AD 95-12-17

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-100 and -200 series airplanes, that requires various inspections for cracks in the outboard chord of the frame at body station (BS) 727 and in the outboard chord of stringer 18A; and repair or replacement of cracked parts. This amendment is prompted by reports of fatigue cracks in those outboard chords. The actions specified by this AD are intended to prevent such fatigue cracking, which could result in reduced structural integrity of the outboard chords, and subsequent rapid decompression of the airplane.

Final rule

95-12-17 BOEING: Amendment 39-9268. Docket 94-NM-159-AD. \n\n\tApplicability: Model 737-100 and 200 series airplanes, line numbers 1 through 999, 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 use the authority provided in paragraph (h) to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafe condition; or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any airplane from the applicability of this AD. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent reduced structural integrity of the outboard chords, and subsequent rapid decompression of the airplane, accomplish the following: \n\n\t(a)\tFor airplanes on which the body station (BS) 727 frame upper outboard chord has been replaced in accordance with Boeing Service Bulletin 737-53-1088: Prior to the accumulation of 30,000 total flight cycles since replacement of the upper outboard chord, or within 4,500 flight cycles after the effective date of this AD, whichever occurs later, perform close visual, pulse echo shear wave (PESW), and high frequency eddy current (HFEC) inspections to detect cracks in the outboard chord of the frame at Body station (BS) 727 and in the outboard chord of stringer 18A, in accordance with Part I of the Accomplishment Instructions of either Boeing Alert Service Bulletin 737-53A1166, datedJune 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995. \n\n\t(b)\tRepeat the inspections required by paragraph (a) of this AD as follows, until the optional terminating action described in paragraph (g) of this AD is accomplished: \n\n\t\t(1)\tIf, at the time of the most recent inspection required by paragraph (a) or (b) of this AD, the airplane has accumulated 27,000 or more total flight cycles, but fewer than 50,000 total flight cycles, since the replacement of the outboard chord: Perform the next inspection within 15,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 15,000 flight cycles until the airplane has accumulated 50,000 or more total flight cycles since the replacement of the outboard chord; then perform the inspections required by paragraph (b)(2) of this AD. \n\n\t\t(2)\tIf, at the time of the most recent inspection required by paragraph (a) or (b) of this AD, the airplane has accumulated 50,000 or more total flight cycles, but fewer than 60,000 total flight cycles, since the replacement of the outboard chord: Perform the next inspection within 7,500 flight cycles. Repeat the inspection thereafter at intervals not to exceed 7,500 flight cycles until the airplane has accumulated 60,000 or more total flight cycles since the replacement of the outboard chord; then perform the inspections required by paragraph (b)(3) of this AD. \n\n\t\t(3)\tIf, at the time of the most recent inspection required by paragraph (a) or (b) of this AD, the airplane has accumulated 60,000 or more total flight cycles, but fewer than 70,000 total flight cycles, since the replacement of the outboard chord: Perform the next inspection within 5,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 5,000 flight cycles until the airplane has accumulated 70,000 or more total flight cycles since the replacement of the outboard chord; then perform the inspections required by paragraph (b)(4) of this AD.(4)\tIf, at the time of the most recent inspection required by paragraph (a) or (b) of this AD, the airplane has accumulated 70,000 or more total flight cycles since replacement of the outboard chord: Perform the next inspection within 3,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles. \n\n\t(c)\tFor airplanes on which the BS 727 frame outboard chord has not been replaced or on which only the lower outboard chord has been replaced in accordance with Boeing Service Bulletin 737-53-1088: Perform close visual, PESW, and HFEC inspections to detect cracks in the outboard chord of the frame at BS 727 and in the outboard chord of stringer 18A, in accordance with Part I of the Accomplishment Instructions of either Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995. Perform these inspections initially at the time specified in paragraph (c)(1), (c)(2), (c)(3), or (c)(4), as applicable. Repeat these inspections thereafter at the intervals specified in paragraph (d) of this AD. \n\n\t\t(1)\tFor airplanes that have accumulated 27,000 or more total flight cycles, but fewer than 50,000 total flight cycles, as of the effective date of this AD: Inspect prior to the accumulation of 4,500 flight cycles after the effective date of this AD. \n\n\t\t(2)\tFor airplanes that have accumulated 50,000 or more total flight cycles, but fewer than 60,000 total flight cycles, as of the effective date of this AD: Inspect prior to the accumulation of 2,500 flight cycles after the effective date of this AD. \n\n\t\t(3)\tFor airplanes that have accumulated 60,000 or more total flight cycles, but fewer than 70,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 1,500 flight cycles after the effective date of this AD. \n\n\t\t(4)\tFor airplanes that have accumulated 70,000 or more total flight cycles as of the effective date of thisAD: Inspect prior to the accumulation of 500 flight cycles or within 90 days after the effective date of this AD, whichever occurs first. \n\n\t(d)\tRepeat the inspections required by paragraph (c) of this AD as follows, until the optional terminating action described in paragraph (g) of this AD is accomplished: \n\n\t\t(1)\tIf, at the time of the most recent inspection required by paragraph (c) or (d) of this AD, the airplane has accumulated 27,000 or more total flight cycles, but fewer than 50,000 total flight cycles: Perform the next inspection within 15,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 15,000 flight cycles until the airplane has accumulated 50,000 or more total flight cycles; then perform the inspections required by paragraph (d)(2) of this AD. \n\n\t\t(2)\tIf, at the time of the most recent inspection required by paragraph (c) or (d) of this AD, the airplane had accumulated 50,000 or more total flight cycles, but fewer than 60,000 total flight cycles: Perform the next inspection within 7,500 flight cycles. Repeat the inspection thereafter at intervals not to exceed 7,500 flight cycles until the airplane has accumulated 60,000 or more total flight cycles; then perform the inspections required by paragraph (d)(3) of this AD. \n\n\t\t(3)\tIf, at the time of the most recent inspection required by paragraph (c) or (d) of this AD, the airplane had accumulated 60,000 or more total flight cycles, but fewer than 70,000 total flight cycles: Perform the next inspection within 5,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 5,000 flight cycles until the airplane has accumulated 70,000 or more total flight cycles; then perform the inspections required by paragraph (b)(4) of this AD. \n\n\t\t(4)\tIf, at the time of the most recent inspection required by paragraph (c) or (d) of this AD, the airplane had accumulated 70,000 or more total flight cycles: Perform the next inspection within 3,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles. \n\n\t(e)\tIf any crack is found in the outboard chord of stringer 18A during any inspection required by this AD, repair prior to further flight, in accordance with either paragraph (e)(1) or (e)(2) of this AD. \n\n\t\t(1)\tBoeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995, or \n\t\t(2)\tA method approved by the Manager, Seattle Aircraft Certification Office, FAA, Transport Airplane Directorate. \n\n\t(f)\tIf any crack is found in the outboard chord of the frame at BS 727 during any inspection required by this AD, accomplish paragraph (f)(1) or (f)(2) of this AD, as applicable, in accordance with either Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995. \n\n\t\t(1)\tFor any crack that extends from the forward edge of the chord or from the forward fastener hole, but that does not extend past the second fastener hole, accomplish either paragraph (f)(1)(i) or (f)(1)(ii) of this AD. Thereafter, perform initial and repetitive inspections in accordance with paragraphs (a) and (b) of this AD. \n\n\t\t\t(i)\tPrior to further flight, install the time limited repair. Prior to the accumulation of 4,500 flight cycles or within 18 months, after accomplishing the time-limited repair, whichever occurs first, replace the outboard chord. Or \n\n\t\t\t(ii)\tPrior to further flight, replace the outboard chord. \n\tNOTE 2: Boeing Alert Service Bulletin 737-53A1166 references Boeing Service Bulletin 737- 53-1088 as an additional source of service information for procedures to replace the chord. \n\n\t\t(2)\tFor any crack that extends from the forward edge of the chord, or from the forward fastener hole, and that extends past the second fastener hole, prior to further flight, replace the outboard chord in accordance with the alert service bulletin. Thereafter, perform initial and repetitive inspections in accordance with paragraphs (a) and (b) of this AD. \n\n\t(g)\tAccomplishment of the following actions in accordance with either Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994, or Revision 1, dated May 25, 1995, constitutes terminating actions for the requirements of this AD: \n\n\t\t(1)\tFor airplanes on which no crack is found: Install the preventative modification in accordance with the alert service bulletin. \n\n\t\t(2)\tFor airplanes on which any crack is found: Prior to further flight, replace the cracked chord and install the preventative modification in accordance with the alert service bulletin. \n\n\t(h)\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 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. \n\n\tNOTE 3: 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(i)\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(j)\tThe inspections and replacement shall be done in accordance with either Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994, including Addendum, or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995, including Addendum. 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(k)\tThis amendment becomes effective on August 18, 1995.

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 737-100 and -200 series airplanes was published in the Federal Register on December 7, 1994 (59 FR 63065). That action proposed to require various inspections for cracks in the outboard chord of the frame at body station (BS) 727 and in the outboard chord of stringer 18A; and repair or replacement of cracked parts. That action also provides for an optional terminating action for the required inspections. \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\n\tTwo commenters support the proposed rule. \n\n\tThe manufacturer requests that, in the Discussion section of the proposed rule, a reference to "chords" be changed to "chord." The FAA acknowledges that "chord" would be moreaccurate. However, since the Discussion section does not appear in the final rule, no change to the final rule is necessary. \n\n\tThe manufacturer also requests that certain clarifications be made to the proposed rule. The manufacturer notes that the addition of the words "BS 727" in paragraphs (a) and (c) will clarify that it is the BS 727 upper outboard chord, not the S-18A chord, that is being referred to. The manufacturer also notes that changing the words "outboard chords" with "cracked chord" in paragraph (g)(2) would clarify the intent of the replacement requirements of that paragraph. The FAA concurs, and has revised the final rule accordingly. \n\n\tTwo commenters request that the final rule reference a new revision of Boeing Service Bulletin 737-53A1166 that includes procedures for repair of cracking in the S-18A outer chord. The commenters note that the service bulletin specified in the proposed rule only describes the inspection of S-18A and does not provide repair instructions in the event that cracking is detected. The FAA concurs. Since issuance of the proposed rule, the FAA has reviewed and approved Boeing Service Bulletin 737-53A1166 Revision 1, dated May 25, 1995, which describes repair procedures for cracking of stringer 18A outer chord. Paragraph (e) of the final rule has been changed to add a reference to this revised service bulletin as an additional source of service information. \n\n\tOne commenter states that the proposed Pulse Echo Shear Wave (PESW) inspection is redundant, since the proposed rule also would require a High Frequency Eddy Current (HFEC) inspection. The commenter also states that the HFEC inspection is more accurate for detecting cracks than the PESW inspection. The commenter therefore requests that the FAA remove the requirement to perform the PESW inspection from the proposed rule. The FAA does not concur. The PESW inspection is necessary to detect cracking that is not common to the fastener holes; the HFEC inspection only would detect cracks that extend into the fastener hole. \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\n\tThere are approximately 999 Boeing Model 737-100 and -200 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 296 airplanes of U.S. registry will be affected by this AD, that it will take approximately 4 work hours per airplane to accomplish the required inspections, and that the average labor rate is $60 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $71,040, or $240 per airplane, per inspection cycle. \n\n\tThe total 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 that will be provided by this AD action, it will take approximately 50 work hours to accomplish it, at an average labor rate of $60 per work hour. Required parts will cost approximately $3,680 per airplane. Based on these figures, the total cost impact of this optional terminating action is estimated to be $6,680 per airplane. \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\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\n\tAccordingly, 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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\tThe 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. § 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive: