[Federal Register Volume 63, Number 1 (Friday, January 2, 1998)]
[Proposed Rules]
[Pages 126-136]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-34166]



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Part II





Department of Transportation





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Federal Aviation Administration



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14 CFR Parts 91, 121, 125, and 129



Repair Assessment for Pressurized Fuselages; Proposed Rule



Proposed Advisory Circular (AC) 120-XX, Repair Assessment of 
Pressurized Fuselages; Notice

  Federal Register / Vol. 63, No. 1 / Friday, January 2, 1998 / 
Proposed Rules  

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 91, 121, 125, and 129

[Docket No. 29104; Notice No. 97-16]
RIN 2120-AF81


Repair Assessment for Pressurized Fuselages

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking.

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SUMMARY: This proposed rulemaking would require incorporation of repair 
assessment guidelines for the fuselage pressure boundary (fuselage 
skins and pressure webs) of certain transport category airplane models 
into the FAA-approved maintenance or inspection program of each 
operator of those airplanes. This action is the result of concern for 
the continued operational safety of airplanes that are approaching or 
have exceeded their design service goal. The purpose of the repair 
assessment guidelines is to establish a damage-tolerance based 
supplemental inspection program for repairs to detect damage, which may 
develop in a repaired area, before that damage degrades the load 
carrying capability of the structure below the levels required by the 
applicable airworthiness standards.

DATES: Comments must be submitted on or before April 2, 1998.

ADDRESSES: Comments on this document may be mailed in triplicate to: 
Federal Aviation Administration, Office of the Chief Counsel, 
Attention: Rules Docket (AGC-200), Docket No. 29104, 800 Independence 
Avenue SW., Washington, DC 20591; or delivered in triplicate to: Room 
915G, 800 Independence Avenue SW., Washington, DC 20591. Comments 
delivered must be marked Docket No. 29104. Comments may also be 
submitted electronically to: [email protected]. Comments may be 
examined in Room 915G weekdays, except Federal holidays, between 8:30 
a.m. and 5:00 p.m. In addition, the FAA is maintaining an information 
docket of comments in the Transport Airplane Directorate (ANM-100), 
Federal Aviation Administration, Northwest Mountain Region, 1601 Lind 
Avenue SW., Renton, WA 98055-4056. Comments in the information docket 
may be examined weekdays, except Federal holidays, between 7:30 a.m. 
and 4:00 p.m.

FOR FURTHER INFORMATION CONTACT:

Dorenda Baker, Manager, Aging Aircraft Program, ANM-109, FAA Transport 
Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue 
SW., Renton, WA 98055-4056; telephone (425) 227-2109, facsimile (425) 
227-1100.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    Interested persons are invited to participate in this proposed 
rulemaking by submitting such written data, views, or arguments as they 
may desire. Comments relating to the environmental, energy, federalism, 
or economic impact that might result from adoption of the proposals in 
this notice are also invited. Substantive comments should also be 
accompanied by cost estimates. Commenters should identify the 
regulatory docket or notice number and submit comments in triplicate to 
the Rules Docket address specified above. All comments received on or 
before the closing date for comments will be considered by the 
Administrator before taking action on this proposed rulemaking. The 
proposals contained in this notice may be changed in light of the 
comments received. All comments received will be available in the Rules 
Docket for examination by interested persons, both before and after the 
closing date for comments. A report summarizing each substantive public 
contact with FAA personnel concerned with this rulemaking will be filed 
in the docket. Commenters wishing the FAA to acknowledge receipt of 
their comments submitted in response to this notice must include a 
self-addressed, stamped postcard on which the following statement is 
made: ``Comments to Docket No. 29104. The postcard will be date stamped 
and returned to the commenter.

Availability of the NPRM

    An electronic copy of this document may be downloaded using a modem 
and suitable communications software from the FAA regulations section 
of the Fedworld electronic bulletin board service (telephone: 703-321-
3339), the online Federal Register database through GPO Access 
(telephone: 202-512-1661), or the FAA's Aviation Rulemaking Advisory 
Committee Bulletin Board service (telephone: 202-267-5948).
    Internet users may reach the FAA's web page at http://www.faa.gov 
or GPO's Federal Register web page at http://www.access.gpo.gov/
su__docs for access to recently published rulemaking documents.
    Any person may obtain a copy of this NPRM by submitting a request 
to the Federal Aviation Administration, Office of Rulemaking, ARM-1, 
800 Independence Avenue SW., Washington, D.C. 20591, or by calling 
(202) 267-9677. Communications must identify the notice number of this 
NPRM. Persons interested in being placed on a mailing list for future 
rulemaking documents should request from the Office of Public Affairs, 
Attention: Public Inquiry Center, APA-230, 800 Independence Ave SW., 
Washington, D.C. 20591, or by calling (202) 267-3484, a copy of 
Advisory Circular No. 11-2A, Notice of Proposed Rulemaking Distribution 
System, which describes the application procedure.

Background

    This proposal, to require the incorporation of repair assessment 
guidelines into the maintenance or inspection program for certain 
transport category airplanes, follows from commitments made by the FAA 
and the aviation community in June 1988 to address the issues 
concerning the safety of aging transport airplanes.
    In April 1988, a high-cycle transport airplane enroute from Hilo to 
Honolulu, Hawaii, suffered major structural damage to its pressurized 
fuselage during flight. This accident was attributed in part to the age 
of the airplane involved. The economic benefit of operating certain 
older technology airplanes has resulted in the operation of many such 
airplanes beyond their previously projected retirement age. Because of 
the problems revealed by the accident in Hawaii and the continued 
operation of older airplanes, both the FAA and industry generally 
agreed that increased attention needed to be focused on the aging fleet 
and on maintaining its continued operational safety.
    In June 1988, the FAA sponsored a conference on aging airplanes. As 
a result of that conference, an aging aircraft task force was 
established in August 1988 as a sub-group of the FAA's Research, 
Engineering, and Development Advisory Committee, representing the 
interests of the aircraft operators, aircraft manufacturers, regulatory 
authorities, and other aviation representatives. The task force, then 
known as the Airworthiness Assurance Task Force (AATF), set forth five 
major elements of a program for keeping the aging fleet safe. For each 
airplane model in the aging transport fleet, (1) select service 
bulletins describing modifications and inspections necessary to 
maintain structural integrity; (2) develop

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inspection and prevention programs to address corrosion; (3) develop 
generic structural maintenance program guidelines for aging airplanes; 
(4) review and update the Supplemental Structural Inspection Documents 
(SSID) which describe inspection programs to detect fatigue cracking; 
and (5) assess damage-tolerance of structural repairs. Structures Task 
Groups sponsored by the Task Force were assigned the task of developing 
these elements into usable programs.
    Today the Task Force, which has been reestablished as the 
Airworthiness Assurance Working Group (AAWG) of the Aviation Rulemaking 
Advisory Committee (ARAC), has completed its work on the first four 
elements. This proposed rulemaking addresses the fifth element, the 
assessment of repair damage tolerance.

Related Regulatory Activity

    In addition to the initiatives previously discussed, there are 
other activities associated with FAA's Aging Aircraft Program. These 
include FAA's response to the Aging Aircraft Safety Act and future 
rulemaking to mandate corrosion prevention and control programs for all 
airplanes used in air transportation.
    The Aging Aircraft Safety Act of 1991 (Pub. L. 49 U.S.C. 44717) 
instructed the Administrator to prescribe regulations that ensure the 
continuing airworthiness of aging aircraft through inspections and 
reviews of the maintenance records of each aircraft an air carrier uses 
in air transportation. In response to the Act, the FAA published notice 
93-14 on October 5, 1993 (58 FR 51944). The FAA has reviewed the public 
comments to that Notice and anticipates regulatory action in the near 
future based on those comments and other considerations.
    In addition, the FAA has found that some operators do not have a 
programmatic approach to corrosion prevention and control programs 
(CPCP). In its accident investigation report (NTSB/AAR-89/03) on the 
Aloha accident, the NTSB recommended that the FAA mandate a 
comprehensive and systematic CPCP. Therefore, the FAA is considering 
rulemaking to mandate CPCPS for all airplanes used in air 
transportation. As part of that deliberation, the FAA is considering 
the corrosion prevention and control programs recommended by the AATF 
and adopted by the FAA through Airworthiness Directives (ADs); those 
ADs affect all of the airplanes affected by this proposal.

The Aviation Rulemaking Advisory Committee

    The ARAC was formally established by the FAA on January 22, 1991 
(56 FR 2190), to provide advice and recommendations concerning the full 
range of the FAA's safety-related rulemaking activity. This advice was 
sought to develop better rules in less overall time using fewer FAA 
resources than are currently needed. The committee provides the 
opportunity for the FAA to obtain firsthand information and insight 
from interested parties regarding proposed new rules or revisions of 
existing rules.
    There are over 60 member organizations on the committee, 
representing a wide range of interests within the aviation community. 
Meetings of the committee are open to the public, except as authorized 
by section 10(d) of the Federal Advisory Committee Act.
    The ARAC establishes working groups to develop proposals to 
recommend to the FAA for resolving specific issues. Tasks assigned to 
working groups are published in the Federal Register. Although working 
group meetings are not generally open to the public, all interested 
parties are invited to participate as working group members. Working 
groups report directly to the ARAC, and the ARAC must concur with a 
working group proposal before that proposal can be presented to the FAA 
as an advisory committee recommendation.
    The activities of the ARAC will not, however, circumvent the public 
rulemaking procedures. After an ARAC recommendation is received and 
found acceptable by the FAA, the agency proceeds with the normal public 
rulemaking procedures. Any ARAC participation in a rulemaking package 
will be fully disclosed in the public docket.
    By Federal Register notice dated November 30, 1992 (57 FR 56627), 
the AATF was placed under the auspices of the Aviation Rulemaking 
Advisory Committee (ARAC) and renamed as the Airworthiness Assurance 
Working Group. One of the specific tasks assigned to the AAWG was to 
develop recommendations concerning whether new or revised requirements 
and compliance methods for structural repair assessments of existing 
repairs should be initiated and mandated for the Airbus A300; BAC 1-11; 
Boeing 707/720, 727, 737, 747; Douglas DC-8, DC-9/MD-80, DC-10; Fokker 
F-28; and Lockheed L-1011 airplanes.

The Concern Posed By Older Repairs

    The basic structure of each of the large jet transports that would 
be affected by this proposed rule was required at the time of original 
certification to meet the applicable regulatory standards for fatigue 
or fail-safe strength. Repairs and modifications to this structure were 
also required to meet these same standards.
    These early fatigue or fail-safe requirements did not provide for 
timely inspection of critical structure so that damaged or failed 
components could be dependably identified and repaired or replaced 
before a hazardous condition developed. In 1978 a new certification 
requirement called damage tolerance was introduced to assure the 
continued structural integrity of transport category airplanes 
certificated after that time. This concept was adopted as an amendment 
to Sec. 25.571 by Amendment 25-45 (43 FR 46242), and for existing 
designs, guidance material based on this rule was published in 1981 as 
Advisory Circular (AC) 91-56, Supplemental Structural Inspection 
Program for Large Transport Category Airplanes.
    Damage tolerance is a structural design and inspection methodology 
used to maintain safety considering the possibility of metal fatigue or 
other structural damage (i.e., safety is maintained by adequate 
structural inspection until the damage is repaired). The underlying 
principle for damage tolerance is that the initiation and growth of 
structural fatigue damage can be anticipated with sufficient precision 
to allow inspection programs to safely detect damage before it reaches 
a critical size. A damage-tolerance evaluation entails the prediction 
of sites where fatigue cracks are most likely to initiate in the 
airplane structure, the prediction of the crack trajectories and rates 
of growth under repeated airplane structural loading, the prediction of 
the size of the damage at which strength limits are exceeded, and an 
analysis of the potential opportunities for inspection of the damage as 
it progresses. This information is used to establish an inspection 
program for the structure that, if rigorously followed, will be able to 
detect cracking that may develop before it precipitates a major 
structural failure. A damage-tolerant structure is one in which damage 
would be detected by reliance on normally performed maintenance and 
inspection actions long before it becomes hazardous.
    The evidence to date is that when all critical structure is 
included, the damage-tolerant concept, and the supplemental inspection 
programs that

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are based on it, provide the best assurance of continued structural 
integrity that is currently available. In order to apply this concept 
to existing transport airplanes, beginning in 1984, the FAA issued a 
series of Airworthiness Directives (AD's) requiring compliance with the 
first supplemental inspection programs resulting from application of 
this concept to existing airplanes. Nearly all of the airplane models 
affected by this proposed rule are now covered by such AD's. Generally, 
these AD's require that operators incorporate Supplemental Structural 
Inspection Documents (SSID's) into their maintenance programs for the 
affected airplanes. These documents were derived from damage-tolerance 
assessments of the originally certificated type designs for these 
airplanes. For this reason, the majority of AD's written for the SID 
program did not attempt to address issues relating to the damage 
tolerance of repairs that had been made to the airplanes. The objective 
of this proposed rule is to provide that same level of assurance for 
areas of the structure that have been repaired.
    Repairs are a concern on older airplanes because of the possibility 
that they may develop, cause, or obscure metal fatigue, corrosion, or 
other damage during service. This damage might occur within the repair 
itself or in the adjacent structure and might ultimately lead to 
structural failure. The damage-tolerance evaluation of a repair would 
be used in an assessment program to establish an appropriate inspection 
program, or a replacement schedule if the necessary inspection program 
is too demanding or not possible. The objective of the repair 
assessment is to assure the continued structural integrity of the 
repaired and adjacent structure based on damage-tolerance principles.
    In general, repairs present a more challenging problem to solve 
than the original structure because they are unique and tailored in 
design to correct particular damage to the original structure. Whereas 
the performance of the original structure may be predicted from tests 
and from experience on other airplanes in service, the behavior of a 
repair and its effect on the fatigue characteristics of the original 
structure are generally not known to the same extent as for the basic 
unrepaired structure.
    The available service record and surveys of out-of-service and in-
service airplanes have indicted that existing repairs perform well. 
Although the cause of an airplane accident has never been attributed to 
properly applied repairs using the original repair data, repairs may be 
of concern as time-in-service increases for the following reasons:
    1. As airplanes age, both the number and age of the existing 
repairs increase. Along with this increase in the number of and age of 
repairs is the possibility of unforeseen repair interaction, autogenous 
failure, or other damage occurring in the repaired area. The continued 
operational safety of these airplanes depends primarily on a 
satisfactory maintenance program (inspections conducted at the right 
time, in the right place, using the most appropriate technique). To 
develop this program, a damage tolerance evaluation of repairs to 
flight-critical structure is essential. The longer an airplane is in 
service, the more important this evaluation and a subsequent inspection 
program become.
    2. The practice of damage-tolerance methodology has evolved 
gradually over the last 20 plus years. Some repairs described in the 
airplane manufacturers' Structural Repair Manuals (SRMs) were not 
designed to current standards. Repairs accomplished in accordance with 
the information contained in the early versions of the SRMs may require 
additional inspections if evaluated using the current methodology.
    3. Because a regulatory requirement for damage tolerance was not 
applied to airplane designs type certificated before 1978, the damage-
tolerance characteristics of repairs may vary widely and are largely 
unknown.

Development of Recommendation

    To address the ARAC assignment on repairs, the AAWG tasked the 
manufacturers to develop repair assessment guidelines requiring 
specific maintenance programs to maintain the damage-tolerance 
integrity of the basic airframe. The following criteria were developed 
to assist the manufacturers in the development of that guidance 
material:
     Specific repair size limits for which no assessment is 
necessary should be selected for each model of airplane.
     Repairs that do not conform to SRM standards must be 
reviewed and may require further action.
     Repairs must be reviewed where the repair has been 
installed in accordance with SRM data that have been superseded or 
rendered inactive by new damage-tolerant designs.
     Repairs in close proximity to other repairs or 
modifications require review to determine their impact on the continued 
airworthiness of the airplane.
     Repairs that exhibit structural distress should be 
replaced before further flight.
    To identify the scope of the overall program, fleet data were 
required. This resulted in the development of a five-step program to 
develop factual data for the development of the rule. The five-step 
AAWG program consisted of:
     Development of model specific repair assessment guidelines 
using AAWG repair criteria.
     Completion of a survey of a number of operators' airplanes 
to assess fuselage skin repairs, and to validate the approach of the 
manufacturer's repair assessment guidelines.
     Determination of the need for and the development of a 
world-wide survey.
     Collection and assessment of results to determine further 
necessary actions.
     Development of specific manufacturer/operator/FAA actions.
    Early in the development of this task, each manufacturer began to 
prepare model specific repair assessment guidelines. When sufficiently 
developed, these draft guidelines were shared with the operators to get 
feedback on acceptability and suggestions for improvement. The 
operators stressed the need for commonality in approach and ease of use 
of the guidelines. They also expressed the need for guidelines that 
could be used on the shop floor without engineering assistance and 
without extensive training.
    Meanwhile, the AAWG conducted two separate surveys of existing 
repairs on airplanes to collect necessary data. The first survey was 
conducted in March 1992 on certain large transport category airplanes 
being held in storage. Teams, comprised of engineering representatives 
from various organizations, including FAA's Aircraft Certification and 
Flight Standards offices, operators, and manufacturers, surveyed 356 
external fuselage skin repairs on 30 airplanes of 6 types. Using repair 
classification criteria developed by the individual airplane 
manufacturers, the teams concluded that the general quality of the 
repairs appeared good. Forty percent of the repairs were adequate, 
requiring no supplemental inspections, and sixty percent needed a more 
comprehensive damage-tolerance based assessment, with the possibility 
that supplemental inspections might be needed. Some determining factors 
on the need for further assessment were the size of the repair and its 
proximity to other repairs. While the survey sample size was very small 
compared to the total population of transport airplanes type 
certificated

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prior to 1978, it provided objective information on the quality and 
damage-tolerance characteristics of existing airplane repairs.
    In 1994, the AAWG requested that the manufacturers conduct a second 
survey on airplane repairs to validate the 1992 results and to provide 
additional information relative to the estimated cost of the assessment 
program. The manufacturers were requested to visit airlines operating 
their products and to conduct surveys on airplanes in heavy 
maintenance. An additional 35 airplanes were surveyed in which 695 
repairs were evaluated. This survey was expanded to include all areas 
of the airframe. The evaluation revealed substantially similar results 
to the 1992 results in which forty percent of the repairs were 
classified as adequate, and sixty percent of the repairs required 
consideration for additional supplemental inspection during service. In 
addition, only a small number of repairs (less than 10 percent) were 
found on portions of the airframe other than the external fuselage 
skin.
    The AAWG proposed that the repair assessment be initially limited 
to the fuselage pressure boundary (fuselage skins and bulkhead webs); 
if necessary, future rulemaking would address the remaining primary 
structure. This limitation is based on two considerations.
    First, the fuselage is more sensitive to structural fatigue than 
other airplane structure because its normal operating loads are closer 
to its limit design loads. Stresses in a fuselage are primarily 
governed by the pressure relief valve settings of the environmental 
control system, and these are less variable from flight to flight than 
the gust or maneuver loads that typically determine the design stresses 
in other structure. Second, the fuselage is more prone to damage from 
ground service equipment than other structure and requires repair more 
often. The result of the second survey described above supports the 
conclusion that repairs to the fuselage are far more frequent than to 
any other structure.
    This proposed rule would only apply to eleven large transport 
category airplane models. (In the original ARAC task, the 707 and 720 
were counted as one model. This proposed rule addresses the 707 and 720 
models separately due to their different flight cycle implementation 
times.) The reason for this limitation is that the original tasking to 
the ARAC limited the scope of the work to the eleven oldest models of 
large transport category airplanes then in regular service. This 
tasking identified those airplanes for which the greatest concern 
exists as to the status of primary structure repairs. Derivatives of 
the original airplanes models are covered to the extent that the 
structure has not been upgraded to meet damage tolerance requirements.
    Those transport category airplanes that have been certificated to 
regulatory standards that include the requirements for damage tolerant 
structure under Sec. 25.571 of 14 CFR part 25, as amended by Amendment 
25-45, are not included. These later requirements make it incumbent on 
the operating certificate holder to return the structure to the 
original certification basis by installing only those repairs that meet 
the airplane's damage-tolerant certification basis. The AAWG, in its 
final report on this subject, did recommend continued monitoring of 
repairs on the newer airplanes, with the possibility of additional 
rulemaking if conditions warrant. (A copy of the AAWG's final report is 
included in the public docket for this rulemaking.)
    As a result of the AAWG activities, the manufacturers have 
recognized the need for, and made a commitment to develop, for each 
affected airplane model, a repair assessment guidelines document and a 
Structural Repair Manual, updated to include the results of a damage-
tolerance assessment. When referring to these documents and related 
actions in this proposed rule, the FAA is referring to actions the 
manufacturers have agreed to take.
    It was also recognized by the AAWG that repair assessment 
guidelines would add to, or in some cases appear to be in conflict 
with, existing repair approval data. All repairs assessed under this 
proposed rule should have been previously approved by the FAA using an 
FAA-approved SRM, an FAA-approved Service Bulletin, or a repair scheme 
approved by an FAA Designated Engineering Representative or an SFAR 36 
authorization holder. To avoid the appearance of conflicts between FAA 
approved data sources, the manufacturers have agreed to update the 
affected SRMs, as well as repairs identified in Service Bulletins, to 
determine requirements for supplemental inspections, if not already 
addressed.
    Structural modifications and repairs mandated by Airworthiness 
Directives do not always contain instructions for future supplemental 
inspection requirements. The manufacturers have agreed to evaluate the 
need for post modification inspections for these mandated modifications 
and repairs. A list of Service Bulletins that are the subject of 
Airworthiness Directives will be contained in the model specific repair 
assessment guidelines, with required post modification/repair 
inspection programs as required. A list of other structural Service 
Bulletins will be provided in the model specific repair assessment 
guidelines with associated inspection thresholds and repeat intervals. 
The manufacturers have agreed to complete their review of Service 
Bulletin related skin repairs in conjunction with the initial SRM 
updates.
    These agreements notwithstanding, there is still a possibility that 
the requirements in the repair assessment guidelines will not agree 
with that in an AD, especially if the AD was written to address a 
modification to the airplane made by someone other than the original 
manufacturer. Federal Aviation Regulations would require that 
compliance be shown with both the AD and this proposed rule. Such dual 
compliance can be avoided in the longer term by working with the 
manufacturer, if that is the source of difficulty, or by securing an 
Alternative Method of Compliance (AMOC) to the AD. In the short term, 
compliance with the earlier threshold, shorter repeat inspection 
interval or more stringent rework/replace schedule would always 
constitute compliance with the less stringent requirement. Thus, the 
operator would not be faced with an unresolvable conflict.
    The AATF originally recommended that the use of repair assessment 
guidelines be mandated by Airworthiness Directive. The FAA concluded 
that an unsafe condition necessitating AD action had not been 
established for repairs, and this position is supported by both repair 
surveys. However, the FAA also considered, and the AAWG agreed, that 
the long term concern with repairs on older airplanes, as described 
earlier, does warrant regulatory action, and this proposed rule 
addresses that concern.
    The AAWG also recognized that the concerns discussed above for the 
safety of existing repairs would also apply to the long-term safety of 
future repairs to these airplanes. Therefore, the AAWG considered that 
new repairs should also be subject to damage-tolerance assessments. It 
is expected that most new repairs will be installed in accordance with 
an FAA-approved SRM that has been updated to include this damage-
tolerance assessment. However, in the event that a new repair is 
installed for which no such assessment has been made, or is available, 
the repair assessment guidelines prepared to meet the requirements of 
this proposal should be used. The intent of this proposed rule is that 
all repairs to

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the fuselage pressure boundary will be evaluated for damage-tolerance, 
and that any resulting inspection schedule will be specified and the 
work accomplished, regardless of when, or by whom the repair was 
installed.

Repair Assessment Guidelines

    The next step in the AAWG's program for this task was to develop a 
repair assessment methodology that is effective in evaluating the 
continued airworthiness of existing repairs for the fuselage pressure 
boundary on affected transport category airplane models. Older airplane 
models may have many structural repairs, so the efficiency of the 
assessment procedure is an important consideration. In the past, 
evaluation of repairs for damage-tolerance would require direct 
assistance from the manufacturer. Considering that each repair design 
is different, that each airplane model is different, that each area of 
the airplane is subjected to a different loading environment, and that 
the number of engineers qualified to perform a damage-tolerance 
assessment is small, the size of an assessment task conducted in that 
way would be unmanageable. Therefore, a new approach was developed.
    Since repair assessment results will depend on the model specific 
structure and loading environment, the manufacturers were tasked to 
create an assessment methodology for the types of repairs expected to 
be found on each affected airplane model. Since the records on most of 
these repairs are not readily available, locating the repairs will 
necessitate surveying the structure of each airplane. A survey form was 
created that may be used to record key repair design features needed to 
accomplish a repair assessment. Airline personnel not trained as 
damage-tolerance specialists can use the form to document the 
configuration of each observed repair.
    Using the information from the survey form as input data, the 
manufacturers have developed simplified methods to determine the damage 
tolerance characteristics of the surveyed repairs. Although the repair 
assessments should be performed by well trained personnel familiar with 
the model specific repair assessment guidelines, these methods enable 
an engineer or technician, not trained as a damage-tolerance 
specialist, to perform the repair assessment without the assistance of 
the manufacturer.
    From the information on the survey form, it is also possible to 
classify repairs into one of three categories:

    Category A: A permanent repair for which the baseline zonal 
inspection (BZI), (typical maintenance inspection intervals assumed 
to be performed by most operators), is adequate to ensure continued 
airworthiness (inspectability) equal to the unrepaired surrounding 
structure.
    Category B: A permanent repair that requires supplemental 
inspections to ensure continued airworthiness.
    Category C: A temporary repair that will need to be rewarded or 
replaced prior to an established time limit. Supplemental 
inspections may be necessary to ensure continued airworthiness prior 
to this limit.

    This methodology is being generated by the airplane manufacturers. 
Model specific repair assessment guidelines will be prepared by the 
manufacturers for the eleven aging airplane models. Uniformity and 
similarity of these repair assessment procedures between models is 
important to simplify operator workload. The manufacturers have spent 
considerable time over the last four years to achieve commonality of 
the repair assessment process. The inspection intervals contained in 
the FAA-approved model specific guidelines documents are based on 
residual strength, crack growth, and inspectability evaluations. The 
manufacturers are endeavoring to make the inspection methods and 
intervals compatible with typical operator maintenance practice. Thus, 
internal inspections would be acceptable at ``D-check'' intervals, or 
equivalent cycle limit, while simpler external inspections could be 
accommodated at multiple ``C-check'' intervals, or equivalent cycle 
limit. If the inspection method and intervals for a given repair are 
not compatible with the operator's maintenance schedule, the repair 
could be replaced with a more damage-tolerant repair.
    The model specific repair assessment guidelines documents are 
scheduled to be published no later than July 1, 1997, and will require 
approval by the FAA Aircraft Certification Office (ACO) having 
cognizance over the type certificate. Once approved, this material can 
also be used for evaluating the damage-tolerance characteristics of new 
repairs for continued airworthiness.
    In order to further facilitate the assessment process, the 
manufacturers have agreed to update model specific SRMs to reflect 
damage tolerance repair considerations. The goal is to complete these 
updates by the first revision cycle of the model specific SRM, after 
the release of the associated repair assessment guidelines document. 
Consistent with the result of the surveys, only fuselage pressure 
boundary repairs are under consideration in this proposal.
    The general section of each SRM, Chapter 51, will contain brief 
descriptions of damage tolerance considerations, categories of repairs, 
description of baseline zonal inspections, and the repair assessment 
logic diagram. Chapter 53 of the SRM for pressurized fuselage skin will 
be updated to identify repair categories and related information.
    In updating each SRM, existing location-specific repairs should be 
labeled with appropriate repair category identification (A, B, or C), 
and specific inspection requirements for B and C repairs should also be 
provided as applicable.
    Structural Repair Manual descriptions of generic repairs will also 
contain repair category considerations regarding size, zone, and 
proximity. Detailed information for determination of inspection 
requirements will be provided in separate repair assessment guidelines 
documents for each model. Repairs which were installed in accordance 
with a once current SRM, but which have now been superseded by a new 
damage-tolerant design, will require review. Such superseded repairs 
may be reclassified to Category B or C, requiring additional 
inspections and/or rework.

Repair Assessment Process

    There are two principle techniques that can be used to accomplish 
the repair assessment. The first technique involves a three stage 
procedure. This technique could be well suited for operators of small 
fleets. The second technique involves the incorporation of the repair 
assessment guidelines as part of an operator's routine maintenance 
program. This approach could be well suited for operators of large 
fleets and would evaluate repairs at predetermined planned maintenance 
visits as part of the maintenance program. Manufacturers and operators 
may develop other techniques, which would be acceptable as long as they 
fulfill the objectives of this proposed rule, and are FAA approved.
    The first technique generally involves the execution of the 
following three stages:
Stage 1--Data Collection
    This stage specifies what structure should be assessed for repairs 
and collects data for further analysis. If a repair is on a structure 
in an area of concern, the analysis continues, otherwise the repair 
does not require classification per this program.
    Repair assessment guidelines for each model will provide a list of 
structure for which repair assessments are required.

[[Page 131]]

Some manufacturers have reduced this list by determining the inspection 
requirements for critical details. If the requirements are equal to 
normal maintenance checks (e.g., BZI checks), those details were 
excluded from this list.
    Repair details are collected for further analysis in Stage 2. 
Repairs that do not meet the static strength requirements or are in a 
bad condition are immediately identified, and corrective actions must 
be taken before further flight.
Stage 2--Repair Categorization
    The repair categorization is accomplished by using the data 
gathered in Stage 1 to answer simple questions regarding structural 
characteristics.
    If the maintenance program is at least as rigorous as the BZI 
identified in the manufacturer's model specific repair assessment 
guidelines, well designed repairs in good condition meeting size and 
proximity requirements are Category A. Simple condition and design 
criteria questions are provided in Stage 2 to define the lower bounds 
of Category B and Category C repairs. The process continues for 
Category B and C repairs.
Stage 3--Determination of Structural Maintenance Requirements
    The supplemental inspection and/or replacement requirements for 
Category B and C repairs are determined in this stage. Inspection 
requirements for the repair are determined by calculation or by using 
predetermined values provided by the manufacturer, or other values 
obtained using an FAA-approved method.
    In evaluating the first supplemental inspection, Stage 3 will 
define the inspection threshold in flight cycles measured from the time 
of repair installation. If the time of installation of the repair is 
unknown and the airplane has exceeded the assessment implementation 
times or has exceeded the time for first inspection, the first 
inspection should occur by the next ``C-check'' interval, or equivalent 
cycle limit after the repair data is gathered (Stage 1).
    An operator may choose to accomplish all three stages at once, or 
just Stage 1. In the latter case, the operator would be required to 
adhere to the schedule specified in the FAA-approved model specific 
repair assessment guidelines for completion of Stages 2 and 3.
    Incorporating the maintenance requirements for Category B and C 
repairs into an operator's individual airplane maintenance or 
inspection program completes the repair assessment process for the 
first technique.
    The second technique would involve setting up a repair maintenance 
program to evaluate all fuselage pressure boundary repairs at each 
predetermined maintenance visit to confirm that they are permanent. 
This technique would require the operator to choose an inspection 
method and interval in accordance with the FAA-approved repair 
assessment guidelines. The repairs whose inspection requirements are 
fulfilled by the chosen inspection method and interval would be 
inspected in accordance with the regular FAA-approved maintenance 
program. Any repair that is not permanent, or whose inspection 
requirements are not fulfilled by the chosen inspection method and 
interval, would either be: (1) Upgraded to allow utilization of the 
chosen inspection method and interval, or (2) individually tracked to 
account for the repair's unique inspection method and interval 
requirements. This process is then repeated at the chosen inspection 
interval.
    Repairs added between the predetermined maintenance visits, 
including interim repairs installed at remote locations, would be 
required either to have a threshold greater than the length of the 
predetermined maintenance visit or to be tracked individually to 
account for the repair's unique inspection method and interval 
requirements. This would ensure the airworthiness of the structure 
until the next predetermined maintenance visit, at which time the 
repair would be evaluated as part of the repair maintenance program.
    Whichever technique is used, there may be some repairs that cannot 
easily be upgraded to Category A for cost, downtime, or technical 
reasons. Such repairs will require supplemental inspections, and each 
operator should make provisions for this when incorporating the repair 
assessment guidelines into its maintenance program.

Repair Assessment Implementation Time

    The implementation time for the assessment of existing repairs is 
based on the findings of the repair surveys and fatigue damage 
considerations. The repair survey findings indicated that all repairs 
reviewed appeared to be in good structural condition. This tended to 
validate the manufacturer's assumptions in designing both the repair 
and the basic structure. Since the manufacturer had based the design 
stress levels on a chosen Design Service Goal (DSG), it was concluded 
that the repair assessment needed to be implemented sometime before a 
specific model reached its DSG. Based on this logic, the manufacturers 
and operators established an upper bound for an assessment to be 
completed and then reduced it to establish an ``implementation time,'' 
defined as 75 percent of DSG in terms of flight cycles.
    Therefore, under this approach, incorporation of the repairs 
assessment guidelines into an airplane's maintenance or inspection 
program ideally should be accomplished before an airplane accumulates 
75 percent of DSG. After the guidelines are incorporated into the 
maintenance or inspection program, operators should begin the 
assessment process for existing fuselage repairs within the flight 
cycle limit specified in the FAA-approved model specific repair 
assessment guidelines. There are three deadlines for beginning the 
repair assessment process, depending on the cycle age of the airplane 
on the effective date of the rule.
1. Airplane Cycle Age Equal to or less than Implementation Time on the 
Rule Effective Date
    The operator would be required to incorporate the guidelines in its 
maintenance or inspection program by the flight cycle implementation 
time, or one year after the effective date of the rule, whichever 
occurs later. The assessment process would begin (e.g., accomplishment 
of Stage 1) on or before the cycle limit specified in the repair 
assessment guidelines (generally equivalent to a ``D'' check) after 
incorporation of the guidelines.
2. Airplane Cycle Age greater than the Implementation Time but less 
than the DSG on the Rule Effective Date
    The operator would be required to incorporate the guidelines in its 
maintenance or inspection program within one year of the rule effective 
date. The assessment process would begin (e.g., accomplishment of Stage 
1) on or before the cycle limit in the repair assessment guidelines 
(generally equivalent to a ``D'' check), not to exceed the cycle limit 
computed by adding the DSG to the cycle limit equivalent of a ``C'' 
check (also specified in the repair assessment guidelines) after 
incorporation of the guidelines.
3. Airplane Cycle Age greater than the DSG on the Rule Effective Date
    The operator would be required to incorporate the guidelines in its 
maintenance or inspection program within one year of the rule effective

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date. The assessment process would begin (e.g., accomplishment of Stage 
1) on or before the cycle limit specified in the repair assessment 
guidelines (equivalent to a ``C'' check) after incorporation of the 
guidelines.
    In each of these three cases, the assessment process would have to 
be completed, the inspections conducted, and any necessary corrective 
action taken, all in accordance with the schedule specified in the FAA-
approved repair assessment guidelines.

Discussion of the Proposed Rule

    This proposed rule is intended to ensure that a comprehensive 
repairs assessment for damage-tolerance be completed for fuselage 
pressure boundary repairs, and that the resulting inspections, 
modifications and corrective actions (if any) be accomplished in 
accordance with the model specific repair assessment guidelines. To 
comply with this, the operator would need to consider the following:
    1. The means by which the FAA-approved repair assessment guidelines 
are incorporated into a certificate holder's FAA-approved maintenance 
or inspection program, as would be required by the proposed rule, is 
subject to approval by the certificate holder's principal maintenance 
inspector (PMI) or other cognizant airworthiness inspector.
    2. The repair assessment guidelines must be approved by the FAA 
Aircraft Certification Office (ACO) having cognizance over the type 
certificate of the airplane.
    3. This rule would not impose any new reporting requirements; 
however, normal reporting required under 14 CFR 121.703 would still 
apply.
    4. This rule would not impose any new FAA recordkeeping 
requirements. However, as with all maintenance, the current operating 
regulations (e.g., 14 CFR 121.380) already impose recordkeeping 
requirements that would apply to the actions required by this proposed 
rule. When incorporating the repair assessment guidelines into its 
approved maintenance program, each operator should address the means by 
which it will comply with these recordkeeping requirements. That means 
of compliance, along with the remainder of the program, would be 
subject to approval by the cognizant PMI or other cognizant 
airworthiness inspector.
    5. The scope of the assessment is limited to repairs on the 
fuselage pressure boundary (fuselage skins and pressure webs).
    a. A list of Service Bulletins that are the subject of AD's will be 
contained in the model specific repair assessment guidelines with 
required post modification/repair inspection programs, as required.
    b. A list of other structural Service Bulletins will be provided in 
the model specific repair assessment guidelines with associated 
inspection threshold and repeat intervals.
    6. The repair assessment guidelines provided by the manufacturer do 
not generally apply to structure modified by a Supplemental Type 
Certificate (STC). The operator, however, would still be responsible, 
under this proposed rule, to provide repair assessment guidelines 
applicable to the entire fuselage external pressure boundary that meets 
the program objectives specified in Advisory Circular 121-XX. This 
means that the operator should develop, submit, and gain FAA approval 
of guidelines to evaluate repairs to such structure.
    It is recognized that operators do not usually have the resources 
to determine a DSG or to develop repair assessment guidelines, even for 
a very simple piece of structure. The FAA expects the STC holder to 
assist the operators in preparing the required documents. If the STC 
holder is out of business, or is otherwise unable to provide 
assistance, the operator would have to acquire the FAA-approved 
guidelines independently. To keep the airplanes in service, it is 
always possible for operators, individually or as a group, to hire the 
necessary expertise to develop and gain approval of repair assessment 
guidelines and the associated DSG. Ultimately, the operator remains 
responsible for the continued safe operation of the airplane.
    The cost and difficulty of developing guidelines for modified 
structure may be less than that for the basic airplane structure for 
three reasons. First, the only modifications made by persons other than 
the manufacturer that are of concern in complying with this proposed 
rule are those that affect the fuselage pressure boundary. Of those 
that do affect this structure, many are small enough to qualify as 
Category A repairs under the repair assessment guidelines, based solely 
on their size. Second, if the modified structure is identical, or very 
similar, to the manufacturer's original structure, then only a cursory 
investigation may be necessary. In such cases, the manufacturer's 
repair assessment guidelines may be shown to be applicable with few, if 
any, changes. If the operator determines that a repair to modified 
structure can be evaluated using the manufacturer's model specific 
repair assessment guidelines, that determination should be documented 
and submitted to the operator's PMI or other cognizant airworthiness 
inspector for approval. For all other repairs, a separate program would 
need to be developed. Third, the modification may have been made so 
recently that no repair assessment guidelines would be needed for many 
years. Compliance with this proposed rule could be shown by 
establishing the DSG for the new modified structure, calculating an 
implementation time that is equal to three quarters of that DSG, and 
then adding a statement to the operations specifications that repair 
assessment guidelines would be incorporated into the maintenance 
program by that time. If the modified structure is very similar to the 
original, then the DSG for the modified structure may also be very 
similar. No repair assessment guidelines would be needed until 75 
percent of that goal is reached. For example, in the case of a large 
cargo door, such installations are often made after the airplane has 
reached the end of its useful life as a passenger-carrying airplane. 
For new structure, the clock would start on repair assessment at the 
time of installation. Further, since the DSG is measured in cycles, and 
cargo operation usually entails fewer operational cycles than passenger 
operations, the due date for incorporation of the repair assessment 
guidelines for that structure could be many years away.
    Compliance with this proposed rule would require that conditions 
such as those described above be properly documented in each operator's 
FAA-approved maintenance program; however, the cost of doing so should 
not be significant. There should be very few examples where the STC 
holder is unavailable, and the operators must bear the cost of 
developing a complete repair assessment guidelines document. Guidance 
on how to comply with this aspect of the proposed rule is also 
discussed in the accompanying Advisory Circular 120-XX.
    7. An operator's repair assessment program would have to include 
damage-tolerance assessments for new repairs. Repairs made in 
accordance with the revised version of the SRM would already have a 
damage-tolerance assessment performed; otherwise, the manufacturer's 
repair assessment guidelines could be used for this purpose, or 
operators may develop other methods as long as they achieve the same 
objectives.
    8. Once the airworthiness inspector having oversight 
responsibilities is

[[Page 133]]

satisfied that the operator's continued airworthiness maintenance or 
inspection program contains all of the elements of the FAA-approved 
repair assessment guidelines, the airworthiness inspector would approve 
an operation specification(s) or inspection program revision. This 
would have the effect of requiring use of the approved repair 
assessment guidelines.
    In summary, based on discussions with representatives of the 
affected industry, recommendations from ARAC, and a review of current 
rules and regulations affecting repair of primary structure, the FAA 
recognizes the need for a repairs assessment program to be incorporated 
into the maintenance program for certain transport category airplanes.
    The proposed rule would prohibit the operation of certain transport 
category airplanes operated under 14 CFR parts 91, 121, 125, and 129 
beyond a specified compliance time, unless the operator of those 
airplanes had incorporated FAA-approved repair assessment guidelines 
applicable to the fuselage pressure boundary in its operation 
specification(s) or approved inspection program, as applicable.

FAA Advisory Material

    In addition to the amendments proposed in this notice, the ARAC has 
developed Advisory Circular 120-XX, ``Repair Assessment of Pressurized 
Fuselages.'' This AC would provide guidance for operators of the 
affected transport category airplanes on how to incorporate FAA-
approved repair assessment guidelines into their FAA-approved 
maintenance or inspection program. Public comments concerning the 
proposed AC are invited by separate notice published elsewhere in this 
issue of the Federal Register.

Regulatory Evaluation

    Changes to federal regulations must undergo several economic 
analyses. First, Executive Order 12866 directs Federal agencies to 
promulgate new regulations or modify existing regulations only if the 
potential benefits to society justify its costs. Second, the Regulatory 
Flexibility Act of 1980 requires agencies to analyze the economic 
impact of regulatory changes on small entities. Finally, the Office of 
Management and Budget directs agencies to assess the effects of 
regulatory changes on international trade. In conducting these 
assessments, the FAA has determined that this proposed rule: (1) Would 
generate benefits exceeding its costs and is not ``significant'' as 
defined in Executive Order 12866; (2) is not ``significant'' as defined 
in DOT's Policies and Procedures; (3) would not have a significant 
impact on a substantial number of small entities; and (4) would not 
constitute a barrier to international trade. These analyses, available 
in the docket, are summarized below.

Regulatory Evaluation Summary

Costs and Benefits

    The proposed rule would result in costs to the manufacturers and 
operators of the affected airplanes and to the FAA. Costs to 
manufacturers would include revising the Structural Repair Manuals, 
developing repair assessment guidelines, and developing and conducting 
training programs for Original Equipment Manufacturers' Engineers, 
airplane operators' inspectors, and the FAA's PMIs or other cognizant 
airworthiness inspector. Costs to operators would include inspector 
training, integrating the assessment program into the maintenance 
program for each airplane model, assessing and subsequently inspecting 
repairs, and maintaining records. Cost to the FAA would include PMI/
other cognizant airworthiness inspector training and review/approval of 
assessment programs.
    The FAA estimates that the total cost to all affected manufacturers 
would be $43.3 million over the years 1995 through 2020, or $26.9 
million discounted to present value. The equivalent annualized cost 
would be $2.3 million. Although this proposed rule would not directly 
impose any costs on manufacturers, the FAA recognizes that 
manufacturers have incurred, and will continue to incur, costs in order 
to develop and provide data to operators that will enable them to 
comply with the proposal. The FAA has chosen to attribute these costs 
to the proposed rule, beginning in 1995. The total cost to airplane 
operators would be $25.5 million over the years 1997 through 2020, or 
$10.2 million discounted to present value. The equivalent annualized 
cost would be $893,622. The total costs to the FAA would be $516,000, 
or $324,358 discounted to present value. The equivalent annualized cost 
would be $28,280. The total cost of the proposed rule to all affected 
entities would be $69.3 million, or $37.5 million discounted to present 
value. The equivalent annualized cost would be $3.2 million.
    The cause of an airplane accident has never been attributed to a 
properly applied repair to the airplane models that would be affected 
by the proposed rule. Nevertheless, airplanes designed and certificated 
to older technology are operated beyond their original design service 
objectives, and the FAA has determined that the repair assessment 
program to ensure the continued airworthiness of these aging airplanes 
could prevent structural failure and resulting accidents. The benefits 
of the proposed rule, therefore, are based on the avoidance of such 
accidents.
    The FAA estimates that the prevention of an accident resulting in 
the loss of an average affected airplane and half its passengers and 
crew would result in present value benefits of $46.8 million, assuming 
that the accident would otherwise have occurred midway through the 
analysis period. The FAA cannot predict the number of accidents that 
would be prevented by this proposed rule. Based on one such prevented 
loss, however, the FAA has determined that the proposed rule would be 
cost-beneficial.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily and 
disproportionately burdened by government regulations. The RFA requires 
a Regulatory Flexibility Analysis if the proposed or final rule would 
have significant economic impact, either detrimental or beneficial, on 
a substantial number of small entities. FAA Order 2100.14A, Regulatory 
Flexibility Criteria and Guidance, prescribes standards for complying 
with RFA review requirements in FAA rulemaking actions. The Order 
defines ``small entities'' in terms of 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 entities subject to the 
proposed or final rule.
    The proposed rule would affect Boeing Commercial Airplane Group, 
Douglas Aircraft Company, Lockheed Aeronautical Systems Company, 
Airbus, British Aerospace, and Fokker Aircraft B.V. Order 2100.14A 
specifies a size threshold for classification as a small manufacturer 
as 75 or fewer employees. Since none of these manufacturers has 75 or 
fewer employees, the proposed rule would not have a significant 
economic impact on a substantial number of small manufacturers.
    The proposed rule would also affect operators of certain U.S.-
registered B707/720, B727, B737, B747, DC-8, DC-9/MD80, DC-10, L-1011, 
A300, BAC 1-11 and F28 airplanes. Order 2100.14A

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specifies a size threshold for classification as a small operator as 
ownership of 9 or fewer aircraft. The annualized cost thresholds for 
significant impact, expressed in 1995 dollars, are $119,900 for a 
scheduled air carrier whose fleet of airplanes have seating capacities 
of over 60, $67,000 for other scheduled air carriers, and $4,700 for an 
unscheduled operator. The FAA examined the annualized costs of the 
proposed rule to ``small'' operators of the current fleet of affected 
airplanes and determined that no small operator's annualized cost would 
exceed the threshold of $4,700. Therefore, the proposed rule would not 
have a significant impact on a substantial number of small operators.

International Trade Impact Assessment

    The proposed rule would not constitute a barrier to international 
trade, including the export of American airplanes to foreign countries 
and the import of foreign airplanes into the United States.

Federalism Implications

    The regulations proposed herein will not have substantial direct 
effects on the States, or on the relationship between the national 
government and the States, or on the distribution of power and 
responsibility among the various levels of the government. Therefore, 
in accordance with Executive Order 12612, it is determined that this 
proposed rule would not have significant federalism implications to 
warrant the preparation of a Federalism Assessment.

International Civil Aviation Organization (ICAO) and Joint Aviation 
Regulations

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to comply with ICAO 
Standards and Recommended Practices to the maximum extent practicable. 
The FAA has determined that this proposed rule would not conflict with 
any international agreement of the United States.

Paperwork Reduction Act

    There are no new requirements for information collection associated 
with this proposed rule that would require approval from the Office of 
Management and Budget pursuant to the Paperwork Reduction Act of 1995 
(44 U.S.C. 3507(d)).

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 
distributions as he or she considers appropriate. Because this proposed 
rule would apply to the operation of certain transport category 
airplanes under parts 91, 121, 125, and 129 of Title 14, if could, if 
adopted, affect intrastate aviation in Alaska. The FAA therefore 
specifically requests comments on whether there is justification for 
applying the proposed rule differently to intrastate operations in 
Alaska.

Conclusion

    Because the proposed repair assessment programs are not expected to 
result in substantial economic cost, the FAA has determined that this 
proposed regulations is not a significant regulatory action under 
Executive Order 12866. The FAA has also determined that this proposal 
is not significant under DOT Regulatory Policies and Procedures (44 FR 
11034, February 25, 1979). In addition, the FAA certifies that this 
proposal, if adopted, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act, since none are 
affected. An initial evaluation of this proposal, including a 
Regulatory Flexibility Determination and an International Trade Impact 
Analysis, has been placed in the docket. A copy may be obtained by 
contacting the person identified under the caption FOR FURTHER 
INFORMATION CONTACT.

List of Subjects

14 CFR Part 91

    Aircraft, Aviation safety, Maintenance, Rebuilding, Pressurized 
fuselage repair and alteration.

14 CFR Parts 121, 125, and 129

    Air carriers, Aircraft, Aviation safety, Pressurized fuselage 
repair assessment, Safety, Transportation.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend 14 CFR parts 91, 121, 125, and 129 of 
the Federal Aviation Regulations as follows:

PART 91--GENERAL OPERATING AND FLIGHT RULES

    1. The authority citation for part 91 continues to read:

    Authority: 49 U.S.C. 106(g), 40103, 40113, 40120, 44101, 44111, 
44701, 44709, 44711, 44712, 44715, 44716, 44717, 44722, 46306, 
46315, 46316, 46502, 46504, 46506-46507, 47122, 47508, 47528-47531.

    2. A new Sec. 91.410 is added to read as follows:


Sec. 91.410  Repair assessment for pressurized fuselages.

    No certificate holder may operate an Airbus Model A300, British 
Aerospace Model BAC 1-11, Boeing Model 707, 720, 727, 737 or 747, 
McDonnell Douglas Model DC-8, DC-9/MD-80 or DC-10, Fokker Model F28, or 
Lockheed Model L-1011 airplane beyond the applicable flight cycle 
implementation time specified in the following paragraphs, or [a date 
one year after the effective date of the amendment], whichever occurs 
later, unless repair assessment guidelines applicable to the fuselage 
pressure boundary (fuselage skin and bulkhead webs) that have been 
approved by the FAA Aircraft Certification Office (ACO) having 
cognizance over the type certificate for the affected airplane are 
incorporated within its inspection program:
    (a) For the A300, the flight cycle implementation time is:
    (1) Model B2, 36,000 flights.
    (2) Model B4-100, 30,000 flights above the window line, and 36,000 
flights below the window line.
    (3) Model B4-200, 25,500 flights above the window line, and 34,000 
flights below the window line.
    (b) For all models of the BAC 1-11, the flight cycle implementation 
time is 60,000 flights.
    (c) For all models of the Boeing 707, the flight cycle 
implementation time is 15,000 flights.
    (d) For all models of the Boeing 720, the flight cycle 
implementation time is 23,000 flights.
    (e) For all models of the Boeing 727, the flight cycle 
implementation time is 45,000 flights.
    (f) For all models of the Boeing 737, the flight cycle 
implementation time is 60,000 flights.
    (g) For all models of the Boeing 747, the flight cycle 
implementation time is 15,000 flights.
    (h) For all models of the Douglas DC-8, the flight cycle 
implementation time is 30,000 flights.
    (i) For all models of the Douglas DC-9/MD-80, the flight cycle 
implementation time is 60,000 flights.
    (j) For all models of the Douglas DC-10, the flight cycle 
implementation time is 30,000 flights.
    (k) For all models of the Lockheed L-1011, the flight cycle 
implementation time is 27,000 flights.

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    (l) For the Fokker F-28 Mark 1000, 1000C, 2000, 3000, 3000C, and 
4000, the flight cycle implementation time is 60,000 flights.

PART 121--OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL 
OPERATIONS

    1. The authority citation for part 121 continues to read:

    Authority: 49 U.S.C. 106(g), 40113, 40119, 44101, 44701-44702, 
44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-44904, 
44912, 46105.

    2. A new Sec. 121.370 is added to read as follows:


Sec. 121.370  Repair assessment for pressurized fuselages.

    No certificate holder may operate an Airbus Model A300, British 
Aerospace Model BAC 1-11, Boeing Model 707, 720, 727, 737 or 747, 
McDonald Douglas Model DC-8, DC-9/MD-80 or DC-10, Fokker Model F28, or 
Lockheed Model L-1011 airplane beyond the applicable flight cycle 
implementation time specified in the following paragraphs, or [a date 
one year after the effective date of the amendment], whichever occurs 
later, unless its operation specifications have been revised to 
reference repair assessment guidelines applicable to the fuselage 
pressure boundary (fuselage skin and bulkhead webs), and those 
guidelines are incorporated in its maintenance program. The repair 
assessment guidelines must be approved by the FAA Aircraft 
Certification Office (ACO) having cognizance over the type certificate 
for the affected airplane.
    (a) For the A300, the flight cycle impelementation time is:
    (1) Model B2, 36,000 flights.
    (2) Model B4-100, 30,000 flights above the window line, and 36,000 
flights below the window line.
    (3) Model B4-200, 25,500 flights above the window line, and 34,000 
flights below the window line.
    (b) For all models of the BAC 1-11, the flight cycle implementation 
time is 60,000 flights.
    (c) For all models of the Boeing 707, the flight cycle 
implementation time is 15,000 flights.
    (d) For all models of the Boeing 720, the flight cycle 
implementation time is 23,000 flights.
    (e) For all models of the Boeing 727, the flight cycle 
implementation time is 45,000 flights.
    (f) For all models of the Boeing 737, the flight cycle 
implementation time is 60,000 flights.
    (g) For all models of the Boeing 747, the flight cycle 
implementation time is 15,000 flights.
    (h) For all models of the Douglas DC-8, the flight cycle 
implementation time is 30,000 flights.
    (i) For all models of the Douglas DC-9/MD-80, the flight cycle 
implementation time is 60,000 flights.
    (j) For all models of the Douglas DC-10, the flight cycle 
implementation time is 30,000 flights.
    (k) For all models of the Lockheed L-1011, the flight cycle 
implementation time is 27,000 flights.
    (l) For the Fokker F-28 Mark 1000, 1000C, 2000, 3000, 3000C, and 
4000, the flight cycle implementation time is 60,000 flights.

PART 125--CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING 
CAPACITY OF 20 OR MORE PASSENGERS OR A MAXIMUM PAYLOAD CAPACITY OF 
6,000 POUNDS OR MORE

    1. The authority citation for part 125 continues to read:

    Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44710-
44711, 44713, 44716-44717, 44722.

    2. A new Sec. 125.248 is added to read as follows:


Sec. 125.248  Repair assessment for pressurized fuselages.

    No certificate holder may operate an Airbus Model A300, British 
Aerospace Model BAC 1-11, Boeing Model 707, 720, 727, 737 or 747, 
McDonnell Douglas Model DC-8, DC-9/MD-80 or DC-10, Fokker Model F28, or 
Lockheed Model L-1011 beyond the applicable flight cycle implementation 
time specified in the following paragraphs or [a date one year after 
the effective date of the amendment], whichever occurs later, unless 
its operation specifications have been revised to reference repair 
assessment guidelines applicable to the fuselage pressure boundary 
(fuselage skin and bulkhead webs), and those guidelines are 
incorporated in its maintenance program. The repair assessment 
guidelines must be approved by the FAA Aircraft Certification Office 
(ACO) having cognizance over the type certificate for the affected 
airplane.
    (a) For the A300, the flight cycle implementation time is:
    (1) Model B2, 36,000 flights.
    (2) Model B4-100, 30,000 flights above the window line, and 36,000 
flights below the window line.
    (3) Model B4-200, 25,500 flights above the window line, and 34,000 
flights below the window line.
    (b) For all models of the BAC 1-11, the flight cycle implementation 
time is 60,000 times.
    (c) For all models of the Boeing 707, the flight cycle 
implementation time is 15,000 times.
    (d) For all models of the Boeing 720, the flight cycle 
implementation time is 23,000 times.
    (e) For all models of the Boeing 727, the flight cycle 
implementation time is 45,000 flights.
    (f) For all models of the Boeing 737, the flight cycle 
implementation time is 60,000 flights.
    (g) For all models of the Boeing 747, the flight cycle 
implementation time is 15,000 flights.
    (h) For all models of the Douglas DC-8, the flight cycle 
implementation time is 30,000 flights.
    (i) For all models of the Douglas DC-9/MD-80, the flight cycle 
implementation time is 60,000 flights.
    (j) For all models of the Douglas DC-10, the flight cycle 
implementation time is 30,000 flights.
    (j) For all models of the Lockheed L-1011, the flight cycle 
implementation time is 27,000 flights.
    (l) For the Fokker F-28 Mark 1000, 1000C, 2000, 3000, 3000C, and 
4000, the flight cycle implementation time is 60,000 flights.

PART 129--OPERATIONS: FOREIGN AIR CARRIERS AND FOREIGN OPERATORS OF 
U.S.-REGISTERED AIRCRAFT ENGAGED IN COMMON CARRIAGE

    1. The authority citation for part 129 continues to read:

    Authority: 49 U.S.C. 106(g), 40104-40105, 40113, 40119, 44701-
44702, 44712, 44716-44717, 44722, 44901-44904, 44906.

    2. A new Sec. 129.32 is added to read as follows:


Sec. 129.32  Repair assessment for pressurized fuselages.

    No certificate holder may operate an Airbus Model A300, British 
Aerospace Model BAC 1-11, Boeing Model 707, 720, 727, 737 or 747, 
McDonnell Douglas Model DC-8, DC-9/MD-80 or DC-10, Fokker Model F28, or 
Lockheed Model L-1011 beyond the applicable flight cycle implementation 
time specified in the following paragraphs, or [a date one year after 
the effective date of the amendment], whichever occurs later, unless 
its operation specifications have been revised to reference repair 
assessment guidelines applicable to the fuselage pressure boundary 
(fuselage skin and bulkhead webs), and those guidelines are 
incorporated in its maintenance program. The repair assessment 
guidelines must be approved by the FAA Aircraft Certification Office 
(ACO) having cognizance over the type certificate for the affected 
airplane.

[[Page 136]]

    (a) For the A300, the flight cycle implementation time is:
    (1) Model B2, 36,000 flights.
    (2) Model B4-100, 30,000 flights above the window line, and 36,000 
flights below the window line.
    (3) Model B4-200, 25,500 flights above the window line, and 34,000 
flights below the window line.
    (b) For all models of the BAC 1-11, the flight cycle implementation 
time is 60,000 flights.
    (c) For all models of the Boeing 707, the flight cycle 
implementation time is 15,000 flights.
    (d) For all models of the Boeing 720, the flight cycle 
implementation time is 23,000 flights.
    (e) For all models of the Boeing 727, the flight cycle 
implementation time is 45,000 flights.
    (f) For all models of the Boeing 737, the flight cycle 
implementation time is 60,000 flights.
    (g) For all models of the Boeing 747, the flight cycle 
implementation time is 15,000 flights.
    (h) For all models of the Douglas DC-8, the flight cycle 
implementation time is 30,000 flights.
    (i) For all models of the Douglas DC-9/MD-80, the flight cycle 
implementation time is 60,000 flights.
    (j) For all models of the Douglas DC-10, the flight cycle 
implementation time is 30,000 flights.
    (k) For all models of the Lockheed L-1011, the flight cycle 
implementation time is 27,000 flights.
    (l) For the Fokker F-28 Mark 1000, 1000C, 2000, 3000, 3000C, and 
4000, the flight cycle implementation time is 60,000 flights.

    Issued in Washington, D.C. on December 22, 1997.
Thomas E. McSweeney,
Director, Aircraft Certification Service.
[FR Doc. 97-34166 Filed 12-31-97; 8:45 am]
BILLING CODE 4910-13-M