Discussion \n\n\n\tWe issued a supplemental notice of proposed rulemaking (SNPRM) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to the specified products. That SNPRM published in the Federal Register on August 30, 2010 (75 FR 52907). The original NPRM (73 FR 5768, January 31, 2008) proposed to require inspections for scribe lines in affected lap and butt splices, wing-to-body fairing locations, and external repair and cutout reinforcement areas; and related investigative and corrective actions if necessary. The SNPRM proposed to revise the original NPRM by adding inspections for certain airplanes and revising certain compliance times including reducing the compliance time for certain repetitive inspections. \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 (75 FR 52907, August 30, 2010) and the FAA's response to eachcomment. \n\nRequest To Revise Certain Inspection Requirements \n\n\n\tBoeing requested that we revise the SNPRM (75 FR 52907, August 30, 2010) to include an additional exception to the service bulletin specifications. The SNPRM referred to Boeing Service Bulletin 747- 53A2563, Revision 4, dated May 6, 2010, as the appropriate source of service information for the post-repair inspections. Revision 4 of this service bulletin includes lap joint repair instructions in the Accomplishment Instructions, and refers to post-repair instructions in Parts 17 and 18. The post-repair inspection instructions incorrectly refer to inspections per the Boeing 747 Supplemental Structural Inspection Document (SSID) D6-35022. Boeing reported that it plans to remove the reference to the SSID and update the post-repair inspections when Boeing Service Bulletin 747-53A2563 is revised. Boeing therefore requested that we revise the SNPRM to require operators to contact the FAA to request the appropriate post-repair inspections rather than follow the post-repair inspections given in Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010. \n\tWe partially agree with the request. Although we agree with the information and rationale provided by the commenter, we have determined that the inspection procedures described in Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010, are adequate for the purpose of this AD. It is not necessary to further burden the operators with a requirement to contact the FAA for post-repair inspection instructions, when adequate inspections already exist. Operators may, however, contact the FAA with an alternative method to the inspection procedures specified in Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010, in accordance with the procedures specified in paragraph (m) of this AD. \n\n((Page 13188)) \n\nRequest To Remove Certain Inspection Requirement \n\n\n\tBoeing and Delta Airlines requested that we revise paragraph (g) ofthe SNPRM (75 FR 52907, August 30, 2010) to remove the requirement to inspect for scribe lines around the perimeter of the wing-to-body fairing. The commenters stated that this inspection has been removed from Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010. Boeing noted that repetitive inspections for cracks at previously discovered scribe lines along the wing-to-body fairing may still be necessary, as specified in Table 17 of paragraph 1.E., ''Compliance,'' of Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010. \n\tWe partially agree with the request. We agree that the initial inspection of the wing-to-body fairing for scribe lines is not required; this action was removed from Boeing Service Bulletin 747- 53A2563, Revision 3, dated June 11, 2009; and Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010. But we disagree that it is necessary to change the final rule to specify this provision; Note 1, which was added to the SNPRM (75 FR 52907, August 30, 2010) and retained in this final rule, accounts for this requested change. We have not changed the final rule regarding this issue. \n\nRequest To Clarify Reporting Requirement \n\n\n\tDelta requested that we revise paragraph (j) of the SNPRM (75 FR 52907, August 30, 2010) (paragraph (k) in this final rule) to specify that the inspection report is required only for the initial inspection for scribe lines. The commenter noted that the service bulletin has no provision for reporting requirements for any repetitive inspections done during the limited return to service (LRTS) program specified in Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010. \n\tWe agree to clarify that a report is not required for any inspection accomplished per the LRTS program. We have added this clarification in paragraph (k) in this final rule. \n\nRequest To Extend Certain Compliance Times \n\n\n\tAir New Zealand discussed the implications of scribe lines found before the applicable inspection threshold. This commenter asserted that a scribe line could be present on the airplane from its date of manufacture, and that Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010, effectively declares there is no safety implication resulting from this scribe line until the relevant inspection threshold. Yet the SNPRM (75 FR 52907, August 30, 2010) would require that a scribe line found before the inspection threshold must immediately be repaired or further inspected. Air New Zealand asserted that, if scribe lines are discovered early, this requirement would add to the maintenance burden without increasing safety. \n\tWe infer that the commenter is requesting that we revise the SNPRM (75 FR 52907, August 30, 2010) to extend the time for corrective action on known scribe lines to match the threshold specified in the service information, instead of requiring action before further flight. We disagree. We have determined that, in this case, due to the safety implications and consequences of this type of known damage, operators must repair or inspect scribed structure before further flight. We have not changed the final rule regarding this issue. \n\nRequest To Remove Certain Airplanes From Inspection Requirements \n\n\n\tCargolux Airlines asserted that certain airplanes should not be subject to the inspection requirement, and requested that we revise the SNPRM (75 FR 52907, August 30, 2010) to exclude airplanes delivered without fillet seals at lap joints, and airplanes with fillet seals that were applied but never removed. The operator noted that Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010, provides some exceptions for airplanes that had never been stripped or repainted, and for airplanes on which any sealant removal was always done in accordance with Appendix A of this service bulletin. The operator also noted, on the other hand, that no exception exists if fillet seals were never applied, or were applied but never removed. Paragraph 1.D. of this service bulletin specifies that scribe lines are made while fillet seals are removed during repainting. The commenter concluded that if no fillet seal was ever applied at a lap joint location, or if an applied fillet seal was never removed, no scribe line can exist. \n\tWe disagree with the commenter's request to remove certain airplanes from the inspections required by this AD. As noted in paragraph 1.E.1 of Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010, certain inspections are still necessary even if no fillet seal has ever been removed. We do not agree to exempt airplanes on which no fillet seal has ever been removed from those inspections. The valid exceptions to certain inspections are explained further in Paragraphs 1.E.1 through 1.E.4 of Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010. Note 1 of this AD states that the exemptions noted in paragraph 1.E. of Boeing Service Bulletin 747- 53A2563, Revision 4, dated May6, 2010, apply to this AD. It is not necessary to change the final rule regarding this issue. \n\nRequest To Revise Compliance Time \n\n\n\tBritish Airways (BA) requested that we revise the SNPRM (75 FR 52907, August 30, 2010) to allow low-time airplanes (with fewer than 17,500 total accumulated flight cycles) to be inspected in area 1 of the fuselage at the later of 1,500 flight cycles after the effective date of the AD, and the next ''D'' check after the airplane has accumulated 15,000 total cycles without exceeding 19,000 total flight cycles. BA noted that Boeing recommends a 15,000-flight-cycle threshold for the area 1 inspections, and that the inspections should be done during a ''D'' check to avoid unscheduled downtime. As a result, to align with a ''D'' check, the inspections for low-time airplanes may have to occur as early as 12,000 total flight cycles for long-haul airplanes, and even earlier for short-haul airplanes. The commenter added that Boeing Service Bulletin 747-53A2563, Revision 4, dated May 6, 2010, also includes procedures for inspecting for scribe lines around external fuselage repairs, and as such, shares commonality with the need to assess repairs as detailed in Boeing SSID D6-36181, which the FAA approved in 2008. This program's threshold is the first ''D'' check after the airplane has accumulated 15,000 total flight cycles. The commenter felt it would be appropriate to carry out the scribe line inspection of area 1 and the repair assessment program at the same time. BA stated that it understands that the term ''D check'' means different things to different operators, but pointed out that in the past the FAA has been able to clarify this, for example, in paragraph 217 of FAA Advisory Circular 120-93, dated November 20, 2007 (http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/1ab39b4ed563b08985256a35006d56af/f73fd2a31b353a71862573b000521928!OpenDocument), which states as follows: \n\n\n\tAirplanes less than 75 percent ofDSG (design service goal) on December 18, 2009. Operators complete a survey at the first heavy maintenance check (time limit equivalent to a ''D-check'') after an individual airplane reaches 75% of the DSG, not to exceed the DSG. \n\n((Page 13189)) \n\n\n\tNote: A heavy maintenance check (D-check or equivalent airplane inspection) is an airplane maintenance visit where the major structural inspections are performed. In some cases, this may be a formal D-check or, in the case of a Maintenance Steering Group (MSG)-2 or -3 based maintenance program, the D-check equivalent may be the ''C-check'' multiple that contains the majority of the major structural inspections, such as a ''C-4'' which is sometimes called a heavy maintenance visit. \n\n\n\tBA stated that its proposed variation on the threshold for area 1 would follow this convention, but have the additional safeguard that the airplane would not exceed 19,000 total flight cycles before inspection. Younger airplanes therefore would havethe same or greater level of safety than airplanes currently inspected at 17,500 total flight cycles and allowed a 1,500-flight-cycle grace period. BA reported that, of 314 Model 747 airplanes that have accumulated more than 19,000 total flight cycles, none had experienced cracking from scribe lines--even though exploratory inspections to date suggest that scribe lines are commonplace. \n\tWe disagree with the request to revise the compliance time as suggested. We do not specify compliance times in terms of letter checks because, as the commenter noted, maintenance schedules vary among operators. We have determined that the compliance times as proposed are appropriate to address the identified unsafe condition. The minimum grace period for compliance with this AD is 1,500 flight cycles for airplanes with fewer than 17,500 total flight cycles, which corresponds to approximately 3 years based on a typical utilization of 500 flight cycles per year for long-haul airplanes. A 3-year grace period should be sufficient for operators to plan for the scribe line inspections, and will allow for timely data collection for use in developing final action and determining whether this AD should be revised in the future. We have not changed the final rule regarding this issue. Under the provisions of paragraph (m) in this final rule, however, we may consider requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. \n\nRequest for Alternative Inspection Program \n\n\n\tKLM requested that we revise the SNPRM (75 FR 52907, August 30, 2010) to exclude from the inspection program the CLAD layer of the skin (up to a certain depth/percentage, to be determined by the type certificate holder). KLM asserted that scribe lines found in the CLAD layer are not critical for continued operation and do not require repeat inspections as specified in the LRTS program. KLM also requested investigation of a single fatigue crack evolving from a scribe line found in the CLAD layer, not in the base material. KLM requested that the proposed AD be revised to allow blending scribe lines found in CLAD layers as a corrective action. KLM suggested that scribe lines might have no effect on the CLAD layer, and suggested that a program be developed for inspecting scribe lines in the CLAD layer of the skin. \n\tWe agree that additional studies on scribe lines within CLAD layers might benefit the development of new inspection programs and relieve certain inspection criteria. But we disagree to change this aspect of the SNPRM (75 FR 52907, August 30, 2010) at this time, because no such inspection program exists. To delay this action would be inappropriate, since we have determined that an unsafe condition exists and we must proceed to mandate the inspections as proposed to ensure continued safety. In the future, we might consider additional rulemaking to include new inspections, if a new inspection program is developed, approved, and available. In the meantime, under the provisions of paragraph (m) of this final rule, we will consider requests for approval of an alternative method of compliance if sufficient data are submitted to substantiate that the alternative inspection program would provide an acceptable level of safety. We have not changed the final rule regarding this issue. \n\nExplanation of Additional Change Made to This AD \n\n\n\tWe have revised the heading for and wording in paragraph (l) of this AD; this change has not changed the intent of that paragraph. \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 the AD with the changes described previously. We also determined that these changes will not increase the economic burden on any operator or increase the scope of the AD. \n\nCosts of Compliance \n\n\n\tWe estimate that this AD affects 219 airplanes of U.S. registry. We estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tNumber of \n\tAverage labor Cost per U.S.- \n\tAction Work hours rate per hour airplane registered Fleet cost \n\tairplanes ---------------------------------------------------------------------------------------------------------------- Detailed inspections......... 1,020 to 1,140. $85 $86,700 to 219 $18,987,300 to \n\t$96,900. $21,221,100. ---------------------------------------------------------------------------------------------------------------- \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 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\n((Page 13190)) \n\n\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.