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 777-200, 777-200LR, 777-300ER, and 777F series airplanes. The NPRM published in the Federal Register on July 1, 2014 (79 FR 37243). The NPRM was prompted by a report indicating that sealant might not have been applied in production to the wing skin panel gaps above certain underwing fittings. The NPRM proposed to require an inspection for missing sealant, and applicable other specified, related investigative and corrective actions. We are issuing this AD to detect and correct missing sealant from the wing skin panel gaps above the underwing fittings, which could result in corrosion and fatigue cracking in the wing skin panel, and consequent loss of limit load capability of the wing skin and potential subsequent structural failure of the wings. \n\nComments \n\n\n\tWe gave the public the opportunityto participate in developing this AD. The following presents the comments received on the NPRM (79 FR 37243, July 1, 2014) and the FAA's response to each comment. Boeing concurs with the contents of the NPRM. \n\nRequest To Accept Approved Repairs Without Need for Alternative Methods of Compliance (AMOC) \n\n\n\tFedEx requested that any FAA-approved repair be accepted without the requirement of obtaining an AMOC. \n\tWe do not agree with the request. The FAA does not consider that any FAA-approved repair will be acceptable to repair this condition. As the sealant was missing from the airplane at the time of initial delivery, it may not have been restored in prior repairs. In addition, repairs may not have detected all corrosion because the repair might not have included the inspection information contained in Boeing Service Bulletin 777-57A0097, Revision 1, dated May 4, 2015. \n\tRepairs for this AD must be approved by the Manager, Seattle ACO, FAA; or by the Boeing Organization Designation Authorization (ODA) using FAA Form 8100-9 in accordance with the procedures specified in paragraph (j)(3) of this AD. We intend to delegate authority to approve AMOCs to the Boeing ODA for the repair approval process. In addition to knowledge of the unsafe condition, the Boeing ODA is knowledgeable about the original airplane design and compliance substantiation. We have not changed this AD regarding this issue. \n\nRequest To Withdraw NPRM (79 FR 37243, July 1, 2014) \n\n\n\tAmerican Airlines (AAL) stated that the Boeing 777 Maintenance Review Board Report (MRBR) has existing inspections intended to identify deterioration of sealant, as well as any corrosion or cracking. These inspections will detect deterioration or damage to the fillet seal that would lead to moisture ingression to the area of concern. AAL therefore considers the NPRM (79 FR 37243, July 1, 2014) to be unwarranted. \n\tWe disagree with the commenter's request to withdraw the NPRM (79 FR 37243, July 1, 2014). Evaluation of the quality escapement revealed that, under certain environmental conditions, moisture can get trapped within a cavity directly under the nacelle fittings that are normally filled with sealant. With the presence of moisture in this cavity, the existing corrosion protection would degrade within an estimated ten years of service, and corrosion pitting would form on the stringer surface. Under flight loading, cracks would initiate and propagate from the corrosion pits until the stringer would no longer be able to sustain limit load, and would eventually fail. This corrosion and cracking would not be detected by the existing maintenance program prior to stringer failure. We have not changed this AD regarding this issue. \n\nRequest for Validated Inspection Procedures \n\n\n\tAmerican Airlines (AAL) stated that accomplishing the actions specified in Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, could be detrimental to aircraft safety. According to AAL, any attemptat the sealant removal to do the inspection based upon the existing instructions in Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, could potentially damage or degrade the protective surface finish of the wing skin or underwing fitting and lead to future corrosion or fatigue cracking. \n\tAAL stated that it attempted and failed to accomplish the inspection in accordance with Boeing Alert Service Bulletin 777- 57A0097, dated January 10, 2014, because access to some of the intended inspection areas was severely inhibited by hydraulic lines. AAL also stated that any sealant, if present, would have been applied to the entire gap, so inspection from only one side should be sufficient. In addition, AAL used the recommended tooling and alternate tooling as specified in Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, but experienced multiple problems with the use of this tooling. In addition, AAL requested that Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, be validated with workable tooling on an in-service airplane prior to any future action. \n\tWe infer that the commenter is requesting that we delay issuance of the final rule pending validation of the existing procedures. We do not agree. AAL reported ''multiple problems with the use of this tooling,'' but did not describe any specific problems. However, we understand that the tools themselves require frequent but inexpensive replacement. We have determined that use of the appropriate tools and processes to remove the sealant from underneath the fitting should not damage the skin or adjacent structures. \n\tBoeing has performed and validated the procedures in Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, on certain airplanes that are representative of the fleet on the flight line before delivery with no damage to the skin or adjacent structures. However, Boeing has revised Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, to clarify the sealant removal process and tooling, to ensure that it will not damage the skin. We also discussed AAL's concerns with Boeing, and Boeing reported that they have provided AAL with assistance. Boeing is also willing to work with any other operator that is having difficulty implementing the SB. \n\tBoeing considers that the revision of Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, should address AAL's concerns about \n\n((Page 45855)) \n\nthe tooling and procedures for sealant removal. We have revised paragraphs (c), (g), (h)(1), and (h)(2) of this AD to refer to Boeing Service Bulletin 777-57A0097, Revision 1, dated May 4, 2015. We have added new paragraph (i) to this AD to give credit for actions done before the effective date of this AD using Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014. We have redesignated subsequent paragraphs accordingly. The FAA will consider approving alternative procedures if they are shown to be effective.Request for Additional Time \n\n\n\tAAL requested that, once Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, is validated, sufficient time should be provided to allow operators to procure such tooling. \n\tWe infer that the commenter is requesting an extension to the compliance time. We do not agree with the commenter's request to extend the compliance time. We coordinated with Boeing regarding tool availability and fabrication. The tools stated in Boeing Service Bulletin 777-57A0097, dated January 10, 2014; and Revision 1, dated May 4, 2015; are nonmetallic sealant scrapers, which are widely available, with no lead time to procure these tools. Existing tools may be modified to match the wing panel gaps by cutting them to the correct size. However, we do understand that cutting the tools to size may weaken the tools, which could cause them to fracture and result in more frequent replacement of the tools. Boeing has stated that there is no engineering or drawing work required for fabrication. Any certified aircraft mechanic can fabricate the necessary tools. Boeing stated that during validation of the Boeing Alert Service Bulletin 777-57A0097, dated January 10, 2014, the tools were fabricated in a working shift. 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 37243, July 1, 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 37243, July 1, 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\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tWe reviewed Boeing Service Bulletin 777-57A0097, Revision 1, dated May 4, 2015. The service information describes procedures for the inspection and repair of underwing fitting sealant at wing panel gaps. 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 of this AD. \n\nCosts of Compliance \n\n\n\tWe estimate that this AD affects 6 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 ---------------------------------------------------------------------------------------------------------------- Inspection.................... Up to 104 work- $0Up to $8,840 Up to $53,040. \n\thours x $85 per \n\thour = $8,840. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe estimate the following costs to do any necessary actions that would be required based on the results of the inspection. We have no way of determining the number of aircraft that might need these actions: \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tAction Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- Sealant restoration................... 1 work-hour x $85 per $0 $85. \n\thour = $85. Corrosion inspection.................. 2 work-hours x $85 per $0 $170 per side. \n\thour = $170 per side. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe have received no definitive data that would enable us to provide cost estimates for the on-condition corrosion repair specified in this AD. \n\tAccording to the manufacturer, some of the costs of this AD may be covered under warranty, thereby reducing the cost impact on affected individuals. We do not control warranty coverage for affected individuals. As a result, we have included all costs in our cost estimate. \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\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\n((Page 45856)) \n\n\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.