Discussion \n\n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2011-08-51, Amendment 39-16701 (76 FR 28632, May 18, 2011). AD 2011-08-51 applied to certain The Boeing Company Model 737-300, -400, and -500 series airplanes. The NPRM published in the Federal Register on November 17, 2014 (79 FR 68381). The NPRM was prompted by an evaluation by the DAH that has determined that the lower fastener holes in the lower skin of the fuselage lap splice are subject to WFD. The NPRM proposed to continue to require repetitive inspections of the lap joint at certain stringers along the entire length from certain body stations. The NPRM also proposed to expand the inspection area, require additional inspections for cracks and open pockets, require corrective actions if necessary, and revise the compliance times. We are issuing this AD to detect and correct fatigue cracking of the lower fastener holes in the lower skin of the fuselage lap splice, which could result in reduced structural integrity of the airplane. \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 NPRM (79 FR 68381, November 17, 2014) and the FAA's response to each comment. \n\nRequest To Revise Wording \n\n\n\tBoeing requested that we revise the last sentence in paragraph (k) of the proposed AD (79 FR 68381, November 17, 2014) to clarify that the on-condition actions may be ''inspection or repair'' rather than ''inspection and repair.'' Boeing stated that condition 10 in table 6 of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, describes obtaining inspection or repair instructions. Boeing explained that, depending on the configuration details identified, repetitive inspections alone may be an appropriate action, or a repair may be the appropriate action. \n\tWe agree with the commenter's request. Varying detail configurations and the total flight cycles at the time of the finding are used to determine if an inspection program is adequate to address the unsafe condition or if installation of a repair is required. We have revised the wording in paragraph (k) of this AD to require inspection or repair. \n\nRequest To Clarify Paragraph Heading \n\n\n\tSouthwest Airlines (SWA) stated that the heading ''Repetitive Inspections for Crack Indications at Stringers S-4R and S-4L, Body Station (BS) 360 to BS 908,'' of paragraph (g) of the proposed AD (79 FR 68381, November 17, 2014) is misleading. SWA explained that the heading is confusing since the paragraph contains both an initial inspection and repetitive inspections. \n\tWe agree to clarify the terminology used in the heading. When the term ''repetitive'' is used, it does not necessarily exclude the initial action. Many existing ADs use the term ''repetitive'' in the headers for paragraphs that contain both the initial action and repetitive actions. We find that no change to this AD is necessary regarding this issue. \n\n((Page 51451)) \n\nRequest To Add Clarifying Note \n\n\n\tSWA requested that we add a note in paragraph (g) and paragraph (h) of the proposed AD (79 FR 68381, November 17, 2014) specifying that Group 3 airplanes do not require inspection between BS 540 and BS 727E. SWA stated that Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, specifies no inspections to be accomplished from BS 540 to BS 727E on Group 3 airplanes. SWA stated that, since paragraphs (g) and (h) of the proposed AD and tables 1, 2, and 3 of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, define the inspection area as stringers 4L and 4R from BS 360 to BS 908 for all airplanes, it could be interpreted that the proposed AD would require an increased inspection area for Group 3 airplanes. \n\tWe partially agree with the commenter's request. We disagree to add a note in paragraph (g) and paragraph (h) of this AD. The Accomplishment Instructions of Boeing Alert Service Bulletin 737- 53A1319, Revision 2, dated April 4, 2014, are clear regarding which areas must be inspected. The SUMMARY section of this final rule does specify that the inspection area is increased. However, we have added ''as applicable'' to paragraphs (g) and paragraph (h) of this AD to provide clarification regarding the inspection area. \n\nRequest To Clarify Compliance Times \n\n\n\tSWA requested that we revise paragraph (g) of the proposed AD (79 FR 68381, November 17, 2014) to clarify the compliance times. SWA recommended splitting the paragraph requirements into three separate paragraphs to address three different airplane groups. SWA stated that table 1 of paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, does not account for airplanes that were inspected previously using either Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011, or Boeing Alert Service Bulletin 737-53A1319, Revision 1, dated April 8, 2011. SWA stated that it is unclear how to apply the compliance times in table 1 for these airplanes, and as a result, airplanes with more than 30,000 total flight cycles that were not inspected previously using Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, will have exceeded the compliance times in table 1 upon the effective date of the AD. \n\tSWA stated that since paragraph (n) of the proposed AD (79 FR 68381, November 17, 2014) provides credit for actions required by paragraph (g) of the proposed AD that were performed prior to the effective date of the AD using either Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011, or Boeing Alert Service Bulletin 737- 53A1319, Revision 1, dated April 8, 2011, SWA assumes that the intent of paragraph (g) of the proposed AD is for the operator to accomplish the first inspection in accordance with Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, within 500 cycles from the last inspection accomplished previously in accordance with either the Boeing Alert Service Bulletin, dated April 4, 2011, or Revision 1, dated April 8, 2011. \n\tWe do not agree with the commenter's request to revise paragraph (g) of this AD. However, we do agree to clarify the compliance times. For airplanes that were inspected previously using either Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011, or Boeing Alert Service Bulletin 737-53A1319, Revision 1, dated April 8, 2011, the next inspection must be done within 500 cycles from the last inspection accomplished previously in accordance with either the Boeing Alert Service Bulletin, dated April 4, 2011, or Revision 1, dated April 8, 2011, except as provided by table 2 of paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014. Table 2 of paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, provides optional inspections that may be used after inspections in table 1 of paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737- 53A1319, Revision 2, dated April 4, 2014, have been accomplished. \n\tFor airplanes that were not inspected previously using either Boeing Alert Service Bulletin 737-53A1319, dated April 4, 2011, or Boeing Alert Service Bulletin 737-53A1319, Revision 1, dated April 8, 2011, the initial inspection must be done within the applicable compliance times specified in table 1 of paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014. We have not changed this AD in this regard. \n\nRequest To Clarify Inspection Requirements \n\n\n\tSWA requested that we provide clarification regarding the applicability of table 2 of paragraph 1.E., ''Compliance,'' of Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, for accomplishing the repetitive inspectionsrequired by paragraph (g) of the proposed AD (79 FR 68381, November 17, 2014). SWA stated that the inspection intervals defined in table 2 are dependent on the total flight cycles of airplanes that meet condition 1 (no crack found), and that operators of airplanes that meet condition 2 (any crack found) should contact Boeing for repair instructions prior to further flight. \n\tSWA stated that the alternative repetitive inspection intervals apply only to aircraft that meet condition 1 each time the aircraft is inspected. SWA explained that it is unclear whether or not the operator is able to continue utilizing the table 2 inspection intervals if condition 2 is found during any repetitive inspection on an airplane, or if the operator must revert back to the table 1 repetitive inspection interval from that point forward for that airplane. \n\tWe agree that clarification is necessary. Paragraph (l) of this AD requires a repair if any crack is found. Accomplishment of the repair terminates the repetitive inspections required by paragraphs (g) and (j) of this AD in the repaired area only. Repetitive inspections must be done on all unrepaired areas at the times specified in table 1 or table 2, as applicable. We find that no change to this AD is necessary regarding this issue. \n\nRequests for Credit and Exception to Inspection Requirements \n\n\n\tSWA requested that we include a provision in paragraph (n) of the proposed AD (79 FR 68381, November 17, 2014) to provide credit for the general visual inspection required by paragraph (k) of the proposed AD for skin panels that were replaced using the procedures specified in Figure 35 of Boeing Service Bulletin 737-53-1306, provided that the corrective action for Condition 9 is followed. \n\tSWA also requested that we add an exception in paragraph (m) of the proposed AD (79 FR 68381, November 17, 2014) that allows the operator to omit the inspection required by paragraph (k) of the proposed AD if the corrective action for Condition9 is followed and the operator's records show the part number of the skin assembly installed on the airplane. \n\tTo justify its requests, SWA stated that its airplanes, defined as Group 1 in Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014, on which the crown skin panel replacement was accomplished as described previously in Figure 35 of Boeing Service Bulletin 737-53-1306, were inspected previously to determine if the existing skin assembly was an ''MPN 65C35798-1 (open pockets \n\n((Page 51452)) \n\nadjacent to the STR 4R lap joint)'' or an ''MPN 65C35798-8 (closed pockets adjacent to the STR 4R lap joint).'' SWA stated that the existing skin panel was then replaced with a new skin panel of the same configuration as the removed production panel. SWA explained that if an operator's records show the part number of the skin panel assembly installed, the operator will be able to determine if the panel is configured with Condition 9 or Condition 10 and, therefore, SWA does not need to do the inspection required by paragraph (k) of the proposed AD. \n\tWe disagree with the commenter's requests. The fuselage crown skin replacements described in Boeing Service Bulletin 737-53-1306 are a part of a SWA-specific modification program. We do not consider it appropriate to include various provisions in an AD that are applicable only to a single operator's unique use of an affected airplane. However, an operator may request approval of an alternative method of compliance under the provisions of paragraph (o) of this AD if sufficient data are submitted to substantiate that the fuselage crown skin replacements would provide an acceptable level of safety. We have not changed this AD 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\tAre consistent with the intent that was proposed in the NPRM (79 FR 68381, November 17, 2014) for correcting the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM (79 FR 68381, November 17, 2014). \n\tWe also determined that these changes will not increase the economic burden on any operator or increase the scope of this AD. \n\nInterim Action \n\n\n\tWe consider this AD interim action. An investigation is ongoing, and no terminating action has been developed. Once terminating action is developed, approved, and available, we might consider additional rulemaking. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tWe reviewed Boeing Alert Service Bulletin 737-53A1319, Revision 2, dated April 4, 2014. The service information describes procedures for inspections for crack indications at certain stringers, an inspection for open pockets of the lower skin panel at stringer S-4R, and repairs. This serviceinformation 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 of this AD. \n\nCosts of Compliance \n\n\n\tWe estimate that this AD affects 130 airplanes of U.S. registry. \n\tWe estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Repetitive inspections 6 or 4,270 None.............. $510 or $362,950 $66,300 or \n\t(actions retained from AD work(dash)hours per inspection $47,183,500 per \n\t2011-08-51, Amendment 39- (depending oncycle. inspection \n\t16701 (76 FR 28632, May 18, inspection method) x cycle. \n\t2011)). $85 per work-hour = \n\t$510 or $362,950 per \n\tinspection cycle. Repetitive inspections (new 4 or 550 None.............. $340 or $46,750 $44,200 or \n\taction). work(dash)hours per inspection $6,077,500 per \n\t(depending on cycle. inspection \n\tinspection method) x cycle. \n\t$85 per hour = $340 \n\tor $46,750 per \n\tinspection cycle. One-time inspections (new 5,370 work(dash)hours None.............. $456,450......... $59,338,500. \n\taction). x $85 per hour = \n\t$456,450. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe have received no definitive data that would enable us to provide a cost estimate for the on-condition actions specified in this AD. \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 or develop on products identified in this rulemaking action. \n\nRegulatory FindingsWe 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. \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.