A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747-100 and -200 series airplanes was published in the Federal Register on August 20, 1999 (64 FR 45481). That action proposed to require repetitive inspections of the upper and lower chords of the wing front spar for cracks, and corrective action, if necessary. \n\nComments \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\nRequest to Allow Alternative Inspection Method \n\n\tOne commenter requests that the FAA revise paragraph (a) of the proposal to allow accomplishment of an open hole high frequency eddy current (HFEC) inspection in lieu of the ultrasonic inspection that is specified in paragraph (a) of the proposal. The commenter asserts that accomplishment of an HFEC inspection "equals or exceeds the capability of surface ultrasonic inspections" for detecting cracking of the upper and lower chords of the wing front spar. The commenter states that the HFEC inspection should be accomplished in accordance with Figure 6 of Boeing Service Bulletin 747-57-2305, Revision 1, dated January 21, 1999 (which was referenced in the proposal as the appropriate source of service information for accomplishment of the proposed actions). \n\n\tThe FAA concurs with the commenter's request to approve the alternative inspection method. However, the FAA finds that, rather than revising paragraph (a) of this AD, it is more appropriate to add a NOTE stating that accomplishment of an HFEC inspection in accordance with Figure 6 of the service bulletin is acceptable for compliance with the requirements of paragraph (a) of this AD. NOTE 2 has been added to this final rule accordingly. \n\nRequest to Reference Alternative Terminating Action \n\n\tOne commenter requests that theFAA revise paragraph (b) of the proposed rule to reference accomplishment of certain strut and wing modifications or certain other terminating actions as terminating action for the requirements of this AD. The commenter states that accomplishment of certain modifications meets the intent of the terminating action described in the proposed rule, provided that an HFEC inspection of affected fastener holes has been accomplished (in accordance with Boeing 747 Non-Destructive Test Manual D6-7170, Part 6, Subject 51-00-00, Figure 16) prior to oversizing of the holes, and the holes were found to be free of cracks, corrosion, or damage. \n\n\tThe FAA infers that the commenter is referring to the terminating action specified in paragraph (c) of this AD. The FAA concurs with the commenter's request. The FAA finds that the strut and wing modifications and terminating action referenced by the commenter are already required by certain other AD's, which are described below. \n\nAD 95-10-16, amendment 39-9233 (60 FR 27008, May 22, 1995), applies to certain Boeing Model 747 series airplanes, and requires, among other things, modification of the nacelle strut and wing structure in accordance with Boeing Alert Service Bulletin 747-54A2159, dated November 3, 1994. \n\nAD 95-13-07, amendment 39-9287 (60 FR 33336, June 28, 1995), applies to certain Boeing Model 747 series airplanes, and requires modification of the nacelle strut and wing structure in accordance with Boeing Alert Service Bulletin 747-54A2158, dated November 30, 1994.\n\nAD 99-10-09, amendment 39-11162 (64 FR 25194, May 11, 1999), applies to certain Model 747-100, -200, and 747SP series airplanes, and military type E-4B airplanes. That AD provides for replacement of the wing front spar web with a new shot-peened wing front spar web, in accordance with Boeing Service Bulletin 747-57A2303, Revision 1, dated September 25, 1997, as an optional terminating action for the repetitive inspection requirements of that AD.\n\n\tThe FAA has determined that accomplishment of the wing and strut modification specified in AD 95-10-16 or AD 95-13-07, or the optional terminating action specified in AD 99-10-09, constitutes terminating action for the repetitive inspections required by paragraph (a) of this AD, provided that an HFEC inspection of subject fastener holes has been accomplished (in accordance with Boeing 747 Non-Destructive Test Manual D6-7170, Part 6, Subject 51-00-00, Figure 16) prior to oversizing of the holes, and the holes were found to be free of cracks, corrosion, or damage. The FAA has added NOTE 3 to this final rule accordingly. \n\nRequest to Delete Certain Supplemental Structural Inspection Document Inspections \n\n\tOne commenter requests that the FAA revise the proposal by adding a paragraph that eliminates the requirement for certain inspections to be accomplished in accordance with the Supplemental Structural Inspection Document (SSID). The commenter justifies its request by saying that oversizing the web-to-chord fastener holes, as described in the optional terminating action in Boeing Service Bulletin 747-57-2305, Revision 1, will "zero time" the fastener holes, renewing the fatigue life. The commenter states that, if this optional terminating action is accomplished, SSID inspections W-24B at the front spar web-to-chord fastener holes between the upper link fittings and W-24C at the front spar web-to-chord fastener holes at the outboard upper link fittings would no longer be necessary. \n\n\tThe FAA partially concurs with the commenter's request. The FAA acknowledges that, following accomplishment of the optional terminating action, fatigue life will be renewed in the affected web-to-chord fastener holes. However, the SSID inspections that the commenter references are required, along with various other inspections, by AD 94-15-12, amendment 39-8983 (59 FR 37933, July 26, 1994), and AD 94-15-18, amendment 39-8989 (59 FR 41233, August 11, 1994). The FAA finds that deleting SSID inspections required by other AD's is not an appropriate action to take in this AD. Therefore, no change to the final rule is necessary in this regard. \n\nRequest to Allow Use of Original Issue of Service Bulletin\n \n\tOne commenter requests that the FAA revise paragraphs (a), (b), and (c) of the proposal to reference the original issue of Boeing Service Bulletin 747-57-2305, dated October 8, 1998, in addition to Revision 1 of the service bulletin, as appropriate sources of service information for the actions required by this AD. The commenter states that there is no substantial difference between the two versions of the service bulletin, and the inspection methods and procedures for terminating action are the same. The commenter states that Revision 1 adds missing fastener codes and revises grip lengths of fasteners. Further, the commenter states that operators that accomplished inspections or terminating action in accordance with the original issue of the service bulletin should not be required to perform the inspections or terminating action in accordance with Revision 1, nor should they be required to apply for an alternative means of compliance. \n\n\tThe FAA does not concur with the commenter's request. The FAA considers the grip length of fasteners (one of the items changed between the original issue and Revision 1) important for proper clamp-up, and the FAA has been advised that certain fasteners specified in the original issue of the service bulletin had grip lengths that were too long. In addition, the FAA considers the fact that certain fastener codes were missing from the original issue of the service bulletin to be significant, in that it could result in installation of fasteners that are not structurally satisfactory. Also, Revision 1 of the service bulletin deleted inspections of the fasteners in the upper and lower chords between the upper link fittings. For these reasons, the FAA does not find that accomplishment of the actions required by this AD in accordance with the original issue of the service bulletin is acceptable for compliance with this AD. No change to the final rule is necessary in this regard. \n\nRequest to Revise Statement of Unsafe Condition \n\n\tOne commenter, the airplane manufacturer, requests that the FAA revise the reason for issuing the proposed rule. The proposed rule states that "the actions specified by the proposed AD are intended to detect and correct fatigue cracking of the upper and lower chords of the wing front spar, which could result in reduced structural capability and possible fuel leakage onto an engine and a resultant fire." The commenter states that the correct reason for issuing the AD is that cracks addressed by Boeing Service Bulletin 747-57-2305 are subject to Item W-24A and W-24B in Boeing Document D6-35022, "Supplemental Structural Inspection Document." The commenter also states that the service bulletin was issued to address undetected cracks in the front spar chords that could result in extensive labor hours and downtime if the cracks propagate to the extent that replacement of a section of chord is necessary. \n\n\tThe commenter concludes that there are no safety-of-flight issues associated with such cracking, and that fuel leakage due to undetected cracks is very unlikely because, for leakage to occur, cracks in the chord would have to grow through the thickness of the chord, beyond the upper or lower edges of the front spar web, and beyond the fillet seal. \n\n\tThe FAA does not concur with the commenter's request. The statement of unsafe condition, as stated in the proposal, specifies what could happen if the inspections of the front spar upper and lower chords that will be required by this AD are not accomplished. The fact that fuel leaks have not been detected to date does not preclude leaks from occurring in the future. For example, even though an operator may have accomplished the strut and wing modification required by another AD (asdiscussed previously), if an HFEC inspection to detect cracking of the fastener holes was not accomplished, a crack may still be present and could grow to the point that fuel leakage occurs. The FAA finds no justification for revising the statement of unsafe condition as the commenter suggested. Therefore, no change to the final rule is necessary in this regard. \n\nConclusion \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.\n\nCost Impact \n\n\tThere are approximately 332 Model 747-100 and -200 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 137 airplanes of U.S. registry will be affected by this AD, that it will take approximately 2 work hoursper airplane to accomplish the required inspection, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the inspection required by this AD on U.S. operators is estimated to be $16,440, or $120 per airplane, per inspection cycle. \n\n\tThe cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\n\tShould an operator elect to accomplish the optional terminating action rather than continue the repetitive inspections, it will take approximately 37 work hours per airplane to accomplish the modification, at an average labor rate of $60 per work hour. Required parts will cost approximately $5,000 per airplane. Based on these figures, the cost impact of this optional terminating action is estimated to be $7,220 per airplane. \n\nRegulatory Impact \n\n\tThe regulations adopted herein 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. \n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (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. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." \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, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: