AD 98-07-15

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes, that requires an internal visual inspection to detect cracks of the skin and internal doublers above main entry door 1 at body station 460, and various follow-on actions. This amendment is prompted by reports indicating that multiple fatigue cracks were found in both internal skin doublers. The actions specified by this AD are intended to detect and correct such fatigue cracking, which could result in reduced structural integrity of the fuselage and consequent rapid depressurization of the cabin.

Final rule

98-07-15 BOEING: Amendment 39-10435. Docket 96-NM-245-AD. \n\n\tApplicability: Model 747 series airplanes, having line numbers 207 through 1088 inclusive, certificated in any category. \n\n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (e) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo detect and correct fatigue cracking in the internal skin doublers, which could result in reduced structural integrity of the fuselage and consequent rapid depressurization of the cabin, accomplish the following: \n\n\t(a)\tFor airplanes identified as Groups 1 through 10, inclusive, in Boeing Service Bulletin 747-53A2396, Revision 1, dated February 22, 1996: Prior to the accumulation of 13,000 flight cycles, or within 18 months after the effective date of this AD, whichever occurs later, perform an internal visual inspection to detect cracks of the skin and internal doublers above main entry door 1 at body station (STA) 460, in accordance with Part 2 -Inspection of the Accomplishment Instructions of Boeing Service Bulletin 747-53A2396, Revision 1, dated February 22, 1996. For the purposes of this AD, the number of flight cycles in which cabin differential pressure occurs at 2.0 pounds per square inch (psi) or less need not be counted when determining the number of flight cycles that have occurred on the airplane. \n\n\t\t(1)\tIf no crack is detected during the internal visual inspection required by paragraph (a) of this AD, prior to further flight, perform an open hole high frequency eddy current (HFEC) inspection to detect cracks of the skin and internal doublers above main entry door 1, in accordance with Figure 10 of the service bulletin. \n\n\t\t\t(i)\tIf no crack is detected during the open hole HFEC inspection required by paragraph (a)(1) of this AD, prior to further flight, install an external doubler in accordance with Part 4 - Modification of the Accomplishment Instructions of the service bulletin. \n\n\t\t\t(ii)\tIf any crack is detected during the open hole HFEC inspection, prior to further flight, perform a visual inspection to detect damage of the adjacent structure within 20 inches of the cracks, in accordance with Part 3 - Repair of the Accomplishment Instructions of the service bulletin. If any damage is detected, prior to further flight, repair it inaccordance with Part 3 - Repair, or the NOTE specified in paragraph G. of Part 2 - Inspection of the Accomplishment Instructions of the service bulletin. \n\n\t\t(2)\tIf any crack is detected during the internal visual inspection required by paragraph (a) of this AD, prior to further flight, perform a visual inspection to detect damage of the adjacent structure within 20 inches of the cracks, in accordance with Part 3 - Repair of the Accomplishment Instructions of the service bulletin. Prior to further flight following accomplishment of this visual inspection, repair any cracked skin or internal doublers, and/or repair adjacent damaged structure, in accordance with Part 3 - Repair of the Accomplishment Instructions of the service bulletin. \n\n\t(b)\tPerform either an internal surface HFEC or external low frequency eddy current (LFEC) inspection to detect damage of the repaired or modified area, in accordance with Part 6 - After- Repair or After-Modification Inspection Program of the Accomplishment Instructions of Boeing Service Bulletin 747-53A2396, Revision 1, dated February 22, 1996; at the time specified in paragraph (b)(1) or (b)(2) of this AD, as applicable. \n\n\t\t(1)\tFor airplanes identified as Groups 1 through 10, inclusive, in Boeing Service Bulletin 747-53A2396, Revision 1, dated February 22, 1996: Inspect within 15,000 flight cycles following accomplishment of either paragraph (a)(1) or (a)(2) of this AD. \n\n\t\t(2)\tFor airplanes identified as Group 11 in Boeing Service Bulletin 747-53A2396, Revision 1, dated February 22, 1996: Inspect prior to the accumulation of 15,000 total flight cycles. \n\n\t(c)\tIf no damage is detected during any inspection required by paragraph (b) of this AD, repeat the inspections required by paragraph (b) of this AD at the following intervals: \n\n\t\t(1)\tIf the immediately preceding inspection was conducted using HFEC techniques, conduct the next inspection within 6,000 flight cycles. \n\n\t\t(2)\tIf the immediately preceding inspection was conducted using LFEC techniques, conduct the next inspection within 3,000 flight cycles. \n\n\t(d)\tIf any damage is detected during any inspection required by paragraph (b) of this AD, prior to further flight, repair it in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. \n\n\t(e)\tAn 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 ACO. 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. \n\tNOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n\t(f)\tSpecial flight permits may be issued in accordance with sections 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. \n\n\t(g)\tThe actions shall be done in accordance with Boeing Service Bulletin 747-53A2396, Revision 1, dated February 22, 1996. 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. \n\n\t(h)\tThis amendment becomes effective on May 7, 1998.

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 April 25, 1997 (62 FR 20132). That action proposed to require an internal visual inspection to detect cracks of the skin and internal doublers above main entry door 1 at body station 460, and various follow-on actions. \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\nSupport for the Proposal \n\n\tOne commenter supports the proposed rule. \n\nRequest to Revise Method of Counting Accumulated Flight Cycles \n\n\tOne commenter, the manufacturer, requests that the FAA expand the definition of the term "flight cycles" as used in the compliance times for this proposed AD. The manufacturer requests that the FAA specify that, for the purposes of this AD, flight cycles that occur while operating with a cabin differential pressure of 2.0 pounds per square inch (psi) or less need not be considered or counted as a flight cycle when determining the number of flight cycles relative to the proposed compliance thresholds. The manufacturer states that the fuselage skin in the upper forward portion of the airplane is almost exclusively subjected to pressure loading, and there are no data to support counting all flight cycles for fatigue or crack growth. \n\n\tThe manufacturer further states that finite element data indicate that more than 97 percent of the loading in this area is directly due to cabin differential pressure. Similarly, strain gages installed common to an adjacent lap splice indicated that ground loading and flight loading are insignificant when compared to pressurization loading.\n \n\tAdditionally, the manufacturer states that if the provision to eliminate counting flight cycles that occur whileoperating with a cabin differential pressure of 2.0 psi or less is not permitted, several operators that use non-pressurized touch-and-go cycles for crew training will be adversely affected. The manufacturer also points out that if operators are required to count all flight cycles for this rule, some of these airplanes could be approaching the 13,000 cycle threshold, yet actually have less than 2,700 flight cycles that are actually pressurized. \n\n\tThe FAA concurs that, in this case, flight cycles shall be defined as flight cycles that have a cabin differential pressure of more than 2.0 psi. The FAA has reviewed substantiating data submitted by the manufacturer and has determined that the primary fatigue loading at the subject location (on Boeing Model 747 series airplanes) is due to cabin differential pressure cycles with an insignificant contribution from ground and flight loads. Therefore, the FAA has added a provision to the final rule that specifies the definition of flight cycles for the purposes of this AD.\n\nRequest to Shorten the Compliance Time \n\n\tOne group of commenters requests that the FAA shorten the compliance time for the initial internal visual inspection to detect cracks of the skin and internal doublers from 18 months to 9 months in order to ensure the safety of the flying public. The commenters believe that shortening the compliance time will make the AD process more effective and will prevent an event similar to that which occurred in April 1988 on a Model 737 series airplane. \n\n\tThe FAA does not concur that a shorter compliance time is needed. After consideration of all the available information, the FAA concludes that a reduction of the proposed compliance time, without prior notice and opportunity for public comment, is not warranted. In developing an appropriate compliance time, the FAA considered the safety implications and normal maintenance schedules for accomplishment of the various inspections and determined that 18 monthswas the most cost-effective compliance time. Further, the proposed compliance time of 18 months was arrived at with operator, manufacturer, and FAA concurrence. To reduce the compliance time of the proposal would necessitate (under the provisions of the Administrative Procedure Act) reissuing the notice, reopening the period for public comment, considering additional comments received, and eventually issuing a final rule; the time required for that procedure may be as long as four additional months. In comparing the actual compliance date of the final rule after completing such a procedure to the compliance date of this final rule as issued, the increment in time is minimal. In light of this, and in consideration of the amount of time that has already elapsed since issuance of the original notice, the FAA has determined that further delay of this final rule action is not appropriate. However, if additional data are presented that would justify a short compliance time, the FAA mayconsider further rulemaking on this issue.\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 change previously described. The FAA has determined that this change will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCost Impact \n\n\tThere are approximately 880 Boeing Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 143 airplanes of U.S. registry will be affected by this AD. Each of these airplanes has a left- and right-side main entry door 1. \n\n\tIt will take approximately 76 work hours per airplane to accomplish the required internal visual inspection, at an average labor rate is $60 per work hour. Based on these figures, the cost impact of the internal visual inspection required by this AD on U.S. operators is estimated to be $652,080, or $4,560 per airplane. \n\n\tShould an operator be required to accomplish the specified preventative modification, it will take approximately 100 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $1,094 per airplane. Based on these figures, the cost impact of the preventative modification (if accomplished) specified in this AD on U.S. operators is estimated to be $1,014,442, or $7,094 per airplane. \n\n\tIt will take approximately 40 work hours per airplane to accomplish the required high frequency eddy current (HFEC) or low frequency eddy current (LFEC) inspection (i.e., post- modification), at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the HFEC or LFEC inspection required by this AD on U.S. operators is estimated to be $343,200, or $2,400 per airplane, per inspection cycle. \n\n\tShould an operator be required to accomplish the specified repair, it will take approximately 212 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $2,602 per airplane. Based on these figures, the cost impact of the repair (if accomplished) specified by this AD on U.S. operators is estimated to be $2,191,046, or $15,322 per airplane. \n\n\tThe cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\nRegulatory Impact \n\n\tThe 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. \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\n List of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14CFR part 39) as follows:\n\n PART 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. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: