AD 2017-10-07

We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 737-400 series airplanes. This AD was prompted by an evaluation by the design approval holder (DAH), which indicates that the aft fuselage skin is subject to widespread fatigue damage (WFD), and reports of aft fuselage skin cracking. This AD requires repetitive inspections to detect cracking of the aft fuselage skin, inspections to detect missing or loose fasteners and any disbonding or cracking of bonded doublers, permanent repairs of time-limited repairs, related investigative and corrective actions if necessary, and skin panel replacement. We are issuing this AD to address the unsafe condition on these products.

Final rule.

Adoption of the Amendment \n\n\n\tAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n0 1. The authority citation for part 39 continues to read as follows: \n\n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n\n\nSec. 39.13 (Amended) \n\n0 2. The FAA amends Sec. 39.13 by adding the following new airworthiness directive (AD): \n\n2017-10-07 The Boeing Company: Amendment 39-18881; Docket No. FAA- 2016-6666; Directorate Identifier 2015-NM-124-AD. \n\n(a) Effective Date \n\n\n\tThis AD is effective July 5, 2017. \n\n(b) Affected ADs \n\n\n\tNone. \n\n(c) Applicability \n\n\n\tThis AD applies to Boeing Model 737-400 series airplanes, certificated in any category, as identified in Boeing Special Attention Service Bulletin 737-53-1187, Revision 3, dated July 10, 2015 (''SASB 737-53-1187 R3''). \n\n(d) Subject \n\n\n\tAir Transport Association (ATA) of America Code 53, Fuselage. \n\n(e) Unsafe Condition \n\n\n\tThis AD was prompted by an evaluation by the design approval holder (DAH) which indicates that the aft fuselage skin is subject to widespread fatigue damage (WFD) and reports of aft fuselage skin cracking. We are issuing this AD to detect and correct cracking in the aft fuselage skin along the longitudinal edges of the bonded skin doubler, which could result in possible rapid decompression \n\n((Page 24478)) \n\nand reduced structural integrity of the airplane. \n\n(f) Compliance \n\n\n\tComply with this AD within the compliance times specified, unless already done. \n\n(g) Inspections, Related Investigative and Corrective Actions \n\n\n\tAt the applicable times specified in tables 1, 2, and 3 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3, except as provided by paragraph (h)(1) and (h)(2) of this AD: Do the applicable inspections to detect cracks in the aft fuselage skin panels; and do all applicable related investigative and corrective actions; in accordance with the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraphs (h)(3) and (h)(4) of this AD. Do all applicable related investigative and corrective actions before further flight. Repeat the applicable inspections thereafter at the applicable intervals specified in tables 1, 2, and 3 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3. Accomplishment of a repair in accordance with ''Part 4: Repair'' of the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraph (h)(3) of this AD, is terminating action for the repetitive inspections required by this paragraph at the repaired locations only. \n\n(h) Exceptions to SASB 737-53-1187 R3 \n\n\n\t(1) Where SASB 737-53-1187 R3, specifies compliance times ''after the Revision 3 date of this service bulletin,'' this AD requires compliance within the specified compliance times after the effective date of this AD. \n\t(2) The Condition column of Paragraph 1.E., ''Compliance,'' of SASB737-53-1187 R3, refers to airplanes in certain configurations as of the ''issue date of Revision 3 of this service bulletin.'' However, this AD applies to airplanes in the specified configurations as of the effective date of this AD. \n\t(3) Where SASB 737-53-1187 R3 specifies contacting Boeing for repair instructions or work instructions, before further flight, repair or perform the work instructions using a method approved in accordance with the procedures specified in paragraph (n) of this AD, except as required by paragraph (h)(4) of this AD. \n\t(4) For airplanes on which an operator has a record that a skin panel was replaced with a production skin panel before 53,000 total flight cycles: At the applicable time for the next inspection as specified in tables 1, 2, and 3 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3, except as provided by paragraph (h)(1) and (h)(2) of this AD: Perform inspections and applicable corrective actions using a method approved in accordance with the procedures specified in paragraph (n) of this AD. \n\n(i) Actions for Airplanes With a Time-Limited Repair Installed \n\n\n\t(1) For airplanes with a time-limited repair installed as specified in Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007: At the applicable times specified in table 4 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3, except as provided by paragraphs (h)(1) and (h)(2) of this AD: Do the actions specified in paragraphs (i)(1)(i) and (i)(1)(ii) of this AD. \n\t(i) Do the applicable inspections to detect missing or loose fasteners and any disbonding or cracking of bonded doublers; and do all applicable related investigative and corrective actions; in accordance with the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraph (h)(3) of this AD. Do all applicable related investigative and corrective actions before further flight. Repeat the applicable inspections thereafter at the applicable intervals specifiedin table 4 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3. \n\t(ii) Make the time-limited repair permanent; and do all applicable related investigative and corrective actions; in accordance with Part 6 of the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraph (h)(3) of this AD. Do all applicable related investigative and corrective actions before further flight. Accomplishing the permanent repair required by this paragraph terminates the inspections required by paragraph (i)(1)(i) of this AD for the permanently repaired area only. \n\t(2) For airplanes with a time-limited repair installed as specified in SASB 737-53-1187 R3: At the applicable times specified in table 5 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3, except as provided by paragraph (h)(2) of this AD: Do the actions specified in paragraphs (i)(2)(i) and (i)(2)(ii) of this AD. \n\t(i) Do the applicable inspections to detect missing or loose fasteners and any disbondingor cracking of bonded doublers; and do all applicable corrective actions; in accordance with the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraph (h)(3) of this AD. Do all applicable corrective actions before further flight. Repeat the applicable inspections thereafter at the applicable intervals specified in table 5 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3. \n\t(ii) Make the time-limited repair permanent; and do all applicable related investigative and corrective actions; in accordance with Part 6 of the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraph (h)(3) of this AD. Do all applicable related investigative and corrective actions before further flight. Accomplishing the permanent repair required by this paragraph terminates the inspections required by paragraph (i)(2)(i) of this AD for the permanently repaired area only. \n\n(j) Modification of Certain Permanent Repairs \n\n\n\tFor airplanes with an existing time-limited repair that was made permanent as specified in Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007: At the applicable time specified in table 6 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3, except as provided by paragraph (h)(1) of this AD: Modify the existing permanent repair; and do all applicable related investigative and corrective actions; in accordance with Part 6 of the Accomplishment Instructions of SASB 737-53-1187 R3, except as required by paragraph (h)(3) of this AD. Do all applicable related investigative and corrective actions before further flight. \n\n(k) Post-Repair Inspections \n\n\n\tTable 7 of paragraph 1.E., ''Compliance,'' of SASB 737-53-1187 R3, specifies post-repair airworthiness limitation inspections in compliance with 14 CFR 25.571(a)(3) at the repaired locations, which support compliance with 14 CFR 121.1109(c)(2) or 129.109(b)(2). As airworthiness limitations, these inspections are required by maintenance and operational rules. It is therefore unnecessary to mandate them in this AD. Deviations from these inspections require FAA approval, but do not require an alternative method of compliance. \n\n(l) Skin Panel Replacement \n\n\n\tAt the later of the times specified in paragraphs (l)(1) and (1)(2) of this AD: Replace the applicable skin panels, and do all applicable related investigative and corrective actions, in accordance with the Accomplishment Instructions of SASB 737-53-1187 R3. Do all applicable related investigative and corrective actions before further flight. Doing the skin panel replacement required by this paragraph terminates the inspection requirements of paragraphs (g), (i), and (j) of this AD for that skin panel only, provided the skin panel replacement was done with a production skin panel after 53,000 total flight cycles, or with the skin panel replacement kit (S-20 to S-25 (left and right)) specified in Boeing Service Bulletin 737-53-1187. \n\t(1) Before 60,000 total flight cycles, but not before 53,000 total flight cycles. \n\t(2) Within 6,000 flight cycles after the effective date of this AD, but not before 53,000 total flight cycles. \n\n(m) Credit for Previous Actions \n\n\n\t(1) This paragraph provides credit for the actions required by paragraph (g) of this AD, if those actions were performed before the effective date of this AD using Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007, except as required by paragraph (h)(4) of this AD. Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007, was incorporated by reference in AD 2009-21-01, Amendment 39-16038 (74 FR 52395, October 13, 2009) (''AD 2009-21- 01''). \n\t(2) This paragraph provides credit for the actions required by paragraph (l) of this AD, if those actions were performed before the effective date of this AD using Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007, except as required by paragraph (h)(4) of this AD. Boeing Service Bulletin 737-53-1187, Revision 2, dated May 9, 2007, was incorporated by reference in AD 2009-21-01. \n\t(3) This paragraph provides credit for the actions required by paragraph (l) of this AD, if those actions were performed before November 17, 2009 (the effective date of AD 2009-21-01) using Part III of the Accomplishment Instructions of Boeing \n\n((Page 24479)) \n\nService Bulletin 737-53-1187, dated November 2, 1995; or Part III of the Accomplishment Instructions of Boeing Service Bulletin 737-53- 1187, Revision 1, dated January 16, 1997, except as required by paragraph (h)(4) of this AD. Boeing Service Bulletin 737-53-1187, dated November 2, 1995; and Boeing Service Bulletin 737-53-1187, Revision 1, dated January 16, 1997; are not incorporated by reference in this AD. \n\n(n) Alternative Methods of Compliance (AMOCs) \n\n\n\t(1) The Manager, Los Angeles Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19.In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the ACO, send it to the attention of the person identified in paragraph (o)(1) of this AD. Information may be emailed to: 9-ANM-LAACO-AMOC-Requests@faa.gov. \n\t(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local flight standards district office/certificate holding district office. \n\t(3) An AMOC that provides an acceptable level of safety may be used for any repair, modification, or alteration required by this AD if it is approved by the Boeing Commercial Airplanes Organization Designation Authorization (ODA) that has been authorized by the Manager, Los Angeles ACO, to make those findings. To be approved, the repair method, modification deviation, or alteration deviation must meet the certification basis of the airplane and the approval must specifically refer to this AD. \n\t(4) AMOCs approved for repairs for AD 2009-21-01 are approved as AMOCs for the corresponding provisions of paragraph (g) of this AD. \n\t(5) Except as specified in paragraph (n)(6) of this AD, AMOCs approved for previous modifications done as optional terminating action for AD 2009-21-01 are approved as AMOCs for the modification required by paragraph (l) of this AD provided the previous modification was done after the airplane had accumulated 53,000 total flight cycles or more. \n\t(6) AMOCs approved for previous modifications done as optional terminating action for AD 2009-21-01 are approved as AMOCs for the modification required by paragraph (l) of this AD provided the skin modification replacement is done using the skin panel kit specified Boeing Service Bulletin 737-53-1187. \n\n(o) Related Information \n\n\n\t(1) For more information about this AD, contact Jennifer Tsakoumakis, Aerospace Engineer, Airframe Branch, ANM-120L, FAA, Los Angeles ACO, 3960 Paramount Boulevard, Lakewood, CA 90712-4137; phone: 562-627-5264; fax: 562-627-5210; email: jennifer.tsakoumakis@faa.gov. \n\t(2) Service information identified in this AD that is not incorporated by reference is available at the addresses specified in paragraphs (p)(3) and (p)(4) of this AD. \n\n(p) Material Incorporated by Reference \n\n\n\t(1) The Director of the Federal Register approved the incorporation by reference (IBR) of the service information listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51. \n\t(2) You must use this service information as applicable to do the actions required by this AD, unless the AD specifies otherwise. \n\t(i) Boeing Special Attention Service Bulletin 737-53-1187, Revision 3, dated July 10, 2015. \n\t(ii) Reserved. \n\t(3) For Boeing service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone: 562-797-1717; Internet: https://www.myboeingfleet.com. \n\t(4) You may view this service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, WA. For information on the availability of this material at the FAA, call 425-227-1221. \n\t(5) You may view this service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/federal-register/cfr/ibr-locations.html.

Discussion \n\n\n\tWe issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain Boeing Model 737- 400 series airplanes. The NPRM published in the Federal Register on May 13, 2016 (81 FR 29809) (''the NPRM''). The NPRM was prompted by an evaluation by the DAH, which indicates that the aft fuselage skin is subject to WFD, and reports of aft fuselage skin cracking. The NPRM proposed to require repetitive inspections to detect cracking of the aft fuselage skin, inspections to detect missing or loose fasteners and any disbonding or cracking of bonded doublers, permanent repairs of time-limited repairs, related investigative and corrective actions if necessary, and skin panel replacement. We are issuing this AD to prevent cracking in the aft fuselage skin along the longitudinal edges of the bonded skin doubler, which could result in possible rapid decompression and reduced structural integrity of the airplane. \n\nComments \n\n\n\tWe gave the public the opportunity to participate in developing this AD. The following presents the comments received on the NPRM and the FAA's response to each comment. \n\nRequest To Specify Repair Procedures \n\n\n\tBoeing requested that we revise the proposed AD to address repairs that are \n\n((Page 24476)) \n\ninstalled on the airplane for reasons other than chem-mill cracking. Boeing provided suggested language for the AD. \n\tWe do not agree with Boeing's request. Paragraph 3.B.1 in the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-53-1187, Revision 3, dated July 10, 2015 (''SASB 737-53- 1187 R3''), which is the referenced source of service information in this AD, already addresses the issue raised by Boeing. SASB 737-53-1187 R3 does not make a distinction between repairs installed for chem-mill cracking and repairs installed for other reasons. Therefore, repairs that are installed for any reason, provided they meet the service information criteria, are already addressed. We have not changed this AD in this regard. \n\nRequest To Revise Compliance Time in Paragraph (h)(4) of the Proposed AD \n\n\n\tBoeing requested that we revise the compliance time in paragraph (h)(4) of the proposed AD from the time specified in SASB 737-53-1187 R3, to a time approved by the FAA through the alternative method of compliance (AMOC) process. \n\tBoeing provided examples of how replacing skin panels at certain compliance times would require further skin panel replacement before reaching the airplane limit of validity. Boeing explained that the NPRM proposed skin panel replacement at 60,000 total flight cycles; therefore, an FAA approval to adjust the compliance time from total flight cycles to cycles after skin panel replacement would be required. \n\tWe partially agree with Boeing's request. Airplanes that have had a skin replacement with a production skin panel, as distinguished from an improved-design kit skin panel, prior to 53,000 total flight cycles may be eligible for an adjustment of the inspection threshold. Currently, such an adjustment of the AD compliance time is not delegated to Boeing's authorized representatives, and the change must be approved by the FAA. However, we consider the number of airplanes affected by this scenario to be quite small. Therefore, we have decided to approve such changes to the compliance times on a case-by-case basis using the procedures specified in paragraph (n)(1) of this AD. Although we agree with the comment, we have not changed this AD in this regard. \n\nRequest To Reference Part 6 of the Service Information \n\n\n\tBoeing requested that we revise paragraphs (i)(1)(ii), (i)(2)(ii), and (j) of the proposed AD by specifying doing part 6 of the service information. Boeing stated that specifying the service information part reference would make the language consistent with paragraph (g) of the proposed AD, which specifies the service information part reference. \n\tWeagree with Boeing's request. These changes will increase the paragraphs' clarity. We have revised paragraphs (i)(1)(ii), (i)(2)(ii), and (j) of this AD accordingly. \n\nRequest To Revise Paragraph (l) of the Proposed AD \n\n\n\tBoeing requested that we revise the provision of paragraph (l) of the proposed AD, which would provide for terminating action if the skin panel was replaced with a production skin panel. Boeing indicated that terminating action should also apply to airplanes with the skin panel replacement kit (S-20 to S-25 (left and right)) specified in Boeing Service Bulletin 737-53-1187. Boeing stated that the skin panel replacement using the kit specified in Boeing Service Bulletin 737-53- 1187 does not have the lower flight cycle limit restriction of the production panel replacement. Boeing explained that once the kit skin panel is replaced, the inspections specified in SASB 737-53-1187 R3, are terminated. \n\tWe agree with Boeing's request. The kit skin panels are an improved design compared with the original production skin panels, have different inspection requirements, and provide terminating action. We have revised paragraph (l) of this AD accordingly. \n\nRequest To Remove Flight Cycle Restriction in Paragraphs (m)(2), (m)(3), and (n)(5) of the Proposed AD \n\n\n\tBoeing requested that we revise paragraphs (m)(2), (m)(3), and (n)(5) of the proposed AD by removing the flight-cycle restriction for credit for the skin panel replacement. Boeing explained that the only skin panel replacement specified in the service information referenced in paragraphs (m)(2) and (m)(3) of the proposed AD is the skin panel replacement kit, which can be accomplished at any time. \n\tBoeing stated that it assumed that only the kit skin panel replacements, and not the original production skin panels, are approved as AMOCs for AD 2009-21-01, Amendment 39-16038 (74 FR 52395, October 13, 2009) (''AD 2009-21-01''). Boeing asserted that, therefore, paragraph (n)(5) of the proposedAD should approve previous modifications done as optional terminating action for AD 2009-21-01 as AMOCs for the modification required by paragraph (l) of this AD without the flight-cycle restriction. \n\tWe partially agree with Boeing's request. The kit skin panels are an improved design compared with the original production skin panels and have different inspection requirements. We have revised paragraphs (m)(2) and (m)(3) of this AD by removing the flight-cycle restriction. \n\tHowever, in order to address airplanes that have had production skin panels replaced through AMOCs for AD 2009-21-01, paragraph (n)(5) of this AD retains the flight-cycle restriction. \n\tWe agree to approve AMOCs for AD 2009-21-01 that require using the skin panel kit specified in Boeing Service Bulletin 737-53-1187 as AMOCs for the modification required by paragraph (l) of this AD without the flight-cycle restriction. We have added paragraph (n)(6) to this AD, which states that AMOCs approved for previous modifications done as optional terminating action for AD 2009-21-01 are approved as AMOCs for the modification required by paragraph (l) of this AD provided the skin modification replacement was done using the skin panel kit specified in Boeing Service Bulletin 737-53-1187. \n\nConclusion \n\n\n\tWe reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this AD with the changes described previously and minor editorial changes. We have determined that these minor changes: \n\tAre consistent with the intent that was proposed in the NPRM for correcting the unsafe condition; and \n\tDo not add any additional burden upon the public than was already proposed in the NPRM. \n\tWe also determined that these changes will not increase the economic burden on any operator or increase the scope of this AD. \n\nRelated Service Information Under 1 CFR Part 51 \n\n\n\tWe reviewed SASB 737-53-1187 R3. The service information describesprocedures for doing inspections of the fuselage skin, repairs, and skin panel replacement. This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section. \n\nCosts of Compliance \n\n\n\tWe estimate that this AD affects 84 airplanes of U.S. registry. \n\tWe estimate the following costs to comply with this AD: \n\n((Page 24477)) \n\n\n\n\n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost per \n\tAction Labor cost Parts cost product Cost on U.S. operators ---------------------------------------------------------------------------------------------------------------- Inspections.................. Up to 1,568 work- $0 Up to $133,280. Up to $11,195,520. \n\thours x $85 per \n\thour = Up to \n\t$133,280. Skin replacement............. 698 work-hours x $85 185,147 $244,477....... $20,536,068. \n\tper hour = $59,330. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe estimate the following costs to do any necessary repairs that would be required based on the results of the inspections. We have no way of determining the number of aircraft that might need these repairs: \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tAction Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- Time-limited repair............. 24 work-hours x $85 per (\1\) $2,040 per repair. \n\thour = $2,040 per \n\trepair. Permanent repair................ Up to 39 work-hours x (\1\) Up to $3,315 per repair. \n\t$85 per hour = $3,315 \n\tper repair. ---------------------------------------------------------------------------------------------------------------- \1\ We have received no definitive data that would enable us to provide the part cost estimates for the on- \n\tcondition actions specified in this AD. \n\n\n\tWe estimate the following costs to do any necessary post-repair inspections that would be required. We have no way of determining the number of aircraft that might need these inspections: \n\n\n\tPost-Repair Inspection Costs ---------------------------------------------------------------------------------------------------------------- \n\tAction Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- Post-repair inspection................ Up to 7 work(dash)hours x $85 $0 Up to $595. \n\tper hour = $595. ---------------------------------------------------------------------------------------------------------------- \n\nAuthority for This Rulemaking \n\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\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\n\tThis ADwill 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\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a ''significant regulatory action'' under Executive Order 12866, \n\t(2) Is not a ''significant rule'' under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), \n\t(3) Will not affect intrastate aviation in Alaska, and \n\t(4) 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\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.