a full endurance test is an

expensive exercise with no benefit to

the integrity and safety of the airplane.

Particular examples of this are: (1) the

airplane hydraulic system is

substantially based on an existing, well

proven in-service airplane, and (2) the

number and/or nature of services which

are powered hydraulically are such that

the loss of the system has no significant

effect on the airworthiness of the

airplane.’’

The FAA concurs with the commenter

in that testing may not always be

necessary and notes that the proposed

requirement test criteria already include

the provision ‘‘except that analysis may

be used in place of or to supplement

testing, where the analysis is shown to

be reliable and appropriate.’’ The type

and extent of testing guidance covered

in AC adequately address commenter’s

concern. In addition, full system testing

is not required; subsystem or element

testing is allowed. The commenter

further states:

‘‘It should be noted that American

engineers quite often think of endurance

as fatigue testing. It is therefore

recommended that ‘pressure impulse’ be

added after fatigue in this section.’’ The

FAA notes that Paragraph 4c(1) of the

AC adequately defines these terms (for

all engineers) and the associated testing.

For the stated reasons, §§ 25.1435(c)(1),

and (c)(2) are adopted as proposed.

Proposal 12, § 25.1435(c)(3). One

commenter states: ‘‘It is proposed that

this requirement be dispensed with.

This is because (1) in the course of an

airplane production run, the hydraulic

system can undergo many modifications

(including the introduction of a cargo

door system) which affect the system

installation. Yet, it is the norm that this

is a once only test which is conducted

on an early production airplane during

the certification test program, and (2)

each airplane should be inspected with

respect to clearances with the hydraulic

system unpressurized and then

pressurized. It is doubtful whether there

will be any significant movement of the

piping, hoses, components, etc. as a

result of increasing the pressure by

25%.’’

The FAA notes that this test is

conducted only once per installation.

However, the FAA requires that any

significant modification(s) such as

introduction of a cargo door system, a

ram air turbine (RAT), or a tail-skid

system be assessed along with any

associated/affected system(s) to meet

this requirement. There are several

recent examples of such modifications

that will require additional testing. Such

testing may also be supplemented by

analysis if appropriate.

Regarding the commenter’s statement

(2) about insignificant movement of the

piping etc., when pressurized at 25%

above nominal, the FAA concurs and

notes that both the proposed and the

final rule states that instead a full rangeof-motion, testing be conducted at just

below the system relief pressure setting.

The commenter goes on to state ‘‘There

are some reservations with the new test

proposal, as follows:

(1) The requirement to check

clearances may not be easily achieved

for those parts of the system which are

actuated, for example, landing gear,

flight controls.

(2) As the system is pressurized to a

higher value, there may be concerns

about safety, particularly as the services

may operate quicker.

(3) The validity of the test results

could be queried as the flight control

actuators are unloaded.’’

The FAA notes that: (1) Paragraph

4c(3) of the AC adequately addresses

this concern by stating: ‘‘it may be

permissible that certain components of

the system need not be tested if it can

be shown that they do not constitute a

significant part of the system with

respect to the evaluation of adequate

clearances or detrimental effects.’’

(2) The system(s) relief valve(s)

protect against over-pressurization.

Standard safety precautions on the

factory floor while the testing is being

conducted must be practiced. There are

no appreciable differences from full

functional test(s) conducted by the

manufacturer.

(3) The intent is not to check/verify

structural deflections or motion of

surfaces for flight controls. Loading is

not anticipated to cause surface

deflections.

Lastly, the commenter states: ‘‘With

respect to the low pressure side of the

hydraulic system, it is proposed that the

tests be conducted with a dummy return

filter element installed, thereby forcing

all the fluid through the return filter

bypass. This meets the same criteria as

for increasing the system pressure to

125%, that is increasing the pressure

levels to that which could conceivably

occur in service.’’

The FAA notes that the commenter’s

scenario may be applicable to some of

the hydraulic system architectures

(layouts), but not all. It is the FAA’s

policy to allow flexibility for the

applicant to propose a method of

compliance which is acceptable to the

cognizant certification office. Specifying

the proposed dummy filter installation

may be misinterpreted by an applicant

as too restrictive. The commenter’s

suggested method is one means but not

the only means of demonstrating

compliance.

In light of the discussion above and

the explanations already provided in the

AC, § 25.1435(c)(3) is adopted as

proposed.

General: One commenter states: ‘‘It is

considered that the harmonization of

the § /JAR 25.1435 has produced a good

set of airworthiness requirements.

However, there is still a concern that

there are areas within the new

requirements, which could be subject to

interpretation by airworthiness

surveyors. It is recommended that the

FAA/JAA review the advisory material

and ensure that there are no areas where

misinterpretation can occur. The reason

for this comment is not to direct

concern at the professionalism of the

JAA and FAA, but rather there is a

concern that other national authorities

could read in additional requirements

where none were intended.’’ The HWG

together reviewed and developed these

regulations and the associated advisory

material. Both the regulations and the

advisory material are fully harmonized.

A considerable amount of time was

Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations 27401

spent discussing the very issues and

concerns raised by the commenter to

arrive at the final rule and the AC. As

discussed previously in addressing the

comment on Proposal 6, the FAA

believes that these rules are as likely to

produce uniform interpretations as any

other language which can be prudently

adopted.

Another commenter points out that

the word ‘‘must’’ in Paragraphs 4a(1),

a(2), and a(4) of the AC, and the word

‘‘shall’’ in Paragraph 4a(3) of the AC

should be replaced by ‘‘should.’’ The

FAA agrees and the text in the AC has

been revised. The commenter adds that

in Paragraph 4a(1), third paragraph,

reference to ‘‘structural loads’’ should

be replaced by ‘‘external loads.’’ The

FAA does not agree since reference to

structural loads is appropriate as used

in §§ 25.301 and 25.1435(a)(1).

With the exception of the changes

noted in §§ 25.1435(a)(1) and (c) this

final rule is adopted as proposed in

Notice 96–6.

Paperwork Reduction Act

In accordance with the Paperwork

Reduction Act of 1995 (44 U.S.C,

3507(d)), there are no requirements for

information collection associated with

this amendment.

International Compatibility

In keeping with U.S. obligations

under the Convention on International

Civil Aviation, it is FAA policy to

comply with International Civil

Aviation Organization (ICAO) Standards

and Recommended Practices to the

maximum extent practicable. The FAA

has reviewed the corresponding ICAO

Standards and Recommended Practices

and has identified no differences with

these regulations.

Executive Order 12866 and DOT

Regulatory Policies and Procedures

Executive Order 12866, Regulatory

Planning and Review, directs the FAA

to assess both the costs and benefits of

a regulatory change. We are not allowed

to propose or adopt a regulation unless

we make a reasoned determination that

the benefits of the intended regulation

justify its costs. Our assessment of this

proposal indicates that its economic

impact is minimal. Since its costs and

benefits do not make it a ‘‘significant

regulatory action’’ as defined in the

Order, we have not prepared a

‘‘regulatory impact analysis.’’ Similarly,

we have not prepared a ‘‘regulatory

evaluation,’’ which is the written cost/

benefit analysis ordinarily required for

all rulemaking proposals under the DOT

Regulatory and Policies and Procedures.

We do not need to do the latter analysis

where the economic impact of a

proposal is minimal.

Economic Evaluation, Regulatory

Flexibility Determination, International

Trade Impact Assessment, and

Unfunded Mandates Assessment

Changes to Federal regulations must

undergo several 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.

Second, the Regulatory Flexibility Act

of 1980 requires agencies to analyze the

economic impact of regulatory changes

on small entities. Third, the Trade

Agreements Act (19 U.S.C. section

2531–2533) prohibits agencies from

setting standards that create

unnecessary obstacles to the foreign

commerce of the United States. In

developing U.S. standards, this Trade

Act also requires the consideration of

international standards and, where

appropriate, that they be the basis of

U.S. standards. And fourth, the

Unfunded Mandates Reform Act of 1995

requires agencies to prepare a written

assessment of the costs, benefits and

other effects of proposed or final rules

that include a Federal mandate likely to

result in the expenditure by State, local

or tribal governments, in the aggregate,

or by the private sector, of $100 million

or more (adjusted annually for inflation)

in any one year.

In conducting these analyses, the FAA

has determined this rule: (1) has

benefits which do justify its costs, 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; (2)

will not have a significant impact on a

substantial number of small entities; (3)

reduces barriers to international trade;

and (4) does not impose an unfunded

mandate on state, local, or tribal

governments, or on the private sector of

100 million or more in any one year.

These analyses, available in the docket,

are summarized below.

Economic Evaluation

Manufacturers contacted by the FAA

(in its preparation of the economic

evaluation for the NPRM), estimated

that three of the revisions to § 25.1435

(corresponding to proposals 1, 4, and

12) would impose additional costs—

revision 1 (regarding design load factors

for proof and ultimate pressure

conditions), 4 (regarding induced loads,

pressure transients, and fatigue), and 12

(regarding functional testing of the

complete hydraulic system). However,

based on new information from the

same manufacturers related to their

experiences with recent type

certifications, the FAA has determined

that none of the provisions will impose

incremental costs. The rule changes

codify current industry practice and or

conform § 25.1435 to corresponding

sections of the JAR. Adoption of the rule

changes increases harmonization and

commonality between American and

European airworthiness standards.

Harmonizing airworthiness standards

reduces manufacturers’ certification

costs for testing, report preparation,

certification-related travel abroad, etc.

One manufacturer of part 25 large

airplanes estimates that such cost

savings could range between $65,000

and $650,000 per type certification

(pertaining to hydraulic systems’

requirements as discussed in this

rulemaking). Since this estimate has

such a wide range and represents only

one manufacturer, the FAA used the

midpoint of approximately $360,000 for

a conservative estimate of

harmonization cost savings for a part 25

large airplane type certification. A

manufacturer of part 25 small airplanes

estimates such savings at $65,000 per

type certification. The FAA believes

these industry-provided numbers are

reasonable estimates of potential

harmonization cost savings. Potential

safety benefits resulting from

specification of minimum accepted

standards will supplement these cost

savings. Thus, with the described

benefits and no associated incremental

costs, the FAA finds the rule costbeneficial. (Note: All estimates in this

analysis are expressed in 1999 dollars).

Regulatory Flexibility Determination

The Regulatory Flexibility Act of 1980

(the Act) establishes ‘‘as a principle of

regulatory issuance that agencies shall

endeavor, consistent with the objective

of the rule and of applicable statutes, to

fit regulatory and informational

requirements to the scale of the

business, organizations, and

governmental jurisdictions subject to

regulation.’’ To achieve that principle,

the Act requires agencies to solicit and

consider flexible regulatory proposals

and to explain the rationale for their

actions. The Act covers a wide range of

small entities, including small

businesses, not-for-profit organizations,

and small governmental jurisdictions.

Agencies must perform a review to

determine whether a proposed or final

rule will have a ‘‘significant economic

impact on a substantial number of small

entities.’’ If the determination is that it

will, the agency must prepare a

regulatory flexibility analysis as

described in the Act.

27402 Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations

However, if an agency determines that

a proposed or final rule is not expected

to have a significant impact on a

substantial number of small entities,

section 605(b) of the Act provides that

the head of the agency may so certify

and a regulatory flexibility analysis is

not required. The certification must

include a statement providing the

factual basis for this determination, and

the reasoning should be clear.

The rule will affect manufacturers of

transport category airplanes produced

under future new airplane type

certifications. For manufacturers, a

small entity is one with 1,500 or fewer

employees. Since no part 25 airplane

manufacturer has 1,500 or fewer

employees, and, in addition, the rule

imposes no incremental costs, the FAA

certifies that the rule will not have a

significant economic impact on a

substantial number of small

manufacturers.

International Trade Impact Assessment

The Trade Agreement Act of 1979

prohibits Federal agencies from

engaging in any standards or related

activities that create unnecessary

obstacles to the foreign commerce of the

United States. Legitimate domestic

objectives, such as safety, are not

considered unnecessary obstacles. The

statute also requires consideration of

international standards and where

appropriate, that they be the basis for

U.S. standards. In addition, consistent

with the Administration’s belief in the

general superiority and desirability of

free trade, it is the policy of the

Administration to remove or diminish

to the extent feasible, barriers to

international trade, including both

barriers affecting the export of American

goods and services to foreign countries

and barriers affecting the import of

foreign goods and services into the

United States.

In accordance with the above statute

and policy, the FAA has assessed the

potential effect of this final rule and has

determined that it will impose the same

costs on domestic and international

entities and thus has a neutral trade

impact.

Unfunded Mandates Reform Act

The Unfunded Mandates Reform Act

of 1995 (the Act), enacted as Pub. L.

104–4 on March 22, 1995, is intended,

among other things, to curb the practice

of imposing unfunded Federal mandates

on State, local, and tribal governments.

Title II of the Act requires each Federal

agency to the extent permitted by law,

to prepare a written statement assessing

the effects of any Federal mandate in a

proposed or final agency rule that may

result in a $100 million or more

expenditure (adjusted annually for

inflation) in any one year by State, local,

and tribal governments, in the aggregate,

or by the private sector; such a mandate

is deemed to be a significant regulatory

action.

This final rule does not contain such

a mandate. Therefore, the requirements

of Title II of the Unfunded Mandates

Reform Act of 1995 do not apply.

Executive Order 13132, Federalism

The FAA has analyzed this final rule

under the principles and criteria of

Executive Order 13132, Federalism. We

determined that this action will not

have a substantial direct effect on the

States, or the relationship between the

national Government and the States, or

on the distribution of power and

responsibilities among the various

levels of government. Therefore, we

determined that this final rule does not

have federalism implications.

Regulations Affecting Intrastate

Aviation in Alaska

Section 1205 of the FAA

Reauthorization Act of 1996 (110 Stat.

3213) requires the Administrator, when

modifying regulations in Title 14 of the

CFR in a manner affecting intrastate

aviation in Alaska, to consider the

extent to which Alaska is not served by

transportation modes other than

aviation, and to establish such

regulatory distinctions as he or she

considers appropriate. Because this final

rule applies to the certification of future

designs of transport category airplanes

and their subsequent operation, it could

affect intrastate aviation in Alaska. The

Administrator has considered the extent

to which Alaska is not served by

transportation modes other than

aviation, and how the final rule could

have been applied differently to

intrastate operations in Alaska.

However, the Administrator has

determined that airplanes operated

solely in Alaska would present the same

safety concerns as all other affected

airplanes; therefore, it would be

inappropriate to establish a regulatory

distinction for the intrastate operation of

affected airplanes in Alaska.

Environmental Analysis

Federal Aviation Administration

Order 1050.1D defines FAA actions that

may be categorically excluded from

preparation of a National Environmental

Policy Act (NEPA) environmental

impact statement. In accordance with

FAA Order 1050.1D, appendix 4,

paragraph 4(j), this amendment qualifies

for a categorical exclusion.

Energy Impact

The energy impact of the amendment

has been assessed in accordance with

the Energy Policy and Conservation Act

(EPCA) Pub. L. 94–163, as amended (42

U.S.C. 6362) and FAA Order 1053.1. It

has been determined that the final rule

is not a major regulatory action under

the provisions of the EPCA.

List of Subjects in 14 CFR Part 25

Aircraft, Aviation safety, Reporting

and recordkeeping requirements.

The Amendment

In consideration of the foregoing, the

Federal Aviation Administration

amends part 25 of Title 14, Code of

Federal Regulations 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 and 44704.

2. Section 25.1435 is amended by

revising paragraphs (a), (b), and (c) to

read as follows:

§ 25.1435 Hydraulic systems.

(a) Element design. Each element of

the hydraulic system must be designed

to:

(1) Withstand the proof pressure

without permanent deformation that

would prevent it from performing its

intended functions, and the ultimate

pressure without rupture. The proof and

ultimate pressures are defined in terms

of the design operating pressure (DOP)

as follows:

Element Proof

(xDOP)

Ultimate

(xDOP)

1. Tubes and fittings. 1.5 3.0

2. Pressure vessels

containing gas:

High pressure

(e.g., accumulators) ................... 3.0 4.0

Low pressure (e.g.,

reservoirs) .......... 1.5 3.0

3. Hoses ................... 2.0 4.0

4. All other elements 1.5 2.0

(2) Withstand, without deformation

that would prevent it from performing

its intended function, the design

operating pressure in combination with

limit structural loads that may be

imposed;

(3) Withstand, without rupture, the

design operating pressure multiplied by

Federal Register / Vol. 66, No. 95 / Wednesday, May 16, 2001 / Rules and Regulations 27403

a factor of 1.5 in combination with

ultimate structural load that can

reasonably occur simultaneously;

(4) Withstand the fatigue effects of all

cyclic pressures, including transients,

and associated externally induced loads,

taking into account the consequences of

element failure; and

(5) Perform as intended under all

environmental conditions for which the

airplane is certificated.

(b) System design. Each hydraulic

system must:

(1) Have means located at a flightcrew

station to indicate appropriate system

parameters, if

(i) It performs a function necessary for

continued safe flight and landing; or

(ii) In the event of hydraulic system

malfunction, corrective action by the

crew to ensure continued safe flight and

landing is necessary;

(2) Have means to ensure that system

pressures, including transient pressures

and pressures from fluid volumetric

changes in elements that are likely to

remain closed long enough for such

changes to occur, are within the design

capabilities of each element, such that

they meet the requirements defined in

§ 25.1435(a)(1) through (a)(5);

(3) Have means to minimize the

release of harmful or hazardous

concentrations of hydraulic fluid or

vapors into the crew and passenger

compartments during flight;

(4) Meet the applicable requirements

of §§ 25.863, 25.1183, 25.1185, and

25.1189 if a flammable hydraulic fluid

is used; and

(5) Be designed to use any suitable

hydraulic fluid specified by the airplane

manufacturer, which must be identified

by appropriate markings as required by

§ 25.1541.

(c) Tests. Tests must be conducted on

the hydraulic system(s), and/or

subsystem(s) and elements, except that

analysis may be used in place of or to

supplement testing, where the analysis

is shown to be reliable and appropriate.

All internal and external influences

must be taken into account to an extent

necessary to evaluate their effects, and

to assure reliable system and element

functioning and integration. Failure or

unacceptable deficiency of an element

or system must be corrected and be

sufficiently retested, where necessary.

(1) The system(s), subsystem(s), or

element(s) must be subjected to

performance, fatigue, and endurance

tests representative of airplane ground

and flight operations.

(2) The complete system must be

tested to determine proper functional

performance and relation to the other

systems, including simulation of

relevant failure conditions, and to

support or validate element design.

(3) The complete hydraulic system(s)

must be functionally tested on the

airplane in normal operation over the

range of motion of all associated user

systems. The test must be conducted at

the system relief pressure or 1.25 times

the DOP if a system pressure relief

device is not part of the system design.

Clearances between hydraulic system

elements and other systems or structural

elements must remain adequate and

there must be no detrimental effects.

Issued in Renton, Washington, on May 9,

2001.

Donald L. Riggin,

Acting Manager, Transport Airplane

Directorate, Aircraft Certification Service,

ANM–100.

[FR Doc. 01–12232 Filed 5–15–01; 8:45 am]

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