Discussion \n\n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The NPRM published in the Federal Register on June 27, 2013 (78 FR 38608). The NPRM was prompted by a report of cracks in stringer splices at body station STA 360 and STA 908, between stringer (S) S-10L and S-10R; cracks in butt straps between S-5L and S-3L, and S-3R and S-5R; vertical chem-mill fuselage skin cracks at certain butt joints; and an instance of cracking that occurred in all those three structural elements on one airplane. The NPRM proposed to require repetitive inspections for any cracking of stringer splices and butt straps, and related corrective and investigative actions if necessary. We are issuing this AD to detect and correct cracking in the three structural elements, which could result in the airplane not being able to sustain limit load requirements and possibly result in uncontrolled decompression. \n\nComments \n\n\n\tWe gave the public the opportunity to participate in developing this AD. The following presents the comments received on the proposal (78 FR 38608, June 27, 2013) and the FAA's response to each comment. \n\nRequest to Clarify That Post-Repair Inspections Are Not Required by This Final Rule \n\n\n\tBoeing requested clarification that Table 11, ''Stringer Splice Post Repair Inspection,'' in paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012, is not required by paragraph (h) of the NPRM (78 FR 38608, June 27, 2013). Boeing suggested that paragraph (h) of the NPRM be revised to include an exception phrase that references paragraph (i) of the NPRM. Boeing stated that the inspections specified in Table 11, ''Stringer Splice Post Repair Inspection,'' in paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012, are required to support operating requirements for complying with section 121.1109(c)(2) or 129.109(b)(2) of the Federal Aviation Regulations (14 CFR 121.1109(c)(2) or 14 CFR 129.109(b)(2)). Boeing also stated that the way the sentences of paragraph (h) of the NPRM are arranged, the sentences for doing corrective actions and repeating inspections seem to link the corrective actions and the repetitive inspections and imply that Table 11, ''Stringer Splice Post Repair Inspection,'' in paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012, is required by both the NPRM and the Federal Aviation Regulations. \n\n((Page 7378)) \n\n\n\tWe agree to provide clarification, but we do not agree to revise this final rule. Paragraph (h) of the final rule indicates that after the corrective actions are accomplished on a cracked stringer splice, the repetitive inspections are terminated for that stringer splice only. The sentence that includesthe phrase ''repeat the applicable inspections'' is not intended to imply any requirement to accomplish the post repair inspections specified in Table 11, ''Stringer Splice Post Repair Inspection,'' in paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012. Paragraph (i) of this final rule also indicates that accomplishing Table 11, ''Stringer Splice Post Repair Inspection,'' in paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012, is not required. No change to the final rule is necessary in this regard. \n\nRequest To Reference Alternative Service Information Instead of Contacting the Manufacturer for Corrective Actions \n\n\n\tSouthwest Airlines requested that paragraph (j)(1) of the NPRM (78 FR 38608, June 27, 2013) be revised to reference certain service information for corrective action instructions instead of requiring corrective actions that involve contacting the FAA or the Boeing Commercial Airplanes Organization Designation Authorization (ODA) for instructions. Southwest Airlines proposed that paragraph (j)(1) of the NPRM be changed to instead require replacement of cracked butt splice straps using a Boeing production drawing and require inspections for cracking in the fuselage skin using certain portions and revisions of Boeing Service Bulletins 737-53A1210 or 737-53A1234. Southwest Airlines also suggested referencing Repair 31 of section 53-00-01-2R in the Boeing 737-300/-500 Structural Repair Manual as an acceptable means of compliance for repairing any cracking or damage found on the fuselage skins. \n\tWe do not agree. The specific skin inspection requirements after finding a cracked butt joint splice strap might not be covered by the inspections provided in Boeing Service Bulletins 737-53A1210 or 737- 53A1234. The specific skin inspection requirements will be developed based on the specific butt strap cracking that is found, and specific repairs will be developed based on the skin cracking that is found. Operators may request approval of an alternative method of compliance using the procedures specified in paragraph (k) of this AD. We have not changed this final rule in this regard. \n\nRequest To Exclude Service Information Note for Corrosion Findings \n\n\n\tSouthwest Airlines requested that the NPRM (78 FR 38608, June 27, 2013) be revised to exclude General Information Note 12 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737- 53A1322, dated November 5, 2012, from the required actions of the final rule. Southwest Airlines stated that General Information Note 12 specifies to contact Boeing for repair instructions if corrosion is found. Southwest Airlines pointed out that the NPRM does not propose any inspections for corrosion and suggested that any findings of corrosion during the accomplishment of the requirements of this final rule be addressed using the operator's maintenance program. \n\tWe agree to revise this final rule. Cracking, not corrosion, is the primary safety concern addressed by this final rule. If any corrosion is found during any inspection for cracking that is required by this final rule, the corrective action for the corrosion should be provided by the operator's maintenance program. We have added paragraph (j)(3) to this final rule to remove the requirement to comply with General Information Note 12 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012. \n\nRequest To Exclude Service Information Note for Deviations From Modification Drawings \n\n\n\tSouthwest Airlines requested that paragraph (j) of the NPRM (78 FR 38608, June 27, 2013) be revised to provide an exclusion of General Information Note 16 from the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012. Southwest Airlines describes General Information Note 16 as specifying to contact Boeing if the fastener patterns, types, and sizes, or the structure does not agree with the production drawing requirements or applicable modification drawing requirements. Southwest Airlines stated that since there are previous FAA-approved repairs and deviations to modification drawings, and the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012, specify actions to remove and install structure and fasteners, Southwest Airlines expected to encounter numerous conditions that would prevent complying with the actions detailed in the figures of Boeing Alert Service Bulletin 737- 53A1322, dated November 5, 2012. \n\tWe do not agree to exclude General Information Note 16 from the requirements of this final rule to accomplish actions in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1322, dated November 5, 2012. The previously approved repairs or deviations to modification drawings may require changes to the inspection methods used and structure thatmay require removal to accomplish the inspection required by this final rule. Any change from the procedures specified in the service information must be approved as an AMOC under paragraph (k) of the final rule. We have not changed this final rule in this regard. \n\nConclusion \n\n\n\tWe 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: \n\t(Agr)re consistent with the intent that was proposed in the NPRM (78 FR 38608, June 27, 2013) for correcting the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM (78 FR 38608, June 27, 2013). \n\tWe also determined that these changes will not increase the economic burden on any operator or increase the scope of this AD. \n\nCosts of Compliance \n\n\n\tWe estimate that this AD affects 612 airplanes of U.S. registry. \n\tWe estimate the following costs to comply with this AD: \n\n((Page 7379)) \n\n\n\n\n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Inspections.................... Up to 362 work- None............... Up to $30,770, per Up to $18,831,240, \n\thours x $85 per inspection cycle. per inspection \n\thour = $30,770, cycle. \n\tper inspection \n\tcycle. Removal and reinstallation of Up to 2 work-hours $0................. Up to $170, per Up to $104,040, \n\tbutt strap fastener(s). x $85 per hour = inspection cycle. per inspection \n\t$170, per cycle. \n\tinspection cycle. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe estimate the following costs to do any necessary replacements that will be required based on the results of the inspection. We have no way of determining the number of aircraft that might need these replacements: \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product ---------------------------------------------------------------------------------------------------------------- Stringer splice replacement.............. 3 work-hours x $85 per hour Operator-supplied, $255 \n\t= $255. information not available. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tThe work-hour estimate and parts cost information are not available for estimating the cost of a butt strap replacement. \n\nAuthority for This Rulemaking \n\n\n\tTitle 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. \n\tWe 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 ordevelop on products identified in this rulemaking action. \n\nRegulatory Findings \n\n\n\tThis 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. \n\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\t(2) Is not a ''significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), \n\t(3) Will not affect intrastate aviation in Alaska, and \n\t(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. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.