82 FR 44504 - Airworthiness Directives; The Boeing Company Airplanes

DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration

Federal Register Volume 82, Issue 184 (September 25, 2017)

We are superseding Airworthiness Directive (AD) 2008-12-04, which applied to certain The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes. AD 2008-12-04 required various repetitive inspections to detect cracks along the chem-milled steps of the fuselage skin, and to detect missing or loose fasteners in the area of a certain preventive modification or repairs; replacement of the time-limited repair with a permanent repair, if applicable; and applicable corrective actions which would end certain repetitive inspections. This AD reduces the post-modification inspection compliance times, limits installation of the preventive modification to airplanes with fewer than 30,000 total flight cycles, and adds repetitive inspections for modified airplanes. This AD was prompted by an evaluation by the design approval holder (DAH) that indicated that the upper skin panel at the chem-milled step above the lap joint is subject to widespread fatigue damage (WFD) if the modification was installed after 30,000 total flight cycles. We are issuing this AD to address the unsafe condition on these products.

[Federal Register Volume 82, Number 184 (Monday, September 25, 2017)]
[Rules and Regulations]
[Pages 44504-44509]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2017-20114]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2016-9301; Product Identifier 2015-NM-193-AD; Amendment 
39-19056; AD 2017-19-26]
RIN 2120-AA64


Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: We are superseding Airworthiness Directive (AD) 2008-12-04, 
which applied to certain The Boeing Company Model 737-600, -700, -700C, 
-800, and -900 series airplanes. AD 2008-12-04 required various 
repetitive inspections to detect cracks along the chem-milled steps of 
the fuselage skin, and to detect missing or loose fasteners in the area 
of a certain preventive modification or repairs; replacement of the 
time-limited repair with a permanent repair, if applicable; and 
applicable corrective actions which would end certain repetitive 
inspections. This AD reduces the post-modification inspection 
compliance times, limits installation of the preventive modification to 
airplanes with fewer than 30,000 total flight cycles, and adds 
repetitive inspections for modified airplanes. This AD was prompted by 
an evaluation by the design approval holder (DAH) that indicated that 
the upper skin panel at the chem-milled step above the lap joint is 
subject to widespread fatigue damage (WFD) if the modification was 
installed after 30,000 total flight cycles. We are issuing this AD to 
address the unsafe condition on these products.

DATES: This AD is effective October 30, 2017.

[[Page 44505]]

    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in this AD as of October 30, 
2017.

ADDRESSES: For service information identified in this final rule, 
contact Boeing Commercial Airplanes, Attention: Contractual & Data 
Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 
90740; telephone 562-797-1717; Internet https://www.myboeingfleet.com. 
You may view this referenced service information at the FAA, Transport 
Standards Branch, 1601 Lind Avenue SW., Renton, WA. For information on 
the availability of this material at the FAA, call 425-227-1221. It is 
also available on the internet at http://www.regulations.gov by 
searching for and locating Docket No. FAA-2016-9301.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://www.regulations.gov by searching for and locating Docket No. FAA-2016-
9301; or in person at the Docket Management Facility between 9 a.m. and 
5 p.m., Monday through Friday, except Federal holidays. The AD docket 
contains this AD, the regulatory evaluation, any comments received, and 
other information. The address for the Docket Office (phone: 800-647-
5527) is Docket Management Facility, U.S. Department of Transportation, 
Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 
New Jersey Avenue SE., Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Alan Pohl, Aerospace Engineer, 
Airframe Section, FAA, Seattle ACO Branch, 1601 Lind Avenue SW., 
Renton, WA 98057-3356; phone: 425-917-6450; fax: 425-917-6590; email: 
[email protected].

SUPPLEMENTARY INFORMATION:

Discussion

    We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR 
part 39 to supersede AD 2008-12-04, Amendment 39-15547 (73 FR 32991, 
June 11, 2008) (``AD 2008-12-04''). AD 2008-12-04 applied to certain 
The Boeing Company Model 737-600, -700, -700C, -800, and -900 series 
airplanes. The NPRM published in the Federal Register on November 22, 
2016 (81 FR 83745) (``the NPRM''). The NPRM was prompted by an 
evaluation by the DAH that indicated that the upper skin panel at the 
chem-milled step above the lap joint is subject to WFD if the 
modification was installed after 30,000 total flight cycles. The NPRM 
proposed to continue to require various repetitive inspections to 
detect cracks along the chem-milled steps of the fuselage skin, and to 
detect missing or loose fasteners in the area of the preventive 
modification or repairs; replacement of the time-limited repair with a 
permanent repair, if applicable; and applicable corrective actions 
which would end certain repetitive inspections. The NPRM also proposed 
to reduce the post-modification inspection compliance times, limit 
installation of the preventive modification to airplanes with fewer 
than 30,000 total flight cycles, and add repetitive inspections for 
modified airplanes. We are issuing this AD to detect and correct 
cracking of the upper skin panel at the chem-milled step above the lap 
joint, which could result in reduced structural integrity of the 
airplane.

Comments

    We gave the public the opportunity to participate in developing 
this AD. The following presents the comments received on the NPRM and 
the FAA's response to each comment.

Support for the NPRM

    Boeing and United Airlines supported the NPRM.

Effect of Winglets on Accomplishment of the Proposed Actions

    Aviation Partners Boeing stated that installation of winglets, as 
provided in Supplemental Type Certificate (STC) ST00830SE, does not 
affect the ability to accomplish the actions proposed in the NPRM.
    We agree with the commenter. We have redesignated paragraph (c) of 
the proposed AD as (c)(1) and added paragraph (c)(2) to this AD to 
state that installation of STC ST00830SE does not affect the ability to 
accomplish the actions required by this AD. Therefore, for airplanes on 
which STC ST00830SE is installed, a ``change in product'' alternative 
method of compliance (AMOC) approval request is not necessary to comply 
with the requirements of 14 CFR 39.17.

Request To Revise Certain Compliance Time Provisions

    Southwest Airlines (SWA) asked that we revise certain compliance 
language in paragraph (p)(4) of the proposed AD, which stipulated that 
post-repair or post-mod inspections be done at the time specified in 
the service information or at the time specified in the previously 
approved AMOC, ``whichever occurs first.'' SWA stated that previously 
approved AMOCs for post-repair or post-modification supplemental 
inspections that comply with certain regulations may contain unique 
damage tolerance inspection programs that demonstrate a level of safety 
equivalent to that of AD 2008-12-04. SWA added that altering those 
supplemental inspections to post-repair or post-modification 
inspections as specified in Boeing Alert Service Bulletin 737-53A1232, 
Revision 3, dated July 27, 2015, when those are done first, could 
result in incorrect inspection methods to geometrical structure that 
does not conform to the repair or modification definitions specified in 
Revisions 1 and 3 of that service information.
    We partially agree with the commenter's request. We have determined 
that repairs and preventive modifications should be handled separately. 
Fleet experience and subsequent analysis of Model 737-200, -200C, -300, 
-400, and -500 airplanes, which have similar chem-milled step details, 
have shown that certain post-preventative modification inspection 
programs may not adequately address the unsafe condition. Therefore, 
paragraph (p)(4) of this AD has been changed to remove the language 
``preventative modifications'' and remove the reference to the service 
information and ``whichever occurs first'' from the compliance time 
specified. In addition, we have added paragraph (p)(5) to this AD to 
address only the preventive modifications without change to the service 
information and ``whichever occurs first'' language.

Request To Retain Certain Exceptions

    Additionally, SWA asked that paragraphs (j) and (k) of AD 2008-12-
04 be included in the proposed AD. Paragraph (j) of AD 2008-12-04 
provides an allowance for repairs that are FAA-approved and that have a 
minimum of three rows of fasteners above and below the chem-milled 
step. SWA stated that paragraph (k) of AD 2008-12-04 provides a means 
of inspections without an AMOC when an external repair is covering the 
chem-milled step, but that the doubler does not span the step by a 
minimum of three rows of fasteners above and below the chem-milled 
step. SWA added that both paragraphs (j) and (k) of AD 2008-12-04 are 
missing from the proposed AD and should be added, with certain 
clarifications, to paragraph (j) of the proposed AD. First, the repair 
is an external doubler repair. Second, in lieu of the doing the post-
repair supplemental inspections in accordance with table 2 of paragraph 
1.E.,

[[Page 44506]]

``Compliance,'' of Boeing Alert Service Bulletin 737-53A1232, Revision 
3, dated July 27, 2015, the inspections should be done in accordance 
with 14 CFR 121.1109(c)(2) or 14 CFR 129.109(b)(2) supplemental 
inspection requirements, or in accordance with FAA-approved damage 
tolerance inspection requirements.
    SWA also stated that if paragraphs (j) and (k) of AD 2008-12-04 are 
not restated for compliance with existing FAA-approved repairs, 
operators will be required to seek AMOC approvals for such existing 
repairs prior to the inspection threshold or repeat interval of table 1 
of paragraph 1.E., ``Compliance,'' of Boeing Alert Service Bulletin 
737-53A1232, Revision 3, dated July 27, 2015. SWA stated that not 
including the exceptions in paragraphs (j) and (k) of AD 2008-12-04 
could potentially lead to disruption of operations if it is necessary 
to request AMOC approvals during repair discovery, or could burden 
operators with records research to identify these repairs for AMOC 
approvals prior to the required compliance times.
    We agree that an allowance can be made for repairs that meet the 
criteria specified in paragraph (j) of AD 2008-12-04. These repairs 
address the unsafe condition identified in this AD. Therefore, we have 
added paragraph (l)(3) to this AD to include the provision of paragraph 
(j) of AD 2008-12-04 for repairs that were accomplished before the 
effective date of this AD.
    We disagree that post-repair inspections for these repairs should 
be done in accordance with 14 CFR 121.1109(c)(2) or 14 CFR 
129.109(b)(2) supplemental inspection requirements. Post-repair 
inspections for repairs that meet the criteria of paragraph (j) of this 
AD are to be accomplished in accordance with table 2 of paragraph 1.E., 
``Compliance,'' of Boeing Alert Service Bulletin 737-53A1232, Revision 
3, dated July 27, 2015. This is consistent with the DAH's current 
recommendation as well as the requirements of paragraph (j) of AD 2008-
12-04. Paragraph (l)(3) of this AD reflects these provisions.
    We also disagree with the commenter's request to change the word 
``repair'' to ``external doubler repair'' in paragraph (l)(3) of this 
AD because we are retaining the provisions of paragraph (j) of AD 2008-
12-04.
    We also agree to add certain provisions of paragraph (k) of AD 
2008-12-04 to this AD. We have added paragraph (l)(4) to this AD to 
address certain repairs as defined in paragraph (k) of AD 2008-12-04. 
However, paragraph (l)(4) of this AD does not include a reference to 
Boeing Model 737 Non-destructive Test (NDT) Manual, Part 6, Subject 53-
30-20, and instead requires that the inspection be done using FAA-
approved procedures. We have also added Note 1 to paragraph (l)(4) of 
this AD to specify that guidance on the inspection specified in 
paragraph (l)(4) of this AD can be found in Boeing Model 737 NDT 
Manual, Part 6, Subject 53-30-20.

Clarification of Paragraph (i)(1) of This AD

    We have revised the language in paragraph (i)(1) of this AD to 
clarify which modifications are exempt from the actions required by 
paragraph (i)(1) of this AD.

Conclusion

    We reviewed the relevant data, considered the comments received, 
and determined that air safety and the public interest require adopting 
this AD with the changes described previously, and minor editorial 
changes. We have determined that these minor changes:
     Are consistent with the intent that was proposed in the 
NPRM for correcting the unsafe condition; and
     Do not add any additional burden upon the public than was 
already proposed in the NPRM.
    We also determined that these changes will not increase the 
economic burden on any operator or increase the scope of this AD.

Related Service Information Under 1 CFR Part 51

    We reviewed Boeing Alert Service Bulletin 737-53A1232, Revision 3, 
dated July 27, 2015. This service information describes procedures for 
an external detailed inspection and an external nondestructive 
inspection (NDI) for cracks in the fuselage skin at chem-milled steps. 
Corrective actions include a permanent or time-limited repair, a 
preventive modification, and replacement of loose and missing 
fasteners. Related investigative actions include internal and external 
detailed inspections of the repair area. This service information is 
reasonably available because the interested parties have access to it 
through their normal course of business or by the means identified in 
the ADDRESSES section.

Costs of Compliance

    We estimate that this AD affects 376 airplanes of U.S. registry.
    We estimate the following costs to comply with this AD:

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                Cost on U.S.
           Action                   Labor cost         Parts cost       Cost per product          operators
----------------------------------------------------------------------------------------------------------------
Inspections.................  Up to 25 work-hours x              $0  Up to $2,125 per       Up to $799,000 per
                               $85 per hour =                         inspection cycle.      inspection cycle.
                               $2,125 per
                               inspection cycle.
----------------------------------------------------------------------------------------------------------------

    We estimate the following costs to do any necessary repairs and 
replacements that would be required based on the results of the 
inspections. We have no way of determining the number of aircraft that 
might need these replacements:

                                               On-Condition Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                     Cost per
                Action                            Labor cost                   Parts cost             product
----------------------------------------------------------------------------------------------------------------
Fastener replacement..................  Up to 1 work-hour x $85 per    Minimal..................             $85
                                         hour = $85.
----------------------------------------------------------------------------------------------------------------


[[Page 44507]]

    We have received no definitive data that would enable us to provide 
cost estimates for the related investigative actions, certain repairs, 
and other applicable actions specified in this AD.

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. 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.
    We are issuing this rulemaking under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this 
rulemaking action.
    This AD is issued in accordance with authority delegated by the 
Executive Director, Aircraft Certification Service, as authorized by 
FAA Order 8000.51C. In accordance with that order, issuance of ADs is 
normally a function of the Compliance and Airworthiness Division, but 
during this transition period, the Executive Director has delegated the 
authority to issue ADs applicable to transport category airplanes to 
the Director of the System Oversight Division.

Regulatory Findings

    We have determined that this AD will not have federalism 
implications under Executive Order 13132. This AD will not have a 
substantial direct effect on the States, on the relationship between 
the national government and the States, or on the distribution of power 
and responsibilities among the various levels of government.
    For the reasons discussed above, I certify that this AD:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866,
    (2) Is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979),
    (3) Will not affect intrastate aviation in Alaska, and
    (4) Will not have a significant economic impact, positive or 
negative, on a substantial number of small entities under the criteria 
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
1. The authority citation for part 39 continues to read as follows:

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


Sec.  39.13  [Amended]

0
2. The FAA amends Sec.  39.13 by removing Airworthiness Directive (AD) 
2008-12-04, Amendment 39-15547 (73 FR 32991, June 11, 2008), and adding 
the following new AD:

2017-19-26 The Boeing Company: Amendment 39-19056; Docket No. FAA-
2016-9301; Product Identifier 2015-NM-193-AD.

(a) Effective Date

    This AD is effective October 30, 2017.

(b) Affected ADs

    This AD replaces AD 2008-12-04, Amendment 39-15547 (73 FR 32991, 
June 11, 2008) (``AD 2008-12-04'').

(c) Applicability

    (1) This AD applies to The Boeing Company Model 737-600, -700, -
700C, -800, and -900 series airplanes, certificated in any category, 
as identified in Boeing Alert Service Bulletin 737-53A1232, Revision 
3, dated July 27, 2015.
    (2) Installation of Supplemental Type Certificate (STC) 
ST00830SE [http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgstc.nsf/0/184DE9A71EC3FA5586257EAE00707DA6?OpenDocument&Highlight=st00830se] 
does not affect the ability to accomplish the actions required by 
this AD. Therefore, for airplanes on which STC ST00830SE is 
installed, a ``change in product'' alternative method of compliance 
(AMOC) approval request is not necessary to comply with the 
requirements of 14 CFR 39.17.

(d) Subject

    Air Transport Association (ATA) of America Code 53, Fuselage.

(e) Unsafe Condition

    This AD was prompted by a fatigue test that revealed numerous 
cracks in the upper skin panel at the chem-milled step above the lap 
joint, followed by an evaluation by the design approval holder (DAH) 
that indicated that location is subject to widespread fatigue damage 
(WFD) on airplanes on which a certain modification was installed 
after 30,000 total flight cycles. We are issuing this AD to detect 
and correct cracking of the upper skin panel at the chem-milled step 
above the lap joint, which could result in reduced structural 
integrity of the airplane.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Inspections at Locations Without the Preventive Modification, Time-
Limited Repair, or Permanent Repair Installed

    At locations where a preventive modification, time-limited 
repair, or permanent repair has not been installed as specified in 
Boeing Service Bulletin 737-53A1232: At the applicable time 
specified in paragraph 1.E., ``Compliance,'' of Boeing Alert Service 
Bulletin 737-53A1232, Revision 3, dated July 27, 2015, do an 
external detailed inspection and an inspection specified in either 
paragraph (g)(1) or (g)(2) of this AD, for any crack in the fuselage 
skin at the chem-milled steps at specified locations, in accordance 
with Accomplishment Instructions of Boeing Alert Service Bulletin 
737-53A1232, Revision 3, dated July 27, 2015. Do all applicable 
related investigative and corrective actions before further flight 
in accordance with the Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, 
except as required by paragraph (l)(1) of this AD, and except as 
provided in paragraphs (l)(3) and (l)(4) of this AD. Repeat the 
inspections thereafter at the applicable time specified in paragraph 
1.E., ``Compliance,'' of Boeing Alert Service Bulletin 737-53A1232, 
Revision 3, dated July 27, 2015.
    (1) Do an external medium frequency eddy current (MFEC), or 
magneto optic imager (MOI), or C-Scan inspection.
    (2) Do an external ultrasonic phased array (UTPA) inspection.

(h) Repetitive Post-Modification Inspections and Repair at Any Location 
With the Preventive Modification But No Time-Limited or Permanent 
Repair

    At any location with a preventive modification installed as 
specified in Boeing Service Bulletin 737-53A1232: At the applicable 
time specified in paragraph 1.E., ``Compliance,'' of Boeing Alert 
Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, 
except as required by paragraph (l)(2) of this AD, do the actions 
specified in paragraphs (h)(1) and (h)(2) of this AD.
    (1) Do external detailed and external high frequency and medium 
frequency eddy current inspections for any crack, in accordance with 
Part 7 of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1232, Revision 3, dated July 27, 2015. If no crack 
is found during the inspection, repeat the inspections thereafter at 
the applicable time specified in paragraph 1.E., ``Compliance,'' of 
Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015. If any crack is found during any inspection required by 
this paragraph, repair before further flight, in accordance with the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1232, Revision 3, dated July 27,

[[Page 44508]]

2015, except as required by paragraph (l)(1) of this AD.
    (2) Do a detailed inspection for any crack and any loose or 
missing fasteners, in accordance with Part 7 of the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1232, Revision 
3, dated July 27, 2015. Repeat the inspections thereafter at 
applicable time specified in paragraph 1.E, ``Compliance,'' of 
Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015. If any crack is found during any inspection, or any loose 
or missing fastener is found, before further flight, do all 
applicable corrective actions, in accordance with Part V of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1232, Revision 3, dated July 27, 2015, except as specified in 
paragraph (l)(1) of this AD.

(i) Additional Actions for Modified Airplanes

    (1) At any location where a preventive modification as specified 
in Boeing Service Bulletin 737-53A1232 was installed after the 
accumulation of 30,000 total flight cycles, at the applicable time 
specified in paragraph 1.E., ``Compliance,'' of Boeing Alert Service 
Bulletin 737-53A1232, Revision 3, dated July 27, 2015, except as 
required by paragraph (l)(2) of this AD, do all applicable 
investigative and corrective actions using a method approved in 
accordance with the procedures specified in paragraph (p) of this 
AD. For preventive modifications installed on airplanes listed in 
Appendix A of Boeing Alert Service Bulletin 737-53A1232, Revision 3, 
dated July 27, 2015, at the specified total flight cycles: The 
actions specified in this paragraph are not required.
    (2) For airplanes which have installed STC ST01697SE (http://
rgl.faa.gov/Regulatory_and_Guidance_Library/rgstc.nsf/0/
0812969a86af879b8625766400600105/$FILE/ST01697SE.pdf) and the 
preventive modification has been installed after 15,000 total flight 
cycles: Before the accumulation of 25,000 total flight cycles, do 
all applicable investigative and corrective actions using a method 
approved in accordance with the procedures specified in paragraph 
(p) of this AD.

(j) Inspections and Repair at Locations With the Permanent Chem-Milled 
Step Repair Installed

    At any location where a permanent repair has been installed as 
specified in Boeing Service Bulletin 737-53A1232: At the applicable 
time specified in paragraph 1.E., ``Compliance,'' of Boeing Alert 
Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, do 
the inspections specified in paragraph (j)(1) or (j)(2) of this AD, 
in accordance with Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015. 
Repeat the inspections thereafter at the applicable time specified 
in paragraph 1.E., ``Compliance,'' of Boeing Alert Service Bulletin 
737-53A1232, Revision 3, dated July 27, 2015. Do all applicable 
related investigative and corrective actions before further flight 
in accordance with Boeing Alert Service Bulletin 737-53A1232, 
Revision 3, dated July 27, 2015, except as required by paragraph 
(l)(1) of this AD.
    (1) Do an external low frequency eddy current (LFEC) inspection 
for any crack, and doubler external LFEC and external detailed 
inspections for any crack and loose or missing fasteners.
    (2) Do an external LFEC inspection for any crack, a doubler 
external LFEC and external detailed inspections for any crack and 
loose or missing fasteners, and an internal MFEC for any crack.

(k) Inspection and Replacement at Locations With a Chem-Milled Time-
Limited Repair Installed

    At any location where a chem-milled time-limited repair is 
installed, do the actions specified in paragraphs (k)(1) and (k)(2) 
of this AD, at the applicable time specified in 1.E. ``Compliance,'' 
of Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015.
    (1) Do internal and external detailed inspections of the time-
limited repair for any crack, or loose or missing fasteners, in 
accordance with Part IV of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015. 
Repeat the inspections thereafter at the applicable time specified 
in paragraph 1.E., ``Compliance,'' of Boeing Alert Service Bulletin 
737-53A1232, Revision 3, dated July 27, 2015. If any crack is found 
during any inspection, or if any loose or missing fastener is found, 
before further flight, do all applicable corrective actions, in 
accordance with Part IV of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, 
except as specified in paragraph (l)(1) of this AD.
    (2) Replace the time-limited repair with the permanent repair, 
in accordance with Part IV of the Accomplishment Instructions of 
Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015.

(l) Exceptions to Service Information Specifications

    (1) Where Boeing Alert Service Bulletin 737-53A1232, Revision 3, 
dated July 27, 2015, specifies to contact Boeing for repair 
instructions, this AD requires repair before further flight using a 
method approved in accordance with the procedures specified in 
paragraph (p) of this AD.
    (2) Where paragraph 1.E., ``Compliance,'' of Boeing Alert 
Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, 
specifies a compliance time ``after the date of Revision 2 of this 
service bulletin,'' this AD requires compliance within the specified 
compliance time after the effective date of this AD.
    (3) For airplanes on which the actions specified in paragraph 
(g) of this AD are required: Inspections specified in table 1 of 
paragraph 1.E., ``Compliance,'' of Boeing Alert Service Bulletin 
737-53A1232, Revision 3, dated July 27, 2015, are not required in 
areas that are spanned by an FAA-approved repair that has a minimum 
of 3 rows of fasteners above and below the chem-milled step, 
provided that the repair was installed before the effective date of 
this AD. Operators must accomplish post-repair inspections at the 
applicable time specified in table 2 of paragraph 1.E, 
``Compliance,'' of Boeing Alert Service Bulletin 737-53A1232, 
Revision 3, dated July 27, 2015.
    (4) For any airplane that has an external doubler covering the 
chem-milled step, but the doubler does not span the step by a 
minimum of 3 rows of fasteners above and below the chem-milled step 
and the doubler was installed before the effective date of this AD: 
One method of compliance with the inspection requirement of 
paragraph (g) of this AD is to inspect all chem-milled steps covered 
by the repair using non-destructive test (NDT) methods approved in 
accordance with the procedures specified in paragraph (p) of this 
AD. These repairs are to be considered time-limited and are subject 
to the post-repair supplemental inspections and replacement at the 
times specified in table 3 of paragraph 1.E., ``Compliance,'' of 
Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015.
    Note 1 to paragraph (l)(4) of this AD: Guidance for the 
procedures for the alternative inspection specified in paragraph 
(l)(4) of this AD can be found in the Boeing 737 NDT Manual, Part 6, 
Subject 53-30-20.

(m) Optional Terminating Action

    (1) For airplanes that have accumulated 30,000 total flight 
cycles or fewer, or for airplanes on which STC ST01697SE was 
installed and that have accumulated 15,000 total flight cycles or 
fewer, accomplishment of the preventive modification specified in 
Part V of Boeing Alert Service Bulletin 737-53A1232, Revision 3, 
dated July 27, 2015, terminates the inspections required by 
paragraph (g) of this AD in the modified areas only.
    (2) Installation of a permanent repair as specified in Part III 
of Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015, or a time-limited repair as specified in Part IV of Boeing 
Alert Service Bulletin 737-53A1232, Revision 3, dated July 27, 2015, 
terminates the inspections required by paragraph (g) of this AD in 
the repaired areas only.

(n) Installation Limitations of Preventive Modification

    As of the effective date of this AD, installation of the 
preventive modification specified in Boeing Service Bulletin 737-
53A1232 is prohibited on the airplanes identified in paragraphs 
(n)(1) and (n)(2) of this AD.
    (1) Airplanes that have accumulated more than 30,000 total 
flight cycles.
    (2) Airplanes which have installed STC ST01697SE and that have 
accumulated more than 15,000 total flight cycles.

(o) Credit for Previous Actions

    This paragraph provides credit for the corresponding actions 
specified in paragraphs (g), (h), (i), (j), (k), and (m) of this AD, 
if those actions were performed before the effective date of this AD 
using the service information identified in paragraph (o)(1), 
(o)(2), or (o)(3) of this AD.
    (1) Boeing Special Attention Service Bulletin 737-53A1232, dated 
April 2, 2007.

[[Page 44509]]

    (2) Boeing Special Attention Service Bulletin 737-53A1232, 
Revision 1, dated May 18, 2012.
    (3) Boeing Special Attention Service Bulletin 737-53A1232, 
Revision 2, dated July 26, 2013.

(p) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Seattle ACO Branch, FAA, has the authority to 
approve AMOCs for this AD, if requested using the procedures found 
in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request 
to your principal inspector or local Flight Standards District 
Office, as appropriate. If sending information directly to the 
manager of the certification office, send it to the attention of the 
person identified in paragraph (q)(1) of this AD. Information may be 
emailed to: [email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.
    (3) An AMOC that provides an acceptable level of safety may be 
used for any repair, modification, or alteration required by this AD 
if it is approved by the Boeing Commercial Airplanes Organization 
Designation Authorization (ODA) that has been authorized by the 
Manager, Seattle ACO, to make those findings. To be approved, the 
repair method, modification deviation, or alteration deviation must 
meet the certification basis of the airplane, and the approval must 
specifically refer to this AD.
    (4) AMOCs approved previously for repairs for AD 2008-12-04 are 
approved as AMOCs for the installation of the repair specified in 
this AD, provided all post-repair inspections are done at the 
applicable times specified in the AMOC.
    (5) AMOCs approved previously for preventive modifications for 
AD 2008-12-04 are approved as AMOCs for the installation of the 
preventive modification specified in this AD, provided all post-
modification inspections are done at the applicable times specified 
in the AMOC, or in tables 1a and 1b of paragraph 1.E., 
``Compliance,'' of Boeing Alert Service Bulletin 737-53A1232, 
Revision 3, dated July 27, 2015, whichever occurs first. The AMOC 
must include all of the inspections specified in Tables 1a and 1b of 
Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated July 
27, 2015.

(q) Related Information

    (1) For more information about this AD, contact Alan Pohl, 
Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 1601 
Lind Avenue SW., Renton, WA 98057-3356; phone: 425-917-6577; fax: 
425-917-6450; email: [email protected].
    (2) Service information identified in this AD that is not 
incorporated by reference is available at the addresses specified in 
paragraphs (r)(3) and (r)(4) of this AD.

(r) Material Incorporated by Reference

    (1) The Director of the Federal Register approved the 
incorporation by reference (IBR) of the service information listed 
in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
    (2) You must use this service information as applicable to do 
the actions required by this AD, unless the AD specifies otherwise.
    (i) Boeing Alert Service Bulletin 737-53A1232, Revision 3, dated 
July 27, 2015.
    (ii) Reserved.
    (3) For service information identified in this AD, contact 
Boeing Commercial Airplanes, Attention: Contractual & Data Services 
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740; 
telephone 562-797-1717; Internet https://www.myboeingfleet.com.
    (4) You may view this service information at the FAA, Transport 
Standards Branch, 1601 Lind Avenue SW., Renton, WA. For information 
on the availability of this material at the FAA, call 425-227-1221.
    (5) You may view this service information that is incorporated 
by reference at the National Archives and Records Administration 
(NARA). For information on the availability of this material at 
NARA, call 202-741-6030, or go to: http://www.archives.gov/federal-register/cfr/ibr-locations.html.

    Issued in Renton, Washington, on September 14, 2017.
Jeffrey E. Duven,
Director, System Oversight Division, Aircraft Certification Service.
[FR Doc. 2017-20114 Filed 9-22-17; 8:45 am]
BILLING CODE 4910-13-P