[Federal Register Volume 59, Number 112 (Monday, June 13, 1994)] [Unknown Section] [Page 0] From the Federal Register Online via the Government Publishing Office [www.gpo.gov] [FR Doc No: 94-13852] [[Page Unknown]] [Federal Register: June 13, 1994] ----------------------------------------------------------------------- DEPARTMENT OF TRANSPORTATION 14 CFR Part 39 [Docket No. 93-NM-139-AD; Amendment 39-8937; AD 94-12-09] Airworthiness Directives; Boeing Model 747 Series Airplanes AGENCY: Federal Aviation Administration, DOT. ACTION: Final rule. ----------------------------------------------------------------------- SUMMARY: This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires inspections to detect fatigue-related skin cracks and corrosion of the skin lap joints in the fuselage upper lobe, and repair, if necessary. This amendment also requires modification of certain lap joints and inspections of modified lap joints. This amendment is prompted by a structural review of Model 747 series airplanes. The actions specified by this AD are intended to prevent rapid decompression of the airplane and the inability to carry fail-safe loads, due to the problems associated with fatigue cracking and corrosion. DATES: Effective July 13, 1994. The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of July 13, 1994. ADDRESSES: The service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. FOR FURTHER INFORMATION CONTACT: Steven Fox, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2777; fax (206) 227-1181. SUPPLEMENTARY INFORMATION: 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 series airplanes was published in the Federal Register on February 24, 1994 (59 FR 8875). That action proposed to require inspections to detect fatigue-related skin cracks and corrosion of the skin lap joints in the fuselage upper lobe, and repair, if necessary. That action also proposed to require modification of certain lap joints and inspections of modified lap joints. Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. One commenter supports the proposal. One commenter requests that proposed inspection requirements be revised. This commenter requests that, if the visual inspection [proposed in paragraph (a)(1) of the AD] reveals any evidence of corrosion, operators should be allowed to perform a low frequency eddy current (LFEC) inspection of the entire length of the lap joint to determine if corrosion exceeds 10% of the skin thickness. If this LFEC inspection is accomplished, the commenter also requests that the visual inspection repetitive interval specified in paragraph (a)(1) be extended from the proposed 2,000 landings to 3,000 landings so that the interval corresponds with other major structural inspection intervals. The FAA cannot concur with this request, since the commenter provided neither specific inspection instructions nor data to justify the effectiveness of the proposed procedures. Under the provisions of paragraph (i) of the final rule, however, operators may apply for the approval of an alternative method of compliance with the AD, or adjustment of the compliance time, if sufficient justification is presented to the FAA. Two commenters request that proposed paragraph (a) be clarified with regard to the inspections and inspection interval required after a lap joint has been modified. These commenters request that, for lap joints that have been modified by either the full or partial modification procedures described in the referenced Boeing service bulletin, operators be allowed a period of time during which no inspections are required for those lap joints. The referenced Boeing service bulletin, as well as proposed paragraph (f), state that post- modification inspections are to start at 10,000 cycles, 7,000 cycles, or 5,000 cycles after modification of the skin lap joints, depending upon the type of modification that has been accomplished. However, as worded in paragraph (a) of the proposal, the same inspections meant to detect cracks and corrosion in unmodified skin lap joints would be required to be performed on modified skin lap joints until the inspections specified in proposed paragraph (f) begin. The FAA concurs that clarification of this requirement is necessary. It was not the FAA's intent to require that the initial-type of inspections of unmodified lap joints be performed on modified lap joints. Accordingly, paragraphs (a)(1) and (a)(3) have been revised to indicate that the inspections of the specified lap joints are to continue at repetitive intervals only until the lap joints are modified in accordance with the requirements of paragraph (e). Several commenters request that the compliance time for accomplishing the ``full'' modification on certain lap joints, as specified in paragraph (b)(2), be extended from the proposed 15 months to 18 months. Additionally, these commenters request that the compliance time for a similar requirement specified in paragraph (c)(2) be extended from the proposed 30 months to 36 months. The commenters state that, by extending these compliance times, operators would be able to accomplish the modification during a scheduled maintenance interval (``C'' check), and thereby eliminate the need to schedule special times for the accomplishment of this modification, at additional expense. The FAA concurs. It was the FAA's intent that the modification be performed at a main base during regularly scheduled maintenance where special equipment and trained maintenance personnel will be available if necessary. Accordingly, the final rule has been revised to specify compliance times as requested by the commenters. The FAA has determined that this extension will not adversely affect safety since the affected lap joints will be subject to repetitive inspections in the interim. Two commenters request that paragraph (e) be revised to extend the compliance time for accomplishment of the ``full'' modification of the specified skin lap joints from the proposed 1,000 cycles (for airplanes that have accumulated nearly or more than 20,000 total flight cycles) to 4 years after the effective date of the final rule. These commenters consider the proposed compliance time to be too short and not consistent with compliance times provided for similar actions in other AD's pertaining to aging aircraft issues. The FAA does not concur. The 1,000 flight cycle compliance time is consistent with the mandatory modification of a lap joint that has been found to have corrosion or cracking, as required by paragraph (b)(2) of this AD. Cold bonded lap joints such as these have a history of numerous findings of fatigue cracks and corrosion. In light of this, and the fact that fatigue cracking is cycle-related, the FAA has determined that modification of these lap joints cannot be delayed any further than 1,000 flight cycles, especially on those airplanes that already have accumulated 20,000 flight cycles, without compromising safety. One commenter requests that the applicability of proposed paragraphs (f)(1), (f)(2), and (f)(3) be revised to clarify that it is the ``lap joint,'' rather than the ``airplane,'' on which the particular modification has been accomplished. The FAA concurs and has revised wording of the final rule to clarify this point. One commenter requests that all references in the rule to ``landings'' be changed to ``cycles.'' The FAA concurs that the reference should be revised. The FAA has reviewed the applicable service information related to this action and finds that the majority of references to recommended compliance times are stated in ``flight cycles.'' Although the FAA normally uses the terms ``landings'' and ``flight cycles'' interchangeably, the FAA considers that it is appropriate in this case to change the verbiage of the AD to match that of the cited service bulletins. Therefore, in this final rule, the FAA has substituted the term ``flight cycles'' for the term ``landings.'' Another commenter, a non-U.S. operator, requests that the proposed rule be revised to include a provision specifying that pressurization cycles of 2.0 psi or less need not be counted as a flight cycle when determining the number of flight cycles relative to the proposed compliance thresholds. This commenter states that a pressurization cycle of 2.0 psi or less is a typical pressure used during flight training, and causes little fatigue damage of the kind addressed by this AD action. The FAA does not concur. The FAA does not consider it appropriate to include various provisions in an AD applicable to a single operator's unique use of an affected airplane. Paragraph (i) of this AD provides for the approval of alternative methods of compliance to address these types of unique circumstances. Further, this commenter does not compile data for each of its airplanes so that an individual airplane's pressurization cycles could be determined; instead, it uses a fleet average to calculate the equivalent number of pressurization cycles. The FAA does not consider it appropriate to use approximations for determining compliance with this AD. After 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. There are approximately 200 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 116 airplanes of U.S. registry will be affected by this proposed AD. The required inspections will entail 100 work hours per airplane per inspection, at an average labor rate of $55 per work hour. (This figure does not include the time necessary for gaining access and closing up.) Based on these figures, the total cost impact of this requirement on U.S. operators is estimated to be $638,000, or $5,500 per airplane, per inspection. The required ``full'' modification will entail approximately 96 work hours for each 200-inch length of uncracked and uncorroded lap joint, at an average labor rate of $55 per work hour. (This figure does not include the time necessary for gaining access and closing up.) There are 100 lap joint sections per airplane, each with a length of 200 inches. The cost of required parts is expected to be negligible. Based on these figures, the total cost impact of this requirement on U.S. operators is estimated to be $61,248,000, or $528,000 per airplane. The initial high frequency eddy current (HFEC) inspection following modification will entail approximately 56 work hours, at an average labor rate of $55 per work hour. Based on these figures, the total cost impact of this requirement AD on U.S. operators is estimated to be $357,280, or $3,080 per airplane. Based upon the figures discussed above, the total cost impact of this AD on U.S. operators is expected to be $62,243,280, or $536,580 per airplane. This total cost figure includes the inspections and modification, for the first year of the average five-year inspection cycle. Additionally, the total cost figure indicated 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. The FAA recognizes that the obligation to maintain aircraft in an airworthy condition is vital, but sometimes expensive. Because AD's require specific actions to address specific unsafe conditions, they appear to impose costs that would not otherwise be borne by operators. However, because of the general obligation of operators to maintain aircraft in an airworthy condition, this appearance is deceptive. Attributing those costs solely to the issuance of this AD is unrealistic because, in the interest of maintaining safe aircraft, most prudent operators would accomplish the required actions even if they were not required to do so by the AD. A full cost-benefit analysis has not been accomplished for this AD. As a matter of law, in order to be airworthy, an aircraft must conform to its type design and be in a condition for safe operation. The type design is approved only after the FAA makes a determination that it complies with all applicable airworthiness requirements. In adopting and maintaining those requirements, the FAA has already made the determination that they establish a level of safety that is cost- beneficial. When the FAA, as in this AD, makes a finding of an unsafe condition, this means that this cost-beneficial level of safety is no longer being achieved and that the required actions are necessary to restore that level of safety. Because this level of safety has already been determined to be cost-beneficial, a full cost-benefit analysis for this AD would be redundant and unnecessary. The regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. For 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. List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. Adoption of the Amendment Accordingly, 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: PART 39--AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. Sec. 39.13 [Amended] 2. Section 39.13 is amended by adding the following new airworthiness directive: 94-12-09 Boeing: Amendment 39-8937. Docket 93-NM-139-AD. Applicability: Model 747 series airplanes, line positions 001 through 200 inclusive, certificated in any category. Compliance: Required as indicated, unless accomplished previously. To prevent rapid decompression of the airplane and the inability to carry fail-safe loads, accomplish the following: (a) Within 1,000 flight cycles after the effective date of this AD, and thereafter at the intervals specified in paragraphs (a)(1), (a)(2), and (a)(3) of this AD, perform inspections at the upper lobe skin panel lap joints in accordance with Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 1993: (1) Perform a detailed external visual inspection to detect cracks and evidence of corrosion (bulging skin between fasteners, blistered paint, dished fasteners, popped rivet heads, or loose fasteners) in accordance with the service bulletin. Repeat that inspection thereafter at intervals not to exceed 2,000 flight cycles until the modification required by paragraph (e) of this AD is accomplished. (2) Perform a high frequency eddy current inspection (HFEC) to detect cracks in the skin at the upper row of fasteners of the skin panel lap joints forward of body station (BS) 1000 in accordance with the service bulletin. Repeat that inspection thereafter at intervals not to exceed 4,000 flight cycles until the modification required by paragraph (e) of this AD is accomplished. (3) Perform a HFEC inspection to detect cracks in the skin at the upper row of fastener holes of the skin panel lap joints aft of BS 1480 to 2360 in accordance with the service bulletin. Repeat that inspection thereafter at intervals not to exceed 6,000 flight cycles until the modification required by paragraph (e) of this AD is accomplished. (b) If any crack is found during any inspection required by this AD, or if any corrosion is found for which material loss exceeds 10 percent of the material thickness, accomplish paragraphs (b)(1) and (b)(2) of this AD in accordance with Boeing Service Bulletin 747-53- 2307, Revision 2, dated October 14, 1993. (1) Prior to further flight, repair any crack or corrosion found, in accordance with the service bulletin. (2) Within 18 months after accomplishing the repair, accomplish the ``full'' modification described in the service bulletin for the remainder of any skin panel lap joint in which a crack is found, or in which corrosion is found that exceeds 10 percent of the material thickness. (c) If no crack is found during any inspection required by this AD, but corrosion is found for which the material loss does not exceed 10 percent of the material thickness: Accomplish paragraph (c)(1) and (c)(2) of this AD for the entire affected skin panel lap joint in accordance with Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 1993. (1) Within 500 flight cycles after accomplishing the inspection during which the corrosion was found, and thereafter at intervals not to exceed 500 flight cycles until the ``full'' modification required by paragraph (c)(2) of this AD is accomplished: Perform a HFEC inspection to detect cracks of the corroded skin panel lap joint, in accordance with the service bulletin. (2) Within 36 months after accomplishing the inspection during which the corrosion was found: Accomplish the ``full'' modification in accordance with the service bulletin. (d) The inspections required by this AD shall be performed by removing the paint and using an approved chemical stripper; or by ensuring that each fastener head is clearly visible. (e) Except as provided in paragraph (g) of this AD, prior to the accumulation of 20,000 total flight cycles, or within the next 1,000 flight cycles after the effective date of this AD, whichever occurs later: Accomplish the modification described in the service bulletin as a ``full'' modification of the skin panel lap joints at the locations specified in paragraphs (e)(1) and (e)(2) of this AD, as applicable, in accordance with Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 1993. Accomplishment of this modification terminates the repetitive inspection requirements of paragraph (a) of this AD. (1) For airplane line numbers 001 through 058, inclusive: Modify the skin panel lap joints at Stringer 12 (left and right), station 520 to 1,000; and Stringer 19 (left and right), station 520 to 740. (2) For airplane line numbers 59 through 200, inclusive: Modify the skin panel lap joints at Stringer 12 (left and right), station 740 to 1,000; and Stringer 19 (left and right), station 520 to 740. (f) Perform an external HFEC inspection to detect skin cracks of any modified skin panel lap joints at the times specified in paragraphs (f)(1), (f)(2), and (f)(3) of this AD, as applicable, in accordance with Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 1993. Repeat that inspection thereafter at intervals not to exceed 3,000 flight cycles. (1) For skin panel lap joints on which the ``full'' modification has been accomplished: Within 10,000 flight cycles after accomplishment of that modification. (2) For skin panel lap joints on which the ``optional'' (partial) modification has been accomplished: Within 7,000 flight cycles after accomplishment of that modification. (3) For skin panel lap joints having deep countersink fasteners located at Section 42 on which the ``full'' modification, as described in the original issue of the service bulletin, has been accomplished: Within 5,000 flight cycles after accomplishment of that modification. (g) In lieu of the ``full'' modification required by paragraph (e) of this AD, the ``optional'' (partial) modification described in Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 1993, may be accomplished for skin panels that have an outer thickness of 0.090 inches or less, and that do not have any cracks, corrosion, or an existing structural repair on the skin panel lap joint. The ``optional'' (partial) modification shall not be accomplished at deep countersink fastener locations. (h) Accomplishment of the requirements of this AD terminates the requirements of AD 90-15-06, amendment 39-6653. (i) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO. Note: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. (j) Special flight permits may be issued in accordance with Secs. 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. (k) The actions shall be done in accordance with Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 1993. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. (l) This amendment becomes effective on July 13, 1994. Issued in Renton, Washington, on June 2, 1994. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 94-13852 Filed 6-10-94; 8:45 am] BILLING CODE 4910-13-P