The FAA proposed to amend 14 CFR Part 39 with an AD for all Boeing Model 737-100, -200, -200C, -300, -400, and - 500 series airplanes. That action, published in the Federal Register on September 7, 2004 (69 FR 54058), proposed to require repetitive inspections for cracks in the fuselage skin, doubler, bearstrap, and frames surrounding the main, forward, and aft cargo doors; and repair of any cracking. That action also proposed to require inspections of certain existing repairs for cracking, and related corrective action if cracking is found. \n\nComments \n\n\tWe provided the public the opportunity to participate in the development of this AD. We have considered the comments that have been submitted on the proposed AD. \n\nSupportive Comment \n\n\tOne commenter states that the proposed AD will affect only its 737- 200C and -400 fleets, and adds that the proposed detailed inspections and compliance intervals will allow compliance at heavy check maintenance visits. The commenter stipulates that these requirements are acceptable provided there are adequate replacement parts available if discrepancies are found. \n\n\tWe have discussed the issue of obtaining replacement parts with the airplane manufacturer and we anticipate no difficulty in getting the parts to accomplish repairs. \n\nRequest for Credit for Accomplishing AD 93-14-10 \n\n\tOne commenter, the airplane manufacturer, asks that we add a sentence to paragraph (f) of the proposed AD that gives credit for accomplishing the inspections and repairs required by AD 93-14-10, amendment 39-8634 (58 FR 43547, August 17, 1993). The commenter states that the requirements of the proposed AD are equivalent to, or more conservative than, the requirements in AD 93-14-10. \n\n\tWe agree with the commenter that accomplishing the requirements in paragraph (f) of the proposed AD ends the requirements in AD 93-14-10 (referenced as related rulemaking in the preamble of the proposed AD). As specified in the preamble of the proposed AD, during structural inspections, cracks were found in the bearstrap under the fuselage frame flanges at the edges of the forward cargo door. In two cases, cracks were found in the fuselage frames of the aft cargo door where steel repair doublers had been installed using the requirements of AD 93-14-10; therefore, the requirements in this AD exceed the requirements of AD 93-14-10. We have changed paragraph (f) of this AD by adding credit for previously accomplishing AD 93-14-10. \n\nRequest To Add Inspection Type to Paragraph (f) of the Proposed AD \n\n\tThe same commenter states that the first sentence in paragraph (f) specifies, in part, "Do the applicable detailed, general visual, and low and high frequency eddy current inspections for cracks * * *" The commenter asks that a reference to the mid-frequency eddy current (MFEC) inspection be added to paragraph (f). The commenter notes that this inspection is specified in the referenced service bulletin. \n\n\tWeagree with the commenter that the MFEC inspection should be added to paragraph (f), for clarification. An internal MFEC inspection is specified in the referenced service bulletin as an option to accomplishing the detailed visual inspections, and would extend the compliance time for the repetitive inspections, but was not identified in the proposed AD. Paragraph (f) of the proposed AD specified doing the "applicable" inspections for cracks as specified in the referenced tables. However, to clarify the type of inspection, we have changed paragraph (f) of this final rule to include the MFEC inspection. \n\nRequest for Clarification of Location of Inspections for Existing Repairs \n\n\tOne commenter asks for clarification regarding accomplishing inspections of existing repairs around the cargo doors in accordance with the referenced service bulletin. The commenter states that it is unclear which inspection is required if repairs are of a different configuration than those referenced in thefigures in the service bulletin. The commenter notes, for example, that a repair of the cargo door lower corner per Boeing Structural Repair Manual 737-100/200, Figure 46, Detail IV, does not match the Figure 8 repair in the service bulletin. The commenter adds that verbiage needs to be added clarifying whether the "intent" of the service bulletin is to accomplish a MFEC inspection of all outer row fasteners of the repair doubler, no matter what the configuration. \n\n\tWe agree that clarification is necessary. The repairs shown in Figures 8, 9, and 10 of the referenced service bulletin are conceptual illustrations of typical doubler/tripler type repairs. These figures are intended to indicate that the location of the detailed visual or MFEC inspections for cracking is the skin or bearstrap at the outer row fasteners common to the outer edge of the repair. We have added a note after paragraph (f) of the final rule for further clarification. \n\nRequest for Certain Repair InstructionsOne commenter states that repair instructions that are similar to those currently available for Model 737-100 and -200 series airplanes for damaged skin, doubler, and bearstrap around the cargo doors should also be available for Model 737-300, -400, and -500 series airplanes. The commenter adds that it is crucial to limit downtime of aircraft as much as possible, an coordinating repair procedures with Boeing extends the out-of-service time for affected airplanes. \n\n\tWe agree that repair instructions should be made available for Model 737-300, -400 and -500 series airplanes. However, until repair instructions are published for Model 737-300, -400 and -500 series airplanes, the repair must be accomplished according to a method approved by the Manager, Settle Aircraft Certification Office or an Authorized Representative for the Boeing Delegation Option Authorization (DOA) Organization. Repair procedures have been developed for incorporation into the next revision of the 737-300/400/500 SRM and will be submitted to us by Boeing soon. As provided by paragraph (i) of this AD, we will consider approving these repairs as an alternative method of compliance for paragraph (g) of this AD. We have made no change to the final rule in this regard. \n\nClarification of Applicability \n\n\tOne commenter asks why the proposed AD isn't applicable to Model 737-300C series airplanes with a main cargo door installed by PEMCO. The commenter notes that the proposed AD includes Model 737-200C series airplanes with a main cargo door, and asks if excluding the 737-300C is normal. \n\n\tWe acknowledge the commenter's concern and offer clarification. The proposed AD is applicable to Model 737-100, -200, -200C, -300, -400, - 500 series airplanes, including airplanes modified to include a main cargo door. We infer that the commenter's reference to a "Model 737- 300C" is an informal designation for a Model 737-300 series airplane that has been modified to include a main cargo door per a supplemental type certificate. However, no model 737-300C series airplane is identified in the type certificate data sheet. Thus, an airplane with that configuration would be subject to the AD requirements for Model 737-300 series airplanes. In comparison, the Model 737-200C series airplane is identified in the type certificate data sheet. \n\nExplanation of Changer to Proposed AD \n\n\tBoeing has received a DOA. We have revised paragraph (i)(2) of this final rule to delegate the authority to approve an alternative method of compliance for any repair required by this AD to the Authorized Representative for the Boeing DOA Organization rather than the Designated Engineering Representative. \n\nConclusion \n\n\tWe have carefully reviewed the available data, including the comments that have been submitted, and determined that air safety and the public interest require adopting the AD with the change described previously. We have determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCosts of Compliance \n\n\tThere are about 3,132 airplanes of the affected design in the worldwide fleet. We estimate that 870 airplanes of U.S. registry will be affected by this AD. We provide the following cost estimates to comply with this AD, per inspection cycle: \n\n\nGroup \nWork hours \nHourly labor rate \nParts \nCost per airplane \n1 \n24 \n$65 \n$0 \n$1,560 \n2 and 4 \n28 \n65 \n0 \n1,820 \n3 and 5 \n30 \n65 \n0 \n1,950 \n6 and 7 \n28 \n65 \n0 \n1,820 \n\nAuthority for This Rulemaking \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\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 \nrulemaking action. \n\nRegulatory Findings \n\n\tWe 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\n\tFor the reasons discussed above, I certify that this AD: \n\n\t(1) Is not a "significant regulatory action" under Executive Order 12866; \n\n\t(2) Is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\n\t(3) 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\n\tWe prepared a regulatory evaluation of the estimated costs to comply with this AD. See the ADDRESSES section for a location to examine the regulatory evaluation. \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporated by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n2. The FAA amends Sec. 39.13 by adding the following new airworthiness directive (AD):