Examining the Docket \n\n\n\tYou may examine the airworthiness directive (AD) docket on the Internet at http://dms.dot.gov or in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647-5227) is located on the plaza level of the Nassif Building at the street address stated in the ADDRESSES section. \n\nDiscussion \n\n\tThe FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an AD that supersedes AD 2004-03-11, amendment 39-13455 (69 FR 5920, February 9, 2004). The existing AD applies to certain Boeing Model 747-200C and -200F series airplanes. That NPRM was published in the Federal Register on September 16, 2005 (70 FR 54668). That NPRM proposed to require repetitive inspections to find fatigue cracking in the upper chord of the upper deck floor beams, and repair if necessary. For certain airplanes, the NPRM also proposed an optional repair/modification, which extends certain repetitive inspection intervals. \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 received on the NPRM. \n\nRequest To Revise Initial Inspection Threshold for Certain Airplanes \n\n\tFor airplanes that have accumulated 17,000 or more total flight cycles, the Air Transport Association (ATA) on behalf of one of its members, Northwest Airlines, requests that we revise the grace period for the initial inspection threshold specified in paragraph (f)(2) of the NPRM from 90 days to 500 flight cycles. They state that this change would implement a definitive inspection limit to more accurately measure fatigue-related concerns and would align with operators' regularly scheduled heavy maintenance check. \n\n\tWe partially agree. We agree with ATA and Northwest Airlines that cracking of the affected upper deck floor beams isattributed to fatigue, and that a compliance time based on flight cycles is appropriate for inspecting for fatigue cracking. However, we do not agree with their request to revise the grace period for the inspections required by this AD. In developing an appropriate compliance time for this AD, we considered the safety implications, the airplane manufacturer's recommended compliance time, and normal maintenance schedules for the timely accomplishment of the inspections and repair if necessary. In consideration of these items, as well as the reports of significant cracking at the affected floor beams on airplanes that had accumulated as low as 19,580 total flight cycles, we have determined that the 90-day grace period specified in paragraph (f)(2) of this AD is appropriate. For high-cycle airplanes that have accumulated 17,000 or more total flight cycles as of the effective date of this AD, the 90-day grace period is merely a time that we provide the operators to plan for the necessary actions and to avoid immediate grounding of airplanes. This grace period will ensure an acceptable level of safety and will allow the required inspections to be done during scheduled maintenance intervals for most affected operators. However, under the provisions of paragraph (l) of the AD, we may approve requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. Therefore, we find that no change to the final rule is necessary in this regard. \n\nRequest To Clearly Distinguish the Old and New Requirements \n\n\tBoeing requests that we revise paragraphs (g)(1), (h)(1), and (h)(2) of the NPRM to more clearly distinguish between the old and new requirements. They state that those paragraphs specify requirements from AD 2004-03-11, as well as new requirements. They believe that this could cause operators to be confused as to which requirements to comply with. They also state that paragraphs (f) through (k) of the NPRM are under a header titled, "REQUIREMENTS OF AD 2004-03-11,'' which would imply that those paragraphs have no new information. \n\n\tWe agree. For clarification purposes, we have revised the AD as follows: \n\n\tRevised the header "REQUIREMENTS OF AD 2004-03-11'' to "RESTATEMENT OF REQUIREMENTS OF AD 2004-03-11, BUT WITH A NEW REDUCED THRESHOLD AND REDUCED REPETITIVE INTERVALS FOR CERTAIN FLOOR BEAMS''; \n\n\tAdded a new header, "NEW REQUIREMENTS OF THIS AD''; \n\n\tMoved paragraphs (i) and (j) of the NPRM under the new header and reidentified paragraph (j) as paragraph (k); \n\tMoved the sentences in paragraphs (g), (g)(1), and (h)(1) that require operators to do the required actions, as of the effective date of this AD, in accordance with Boeing Alert Service Bulletin 747- 53A2439, Revision 1, dated March 10, 2005; to new paragraph (j), "New Revision of Service Bulletin,'' in the AD; and \n\n\tClarified in paragraphs (h)(1) and (h)(2) that the repetitive inspection interval is 3,000 flight cycles, as shown in Figure 1 of the service bulletin. \n\nRequest To Delete Reference to Part 1 of the Service Bulletin in Paragraphs (g)(1) and (h)(1) \n\n\tBoeing also requests that we delete the reference to "Part 1'' of the Work Instructions of Boeing Alert Service Bulletin 747-53A2439, Revision 1, dated March 10, 2005, in the last sentence of paragraph (g)(1) and in the second sentence of paragraph (h)(1). They state that Revision 1 of the service bulletin specifies that repaired areas are inspected only in accordance with Part 6 of the Work Instructions, and that there is no path that could lead back to Part 1. They also state that paragraph (h) of the NPRM is relevant to repair and post-repair inspections, and that Part 1 applies to neither. \n\n\tWe partially agree. We agree with Boeing that Revision 1 of Boeing Alert Service Bulletin 747-53A2439 refers only to Part 6 for post- repair inspections, and that paragraph (h) is relevant to repair and post-repairinspections. Part 6 describes procedures for inspecting areas that have been repaired in accordance with Figure 8, 9, 10, or 12 of the service bulletin. However, we do not agree with them that the reference to Part 1 should be deleted. The procedures specified in Part 1 are applicable to areas that have been repaired by hole over-sizing only (without reinforcement) in accordance with Part 3. We find that no change to the AD is necessary in this regard. \n\nRequest To Clarify Repetitive Inspection Interval \n\n\tBoeing also requests that we clarify the repetitive inspection intervals in paragraphs (g)(2)(i) through (g)(2)(iii) and (g)(2)(iii)(A) of the NPRM. Because paragraph (g)(2) of the NPRM specifies repetitive inspection requirements, they believe that specifying "repeat'' in paragraphs (g)(2)(i) through (g)(2)(iii) is redundant. They also note that paragraphs (g)(2)(ii) and (g)(2)(iii) state, "Repeat that inspection * * *.'' They point out that, at the time of any inspection if nocrack is found, an operator has a choice of doing the inspection specified in paragraph (g) of the NPRM in accordance with Part 1 or 2 and thus the interval could change. Therefore, they suggest that the compliance time in paragraphs (g)(2)(i) through (g)(2)(iii) apply only to the "next inspection.'' \n\n\tWe partially agree. We agree with Boeing that clarification is necessary. We have revised paragraph (g) to clarify that, during the repetitive inspections, any combination of the applicable inspection methods may be used, provided that the corresponding repetitive interval is used. We do not agree with the changes that they suggested to paragraph (g)(2)(iii)(A). We used that language to correspond with the requirements of paragraph (a)(2) of AD 2004-03-11, which has been revised and re-identified as paragraph (g)(2)(iii)(A) in this AD. \n\nRequest To Refer to Upper Chords Rather Than Airplanes \n\n\tIn addition, Boeing requests that paragraph (h) of the NPRM refer to "upper chords'' instead of "airplanes.'' \n\nThey believe that some operators will inspect or have inspected some upper chords in accordance with Part 1 of the Work Instructions of Boeing Alert Service Bulletin 747-53A2439, dated July 5, 2001; or Revision 1, dated March 10, 2005; and will inspect or have inspected other chords in accordance with Part 2 of the Work Instructions due to more difficult access. They note that the service bulletin recommends the proposed inspection in accordance with Part 2 at some locations. \n\n\tWe partially agree. We agree with Boeing's rationale for revising paragraph (h). However, we find that using the term "areas'' rather than "upper chord,'' as they suggested, in that paragraph will capture all areas that are being inspected in accordance with paragraph (g) of this AD. We have revised paragraph (h) accordingly. \n\nRequest Not To Delay Repetitive Inspections if Optional Repair/ Modification Is Done \n\n\tIn addition, Boeing requests that we delete the second sentence in paragraph (h). As an alternative if that sentence is not deleted, they request that the requirement be clarified in the preamble under "Differences Between the Proposed AD and Service Bulletin.'' They state that Part 2 of the Work Instructions of Boeing Alert Service Bulletin 747-53A2439, dated July 5, 2001; and Revision 1, dated March 10, 2005; provides no instructions path for operators to jump from Part 2 to Part 3, because operators would not choose to do hole repairs if fasteners have not been removed and no cracks have been found. \n\n\tWe do not agree. As explained in the preamble of the NPRM under "Change to Existing AD,'' this AD retains certain requirements of AD 2004-03-11. The optional repair/modification specified in paragraph (h) of this AD corresponds to requirements in paragraph (b) of AD 2004-03- 11. As explained in the preamble under "Request To Expand Provisions for Optional Repair/Modification'' of AD 2004-03-11, we added the second sentence of paragraph (h) of this AD (paragraph (b) of AD 2004- 03-11) based on a request from Boeing. We have determined that providing the optional repair/modification specified in paragraph (h) is beneficial to operators. The repair procedures in Part 3 of the Work Instructions include procedures for doing an open hole high frequency eddy current inspection of the affected fastener holes. Therefore, we have determined that doing the optional repair/modification provides an acceptable level of safety and thus warrants an extension of the threshold for the initiation of the repetitive inspections required by paragraph (g)(2). In addition, we do not agree that this optional action differs from the service bulletin. We find that no change to the final rule is necessary in this regard. \n\nRequest To Add New Inspections and Reduce Inspection Threshold \n\n\tBoeing also requests that, for floor beam chords at stations 440 and 520, we revise paragraph (h)(1) of the NPRM to lower the inspection threshold and to add new inspection requirements for a certain post- repair/modification. They state that analysis has shown that additional inspections and a reduced inspection threshold are needed of the holes in the flange adjacent to the trim-out. \n\n\tWe acknowledge Boeing's concern, but do not agree with their request. Since the suggested changes would expand the scope of the actions in this AD, additional rulemaking (i.e., supplemental NPRM) would be necessary to reopen the comment period. We find that to delay issuance of the AD would be inappropriate in light of the identified unsafe condition, and that the required inspections must be conducted to ensure continued safety. We may consider additional rulemaking, however, once the new inspection method is developed, approved, and available. We find that no change is necessary to this AD in this regard. \n\nRequest To Allow Not Counting Flight Cycles When Cabin Differential Is at 2.0 Pounds Per Square Inch (psi) or Less \n\n\tFurther, Boeing requests that werevise paragraph (i) of the NPRM to allow not counting flight cycles in which cabin differential pressure is at 2.0 psi or less, when determining the number of flight cycles for compliance times. They state that this change would be consistent with the previous requirements for these inspections and is a continuance of the allowance for the upper deck floor beams given in paragraph (c) of AD 2004-03-11. \n\n\tWe do not agree. There have been several instances on other in- service reports where analytical rationales, similar to that of the commenter, have indicated that pressurization cycles less than 2.0 psi should not be counted. However, when fleet records have been examined, the airplanes engaging in such operations are having the same or greater occurrences of crack findings compared to those on which all pressurized flights are counted. As a result, we carefully consider such matters based on all available factors, including individual operator's specific maintenance programs, technical rationale, and fleet experience. We have found that such provisions are applicable only to a small number of operators that may not pressurize their airplanes above 2.0 psi in all their flights. We have determined that the best way to handle such circumstances is for operators to request an alternative method of compliance (AMOC) in accordance with paragraph (l) of this AD, rather than increasing the complexity of the AD by addressing each operator's unique situation. \n\nRequest To Give Credit to Previously Approved AMOC \n\n\tBoeing also requests that we revise paragraph (k)(3) of the NPRM (re-identified as paragraph (l)(3) in this AD) to add provisions for previously approved AMOCs that require post-modification/repair inspections. They contend that previously approved AMOCs meet the intent of paragraph (h) of the NPRM. They state that this change will reduce the need for new AMOCs. \n\n\tWe agree and have added a reference to paragraph (h) in paragraph (l)(3) of this AD. \n\nRequest To Refer to Supplemental Structural Inspection Document (SSID) AD \n\n\tLastly, Boeing requests that additional language be added to the NPRM to address its impact on AD 2004-07-22, amendment 39-13566 (69 FR 18250, April 7, 2004), which mandated the SSID program for Boeing Model 747 airplanes. (One correction of that AD was published in the Federal Register on April 13, 2004 (69 FR 19618); another correction was published on May 3, 2004 (69 FR 24063).) They state that, if the AD is adopted as proposed, operators will be required to do the SSID inspections and the inspections specified in Boeing Alert Service Bulletin 747-53A2439, Revision 1, without an allowance of doing the inspections specified in the service bulletin as a substitute for the SSID inspections. They also state that the inspections in the service bulletin provide damage detection as good as or better than SSID items F-19C for stations 340 through 420 inclusive, and 500; and F-20A for stations 440 and 520. In addition, they prefer that operators do the inspections in accordance with the service bulletin, because of the level of detailed instructions. \n\n\tWe do not agree. We acknowledge that doing the inspections specified in Boeing Alert Service Bulletin 747- \n53A2439, Revision 1, may be acceptable for compliance with certain requirements of AD 2004-07-22; however, no request for an AMOC to that AD has been submitted to us for approval in this regard. In addition, it is more appropriate to address AMOCs under the provisions of the applicable AD rather than a related AD. Under the provisions of paragraph (g) of AD 2004-07-22, we may consider requests for approval of an AMOC if sufficient data are submitted to substantiate that such action would provide an acceptable level of safety. We find that no change to this AD is necessary in this regard. \n\nClarification of AMOC Paragraph \n\n\tWe have revised this action to clarify the appropriate procedure for notifying the principal inspector before using any approved AMOC on any airplane to which the AMOC applies. \n\nConclusion \n\n\tWe have carefully reviewed the available data, including the comments that have been received, and determined that air safety and the public interest require adopting the AD with the changes 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 78 airplanes of the affected design in the worldwide fleet. This AD will affect about 21 airplanes of U.S. registry. \n\n\tThe inspections that are required by AD 2004-03-11 and retained in this AD take about 29 work hours per airplane, at an average labor rate of $65 per work hour. Based on these figures, the estimated cost of the currently required inspections for U.S. airplanes is $39,585, or $1,885 per airplane, per inspection cycle. \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 rulemaking 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 and placed it in the AD docket. 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, Incorporation 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 Federal Aviation Administration (FAA) amends Sec. 39.13 by removing amendment 39-13455 (69 FR 5920, February 9, 2004) and by adding the following new airworthiness directive (AD):