[Federal Register: December 12, 2007 (Volume 72, Number 238)]
[Rules and Regulations]
[Page 70486-70508]
[DOCID:fr12de07-3]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 26, 121, and 129

[Docket No. FAA-2005-21693; Amendment Nos. 26-1, 121-337, 129-44]
RIN 2120-AI32

Damage Tolerance Data for Repairs and Alterations

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: This final rule requires holders of design approvals to make
available to operators damage tolerance data for repairs and
alterations to fatigue critical airplane structure. This rule will
support operator compliance with the Aging Airplane Safety final rule
with respect to the requirement to incorporate into the maintenance
program, a means for addressing the adverse effects repairs and
alterations may have on fatigue critical structure. The intent of this
final rule is to ensure the continued airworthiness of fatigue critical
airplane structure by requiring design approval holders to support
operator compliance with specified damage tolerance requirements.

DATES: These amendments become effective January 11, 2008.

FOR FURTHER INFORMATION CONTACT: If you have technical questions about
this action, contact Greg Schneider, ANM-115, Airframe and Cabin
Safety, Federal Aviation Administration, 1601 Lind Avenue, SW., Renton,
Washington 98057-3356, telephone:<PHONE_NUMBER>); facsimile (425-227-
1232); e-mail<EMAIL_ADDRESS>Direct any legal questions to
Doug Anderson, ANM-7, Office of Regional Counsel, Federal Aviation
Administration, 1601 Lind Avenue, SW., Renton, WA 98057-3356; telephone
(425) 227-2166; facsimile<PHONE_NUMBER>; e-mail
<EMAIL_ADDRESS>

SUPPLEMENTARY INFORMATION:

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is
found in Title 49 of the United States Code. Subtitle I, Section 106
describes the

authority of the FAA Administrator. Subtitle VII, Aviation Programs,
describes in more detail the scope of the agency's authority.
    This rulemaking is promulgated under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701, ``General
requirements.'' Under that section, the FAA is charged with promoting
safe flight of civil aircraft in air commerce by prescribing minimum
standards required in the interest of safety for the design and
performance of aircraft; regulations and minimum standards in the
interest of safety for inspecting, servicing, and overhauling aircraft;
and regulations for other practices, methods, and procedures the
Administrator finds necessary for safety in air commerce. This
regulation is within the scope of that authority because it
prescribes--
     New safety standards for the design of transport category
airplanes, and
     New requirements necessary for safety for the design,
production, operation, and maintenance of those airplanes, and for
other practices, methods, and procedures relating to those airplanes.

Table of Contents

I. Executive Summary
II. Background
    A. Summary of the NPRM
    1. The Proposed Rule
    2. Related Activities
    B. Differences Between the NPRM and the Final Rule
    1. New Part 26 for Design Approval Holders' Airworthiness
Requirements
    2. New Subparts for Airworthiness Operational Rules
    3. Minor Conforming Changes to the Aging Airplane Safety Final
Rule
    4. Other Miscellaneous Changes
    C. Summary of Comments
III. Discussion of the Final Rule
    A. Overview
    1. Final Rule
    2. Guidance Material
    B. Airplane Applicability and Exceptions
    1. Airplane Certification Amendment Level
    2. Parts 91, 125, and 135 Operations
    3. Exception of Airplanes Not Operating in the U.S. Under Part
121 or 129
    C. Fatigue Critical Structure (FCS)
    D. Damage Tolerance Evaluation (DTE)
    E. Damage Tolerance Inspections (DTIs)
    F. DT Data for Repairs
    1. Published Repair Data
    2. Effects of Multiple Repairs
    G. Repair Evaluation Guidelines (REGs)
    H. DT Data for Alterations
    I. Required Documentation
    J. Proprietary Data
    K. Compliance Plan
    1. Process for Continuous Assessment of Service Information
    2. Timing of FAA Approval
    L. Harmonization
    1. Foreign Authority Approval of Required Data
    M. Enforcement
    N. Industry and FAA Resources
    O. Compliance Dates
    P. Costs and Benefits
IV. Final Regulatory Evaluation, Regulatory Flexibility
Determination, International Trade Impact Assessment, and Unfunded
Mandates Assessment
V. The Amendments

I. Executive Summary

    Fatigue cracking has been a major aviation safety concern for many
years. Unless detected and repaired, fatigue cracks can grow to the
point of catastrophic failure. Since 1978 the FAA has required new
types of airplanes to meet damage tolerance \1\ (DT) requirements to
ensure their continued airworthiness. Industry has also used this
method successfully to develop inspection programs for older airplanes.
Since the 1980s, the FAA has mandated that operators of most large
transport airplanes carry out these programs.
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    \1\ Damage tolerance (DT) is a method used to evaluate the crack
growth and residual strength characteristics of structure. Based on
the results, inspections or other procedures are established as
necessary to prevent catastrophic failures due to fatigue. Most
commonly, the maintenance actions developed are directed inspections
for fatigue cracking.
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    While these programs have been largely effective, industry has not
carried out DT methods comprehensively. In particular, while these
programs apply to the airplane ``baseline'' structure (the airplane
structure as originally manufactured), they often do not apply to
repairs and alterations.\2\ This omission is important because
airplanes are subject to many repairs and alterations throughout their
operational lives. If fatigue cracking occurs in a repaired or altered
area, the results can be just as catastrophic as if it had occurred in
the baseline structure.
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    \2\ Various segments of industry use the term ``modification''
to define a design change. We consider this term to be synonymous
with the term ``alteration.'' We use both terms in this rule to mean
a design change that is made to an airplane.
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    The FAA adopted the Aging Airplane Safety final rule (AASFR) \3\ in
early 2005. Among other things, the AASFR requires airline operators of
certain large transport category airplanes \4\ to implement DT-based
inspection programs for airplane structure; that is, structure
susceptible to fatigue cracking that could contribute to a catastrophic
failure. In this final rule, we refer to this structure as ``fatigue
critical structure.'' Most importantly for this rule, the AASFR
requires these inspection programs to ``take into account the adverse
effects repairs, alterations, and modifications may have on fatigue
cracking and the inspection of this airplane structure.''
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    \3\ 70 FR 5518; February 2, 2005.
    \4\ The rule applies to turbine powered airplane models with a
maximum type certificated passenger seating capacity of 30 or more,
or a maximum payload capacity of 7,500 pounds or more.
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    With the AASFR, we now have in place the regulatory means to
provide for comprehensive implementation of DT methods on all large
transport airplanes used by air carriers. To carry out these
requirements fully, however, it is necessary to place corresponding
requirements on the holders of FAA design approvals for these
airplanes. Otherwise, the operators may not be able to obtain the data
and documents they need to comply with the AASFR. As the owners of the
data for these airplanes, the design approval holders \5\ (DAHs) are in
the best position to identify the fatigue critical structure and the
methods and frequency of inspections that may be needed. Therefore,
this final rule requires DAHs to develop and make available to
operators the data and documents they need to support compliance with
the DT requirements of the AASFR.
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    \5\ For purposes of this rule, design approval holders (DAHs)
are holders of type certificates (TCs) or supplemental type
certificates (STCs) issued under 14 CFR part 21.
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    Specifically, this final rule requires DAHs to develop and make
available the following four types of documents to operators:
    (1) Lists of fatigue critical structure (to aid operators in
identifying repairs and alterations that need to be addressed for DT).
    (2) Damage tolerance inspections to provide operators with the
necessary inspection times and methods for the following:
     Repair data published by type certificate (TC) holders.\6\
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    \6\ Published repair data are instructions for accomplishing
repairs, which are published for general use in structural repair
manuals (SRMs) and service bulletins. These data are approved for
general application to a particular airplane model or airplane
configuration.
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     TC holder's future repair data not published for general
use.\7\
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    \7\ This includes repairs that are developed for individual
airplanes at the request of an operator. These repairs are often
complex or unique to a particular airplane or group of airplanes
experiencing similar damage conditions.
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     Repair data developed by supplemental type certificate
(STC) holders.
     Alteration data developed by TC and STC holders.
    (3) Damage tolerance evaluation guidelines for all other repairs
(to enable operators to obtain the necessary damage tolerance
inspections).
    (4) Implementation schedules (to define the necessary timing for
performing damage tolerance

evaluations and developing damage tolerance inspections and for
incorporating the DT data into the operator's maintenance program).
    This final rule transfers the responsibility for developing DT-
based data from operators to DAHs and, therefore, has minimal to no
societal costs. The aviation industry as a whole would also benefit
because DAHs could amortize their development costs for DT data over a
larger fleet.

II. Background

A. Summary of the NPRM

1. The Proposed Rule
    On April 21, 2006, the FAA published in the Federal Register the
Notice of proposed rulemaking (NPRM) entitled, Damage Tolerance Data
for Repairs and Alterations (DAH DT Data NPRM),\8\ which is the basis
of this final rule.
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    \8\ 71 FR 20574.
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    In the DAH DT Data NPRM, the FAA proposed to require DAHs to
develop and make available to operators certain damage tolerance (DT)
data that address the adverse effects repairs, alterations, and
modifications may have on fatigue critical structure. These data are
necessary to support operator compliance with the Aging Airplane Safety
Final Rule (AASFR).\9\ Specifically, we proposed to require DAHs to
develop and make available to operators the following: (1) Lists of
fatigue critical structure for baseline and alteration structure; (2)
Damage tolerance inspections (DTIs) for existing published repair and
alteration data; (3) DTIs for future repair and alteration data; (4)
Repair evaluation guidelines (REGs) that include a process for
conducting airplane surveys, a process for establishing DT Data, and
implementation schedules for the above actions. In addition, we
proposed to require DAHs to develop a compliance plan for meeting these
four requirements and to obtain FAA approval of the plan.
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    \9\ AASFR: 70 FR 5518; February 2, 2005. See also 70 FR 23935;
May 6, 2005: Aging Airplane Safety; Correcting Amendment.
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    The NPRM contains the background and rationale for this rulemaking
and, except where we have made revisions in this final rule, you should
refer to it for that information.
2. Related Activities
    In July 2004, we published the Fuel Tank Safety Compliance
Extension (Final Rule) and Aging Airplane Program Update (Request for
Comments),\10\ where we informed the public of our intent to propose
DAH airworthiness requirements to support certain operational rules. We
requested comments on our proposal.
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    \10\ 69 FR 45936; July 30, 2004.
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    In December 2002, we published the Aging Airplane Safety Interim
final rule; request for comments.\11\ In February 2005, we adopted the
AASFR in which we responded to the comments from the interim rule and
made some changes to that rule. The February 2005 AASFR requires
affected operators to include certain damage tolerance inspections and
procedures in their maintenance programs by December 20, 2010. Today's
final rule is directly related to the AASFR in that it provides a means
for operators to get the data and documents they need to comply with
the AASFR.
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    \11\ 67 FR 72726; December 6, 2002.
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    In July 2005, we published a disposition of comments document,\12\
in which we responded to comments to the July 2004 action. Also in July
2005, we published a policy statement, Safety--A Shared
Responsibility--New Direction for Addressing Airworthiness Issues for
Transport Airplanes,\13\ that explains our criteria for adopting DAH
requirements like those described in this final rule.
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    \12\ 70 FR 40168; July 12, 2005: Fuel Tank Safety Compliance
Extension (Final Rule) and Aging Airplane Program Update (Request
for Comments).
    \13\ 70 FR 40166, July 12, 2005 (PS-ANM110-7-12-2005).
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    On April 21, 2006,\14\ along with the NPRM for this rulemaking, we
published a Notice of Availability (NOA) and request for comments on
draft AC 120-XX \15\ (Damage Tolerance Inspections for Repairs). This
AC included guidance related to repairs, which the Aviation Rulemaking
Advisory Committee's (ARAC) Airworthiness Assurance Working Group
(AAWG) \16\ developed.
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    \14\ 71 FR 20750.
    \15\ Issued as AC 120-93.
    \16\ AAWG Member Organizations: Boeing Commercial Airplanes,
Federal Express (FedEx), Airbus, Air Transport Association (ATA),
American Airlines, British Airways, Continental Airlines, Japan
Airlines, Northwest Airlines, United Airlines, United Parcel Service
(UPS), Airborne Express, U.S. Airways, Federal Aviation
Administration (FAA), and European Aviation Safety Agency (EASA).
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    On July 7, 2006, we published a notice \17\ that granted industry a
90-day extension to comment on the NPRM; and on February 27, 2007, we
published a NOA \18\ and request for comments on revised AC 120-XX,\19\
which includes guidance from the AAWG on both repairs and alterations.
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    \17\ 71 FR 38541.
    \18\ 72 FR 8834.
    \19\ Issued as AC 120-93.
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B. Differences Between the NPRM and the Final Rule

1. New Part 26 for Design Approval Holders' Airworthiness Requirements
    In the NPRM (and other Aging Airplane Program rules), we placed the
DAH airworthiness requirements in part 25, subpart I. As we explained
in the recently adopted Enhanced Airworthiness Program for Airplane
Systems/Fuel Tank Safety final rule (EAPAS/FTS),\20\ we have placed
these requirements in new part 26, and we have moved the enabling
regulations into part 21.\21\ We determined that this was the best
course of action because it keeps part 25 as strictly airworthiness
standards for transport category airplanes, thus maintaining
harmonization and compatibility among the United States, Canada, and
the European Union regulatory systems. Providing references to part 26
in part 21 clarifies how the part 26 requirements will address existing
and future design approvals.
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    \20\ 72 FR 63364; November 8, 2007.
    \21\ Certification Procedures for Products and Parts.
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    In creating new part 26, we renumbered the proposed sections of
part 25, subpart I and we incorporated the changes discussed in this
preamble. A table of this renumbering is shown below.
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    \22\ This section, which includes an applicability table for
part 26, was adopted as part of the EAPAS final rule.
    \23\ These definitions were proposed in Sec.  25.1823(b).

  Table 1.--Relationship of Proposed Part 25 Subpart I to Part 26 Final
                                  Rules
------------------------------------------------------------------------
            Part 26 final rules                   Proposed part 25
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Subpart E--Aging Airplane Safety--Damage    Subpart I--Continued
 Tolerance Data for Repairs and              Airworthiness.
 Alterations.
Sec.   26.5 Applicability table...........  New.\22\
Sec.   26.41 Definitions..................  New.\23\
Sec.   26.43 Holders of and applicants for  Sec.   25.1823 Holders of
 type certificates--Repairs.                 type certificates--Repairs.
Sec.   26.45 Holders of type certificates-- Sec.   25.1825 Holders of
 Alterations and repairs to alterations.     type certificates--
                                             Alterations and repairs to
                                             alterations.
Sec.   26.47 Holders of and applicants for  Sec.   25.1827 Holders of
 a supplemental type certificate--           and applicants for a
 Alterations and repairs to alterations.     supplemental type
                                             certificate--Alterations
                                             and repairs to alterations.

Sec.   26.49 Compliance Plan..............  Sec.   25.1829 Compliance
                                             Plan.
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2. New Subparts for Airworthiness Operational Rules
    We discussed in the preamble to the proposed rule that we would
establish new subparts for airworthiness-related operational rules.
Since there were several other aging airplane proposals (e.g., EAPAS)
published around the same time, each proposal contained language that
established the new subparts and redesignated certain sections of those
rules. We said when any one of those proposals became a final rule, we
would remove the duplicative provisions that established the new
subparts and redesignated sections from the other aging airplane rules.
In the DAH DT Data proposal, we included regulatory text to add
subparts AA and B (Continued Airworthiness and Safety Improvements) to
include the airworthiness requirements from parts 121 and 129,
respectively. We also included regulatory language to redesignate the
section numbers in parts 121 and 129 that were moved to the new
subparts. However, since the EAPAS final rule was the first to be
codified, that final rule adopted subparts AA and B and redesignated
appropriate sections of parts 121 and 129. Therefore, we have removed
the duplicative regulatory text from this final rule.
    To aid understanding of our discussion about the DAH DT Data rule
as it relates to the AASFR, we have indicated below the prior and
redesignated sections of parts 121 and 129 of the AASFR that include
DT-related requirements.

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              Prior sections                    Redesignated sections
------------------------------------------------------------------------
Sec.   121.370a...........................  Sec.   121.1109
Sec.   129.16.............................  Sec.   129.109
------------------------------------------------------------------------

3. Minor Conforming Changes to the Aging Airplane Safety Final Rule
    During the rulemaking process for the DAH DT Data rule, the FAA
determined that minor changes to the AASFR were needed to ensure
clarity of the two rules. The original wording in Sec. Sec.  121.370a
and 129.16 (redesignated as Sec. Sec.  121.1109 and 129.109,
respectively) required that changes to the certificate holder's
maintenance program (i.e., inclusion of DT-based inspections and
procedures and any revisions to them) be approved by the Aircraft
Certification Office (ACO) \24\ or office of the Transport Airplane
Directorate with oversight responsibility for the relevant type
certificate or supplemental type certificate, as determined by the
Administrator.
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    \24\ The regulatory text in this rule refers to the ACO or
office of the Transport Airplane Directorate with oversight
responsibility for the relevant type certificate or supplemental
type certificate as the FAA Oversight Office.
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    Although the ACO will approve the documentation that the DAH DT
Data final rule requires DAHs to submit to the FAA, the DT inspections
and procedures resulting from this documentation, which certificate
holders must incorporate into their maintenance programs, should be
approved by their Principal Maintenance Inspector (PMI). Therefore, we
revised Sec. Sec.  121.1109 and 129.109 to state that it is the PMI's
responsibility to review and approve changes to a certificate holder's
maintenance program.
    Also, we believe the requirements in current Sec. Sec.
121.1109(c)(1) and 129.109(b)(1) that address DT relative to baseline
structure and repairs, alterations, and modifications would be clearer
if they were in separate paragraphs. Therefore, we revised Sec. Sec.
121.1109 and 129.109 to include requirements related to baseline
structure in Sec.  121.1109(c)(1) and Sec.  129.109(b)(1) and those
related to repairs, alterations, and modifications in Sec.
121.1109(c)(2) and Sec.  129.109(b)(2). We also made minor wording
changes for clarity and consistency with the new part 26 requirements
and Advisory Circular (AC) 120-XX,\25\ which describes an acceptable
means of compliance with the DAH DT Data final rule.
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    \25\ Issued as AC 120-93.
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4. Other Miscellaneous Changes
    Based on comments to the proposed rule, we have revised the final
rule as summarized below and discussed in more detail under the
Discussion of the Final Rule heading.
    We extended the compliance times for DAHs to develop the required
lists of fatigue critical structure. For TC holders, we extended the
compliance date for them to submit their lists of fatigue critical
baseline structure to the FAA Oversight Office for review and approval
from 90 to 180 days after the effective date of the final rule. We also
added a provision that makes it clear to future TC holders that the
lists of fatigue critical baseline structure must be submitted as part
of the type certification process.
    In the NPRM, we proposed TC holders submit their lists of fatigue
critical alteration structure to the FAA Oversight Office for review
and approval 90 days after the effective date of the final rule. We
proposed 270 days for STC holders. In the final rule, we extended the
compliance date to 360 days after the effective date of the final rule
for both TC holders and STC holders to submit these lists.
    The NPRM included a requirement for TC and STC holders to develop a
process to enable operators to ``establish'' damage tolerance
inspections (DTIs) for repairs and alterations to fatigue critical
baseline structure (FCBS). This final rule replaces the term
``establish'' with ``obtain.'' We made this change because the term
``obtain'' better reflects the intent of the rule and is meant to be
all inclusive. That is, the operator may ``obtain'' a DTI by
establishing it themselves, or by receiving the DTI directly from a TC
holder, STC holder, or a third party.
    Section 25.1823(f)(1)(iii) (adopted as Sec.  26.43(e)(1)(iii))
proposed an implementation schedule for repairs covered by the repair
evaluation guidelines (REGs). To clarify this proposed requirement, we
revised it in the final rule to specify that the implementation
schedule must identify the times when actions must be taken as specific
numbers of flight cycles, flight hours, or both.
    We revised proposed Sec.  25.1823(f)(3) (adopted as Sec.
26.43(e)(3)) to remove the reference to Sec.  25.1827. That reference
would have required TC holders to make their REGs available to STC
holders. We made this change because TC holders do not need to provide
REGs to STC holders. However, they must provide their lists of fatigue
critical structure (FCS) to STC holders.
    As discussed in more detail later in this preamble, based on
comments submitted to other DAH airworthiness rules, we removed some
provisions of the compliance plan in proposed Sec.  25.1829 (adopted as
Sec.  26.49). Specifically, we removed the proposed requirements in
Sec.  25.1829(a)(3) for DAHs to identify the intended means of
compliance that differ from those described in FAA advisory materials.
Similarly, we removed the requirement in proposed Sec.  25.1829(c) that
would have authorized the FAA Oversight Office to identify deficiencies
in a compliance plan or the DAH's implementation of the plan and to
require specified corrective actions to remedy those deficiencies. We
do not

believe removal of these requirements will adversely affect our ability
to facilitate DAH compliance.
    In Sec.  25.1829(5), we proposed a requirement for including in the
compliance plan a process for continuous assessment of service
information related to structural fatigue damage. As discussed later in
this preamble, we have determined that existing regulations should
enable us to determine whether the objectives of this DAH DT Data final
rule are being met. Therefore, we have removed this provision from this
final rule.
    In addition to the changes discussed above, we made minor changes
to clarify the definitions of damage tolerance inspections and
published repair data in proposed Sec.  25.1823 (the definitions are
now in Sec.  26.41). We also made other minor changes to clarify the
requirements in proposed Sec. Sec.  25.1823 (adopted as Sec.  26.43),
25.1825 (adopted as Sec.  26.45), 25.1827 (adopted as Sec.  26.47), and
25.1829 (adopted as Sec.  26.49).

C. Summary of Comments

    The FAA received multiple comments from 17 commenters, including
the Air Transport Association (ATA) and a collective group of certain
industry representatives who are members of the AAWG.\26\ In the
following discussion of the comments received to the proposed rule, we
will refer to the comments received from those industry representatives
of the AAWG as the ``AAWG industry representatives.'' Also, several of
the AAWG and the ATA member organizations sent separate comments on
behalf of their organizations, with some specifically expressing
support for the comments submitted by the AAWG industry representatives
and the ATA. The comments to the proposed rule covered an array of
topics and contained a range of responses, which we discuss more fully
below under the Discussion of the Final Rule heading. In general,
commenters supported the intent of the rule and the guidance material.
They also requested some changes and clarifications.
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    \26\ AAWG industry representatives (a collective group of
commenters who are members of the AAWG): Boeing Commercial
Airplanes, Federal Express (FedEx), Airbus, American Airlines,
British Airways, Continental Airlines, Japan Airlines, Northwest
Airlines, United Airlines, United Parcel Service (UPS), Airborne
Express, US Airways.
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    Many of the comments to the proposed rule concerned issues specific
to the Widespread Fatigue Damage (WFD) \27\ proposal. The FAA intends
to address the WFD-related comments in a separate action, so we will
not address them here.
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    \27\ 71 FR 19928; April 18, 2006.
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    We also received several comments about the DAH airworthiness
requirements. We addressed many of the same or similar comments and
issues in the July 2005 disposition of comments document to the Fuel
Tank Safety Compliance Extension (Final Rule) and Aging Airplane
Program Update (Request for Comments). In addition, we explained in
detail the need for these requirements in our July 2005 policy
statement. As a result, we will not revisit those comments and issues
here.

III. Discussion of the Final Rule

A. Overview

1. Final Rule
    Fatigue cracking has been a major aviation safety concern for many
years. Unless detected and repaired, fatigue cracks can grow to the
point of catastrophic failure. Since the adoption of Amendment 25-45
\28\ in 1978, the FAA has required new types of airplanes to meet
damage tolerance (DT) requirements to ensure their continued
airworthiness. Industry has also used this method successfully to
develop inspection programs for older airplanes, such as Supplemental
Structural Inspection Programs (SSIP). Since the 1980s, the FAA has
mandated that operators of most large transport airplanes carry out
these programs.
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    \28\ 43 FR 46242; October 5, 1978.
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    Although these programs have been effective for baseline structure
(the airplane structure as originally manufactured), industry has not
comprehensively implemented DT methods for repairs and alterations. For
airplanes certified to Amendment 25-45 and later, repairs and
alterations were not always evaluated for damage tolerance. This
omission is important because airplanes are subject to many repairs and
alterations throughout their operational lives. If fatigue cracking
occurs in a repaired or altered area, the results can be just as
catastrophic as if it had occurred in the baseline structure.
    The AASFR requires airline operators of certain large transport
category airplanes \29\ to implement DT-based inspection programs for
airplane structure; that is, structure susceptible to fatigue cracking
that could contribute to a catastrophic failure. In today's DAH DT Data
final rule, we refer to this structure as ``fatigue critical
structure.'' Most importantly for today's DAH DT Data final rule, the
AASFR requires the maintenance program for the airplane include a means
to address the adverse effects repairs and alterations may have on
airplane structure.
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    \29\ The rule applies to turbine powered airplane models with a
maximum type certificated passenger seating capacity of 30 more, or
a maximum payload capacity of 7,500 pounds or more.
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    With the AASFR, we now have in place the regulatory means to
provide for comprehensive implementation of DT methods on all large
transport category airplanes used by air carriers operating under 14
CFR parts 121 and 129. To carry out these requirements fully, however,
we must place corresponding requirements on the holders of FAA design
approvals for these airplanes. Otherwise, the operators may not be able
to obtain the data and documents they need to comply with the AASFR. As
the owner of the design data for these airplanes, the DAH is in the
best position to identify the fatigue critical structure and the
methods and frequency of inspections that may be needed.
    As indicated in our July 2005 policy statement about the shared
responsibility for addressing airworthiness issues, in cases where
operators must rely on data or documents from DAHs to comply with
operational rules, we will require DAHs to develop that information by
a specified date. This final rule includes such requirements.
    Specifically, 14 CFR 26.43, 26.45, and 26.47 require that the TC
holders and STC holders develop certain information that will provide a
means for operators to address the adverse effects of repairs and
alterations. The information required by this final rule includes the
following:
     List of Fatigue Critical Structure (baseline and
alteration).
     Damage tolerance inspections (DTIs) for existing published
repair data and all future repair data.
     DTIs for all existing and future alteration data.
     Repair evaluation guidelines (REGs), which include--

--Instructions for conducting airplane surveys;
--Instructions an operator uses to obtain DTIs; and
--An implementation schedule that provides timing for the above
actions.
2. Guidance Material
    The FAA has issued Advisory Circular (AC) 120-93, Damage Tolerance
of Repairs and Alterations, concurrently with this rule. The AC
provides TC and STC holders with an acceptable method of compliance
with this final rule. The AC, which was developed through a
collaborative effort between the FAA and the Aviation Rulemaking
Advisory Committee

(ARAC), supports operator compliance with the AASFR with respect to
repairs and alterations.
    As amended by this final rule, Sec.  121.1109(c)(2) of the AASFR
requires operators to incorporate into their maintenance program a
``means'' for addressing the adverse effects that repairs and
alterations may have on fatigue critical structure. This AC provides
guidance that TC holders, STC holders, and operators can use in
developing a means for addressing repairs and alterations.
    To facilitate operators' timely compliance with the AASFR for
repairs, the guidance material in this AC includes implementation
schedules that specify acceptable time frames for when operators can
incorporate required DT data into their maintenance programs. The
implementation schedules allow for a phased-in program where existing
repairs on the older and higher utilization airplanes are assessed
first, and the newer airplanes assessed as they approach their Design
Service Goal (DSG). This approach ensures that DTIs will be available
when needed for both older and newer airplanes.

B. Airplane Applicability and Exceptions

    This rule applies to transport category, turbine powered airplane
models with an original TC issued after January 1, 1958. With certain
exceptions, this rule applies to those airplanes that, as a result of
the original certification or later increase in capacity, have a
maximum type certificated passenger seating capacity of 30 or more or a
maximum payload capacity of 7,500 pounds or more. The final rule
differs from the proposal in that we revised the list of excepted
airplanes to include the Lockheed L-300, deHavilland DHC-7, and Boeing
707/720 airplanes. We included these airplanes on the excepted list
because they are not currently being operated in commercial service in
the U.S., and we do not expect they will be in the future.
1. Airplane Certification Amendment Level
    Airbus and United Parcel Service (UPS) expressed concern that the
requirements of this rule duplicate certain requirements of current
regulations.
    Airbus said because newer airplanes like the A330/A340 and A380
have a state-of-the-art damage tolerance assessment for all activities
related to baseline structure, repairs, and alterations, the TC
holder's activities under proposed Sec. Sec.  25.1823(d) and (e) and
25.1825(c) and (d) would be ``senseless.'' It said applying the
proposed requirements to its newer model airplanes would offer no
additional safety benefit because they are already inherent in the
consistent application of the damage tolerance requirements in Sec.
25.571. It also said the proposed activities for these airplane models
would create an unnecessary administrative burden and would require re-
approval of already DT-justified modifications and repairs. Airbus
asked the FAA to reconsider applying proposed Sec. Sec.  25.1823 and
25.1825 to TC holders as they relate to airplane models A330/A340/A380
and future Airbus models. It suggested addressing this issue under
proposed Sec.  25.1829 in the model-specific compliance plans.
    UPS said if the proposed rule is adopted, it would force operators
to survey every airplane in their fleet to find repairs and then
evaluate them based on guidelines produced by TC holders. UPS believes
airplanes certified to comply with Amendment 25-54 or later already
have DT data developed for fatigue critical structure, which includes
certain baseline structure, as well as all repairs and alterations. UPS
suggested the FAA make the proposed surveys applicable only to
airplanes certified prior to Amendment 25-54. To accomplish this, it
said, the FAA should revise proposed Sec.  25.1823(a) to limit the
applicability to airplanes type certified to pre-Amendment 25-54
requirements.
    As discussed in the NPRM, the FAA has identified several airplane
models certified to Amendment 25-45 or later (including airplane models
certified to Amendment 25-54) for which published repair data have not
been evaluated for DT. Therefore, unless accomplished previously, a
damage tolerance evaluation (DTE) needs to be accomplished for all
airplanes, regardless of the certification level. For those airplanes
certified to Amendment 25-45 or later that have had a DTE completed for
all published repair and alteration data, the compliance plan required
by Sec.  26.49 (proposed as Sec.  25.1829) should contain a statement
to that effect, and the TC holder will need to substantiate this
statement with previously approved data from their certification effort
to show compliance with this rule. TC holders who have already
substantiated compliance with DT requirements should not find
compliance with this rule burdensome.
    Regarding UPS's comment, if the TC holder can substantiate
compliance for its repairs and alterations, it is still likely that
operators have installed repairs and alterations that were not designed
by the TC holder on many airplanes. It is also likely that many of
these repairs and alterations were not assessed for damage tolerance.
Therefore, a survey will still be necessary to identify those repairs
and alterations and to determine if DT data are available to support
operator compliance with the AASFR.
    Bombardier noted that the proposed rule would apply only to DAHs
for airplanes currently operated under parts 121 or 129. It said this
would not change the requirement to maintain damage tolerance for all
airplanes originally certified as damage tolerant under Sec.  25.571
(Amendment 45 or later). It said it presumes these airplanes will
continue to be regulated under Sec.  25.1529, using AC 25.1529-1 as
guidance (and under Canadian Air Regulations & Airworthiness Manual
511.34 for Canadian DAHs). Bombardier asserted that the four DAH
deliverables required by proposed Sec.  25.1823 (lists of fatigue
critical baseline structure, damage tolerance inspections, damage
tolerance evaluation guidelines, and implementation schedules) are
already required under Sec.  25.1529 (with guidance provided in AC
25.1529-1) and could constitute compliance with the proposed rule.
    We agree that TC holders and others designing repairs and
alterations for airplanes certificated to Amendment 25-45 or later
amendments will continue to be required to comply with Sec.  25.1529,
regardless of the types of operations conducted. For airplanes subject
to this DAH DT Data rule, DAHs and operators should use the guidance in
AC 120-93 instead of AC 25.1529-1 for repairs. Because this rule is
entirely consistent with Sec. Sec.  25.571 and 25.1529, DTIs that
comply with this rule will also comply with those sections. To the
extent such data have been developed previously, their compliance will
be simplified.
2. Parts 91, 125, and 135 Operations
    Transport Canada and Mr. Thomas A. Knott expressed concern that the
proposed rule only applies to airplanes operated under parts 121 and
129. Mr. Knott also stated that it leaves out airplanes operated under
parts 91, 125, and 135. Transport Canada expressed concern that the DAH
DT Data proposal and the AASFR do not apply to airplanes operated under
part 125 and would allow airplanes such as the B727 and B747 to operate
as passenger-carrying airplanes under part 125 without having to meet
DT or the aging airplane safety requirements.
    As we discussed earlier in this preamble, the purpose of this rule
is to support parts 121 and 129 operators'

compliance with the AASFR. For the reasons discussed in the preamble to
the AASFR, we limited applicability of the DT requirements
(supplemental inspections) in that rule to certain large transport
airplanes that are typically operated under parts 121 or 129. For the
affected airplanes that are operated under parts 91, 125, or 135, their
utilization is much lower and the risks associated with fatigue damage
that the AASFR is intended to address is, therefore, also much lower.
Because of this, we determined it would not be cost-effective to impose
the AASFR's supplemental inspection requirements on parts 91, 125, or
135 operators.
3. Exception of Airplanes Not Operating in the U.S. Under Part 121 or
129
    Viking Air Limited said it owns seven de Havilland heritage
aircraft, including the DHC-5 Buffalo and DHC-7. Viking Air Limited
said there are about 23 DHC-5s in confirmed operation, and the DHC-7
has about 66 in confirmed operation. Many of those in confirmed
operation are used in military operations and are not subject to part
121 or 129. According to the FAA Registry, no DHC-5 aircraft are
presently registered in the U.S. Therefore, Viking proposed that the
DHC-5 be added as an exception under proposed Sec.  25.1823(h). Viking
Air Limited also said that for the DHC-7, there presently are the
following safety measures in place: Canadian Airworthiness Directive
CF-94-19R1 that mandates a Supplemental Inspection Program; CF-2005-36
that imposes a Structural Life Limit; and CF-98-03 that mandates the
Corrosion Prevention and Control Program. With these actions, the DHC-
7, the commenter stated, has already met the intentions of aging
aircraft initiative for structures.
    The FAA researched its data bases and found that the DHC-5 does not
have a type certificate issued by the U.S. Therefore, there is no need
for an exception for the DHC-5 Buffalo. Furthermore, we have determined
that there are no DHC-7 airplanes currently operated under part 121 or
U.S.-registered DHC-7 airplanes operated under part 129. For the
reasons discussed earlier in this preamble, we added the DHC-7, as well
as the Lockheed L-300 and the Boeing 707/720, to the list of excepted
airplanes in Sec.  26.43(g) of this final rule.

C. Fatigue Critical Structure (FCS)

    This final rule requires TC and STC holders to evaluate their
designs for baseline and alteration structure to identify FCS. They
must also develop lists of FCS and make the lists available to
operators.
    This final rule defines fatigue critical structure as airplane
structure that is susceptible to fatigue cracking that could contribute
to a catastrophic failure, as determined under Sec.  25.571. This is
structure that may need special maintenance actions to manage the
threat of fatigue. This would be the case for structure that has the
potential to develop fatigue cracks that, without intervention, could
lead to a catastrophic failure. The fatigue evaluations are performed
to determine if special actions are needed and if so, to provide the
data needed to define the maintenance action requirements. Fatigue
critical structure may be part of the baseline structure or part of an
alteration to the baseline structure. As explained in the NPRM,\30\ by
referencing Sec.  25.571 in the sentence noted below, we intended to
rely on the many precedents established in finding compliance with this
section.

    \30\ 71 FR 20583.
---------------------------------------------------------------------------

    Because of industry's extensive experience in showing compliance
with the damage tolerance requirements of Sec.  25.571, these key
terms [e.g., fatigue critical structure] should be readily
understood and applied.

    To clarify how the criteria of Sec.  25.571 apply within the
context of this rule, we revised the definition of ``fatigue critical
structure'' by adding the following language: ``Fatigue critical
structure includes structure, which, if repaired or altered, could be
susceptible to fatigue cracking and contribute to a catastrophic
failure.''
    Airbus, the ATA, and UPS, asked for a more detailed definition of
fatigue critical structure. They expressed concern that, as proposed,
the definition is open to varying interpretations, so it may not be
applied consistently across industry or across different airplane
models. UPS added that some STC holders do not have experience in
complying with Sec.  25.571. It asserted, the definition must be clear
so that it can be interpreted and applied in the same manner across the
industry.
    The ATA and UPS said the methodology for identifying fatigue
critical structure should include quantitative criteria for assessing
the criticality of structural elements, based on a comparison of their
operational loads to their design limit loads or ultimate loads; and it
should account for load type and single- and multiple-load paths. Also,
the ATA said, the methodology should define what ``could contribute''
means as stated in the definition of fatigue critical structure. It
recommended possibly using criteria similar to that in Sec.  25.1309 to
clarify the definition.
    The term ``fatigue critical structure,'' as explained in the
proposed rule, is intended to identify the same kind of structure for
which applicants must perform fatigue evaluations to comply with Sec.
25.571.\31\ These evaluations have been required for new type
certificates since the adoption of Amendment 25-45 in 1978.
Furthermore, AC 25-571-1C, published in 1998, provides many examples of
the types of structural elements that should be evaluated. Therefore,
we believe there is little, if any, room for differing interpretations
of this term.
---------------------------------------------------------------------------

    \31\ Sec.  25.571(a): ``An evaluation of the strength, detail
design, and fabrication must show that catastrophic failure due to
fatigue, * * * will be avoided throughout the operational life of
the airplane. This evaluation must be conducted * * * for each part
of the structure which could contribute to a catastrophic failure
(such as wing, empennage, control surfaces, fuselage, engine mounts,
and their related primary attachments) * * *.''
---------------------------------------------------------------------------

    We believe many of the commenters' concerns result from differences
in the way industry has used the term ``principal structural elements''
(PSEs). This term, as used in Sec.  25.571 and AC 25.571, is synonymous
with the term ``fatigue critical structure.'' That is, a PSE is
structure that needs to be evaluated to determine if special
maintenance actions are needed to manage fatigue. And if such actions
are needed, they must be defined. The meaning of PSE in Sec.  25.571
contrasts significantly with its usage in certain industry practices
that have evolved over the years.
    For some TC and STC holders, a PSE is considered to be a specific,
localized area within fatigue critical structure where special,
directed inspections are required by an Airworthiness Directive (AD) or
airworthiness limitations. For example, all longitudinal skin splices
in a pressurized fuselage should be considered fatigue critical
structure if they are not immune to fatigue cracking which could lead
to a catastrophic failure. However, it may be reasonable to manage
fatigue in these splices by only performing a special directed
inspection on the most highly stressed area, which may only constitute
a small percentage of the at-risk structure.
    Some TC and STC holders have identified the PSE as being limited to
this localized area. While this narrow usage of the term might be
acceptable within the context of specific supplemental inspection
documents (SID) or Airworthiness Limitations Sections (ALS), it could
and has led to confusion and inappropriate actions when taken out of
context. For this

reason, we have chosen not to use the term ``principal structural
element'' in this rule.
    The purpose of requiring identification and listing of fatigue
critical structure under this rule is to provide operators with a tool
that will help in the evaluation of existing and future repairs and
alterations. In this context, fatigue critical structure (FCS) is any
structure that, if repaired or altered, could be susceptible to fatigue
cracking and contribute to a catastrophic failure.
    In the case of the longitudinal skin splices discussed above, we
would expect that the FCS listed by the TC holder would include much
more structure than just, for example, the localized area that is being
inspected to gauge the fatigue state of all the splices. A hypothetical
repair applied to even the lowest stress area of the splices could
potentially make it more critical than the highest stressed area
without a repair by increasing and redistributing structural loads. The
result would be a repair needing its own special directed inspection to
prevent potentially catastrophic failure. The only way to cover this
contingency would be to perform a DTE.
    As discussed above, we revised the proposed definition of FCS to
clarify how the criteria of Sec.  25.571 apply in the context of this
rule. As we stated in the NPRM, \32\ we intend for this rule to apply
to future type certificate holders, as well as current holders. Because
the list of FCS required by this rule may be more extensive than the
structure identified as airworthiness limitations items currently
developed by TC applicants, we added provisions to Sec.  26.43
paragraphs (a) and (e) to make it clear that the list of FCS must be
submitted as part of the type certification process. This requirement
will help ensure that, new TC holders are properly addressing DT
requirements in developing structural repair manuals (SRMs) and other
service documents for use by operators. It will also assist operators
in ensuring that a DTE is performed for all repairs and alterations to
structure identified as FCS, as required by the AASFR, from the
beginning of an airplane's operational life.
---------------------------------------------------------------------------

    \32\ 71 FR at 20583.
---------------------------------------------------------------------------

    Regarding the concern that STC holders may not have experience in
complying with Sec.  25.571, current and earlier versions of AC 25.571-
1C provide guidance on identifying PSEs that is also applicable to
identification of FCS under this rule. Also, one reason this rule
requires a compliance plan is to ensure that TC holders, STC holders,
and the FAA have a common understanding of the rule's requirements,
including acceptable compliance methods.
    Regarding suggestions to use quantitative methods or methodologies
used to comply with Sec.  25.1309, our intent is to use the same method
to identify FCS that is required by Sec.  25.571. Paragraph (a) of
Sec.  25.571 states that an evaluation must be conducted for ``each
part of structure that could contribute to a catastrophic failure.''
Therefore, the applicant must determine which parts of structure could
contribute to a catastrophic failure when damaged as a result of
fatigue cracking. Applying a probabilistic approach to determine if and
when a part will contribute to a catastrophic failure has not been
industry practice in complying with Sec.  25.571. TC holders are
required under Sec.  25.571 to perform a damage tolerance evaluation on
structure to determine when fatigue cracking may occur. At that point
an inspection is performed to determine if cracking has occurred. A
probabilistic approach would raise many implementation questions
because fatigue cracking in metallic structure is a certainty and
detection is imperative in order to prevent catastrophic failure of
airplane structure. Probabilistic approaches would not be consistent
with our objective of facilitating timely compliance.

D. Damage Tolerance Evaluation (DTE)

    This rule requires TC holders and STC holders to review their
repair and alteration data and determine if a DTE is needed. Unless
previously accomplished, a DTE must be performed on all repairs and
alterations that affect fatigue critical structure. A DTE is a process
that leads to a determination of maintenance actions necessary to
detect or preclude fatigue cracking that could contribute to a
catastrophic failure. As applied to repairs and alterations, a DTE
includes the evaluation of the repair or alteration and the fatigue
critical baseline structure affected by the repair or alteration.
Acceptable methods for performing DTEs are described in AC 25.571-1C.
    The maintenance actions developed as a result of a DTE may include
inspections, time limits for removal and replacement of repairs,
modification of the repair, alteration to improve its fatigue
characteristics, or in some cases modification of the affected FCS. The
type of maintenance action that is appropriate depends upon the type of
structure affected and the type of fatigue anticipated. For example,
for fatigue cracks that grow at a predictable rate and that can be
detected by inspections, a repetitive inspection program would be
acceptable. For cracks in locations that cannot be inspected and for
cracking that may grow too rapidly to be detected reliably, replacement
or modification may be necessary.
    Section 26.43(c) requires TC holders to perform a DTE of those
repairs specified in their published repair data that affect fatigue
critical structure. Similarly, Sec. Sec.  26.45(c) and 26.47(c) require
TC and STC holders to perform a DTE on their FAA-approved alteration
data. In addition to the published repair and alteration data, this
final rule requires that all future repair and alteration data receive
a DTE to determine if inspections or other actions are necessary to
ensure the airworthiness of the repair or alteration. This rule also
requires TC holders to develop Repair Evaluation Guidelines (REGs) that
will enable operators to survey their airplanes to identify repairs
that affect fatigue critical baseline structure (FCBS) and to obtain
any necessary damage tolerance inspections (DTI) for those repairs. If
the REG directs the operator to obtain assistance from the TC holder
for developing the DTI, the TC holder must make such assistance
available.
    As discussed below, based on comments to the NPRM, we revised the
proposed requirements in Sec. Sec.  25.1825(c) and 25.1827(c) (adopted
as Sec. Sec.  26.45(c)(1) and 26.47(c)(1), respectively)) to clarify
that a DTE must be performed and the DTI developed for the alteration
and the FCBS that is affected by the alteration.
    Boeing and AAWG industry representatives asked that the regulatory
text in proposed Sec. Sec.  25.1825 and 25.1827 be revised to clarify
that both alteration and baseline structure need to be assessed. They
state that the description of the work proposed in these sections of
the NPRM may be interpreted to mean that DTIs only need to be developed
for the alteration that happens to affect FCBS. However, AAWG industry
representatives do not believe this is the interpretation the FAA
intends. AAWG industry representatives recommended that the language in
both Sec. Sec.  25.1825 and 25.1827 be changed to clearly say that the
following three components must be addressed for alterations:

    1. Identification of alterations that affect baseline fatigue
critical structure.
    2. Identification of the structural design details of the
alteration that require DTE.
    3. Identification of the affected design details of the baseline
fatigue critical

structure that require a re-evaluation of their DTE.

    The commenters are correct in that we did not intend for the
development of DTIs to be limited to the alteration structure. When a
DTE is performed for an alteration, the DTE must be applied to both the
alteration and the FCBS that is affected by the alteration. Therefore,
the DTI developed (as determined by the DTE) for an alteration would
apply to the alteration structure and to the FCBS that is affected by
the alteration. As stated above, we revised Sec. Sec.  25.1825(c) and
25.1827(c) (adopted as Sec. Sec.  26.45(c)(1) and 26.47(c)(1),
respectively) to clarify that for the alteration and the FCBS that is
affected by the alteration a DTE must be performed and the DTI
developed.
    The FAA does not believe that Sec. Sec.  25.1825(c) and 25.1827(c)
(adopted as Sec. Sec.  26.45(c) and 26.47(c), respectively) need to be
revised to clarify that alterations that affect FCBS need to be
assessed, or to provide clarification on which structural design
details of an alteration would require a DTE. Sections 25.1825(c)(1)
(adopted as Sec.  26.45(c)(1)) and 25.1827(c)(1) (adopted as Sec.
26.47(c)(1)) already specify that a DTE must be performed for
alterations that affect FCBS. In addition, the structure of the
alteration that requires development of a DTI will be identified as
part of a DTE performed on the alteration. The DTI may need to be
developed for fatigue critical alteration structure or for other
alteration structure that may affect the FCBS. We expect that this
identification would be part of the DTE of the alteration.
    Regarding the commenters' position that the proposed rule needs to
be revised to clarify the design details of the affected FCBS that will
need a re-evaluation of their DTE, the DTE of an alteration will
include an evaluation of the FCS that is affected by the alteration.
Therefore, in performing the evaluation of the affected FCBS, it must
be determined if new or revised DTIs need to be developed for this
structure. Such a determination is made as part of a DTE.
    Mr. Thomas A. Knott, P.E., said the proposed rule ``is fine,''
except it does not address repairs and modifications done under part
43. He said there are many alterations and repairs that were not
approved under an STC or developed by TC holders.
    The FAA acknowledges that there are existing repairs and
alterations that were developed and installed under 14 CFR part 43
without involvement by DAHs. This final rule takes into account these
types of repairs. The guidelines the DAHs are required to develop will
describe procedures for operators to follow in developing DTIs for
repairs. For alterations affecting FCS for which no DAH is responsible,
the AASFR requires operators either to develop the DT data themselves
or contract for their development. Because there is no DAH for these
alterations, they may be especially problematic if the installers
failed to consider the fatigue characteristics of the alterations or
their effects on the baseline structure. Both repairs and alterations
will be identified and assessed as part of surveys conducted to support
compliance with the AASFR.

E. Damage Tolerance Inspections (DTIs)

    A DTI is defined in this final rule as inspections developed as a
result of a DTE. The DTI includes the location of the airplane
structure to be inspected, the inspection method, inspection procedures
that include acceptance and rejection criteria, and the thresholds and
intervals associated with those inspections. The DTI may also specify a
time limit when the repair or alteration needs to be replaced. As
discussed below, this definition reflects minor changes from the one in
the proposed rule.
    Boeing asked that the FAA revise the definition of DTI. It said the
phrase ``and corrective maintenance actions'' could be confused with a
requirement to provide repair instructions or other corrective measures
for a condition found during an inspection. It said, historically, the
only instructions provided are how to accomplish the inspection
contained in the DTI and what action should be taken if the inspection
could not be accomplished. Therefore, Boeing requested that the phrase
``and corrective maintenance actions'' be removed from the definition
and replaced with the phrase, ``or a time limit when the repair needs
to be replaced, or both.''
    We agree and have revised the definition in the final rule as
requested. The purpose of this rule is to support operators'
implementation of damage tolerance inspection programs, as required by
the AASFR. Operators already have access to information on corrective
actions in the form of SRMs and other documents that may be necessary
if the inspections reveal fatigue cracks. Therefore, it is not
necessary to include the phrase ``and corrective maintenance actions''
in the definition of DTI.
    Bombardier asked, with respect to inspections of repairs, that we
clarify the phrase ``the location of the airplane structure to be
inspected'' used in the DTI definition. Bombardier said it understands
this phrase to mean that the DTI should clearly define which regions of
the repair and underlying structure should be inspected and the NDT
(non-destructive testing) method to be used in carrying out the
inspection. It said the DTI should be clearly linked to the repair
data, which will of itself define the repair location.
    The FAA agrees that the DTI should clearly define the areas of the
repair and underlying structure that should be inspected and the
inspection method to be applied. The DTI will be applicable to specific
repair data that will define the repair location. This approach is the
same as that currently used by TC holders in developing SRMs to comply
with Sec.  25.571, Amendment 25-45 and later.

F. DT Data for Repairs

1. Published Repair Data
    This final rule requires TC holders to review their published
repair data and determine if DT data exist for the repairs or if the DT
data need to be developed. This final rule defines published repair
data as instructions for accomplishing repairs, which are published for
general use in SRMs and service bulletins (or equivalent types of
documents). As discussed below, we made minor revisions to the proposed
definition.
    Boeing requested that we revise the definition of ``published
repair data'' to make it clearer. It recommended the following revised
version of the proposed definition:

    Published repair data means applicable instructions for
accomplishing repairs, which are published for general use in
structural repair manuals and service bulletins (or equivalent types
of documents).

    The FAA agrees with the recommended revision to the definition of
``published repair data,'' and we have revised the definition,
accordingly, with a minor change in wording.
    Bombardier said a list of Structural Significant Items (primary
structure) is provided in the SRMs for Bombardier Regional Aircraft. It
urged the FAA to consider rulemaking to require the SRM to be an
approved document. The SRM, Bombardier commented, can then incorporate
all of the instructions for continuing airworthiness required by the
NPRM and described previously in AC 25.1529. It said this approach has
been used by Bombardier and Transport Canada for SRMs and component
maintenance manuals (CMMs) applicable to aircraft and components
certified as damage tolerant to Sec.  25.571 (Amendment 25-45) and
later.

    As explained in the NPRM, SRMs, while not required documents, are
FAA approved. Their purpose is to provide operators with readily
available sources of approved repair data. Because the operational
rules require that major repairs be accomplished according to FAA-
approved data, an SRM that has not been FAA approved would not serve
operators' needs. The SRM, if assessed for damage tolerance under Sec.
25.571 (Amendment 25-45 or later Amendment), should include the
necessary instructions to ensure a particular repair meets the criteria
in AC 25.1529.
2. Effects of Multiple Repairs
    Mr. Glenn Davis commented that DT data should address the effects
of multiple repairs in close proximity on older aircraft, and future
inspections should be based on a ``worst case scenario of the
`combination effect' of the multiple repairs.'' He said the FAA might
consider requiring a time limit for individual or multiple repairs when
the repaired structure would have to be replaced, unless the applicant
or operator can confirm through a rational fatigue analysis, using an
acceptable fatigue model, that the repaired structure does not need to
be replaced. Mr. Davis said such a requirement could be applied to high
stress areas in older aircraft such as pressure bulkheads, door
apertures, attach fitting support structure for wings, and stabilizers.
    The FAA agrees with Mr. Davis's comment that the DT data,
specifically the DTE, should take into account the close proximity of
repairs. AC 25.571-1C provides guidance on determining the effects of
multiple repairs that are in close proximity. In addition, the repair
assessment guideline (RAG) documents developed in support of Sec.
121.370 (redesignated as Sec.  121.1107)\33\ address the effects of
these types of repairs on the pressure vessel. The FAA believes that
existing guidance in AC 25-571-1C, along with guidance developed in AC
120-93, as part of this final rule, adequately addresses this issue.
---------------------------------------------------------------------------

    \33\ Repair Assessment for Pressurized Fuselages final rule (65
FR 24108; April 25, 2000).
---------------------------------------------------------------------------

G. Repair Evaluation Guidelines (REGs)

    This final rule requires TC holders to develop REGs that include
processes operators could use to support compliance with Sec. Sec.
121.1109 and 129.109 for repairs that affect FCBS. The guidelines must
include--
     A process for conducting surveys of affected airplanes to
identify and document all existing repairs that affect FCBS;
     A process that will enable operators to obtain DTIs for
repairs that affect FCBS and for the FCBS affected by the repairs; and
     An implementation schedule that provides the timing for
conducting airplane surveys and for developing and incorporating DTIs
into the operator's maintenance program.
    TC holders must submit the REGs to the FAA Oversight Office for
review and approval and then make them available to affected operators.
    As discussed below, we made several minor revisions to the proposed
REG requirements.
    In Sec.  25.1823(f)(1)(iii) and (f)(4) (adopted as Sec.
26.43(e)(1)(iii) and (e)(4)), we removed the term ``DT data'' from the
phrase ``DT data implementation schedule.'' We made this change because
the term ``DT data implementation schedule'' may be misunderstood to
mean the actual timing of DT inspections (thresholds and inspection
intervals). It was only intended to refer to the timing of major
process related events (i.e., survey, development of DTIs, and
incorporation of the DTI into the maintenance program).
    We revised proposed Sec.  25.1823(f)(1)(iii) (adopted as Sec.
26.43(e)(1)(iii)) to make it clear that the implementation schedule
must identify the times when actions must be taken as specific numbers
of flight cycles, flight hours, or both. In developing its
recommendation regarding implementation schedules, the AAWG proposed an
approach that would have referenced the design service goal (DSG) for
determining the timing of various actions and would have allowed for
variability in DSGs for different airplanes of the same model,
depending upon actual flight lengths and other factors.
    We agree with the AAWG that it is appropriate to allow reference to
DSGs in the implementation schedule to allow for industry resources to
be allocated for compliance when they are needed. For example, the AAWG
recommended that certain actions be taken when an airplane reaches \3/
4\ DSG, before which fatigue cracking is less likely to have occurred.
However, allowing variability in DSG for different airplanes of the
same model would introduce a level of complexity and uncertainty to the
requirements of the operational rules that would jeopardize their
enforceability. Therefore, this rule requires that DSGs be stated as
``hard numbers.''
    We revised Sec.  25.1823(f)(3) (adopted as Sec.  26.43(e)(3)) to
remove the requirement that TC holders must make REGs available to STC
holders. As adopted, this paragraph only requires the TC holder to make
the REGs available to specified operators. We made this change because
if STC holders have access to the TC holder's list of FCS, they will
not need their REGs.
    We also revised Sec.  25.1823(f)(4) (adopted as Sec.  26.43(e)(4)).
The proposed paragraph reads as follows: ``If the guidelines direct the
operator to obtain assistance from the holder of a type certificate,
provide such assistance in accordance with * * *'' We revised this
paragraph in the final rule to replace the words ``provide such
assistance'' with the words ``make such assistance available.'' This
change makes it clear that, as with other requirements for TC holders
to support operators, this rule is not intended to require TC holders
to provide this support without compensation.
    Boeing said proposed Sec.  25.1823(f)(3) specifies that the TC
holder will make available the guideline documents to various entities.
Boeing believes this proposed requirement is in error and the reference
to proposed Sec.  25.1827 should be removed from Sec.  25.1823. Section
25.1827 is applicable to holders of and applicants for an STC. In
reading Sec.  25.1827 and draft AC 120-XX,\34\ Boeing said there is no
need for third parties to have access to the guidelines developed as
part of Sec.  25.1823. According to Sec.  25.1827 and AC 120-XX, the
only data required by an STC holder is the list of fatigue critical
structure, as stipulated in Sec.  25.1823(c)(2). In light of this,
Boeing said, the reference to Sec.  25.1827 should be deleted from
proposed Sec.  25.1823.
---------------------------------------------------------------------------

    \34\ Issued as AC 120-93.
---------------------------------------------------------------------------

    We agree that STC holders do not need the guidelines to comply with
this final rule as long as they have access to the TC holder's list of
FCS. We have revised the final rule as discussed above.
    Boeing commented that proposed Sec.  25.1823(f)(4) appears to be
using incorrect terminology. It said the wording in Sec.  25.1823(f)(4)
could circumvent the current business practices and established
relationships between the TC holder and the operator. Boeing requested
that paragraph (f)(4) be changed as follows:

    If the guidelines direct the operator to obtain assistance from
the holder of a type certificate, the holder of the type certificate
will make available such assistance in accordance with the DT data
implementation schedule.

    It was not our intent to require TC holders to provide assistance
to operators without compensation. As

indicated above, we have revised the final rule as the commenter
requested.
    UPS expressed concern about the effectiveness of the proposed REGs.
The proposed rule, it said, assumes that practical, cost effective REGs
are achievable. However, the proposed procedure will be significantly
more complex than the current Repair Assessment Guideline (RAG)
documents, which only survey fuselage skin. UPS said the current repair
assessment of pressurized fuselage skin results in removal and
replacement of some repairs due to the inability to accurately
determine the exact repair details. Fuselage skin repairs are
relatively easy to assess because almost all damage is cut out and one
side of the repair is accessible for detailed measurements. For other
structure (e.g., stringers, ribs, spars, frames, shear clips, bathtub
fitting) the ability to determine hidden repair details may not be
possible without removing the repair. Consequently, the proposed survey
method of documenting and establishing DTIs on existing repairs could
result in a higher than necessary repair replacement frequency. To
minimize the impact of the DTE of repairs, UPS believes it is vital
that the FCS be properly identified.
    In response to UPS's concerns about the effectiveness of the
proposed REGs, the airplane repair survey process was patterned after
existing RAG documents to minimize the impact of the DTE of repairs. AC
120-93 provides guidance for performing surveys to identify repairs
that may affect FCS.
    Regarding UPS's comment that certain structure may be difficult to
inspect without having to remove the repair, operators should work with
the TC holder in the Structural Task Group (STG) meetings to ensure an
efficient process is developed for assessing repairs to minimize the
unnecessary removal of repairs. The DTE will determine what actions are
necessary to ensure the continued airworthiness of the affected FCBS.
Performing DTIs on these airplanes should be no more difficult than
performing them on airplanes for which repair data already have DTIs
for compliance with the airplane's certification basis. We agree that
it is vital that FCS be properly identified. As discussed previously,
this final rule requires TC holders to apply the same analytical
methods to create this list that they have applied for many years in
complying with Sec.  25.571.

H. DT Data for Alterations

    This final rule requires TC holders to perform DTEs, and develop
DTI, if necessary, for their alterations that affect FCBS. For existing
alterations, TC holders must submit the DT data for FAA approval by
June 30, 2009. For future alterations, the DT data are required before
we approve the alteration data.
    Similarly, STC holders must perform DTEs and develop DTIs for their
alterations that affect FCBS. In addition to alterations, some STC
holders must perform DTEs and develop DTIs, if necessary, for repairs
developed by them that affect any FCS. For existing alterations, STC
holders must submit the DT data for FAA approval by June 30, 2009. For
future alterations, the DT data are required before we approve the
alteration data.
    The sections of the proposal that relate to alterations,
(Sec. Sec.  25.1825 and 25.1827 (adopted as Sec. Sec.  25.45 and 25.47,
respectively)) were revised as discussed below to make them clearer. As
proposed, these sections may be misinterpreted to mean that the TC and
STC holders need to perform a DTE of their alterations as installed on
individual airplanes, addressing variations in the configurations of
these airplanes. Our intent, however, is that they perform a DTE only
of their alteration design data.
    These sections may also be misinterpreted to mean that DTIs only
need to be developed for the FCS of the alteration. In addition, as
stated in the definition of damage tolerance evaluation in proposed
Sec.  25.1823(b), we intended that the DTE would also apply to the FCBS
that is affected by the alteration and that the resulting DTI would
also address the affected baseline structure. To clarify these
requirements, the final rule specifies that TC and STC holders must,
for each alteration affecting FCBS, identify and develop DTIs for both
the FCBS that is affected by the alteration and the fatigue critical
alteration structure. Other than some additional minor wording changes,
there are no other changes to the sections of the final rule pertaining
to alterations.
    The ATA commented that the FAA should limit the number of DTEs
necessary for alterations. Proposed Sec.  25.1825(c) and Sec.
25.1827(c) require TC holders to perform a DTE of each existing and
future alteration and submit DT data for the existing alterations to
the FAA. These provisions would apply to an impracticable number of
alterations, according to the commenter. The ATA recommended,
therefore, that the FAA clarify Sec. Sec.  25.1825(c) and 25.1827(c) to
stipulate that ``each alteration'' applies to each certificate or
approval of an alteration rather than each installation.
    The FAA agrees that it would be impracticable for TC or STC holders
to perform a DTE for alterations as installed on individual airplanes,
which may contain alterations and repairs that would affect the DTE of
which the TC or STC holder is unaware. It was not the FAA's intent to
require TC and STC holders to develop DT data for the actual
installation of their developed design changes (alterations), but
rather to require them to perform a DTE of the design changes affecting
FCBS that are specified in their FAA-approved alteration data. This DTE
must, however, address the range of airplane configurations on which
the TC or STC holder showed the alteration is eligible for
installation. We revised Sec. Sec.  25.1825(c) and 25.1827(c) (adopted
as Sec. Sec.  26.45(c) and 26.47(c), respectively) to clarify that the
DAHs are only responsible for performing DTE of their alteration data,
and not of the alterations as actually installed.

I. Required Documentation

    The ATA said the FAA should define the documents required of DAHs
as specifically as possible, and the product should be delivered to the
FAA for certification or approval in a form ready for direct
installation or incorporation as required by the associated operating
rule. The ATA said adherence to this recommendation should be
facilitated by the participation of Structural Task Groups (STG) in the
development of the DTI and REG. The ATA recommended that the FAA use
consistent terminology in the final rule and in AC 120-XX,\35\ so they
clearly describe the documentation and data DAHs must make available to
operators. It said draft AC 120-XX states that DAHs would provide
operators with a model-specific ``compliance document.'' The NPRM,
however, does not discuss the ``compliance document'' referenced in the
draft AC. Similar to the ATA comment, Horizon Air asked that the rule
define the specific type of required data that DAHs must make available
to operators.
---------------------------------------------------------------------------

    \35\ Issued as AC 120-93.
---------------------------------------------------------------------------

    We agree with the ATA that this final rule should clearly identify
the required data and documents. This final rule requires DAHs to
develop and make available to operators lists of fatigue critical
structure, damage tolerance inspections for their alterations and
repair data (supported by DTE documentation submitted to the FAA),
repair evaluation guidelines, and implementation schedules.
    Based on the Aviation Rulemaking Advisory Committee's (ARAC)

recommendations, the FAA developed AC 120-93 to facilitate DAH
compliance with this rule and operator compliance with the AASFR. This
AC describes a compliance document that would either contain or
reference these required documents. Because the compliance dates for
these documents differ, the DAH would not make the compliance document,
as a whole, available until the last of these documents is approved.
    As described in the AC, this compliance document would support an
operator's development of an Operator's Implementation Plan (OIP). The
OIP would provide the means for addressing the adverse effects of
repairs and alterations. Once this OIP is approved by the operator's
principal maintenance inspector (PMI), the operator would comply with
the AASFR by incorporating the OIP into its maintenance program and
implementing the OIP by performing surveys of its airplanes, obtaining
necessary damage tolerance inspections and procedures, and performing
those inspections and procedures, all in accordance with the approved
implementation schedule contained in the OIP.
    STGs, working under the auspices of the ARAC's Airworthiness
Assurance Working Group (AAWG), may be convened to assist TC holders in
developing airplane model-specific DT data. This rule and AC 120-93
reflect consistent terminology. The DT data to be developed and made
available are described in Sec. Sec.  26.43, 26.45, and 26.47 of this
final rule, as well as in AC 120-93.

J. Proprietary Data

    The ATA said the FAA should work with DAHs to establish a narrow
and clear definition of proprietary data. DAHs have expressed concerns
that the proposed requirements could lead to the disclosure of
proprietary data (e.g., DT documentation). Conversely, operators are
concerned that restrictive disclosure policies could result in REGs and
DTIs that are too general to be used without costly and time-consuming
consultation with the DAH. The ATA recommended that the FAA coordinate
with DAHs to support a goal for documents that must be ``made
available'' under the proposal that would allow operators to comply
autonomously with the DT requirements without consulting with the DAH
more than absolutely necessary. ATA said the FAA can support this
recommendation further by providing guidelines to DAHs and STGs to
ensure that claims of proprietary data are not overstated.
    For many years, the FAA has required DAHs to disclose to affected
persons information they might otherwise consider proprietary. For
example, since 1981, DAHs have been required to provide Instructions
for Continued Airworthiness, including DT data, which DAHs may have
considered proprietary. However, because we have determined that this
information is essential to maintaining the airplanes in an airworthy
condition, we have required DAHs to make it available as a condition
for obtaining and retaining their certificates. Regarding the
usefulness of the documents developed by the DAHs, because we expect
these documents will be developed by DAHs in collaboration with the
affected operators, we anticipate that the operators will ensure they
are useful for their intended purposes. FAA technical specialists will
also be monitoring development of these documents for this purpose.

K. Compliance Plan

    This final rule includes requirements for a compliance plan to
ensure that affected TC and STC holders produce DT data in a timely
manner that are acceptable in content and format. Integral to the
compliance plan are procedures to allow the FAA to monitor progress
toward compliance. The affected TC and STC holders must submit to the
FAA Oversight Office on the compliance dates specified in the rule a
compliance plan that addresses--
     The project schedule for meeting the compliance dates,
including all major milestones;
     A proposed means of compliance with the requirements to
develop and make available DT data; and
     A plan to submit to the FAA Oversight Office, not less
than 60 days before the stated compliance dates, a draft of the
required compliance items.
    Based on comments submitted to other DAH airworthiness rules, the
FAA has determined that we can remove some provisions of proposed Sec.
25.1829 (adopted as Sec.  26.49) without adversely affecting our
ability to facilitate DAH compliance. Specifically, in Sec.
25.1829(a)(3), we proposed a requirement for DAHs to identify the
intended means of compliance that differ from those described in FAA
advisory materials. While this is still a desirable element of any
compliance plan, we have concluded that an explicit requirement is
unnecessary. As with normal type certification planning, we expect that
DAHs will identify these differences and fully discuss them with the
FAA Oversight Office early in the compliance period to ensure that
these differences will ultimately not jeopardize full and timely
compliance.
    Similarly, Sec.  25.1829(c) contains provisions that would have
authorized the FAA Oversight Office to identify deficiencies in a
compliance plan or the DAH's implementation of the plan and to require
specified corrective actions to remedy those deficiencies. While we
anticipate that this process will still occur in the event of potential
non-compliance, we have concluded that it is unnecessary to adopt
explicit requirements to correct deficiencies.
    Ultimately, DAHs are responsible for submitting compliant documents
by the dates specified in Sec. Sec.  26.43, 26.45, and 26.47 of this
final rule. Section 26.49 retains the requirements to submit a
compliance plan and to implement the approved plan. If the FAA
Oversight Office determines that the DAH is at risk of not submitting
compliant documents by the compliance dates because of deficiencies in
either the compliance plan or the DAH's implementation of the plan, the
FAA Oversight Office will document the deficiencies and request DAH
corrective action. Failure to implement proper corrective action under
these circumstances, while not constituting a separate violation, will
be considered in determining appropriate enforcement action if the DAH
ultimately fails to meet the requirements of this section.
    We also added an exception for future TC applicants in Sec.
26.49(a) to make it clear that these applicants are not required to
submit a separate compliance plan for the applicable requirements of
this final rule. These compliance issues should be addressed as part of
the normal certification plan submitted for any type certificate
project.
    Section 25.1829(5) included a proposed requirement to include in
the compliance plan a process for continually assessing service
information related to structural fatigue damage. We have reconsidered
this proposed requirement and concluded that existing regulations \36\
that require both DAHs and operators to report structural defects
should be adequate to enable us to determine whether the objectives of
this final rule are being met. Therefore, we removed this provision
from the final rule.
---------------------------------------------------------------------------

    \36\ 14 CFR 21.3 and 121.703.
---------------------------------------------------------------------------

1. Process for Continuous Assessment of Service Information
    Bombardier, in its comment on the compliance plan, referred to the
proposed requirement that the compliance plan must address a process
for continuous assessment of service information. Bombardier said
feedback

from operators on the effectiveness and findings resulting from DT-
based inspections of baseline structure, as well as repairs and
alterations, may not be adequate to enable them to meet this
requirement.
    As discussed above, we have removed this provision from this final
rule since existing regulations will enable us to determine if the
objectives of this final rule are being met.
2. Timing of FAA Approval
    Airbus expressed concern that the FAA may not have sufficient
resources to handle approval of compliance plans in a timely manner.
Therefore, it recommends a thorough review of FAA resources needed for
this activity before committing to the proposed compliance date.
    FedEx said it understands that the compliance documents must be
approved by the FAA Aircraft Certification Office (ACO) before they are
made available to operators, but the proposed rule does not state when
the documents would be made available to operators. FedEx said the rule
should include a date by which the FAA would approve the DT data that
TC and STC holders provide, as well as a date by which the approved
data will be made available to operators.
    The ATA said the FAA should commit to a schedule for approving the
DT data from DAHs and implementation plans from operators. It requested
that the FAA give an estimate of when industry can expect the FAA to
approve the DT documents and implementation plans, taking into account
the volume of the submissions.
    We are not including time frames in the regulation for our review
and approval of the compliance plans and compliance documents.
Expectations for FAA personnel have been defined in FAA Order 8110.26,
which directs the Aircraft Certification Service and Flight Standards
Service in their roles and responsibilities for implementing these
initiatives. The Order includes expected times for reviewing and
approving DAH compliance plans, plans to correct deficiencies, and
draft and final compliance data and documents. To facilitate
implementation, we will also train affected personnel in their roles
and responsibilities and provide familiarization with requirements of
the regulations and associated guidance. However, our ability to
approve documents, and the timing of our approvals, ultimately depends
on the quality of the documents submitted by the DAHs and their
responsiveness if we identify deficiencies.

L. Harmonization

    The AAWG industry representatives, ATA, Boeing, Embraer, and
Horizon Air commented that the FAA should harmonize the DT Data rule
with EASA and other national airworthiness authorities. If the rule is
not harmonized, the AAWG industry representatives expressed concern
that the FAA's retention of authority to make all necessary compliance
determinations for foreign DAHs will establish ``a substantial
precedent that could create a significant challenge to all future
certification programs.'' The AAWG industry representatives said the
stated requirements advocate ``a procedure that could permit unilateral
and potentially arbitrary certification activities at the whim of any
regulatory authority.''
    Boeing and the ATA said the lack of harmonization will cause
unnecessary conflicts and complexities between the FAA's and foreign
authorities' requirements. Boeing said while it is aware that EASA is
pursuing a similar proposal, EASA may not adopt the same requirements
as the FAA. Also, Boeing said, having to comply with different
requirements in the same time frame would cause added complications and
difficulties with meeting aggressive schedules, and it would result in
unnecessary, additional work for the FAA.
    Both Boeing and the ATA believe harmonization is a standard of
excellence that has been achieved over many years of hard work and this
rule should not interfere with that achievement.
    We agree with the commenters that harmonization of this rule with
other national authorities is an important objective. We fully expect
to coordinate with EASA and other authorities on findings of
compliance. EASA and Transport Canada Civil Aviation (TCCA) have
participated in the AAWG's development of the AC that will support
compliance with this final rule. As a follow-on to this activity, EASA
has proposed the formation of a European Aging Aircraft Working Group
and has requested participation by the FAA. The FAA plans to support
this activity with representatives from both the Aircraft Certification
Service and the Flight Standards Service. There is general agreement
among the authorities on the need to address DT for repairs and
alterations and on the approach adopted in this rule.
    The AAWG industry representatives commented that there is the
potential for creating substantial negative impact in the industry with
respect to airplane certification sales and transfers between U.S. and
foreign entities because the proposal has not been harmonized with
EASA. According to the AAWG industry representatives, the economics of
this impact has not been accounted for in the regulatory evaluation;
therefore, the FAA should assure that the final rule is harmonized to
the extent possible with EASA because of the potential economic issue
for all parties. The AAWG industry representatives also said it appears
that the long-term intention of EASA is to harmonize with the U.S.
requirements by 2008 or 2009. And it said that the implementation time
scales are different between the two authorities' approaches.
    This rule will not have the negative effects suggested by the
commenter. In fact, by requiring DAHs to develop and make available the
data necessary to comply with the AASFR, this rule will facilitate
compliance for all airplanes, which is a prerequisite for
transferability. All authorities recognize that harmonization of this
rule is important in that common requirements will allow expeditious
transfer of airplanes across borders, and we are working towards that
objective.
1. Foreign Authority Approval of Required Data
    Airbus commented that the NPRM preamble indicates that the FAA
cannot accept foreign authority approval for documents under Bilateral
Agreements because these foreign authorities have not yet adopted a
similar rule. It said the Joint Aviation Authorities (JAA) issued and
applied Notice of Proposed Amendment (NPA 20-10) (the European Aviation
Safety Agency (EASA) updated NPA 20-10 to NPA 05/2006), which addresses
the same airworthiness issues and incorporates similar technical
guidance. Moreover, evaluation of repairs, alterations, and
modifications to DT requirements is state-of-the-art and is approved
under the EASA regulatory system on a daily basis.
    Airbus also said it will be at a disadvantage by having to deal
unilaterally with the FAA without the support and involvement of EASA.
Also, it said it would have to coordinate with the FAA's international
branch along with several other non-U.S. TC holders. However, U.S. TC
holders will have a dedicated FAA certification office to work with and
may be able to use their authorized designees to perform compliance
related activities.
    According to Airbus, obtaining support from the FAA is especially
important for proposed Sec. Sec.  25.1823(d) and 25.1825(c) and (d) for
alteration and

repair approvals. Therefore, Airbus requested that the FAA include EASA
in the approval process, such that in the near future the FAA could
accept the majority of the activities performed by EASA under the
Bilateral Agreement. In addition, Airbus requested that the FAA give
non-U.S. TC and STC holders the same level of priority and the same
allocation of FAA resources as U.S. TC and STC holders. This, Airbus
said, would help mitigate delays in reaction and approval time.
    Horizon Air said the proposed rule states that data will be
submitted to the FAA Oversight Office or its properly authorized
designees. In defining ``authorized designees,'' reference is made only
to Designated Engineering Representatives (DERs) specifically
authorized by their supervising ACO.
    Horizon Air also said that currently because of the Bilateral
Agreement between Transport Canada and the FAA, it is able to
incorporate DTE and DTI documentation for Bombardier and deHavilland
airplanes directly into its maintenance program. Under the new rule, it
appears it would be required to submit the developed repair data to the
ACO before being able to implement it. Therefore, Horizon Air requested
that Foreign Authorities, specifically Transport Canada, or their
designees be included under Bilateral Agreements.
    We recognize the important role other national authorities are
likely to play in implementation of this rule. In addition to the on-
going efforts to harmonize these requirements, we have been working
closely with the other national authorities to define appropriate
roles, responsibilities, and relationships among all affected
authorities. As discussed in the NPRM, the compliance planning
provisions are equally important for foreign TC holders, and we expect
to have mutually agreeable arrangements with their authorities on how
compliance planning will be overseen. We expect these other authorities
to play a major role in reviewing their TC holders' compliance plans
and other required documents, which will enable us to provide timely
approvals for all affected TC and STC holders, assuming the submitted
documents comply with the applicable requirements.

M. Enforcement

    Bombardier and UPS expressed concerns about enforcement. Bombardier
asked what mechanism the FAA would use to impose civil penalties on
non-U.S. DAHs. UPS said the proposed rule does not state how the FAA
would handle a DAH that does not complete the damage tolerance
assessment tasks on time. It is also concerned whether the FAA can
effectively enforce the intent of these types of provisions.
    The compliance planning provisions of this rule are intended to
facilitate timely compliance and avoid the need of enforcement for non-
compliance. However, under 49 U.S.C. 46301, the FAA has authority to
take civil penalty action without regard to nationality of the
respondent. The FAA's general enforcement policies, which are set forth
in 14 CFR part 13 and Order 2150.3, will apply to the DAH requirements.
These general policies provide wide discretion for us to impose
administrative action, civil penalties (up to $25,000 per violation per
day) or action against a TC or STC holder's certificate (including
suspension or revocation).
    If a TC or STC holder is found to be non-compliant, we will
consider the circumstances of non-compliance before determining an
appropriate course of action. For example, deliberate violations will
be treated more severely than inadvertent non-compliance. Any
enforcement action the FAA may choose to take will be in consideration
of the circumstances of the violation and defined on a case-by-case
basis.

N. Industry and FAA Resources

    UPS commented that DT analysis depends on complex methodology and
data. Because of this, there are very few DERs in the industry that
have FAA DTE approval authority. UPS suggested it is highly unlikely
that this methodology and relevant data can be streamlined into an
approach that is useful and effective. It suggested the FAA establish
an initiative to authorize additional structures DERs with DTE approval
authority.
    ABX expressed concern that both industry and the FAA have a
shortage of specialists in areas related to the rule. It said FAA ACOs
don't have enough resources to provide the needed support to industry
in a timely manner. It also said the present delegation requirements in
the area of DT are unachievable for non-OEM DERs. Therefore, ABX said
the FAA, with support of the industry, should take the following steps:
     Create different levels of delegation for DTE. If
necessary, keep the requirements the same for full authority but allow
DERs with less than required experience to obtain delegation to show
compliance in specific areas, using previously FAA-approved
methodology.
     Provide training to DERs and/or call for specific college
courses that can substitute the experience to facilitate the
delegation.
     Develop methodologies for DT analysis in the areas that
are frequently needed by operators and STC holders.
     Postpone any rulemakings until the industry has the
required tools to comply with the rule in the mandated time frame.
    Recognizing the limited industry and FAA resources available to
perform and approve DTEs, ARAC has developed guidance material in AC
120-93 that describes a means of compliance with this rule and the
AASFR that allows the available resources to focus on the highest
priority DTEs for repairs. This AC describes an implementation schedule
with a phased-in approach under which existing repairs on the older and
higher-utilization airplanes are assessed first (highest risk repairs),
with newer airplanes being assessed when they approach their design
service goal (DSG). This approach is similar to that established for
certain RAGs developed for compliance with Sec.  121.370\37\
(redesignated as Sec.  121.1107)). Therefore, we find the
implementation schedule approach described in AC 120-93 to be a
rational one. We believe this approach will help ensure that adequate
industry and FAA resources will be available to support timely
compliance with this final rule and with the AASFR.
---------------------------------------------------------------------------

    \37\ Special maintenance program requirements.
---------------------------------------------------------------------------

    The FAA agrees that there is a need for an increased number of
designees having authorization for DT. To address this potential
problem, the FAA is continuing to hold DER seminars to encourage
participation by DERs in these programs. DERs can work with their FAA
Oversight Office to develop a plan that would support expanding their
authorized delegation to include DT. Due to the complexities associated
with DT, particularly those related to performing DTEs on repairs and
alterations, it is necessary to ensure DER candidates have adequate
experience in performing DT and in analyzing repairs and alterations.
The current process for obtaining DT-delegated functions requires DER
applicants to have at least 1 year of experience in performing DTEs.
This experience is necessary for the FAA to gain a level of confidence
that the DER, once authorized to perform DT on repairs and alterations,
will submit DT data that are appropriate and not subject to a need for
extensive review by the FAA Oversight Office.
    For compliance with the AASFR, it is of particular importance that
the DERs have a working knowledge of what is required for showing
compliance with Sec.  25.571 for repairs and alterations. The FAA does
not agree with the

commenter's recommendation to allow DER candidates with less than the
required experience to obtain a delegation for DT, or to substitute the
requirement for experience with college courses to facilitate
delegation. Experience is a key element in ensuring the success of the
FAA's delegation program.
    Regarding the recommendation that the FAA develop methodologies for
DT analysis in the areas that are frequently needed by operators and
STC holders, we believe the methodologies employed today, which have
been used for several years throughout the aviation industry, are
adequate. Damage-tolerance-based programs such as RAGs developed by TC
holders to support operator compliance with Sec.  121.370 (redesignated
as Sec.  121.1107), provide a streamlined approach operators can use
for assessing repairs common to the airplane pressure boundary.
Expansion of these guidelines to address additional structural areas
(e.g., frequently repaired areas), or development of new RAGs, may
support operator compliance with the AASFR. However, these types of DT-
based programs are model specific and typically require TC holder
involvement. Operators should coordinate with TC holders during STG
meetings to determine the need for such programs and how they should be
structured.
    We disagree with the recommendation to postpone this rulemaking
because we do not believe industry needs additional time to comply. As
we have discussed, this final rule is needed to support operator
compliance with the AASFR. That rule was adopted in February 2005.
Delaying adoption of the DAH requirements in this rule would adversely
affect operators' ability to meet the compliance time frame in the
AASFR. In addition, methodologies for performing a DTE have been
applied for several years and are readily available. Also, to reduce
the resource burden, we describe in AC 120-93 an implementation
schedule that may provide more time for operators to obtain DTEs for
alterations for which there are no TC or STC holders. This
implementation schedule may provide, in part, a means for addressing
the potential adverse effects of alterations.
    UPS said some STC holders may not have the resources (either
financially, technically, or both) to comply with the proposal.
Further, it said, the proposal does not address the situation where an
STC holder has gone out of business or has surrendered its STC to the
FAA.
    The FAA recognizes that there may be some occasions where the DAH
is unwilling or unable to comply with the regulations. There may also
be cases where the DAH no longer exists. As stated in the policy
statement, Safety--A Shared Responsibility--New Direction for
Addressing Airworthiness Issues for Transport Category Airplanes, under
these circumstances, the operator is still obligated to comply with the
operational rules. However, the FAA recognizes that such occasions may
significantly complicate the operator's effort to show compliance with
the operational rules. The FAA recommends the affected operators
contact their DAHs early in the compliance process to ensure their
intent to comply. These operators are also encouraged to collaborate
with other operators who may also be impacted by lack of support on a
means for compliance.

O. Compliance Dates

    As noted before, today's final rule supports the AASFR, which
requires operators to incorporate a means to address the adverse
effects of repairs and alterations into their maintenance program by
December 20, 2010. This DAH DT Data final rule includes compliance
dates that require DAHs to make the required DT documents available to
operators in enough time for them to comply with their approved means
for addressing repairs and alterations. The approved means will include
implementation schedules that provide timing for when airplane repair
surveys are to be performed and when DTI or other maintenance actions
for repairs and alterations need to be incorporated into the
maintenance program. Certain of the compliance dates in the DAH DT Data
final rule have changed from those in the proposed rule.
    Specifically, in proposed Sec.  25.1823(g)(1), TC holders would
have 90 days after the effective date of the rule to submit their lists
of fatigue critical baseline structure. In proposed Sec.
25.1825(e)(1), they would have 90 days to submit their lists of fatigue
critical alteration structure. In proposed Sec.  25.1827(e)(1), STC
holders would have 270 days to submit their lists of fatigue critical
alteration structure.
    In the final rule (Sec.  26.43(f)(1)), TC holders have 180 days
from the effective date to submit their lists of fatigue critical
baseline structure. TC and STC holders (Sec. Sec.  26.45(e)(1) and
26.47(e)(1), respectively) have 360 days from the effective date of the
rule to submit their lists of fatigue critical alteration structure.
    The AAWG industry representatives, Boeing, FedEx, and Embraer asked
for an extension of the compliance date in the AASFR and a commensurate
extension of the DAH DT Data rule's compliance date. While several of
the commenters acknowledged the FAA's prior 3-year extension (from 2007
to 2010) to the compliance time for the AASFR, they said if the FAA had
published the DAH DT Data NPRM at the time of that extension, industry
would have had more time to comply with the DAH DT Data final rule.
    The AAWG industry representatives asked us to extend the AASFR
compliance date of December 20, 2010 to December 20, 2013. FedEx asked
the FAA to give operators a minimum of 12 months after receiving the
FAA-approved documents to develop their implementation plan to send to
their FAA Flight Standards District Office. Boeing asked us to extend
the AASFR compliance date to August 18, 2013. It said the FAA should
impose incremental compliance times from the effective date of final
rules, rather than impose a fixed date. For the DAH DT Data final rule,
Boeing believes the FAA should allow DAHs 4 years from the effective
date of the rule to submit their documents to the FAA because of the
addition of the DAH requirements and related compliance plan in this
final rule.
    Except as discussed previously regarding lists of fatigue critical
structure (FCS), we do not believe an extension of the compliance dates
in either rule is appropriate. As several of the commenters
acknowledged, we previously extended the compliance date for the AASFR
by 3 years to allow ARAC time to develop guidance material operators
could use to support compliance with DT requirements related to repairs
and alterations.
    Based on requests from industry, in May 2004, we tasked \38\ ARAC
to develop guidance to support operator compliance with the AASFR.
Included in the tasking notice was a task for ARAC to do the following:
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    \38\ 69 FR 26641; May 13, 2004.

    Oversee the Structural Task Group (STG) activities that will be
coordinated for each applicable airplane model by the respective
type certificate holders and parts 121 and 129 certificate holders.
These STG activities will involve the development of model specific
approaches for compliance with Sec. Sec.  121.370a and 129.16
---------------------------------------------------------------------------
[redesignated as Sec. Sec.  121.1109 and 121.109, respectively]* * *

    In addition, the tasking states that the data developed by the TC
holders via STG meetings, using the guidance material developed by
ARAC, should be completed by December 18, 2009. ARAC accepted this
tasking, which it assigned

to the AAWG, and agreed to complete it by the specified date of
December 18, 2009.
    In the February 2005 AASFR, we extended the December 5, 2007
compliance date adopted in the Aging Airplane Safety Interim final rule
\39\ to December 20, 2010. This extension was meant to give ARAC time
to complete the tasking and allow operators a full year to implement
the resulting program changes. The AAWG developed a schedule for
completion of the tasking by the agreed-upon date. The compliance dates
specified in this DAH DT Data final rule are fully consistent with
these commitments, and none of the commenters have identified reasons
why we should not expect these commitments to be fulfilled.
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    \39\ 67 FR 72726; December 6, 2002.
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    Regarding Boeing's comment that this rule imposes additional
requirements for which they need more time, assuming ARAC and the STGs
fulfill their commitments, we anticipate that the products of the
tasking will enable Boeing and other participating TC holders to meet
the requirements of this rule with little additional effort.
Specifically, regarding compliance planning, this type of planning is
normal business practice, regardless of the requirements of this rule,
as evidenced by the AAWG's schedule development discussed earlier.
    The ATA, Boeing, UPS, FedEx, and AAWG industry representatives
asked that DAHs be given 180 days from the effective date of the final
rule to submit their lists of fatigue critical baseline structure to
the FAA. The ATA and UPS asked that the FAA allow 360 days from the
effective date of the final rule for STC holders to submit their lists
of fatigue critical alteration structure. Airbus requested an extension
of 1 year from the effective date of the final rule to submit its lists
of fatigue critical baseline structure. The commenters believe it is
important to allow DAHs enough time to develop the lists to ensure they
are accurate.
    Boeing and AAWG industry representatives indicated that the FAA
should allow additional time to develop the lists because of their
importance to industry and to other rules like the proposed Widespread
Fatigue Damage (WFD) rule. Boeing said more time would enable it to
consult with the STGs on the format and content of the lists. It also
said more time is needed because of the large numbers of airplanes and
alterations involved and the need for internal coordination to ensure
consistency. It estimates that for its airplane models, it would have
to produce more than 40 lists.
    The ATA, FedEx, and UPS said if DAHs do not have sufficient time to
develop accurate lists, they may produce overly conservative lists that
include all primary structure. The ATA and FedEx add that such lists
would be of little value to operators and would add costs and
complexities to operator compliance with the AASFR. Also, the ATA said
DAHs may opt to recommend replacement of structural elements rather
than inspections and repairs if they do not have enough time to compile
the lists. Airbus commented that it does not have the resources to
complete the necessary assessments and compile the lists in the
proposed time frames. Airbus said the consequence of not having enough
time to develop accurate lists could be either incomplete lists or
extremely long lists.
    The FAA believes additional time to establish the lists of fatigue
critical baseline and alteration structures is appropriate, and has
revised the rule as discussed above. The revised time frames, which
give TC holders 180 days to submit their lists of FCBS and TC and STC
holders 360 days to submit their lists of fatigue critical alteration
structure, should allow sufficient time to develop the lists. This is
particularly true since the TC holders have been required to identify
fatigue critical structure to comply with the damage tolerance
requirements of Sec.  25.571 since 1978. For pre-amendment 25-45
airplanes, the TC holder analysis that led to the development of the
SID documents provide a useful starting point for developing these
lists. As discussed previously, these activities should already be well
underway.

P. Costs and Benefits

    The AAWG industry representatives and Boeing commented on our
statement in the NPRM that the costs of the proposed rule were
accounted for in the AASFR. The AAWG industry representatives believe
that the economics on which the proposed rule is based are questionable
and their basis cannot be determined. Boeing said the FAA assumed that
much of the work required for compliance with the proposed rule was
already completed by the TC holders on other programs, such as the SID
and RAG initiatives. The commenters added that the costs ascribed to
the TC holder in the proposed rule, in fact, did not exist at the time
the original rule was published for comment, nor do they exist today.
    The AAWG industry representatives and Boeing requested that the FAA
revise the basis of the economic evaluation of the proposed rule, and
include accurate estimates of the cost of the development of compliance
data by the TC holders, based on the means of compliance suggested in
AC 120-93.
    The ATA said the FAA should disclose DAH estimates for the cost of
damage tolerance data and documents. The ATA indicated that it does not
concur with the FAA's assertion that the proposed rule has minimal to
no costs. The ATA recommended that the FAA include DAH estimates for
the cost of these documents in its disposition of comments to the
proposal.
    UPS said the costs of the proposed rule changes are understated.
Although the regulatory flexibility analysis in the rulemaking states
that this rule would relieve small-entity part 121 operators of what
could be a significant cost, there is nothing in this proposal that
prevents DAHs from passing all their costs on to the operators.
Although this compensation could be reasonable, it will also likely be
significant. UPS suggested that an accurate cost-benefit analysis be
accomplished and evaluated prior to adopting this rulemaking.
    The requirements to develop damage tolerance (DT) based data for
repairs and alterations were originally established in the Aging
Airplane Safety Interim final rule (AASIFR). These responsibilities
were initially placed on the operators of part 121 and U.S.-registered
part 129 transport category airplanes. The costs and benefits were
computed in the regulatory evaluation for that rulemaking. The
regulatory evaluation for the AASIFR, as well as the regulatory
evaluation for the AASFR, which clarified these requirements,
recognized that to comply with the rule's requirements, operators would
have to develop and implement DT-based inspections and procedures for
the affected airplane structure. This DAH DT Data final rule is a
counterpart to the AASFR; it transfers the responsibility of developing
DT-based data from operators to design approval holders (DAHs).
Therefore, it has minimal to no societal costs.
    We anticipate that by the compliance date for the AASFR, DT
inspection programs for baseline structure, required by this DAH DT
Data final rule, will already be mandated by AD or certification or
operational regulations for all airplanes affected by this final rule.
A significant number of operators subject to the AASFR are small
entities. If each of the small-entity operators individually took the
responsibility for developing DT-based data, the cost for the data
would be significant. By transferring the responsibility from part 121
operators to DAHs, this rule will

relieve those operators of what could be a significant cost.
    While UPS is correct that operators may have to compensate TC
holders for the data they make available, we expect these costs to be
substantially less than if the operators had been required to
individually develop their own data.
    The DAHs, with their greater expertise and access to design data,
are in the best position to identify fatigue critical structure and
methods and frequency of inspections operators need to comply with the
AASFR. DAHs can develop these data with greater efficiency than
individual operators and these costs would be amortized over a larger
fleet. With STG participation, we expect that the resulting compliance
documents will minimize costs for operators and facilitate their
compliance with the AASFR. This final rule will ensure that the
required data are developed in a timely manner to minimize the
possibility for disruption of airline operations when the AASFR
compliance deadline is reached. AC 120-93 is largely a product of ARAC
and reflects industry's view of the most cost effective means for
developing the data operators must implement under the AASFR.

Paperwork Reduction Act

    Under the Paperwork Reduction Act of 1995, (5 CFR
1320.8(b)(2)(vi)), an agency may not conduct or sponsor, and a person
is not required to respond to, a collection of information unless it
displays a currently valid OMB control number. Information collection
requirements in the AASFR previously have been approved by the Office
of Management and Budget (OMB) under the provisions of the Paperwork
Reduction Act of 1995 (44 U.S.C. 3507(d)) and have been assigned OMB
Control Numbers: 2120-0020 and 2120-0008. Part 129 record requirements
can be found in International Civil Aviation Organization Annexes.
    The FAA reviewed data associated with compliance to the AASFR and
data associated with this rule. We have determined that this rule is a
transfer of responsibility only, and there is no additional paperwork
burden on the public. The paperwork burden for compliance with the
AASFR will be reduced as a result of this rule due to a reduction in
the numbers of repairs and alterations that will need an individual
damage tolerance assessment. This is because this rule will require
design approval holders to develop a streamlined approach for assessing
repairs.

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
determined that there are no ICAO Standards and Recommended Practices
that correspond to these regulations.

IV. Final Regulatory 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 (Pub. L. 96-354) requires
agencies to analyze the economic impact of regulatory changes on small
entities. Third, the Trade Agreements Act (Pub. L. 96-39) prohibits
agencies from setting standards that create unnecessary obstacles to
the foreign commerce of the United States. In developing U.S.
standards, the Trade Act requires agencies to consider international
standards and, where appropriate, that they be the basis of U.S.
standards. Fourth, the Unfunded Mandates Reform Act of 1995 (Pub. L.
104-4) 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 annually (adjusted for inflation with base year of
1995). This portion of the preamble summarizes the FAA's analysis of
the economic impacts of this final rule.
    Department of Transportation Order DOT 2100.5 prescribes policies
and procedures for simplification, analysis, and review of regulations.
If the expected cost impact is so minimal that a proposed or final rule
does not warrant a full evaluation, this order permits that a statement
to that effect and the basis for it be included in the preamble if a
full regulatory evaluation of the cost and benefits is not prepared.
Such a determination has been made for this final rule. The reasoning
for this determination follows.
    We begin with a discussion of the AASFR. Then we discuss the
existing certification and operational rules that already require
operators to develop and implement the DT inspections and procedures
this final rule will require.
    This rule transfers the responsibility of developing AASFR DT data
and documents from operators to DAHs. A transfer of responsibility from
one entity to another does not increase societal costs; therefore, this
rule has minimal to no costs. Additionally, the DAH requirements do not
preclude DAHs from recouping their costs by seeking reasonable
compensation from the operators for the required DT data and documents.
The recently published AASFR \40\ requires airline operators of certain
large transport category airplanes to implement DT-based inspections
and procedures for airplane structure susceptible to fatigue cracking
that could contribute to catastrophic failure. Damage tolerance data
are essential for operators to implement and conduct DT-based
inspections and procedures.
---------------------------------------------------------------------------

    \40\ 70 FR 5518, February 2, 2005.
---------------------------------------------------------------------------

    This final rule is a counterpart to the AASFR to ensure that
operators have the necessary data and documents to support timely
compliance with the requirements of Sec. Sec.  121.1109 and 129.109.
Timely operator compliance improves the safety of the fleet.
    This final rule will require DAHs to develop DT inspections and
procedures for repairs and alterations. Existing operational rules
already require DT inspections and procedures for repairs and
alterations to baseline structure. TC Holders of airplanes certified to
Amendment 25-45 (or later), which are affected by this proposal, are
required by Sec.  25.571 to perform a damage tolerance evaluation and
establish, as necessary, damage tolerance inspections or other
procedures. On pre-Amendment 25-45 airplanes, DT inspection and
procedures for the baseline structure are required by airworthiness
directive (AD). Damage tolerance inspections for repairs and
alterations to affected Boeing 727 and 737-100/200 airplanes are also
required by AD. Damage tolerance inspections for repairs to the
pressurized fuselage \41\ for certain pre-Amendment 25-45 airplanes
\42\ are required by Sec.  121.370 (redesignated as Sec.  121.1107). By
December 2010, damage tolerance inspections for the baseline structure
and repairs and alterations will be required by Sec. Sec.  121.1109 and
129.109 for airplanes certificated after January 1, 1958 that have a
passenger seating

capacity of 30 or more or a maximum payload capacity of 7500 pounds or
more. Despite these requirements, in many cases, DT data and documents
have not yet been developed for many repairs and alterations made to
the affected airplanes.
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    \41\ Fuselage, door skins, and bulkhead webs.
    \42\ A-300 (excluding the -600 model), 707, 720, 727, 737-300/