AD 2016-08-03

We are adopting a new airworthiness directive (AD) for all The Boeing Company Model 777-200, -200LR, -300, and -300ER series airplanes. This AD was prompted by reports of fractured forward attach fittings of the inboard flap outboard aft flap track. The fractured fittings were determined to be the result of corrosion pits forming on the inside diameter of the fittings. This AD requires an inspection for the affected part number and serial number of the main flap; various additional repetitive inspections of the fitting, if necessary; and replacement of the fitting or nested bushing installation, if necessary, which would terminate the inspections. This AD also provides an optional terminating action for the repetitive inspections. We are issuing this AD to detect and correct fracture of the fitting, which could result in the loss of the inboard aft flap and could lead to a punctured fuselage, causing injury to the flightcrew and passengers, and damage to the airplane.

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\n2016-08-03 The Boeing Company: Amendment 39-18479; Docket No. FAA- 2015-3147; Directorate Identifier 2014-NM-094-AD. \n\n(a) Effective Date \n\n\n\tThis AD is effective May 18, 2016. \n\n(b) Affected ADs \n\n\n\tNone. \n\n(c) Applicability \n\n\n\tThis AD applies to all The Boeing Company Model 777-200, -200LR, -300, and -300ER series airplanes, certificated in any category. \n\n((Page 21719)) \n\n(d) Subject \n\n\n\tAir Transport Association (ATA) of America Code 57, Wings. \n\n(e) Unsafe Condition \n\n\n\tThis AD was prompted by reports of fractured forward attach fittings of the inboard flap outboard aft flap track. The fractured fittings were determined to be the result of corrosion pits forming on the inside diameter of the fittings. We are issuing this AD to detect and correct fracture of the fitting, which could result in the loss of the inboard aft flap and could lead to a punctured fuselage, causing injury to the flightcrew and passengers, and damage to the airplane. \n\n(f) Compliance \n\n\n\tComply with this AD within the compliance times specified, unless already done. \n\n(g) Inspection To Determine the Part Number \n\n\n\tAt the applicable time specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57- 0094, Revision 1, dated November 5, 2014, except as provided by paragraph (l) of this AD: Do an inspection of the main flap of the inboard flap assembly for affected part and serial numbers, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. A review of airplane maintenance records is acceptable in lieu of this inspection if the part number and serial number of the inboard flap can be conclusively determined from that review. \n\n(h) Additional Inspections \n\n\n\tIf any main flap of the inboard flap assembly having an affected part number and serial number is found during the inspection required by paragraph (g) of this AD: Except as provided by paragraph (l) of this AD, at the applicable time specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, do the terminating action specified in paragraph (k)(1), (k)(2), or (k)(3) of this AD, or do the inspections specified in paragraph (h)(1) or (h)(2) of this AD, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57- 0094, Revision 1, dated November 5, 2014. Repeat the inspections thereafter at the applicabletimes specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57- 0094, Revision 1, dated November 5, 2014, until a terminating action in paragraph (k)(1), (k)(2), or (k)(3) of this AD is done. Accomplishing a terminating action specified in paragraph (k)(1), (k)(2), or (k)(3) of this AD terminates the inspections required by this paragraph for that fitting only. \n\t(1) At the forward attach fitting of the aft flap track of the inboard flap: Do a detailed inspection for cracking and bushing migration, and a high frequency eddy current inspection for cracking, in accordance with Part 2 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57- 0094, Revision 1, dated November 5, 2014. \n\t(2) At the forward attach fitting of the aft flap track of the inboard flap: Do a detailed inspection for cracking and bushing migration, and an ultrasound inspection for cracking, in accordance with Part 3 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\n(i) Corrective Action for Bushing Migration \n\n\n\tIf any bushing migration but no cracking is found during any inspection required by paragraph (h) of this AD: At the applicable times specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, do the actions specified in paragraphs (i)(1) through (i)(3) of this AD. Accomplishment of a terminating action specified in paragraph (i)(3) or (k) of this AD terminates the actions required by this paragraph for that fitting only. \n\t(1) Apply corrosion inhibiting compound BMS 3-23, Type II, around the bushing flanges on each side of the fitting, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. Re-apply the corrosion inhibiting compound at the time specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\t(2) Repeat the inspections specified in paragraph (h)(1) or (h)(2) of this AD, except inspect for cracking only. \n\t(3) Do a terminating action specified in paragraph (i)(3)(i), (i)(3)(ii), or (i)(3)(iii) of this AD. \n\t(i) Install a nested bushing to the forward attach fitting of the aft flap track of the inboard flap, including doing all applicable related investigative actions, in accordance with Part 4 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\t(ii) Replace the forward attach fitting of the aft flap track of the inboard flap with an aluminum fitting, including doing all applicable related investigative actions, in accordance with Part 5 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\t(iii) Replace the forward attach fitting of the aft flap track of the inboard flap with a titanium fitting, including doing all applicable related investigative actions, in accordance with Part 6 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\n(j) Corrective Actions for Cracking \n\n\n\tIf any cracking is found during any inspection required by paragraph (h) or (i)(3) of this AD: At the applicable time specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, do a terminating action specified in paragraph (j)(1) or (j)(2) of this AD. Replacement of the forward attach fitting as specified in paragraph (j)(1) or (j)(2) of this AD terminates the actions in this AD for that fitting only. \n\t(1) Replace the forward attach fitting of the aft flap track of the inboard flap with an aluminum fitting, including doing all applicable related investigative and corrective actions, in accordance with Part 5 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\t(2) Replace the forward attach fitting of the aft flap track of the inboard flap with a titanium fitting, including doing all applicable related investigative and corrective actions, in accordance with Part 6 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\n(k) Optional Terminating Actions \n\n\n\t(1) Installation of the nested bushing to the forward attach fitting of the aft flap track of the inboard flap, in accordance with Part 4 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, terminates the requirements of this AD for that fitting only, provided no cracking is found during any inspection specified in Part 4 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, and all corrosion has been removed. \n\t(2) Replacement of the forward attach fitting of the aft flap track of the inboard flap with an aluminum fitting, in accordance with Part 5 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, terminates the requirements of this AD for that fitting only. \n\t(3) Replacement of the forward attach fitting of the aft flap track of the inboard flap with a titanium fitting, in accordance with Part 6 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, terminates the requirements of this AD for that fitting only. \n\n(l) Exception to the Service Information \n\n\n\tWhere Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, specifies a compliance time ''after the original issue date of this service bulletin,'' this AD requires compliance within the specified compliance time after the effective date of this AD. \n\n(m) Credit for Previous Actions \n\n\n\t(1) This paragraph provides credit for the actions specified in paragraphs (h)(1) and (h)(2) of this AD, if those actions were performed before the effective date of this AD using Boeing Special Attention Service Bulletin 777-57-0094, dated January 29, 2014, which is not incorporated by reference in this AD. \n\t(2) This paragraph provides credit for the actions specified in paragraph (h)(1) of this AD, if those actions were performed before the effective date of this AD using Boeing Multi Operator Message MOM-MOM-13- \n\n((Page 21720)) \n\n0137-01B, dated February 21, 2013, which is not incorporated by reference in this AD. \n\n(n) Alternative Methods of Compliance (AMOCs) \n\n\n\t(1) The Manager, Seattle 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-Seattle-ACO-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, Seattle ACO, to make those findings. To be approved, the repair method, modification deviation, or alterationdeviation must meet the certification basis of the airplane and the approval must specifically refer to this AD. \n\t(4) For service information that contains steps that are labeled as Required for Compliance (RC), the provisions of paragraphs (n)(4)(i) and (n)(4)(ii) apply. \n\t(i) The steps labeled as RC, including substeps under an RC step and any figures identified in an RC step, must be done to comply with the AD. An AMOC is required for any deviations to RC steps, including substeps and identified figures. \n\t(ii) Steps not labeled as RC may be deviated from using accepted methods in accordance with the operator's maintenance or inspection program without obtaining approval of an AMOC, provided the RC steps, including substeps and identified figures, can still be done as specified, and the airplane can be put back in an airworthy condition. \n\n(o) Related Information \n\n\n\t(1) For more information about this AD, contact Eric Lin, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle ACO, 1601 Lind Avenue SW., Renton, WA 98057-3356; telephone: 425-917- 6412; fax: 425-917-6590; email: Eric.Lin@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 777-57-0094, Revision 1, dated November 5, 2014. \n\t(ii) Reserved. \n\t(3) For Boeing service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P. O. Box 3707, MC 2H-65, Seattle, WA 98124-2207; telephone 206-544-5000, extension1; fax 206-766-5680; 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 all The Boeing Company Model 777-200, -200LR, -300, and -300ER series airplanes. The NPRM published in the Federal Register on August 25, 2015 (80 FR 51491) (''the NPRM''). The NPRM was prompted by reports of fractured forward attach fittings of the inboard flap outboard aft flap track. The fractured fittings were determined to be the result of corrosion pits forming on the inside diameter of the fittings. The NPRM proposed to require an inspection for the affected part number and serial number of the main flap; various additional repetitive inspections of the fitting, if necessary; and replacement of the fitting or nested bushing installation, if necessary, which would terminate the inspections. The proposed AD also provided an optional terminating action for the repetitive inspections. We are issuing this AD to detect and correct fracture of the fitting, which could result in the loss of the inboard aft flap and could lead to a punctured fuselage, causing injury to \n\n((Page 21717)) \n\nthe flightcrew and passengers, and damage to 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. Benjamin Kerensa commented that he supports the NPRM. \n\nRequest To Change Terminology \n\n\n\tBoeing requested that we change the phrase ''inboard flap of the main flap'' to ''main flap of the inboard flap assembly'' in paragraphs (g) and (h) of the proposed AD. Boeing stated that this would clarify the inspection location. \n\tWe agree with the commenter's request for the reason provided by the commenter. We have revised paragraphs (g) and (h) of this AD accordingly. \n\nRequest To Clarify Requirements of a Certain Terminating Action \n\n\n\tBoeing requested that we revise the terminating action specified in paragraph (k)(1) of the proposed AD. Boeing recommended that at the end of paragraph (k)(1) of the proposed AD, we add the following language, ''Prior to accomplishing this option, the inspections of paragraph (h) must be accomplished and no cracking must have been found during that inspection.'' Boeing commented that the bushing replacement is only a terminating action if the fitting has been verified to be crack free. \n\tWe agree to clarify the terminating action. As specified in Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, if cracking is found during an inspection that is part of the terminating action, a fitting replacement must be done instead of the terminating action. In addition, Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, specifies that if corrosion cannot be removed during the terminating action, a fitting replacement must be done instead of the terminatingaction. \n\tTherefore, we have revised paragraph (k)(1) of this AD to specify that the terminating action is acceptable provided no cracking is found during any inspection specified in Part 4 of the Accomplishment Instructions of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, and all corrosion has been removed. \n\tWe have also clarified the terminating actions specified in paragraphs (h), (i), (j), (k)(1), (k)(2), and (k)(3) of this AD to specify the terminating actions apply only to that fitting on which the terminating action is done. \n\tIn addition, we have clarified the actions specified in paragraphs (i)(3)(i), (i)(3)(ii), and (i)(3)(iii) of this AD by specifying the actions include doing all applicable related investigative actions. Also, we have clarified the actions specified in paragraphs (j)(1) and (j)(2) of this AD by specifying the actions include doing all applicable related investigative and corrective actions. \n\nRequest To Clarify Terminating Action Is an Option to the Inspections \n\n\n\tBoeing and American Airlines (AA) requested that we clarify that the terminating action can be done instead of the inspections. AA commented to revise the terminating action paragraph to state the following: \n\n\n\tIf any inboard flap of the main flap having an affected part number and serial number is found during the inspection required by paragraph (g) of this AD: Except as provided by paragraph (l) of this AD, at the applicable time specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57- 0094, Revision 1, dated November 5, 2014, do the terminating action in paragraph (k)(1), (k)(2), or (k)(3) of this AD or do the inspections specified in paragraph (h)(1) or (h)(2) of this AD, in accordance with the Accomplishment Instructions of Boeing Special attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. Repeat the inspections thereafter at the applicable times specified in paragraph 1.E., ''Compliance,'' of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, until a terminating action in paragraph (k)(1), (k)(2), or (k)(3) of this AD is done. \n\n\n\tAA commented that this change would align the proposed rule with paragraph 1.E., ''Compliance,'' table 1 and table 2, of Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. AA also stated that this would clearly indicate that the terminating action would preclude having to accomplish first the initial inspection requirement in paragraph (h) of the proposed AD. Boeing requested that we add a sentence to the end of paragraph (h) to specify that the inspections are not required for any affected inboard flap assembly where one of the terminating actions specified in paragraph (k)(1), (k)(2), or (k)(3) of the proposed AD have been done. \n\tWe agree with the commenters' request. We have revised paragraph (h) of this AD to clarify that the terminating actions may preclude the initial inspections because rework or replacement of the parts prevent the unsafe condition. \n\nRequest To Clarify the Applicability \n\n\n\tDelta Airlines (DAL) requested that we clarify whether paragraph (c) of the proposed AD is intended for all Model 777-200, -200LR, -300, and -300ER series airplanes, or all Model 777-200, -200LR, -300 and - 300ER series airplanes, identified as Groups 1, 2, and 4 airplanes in Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. \n\tDAL stated that paragraph (c) of the proposed AD does not contain Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014, to identify the airplane's applicability for the proposed AD. DAL commented that in the proposed rule under ''Differences Between This Proposed AD and the Service Information,'' the airplane's applicability is stated. DAL also stated that the same paragraph states that the proposedAD is applicable only to Groups 1, 2, and 4 airplanes (Model 777-200, -200LR, -300 and -300ER series airplanes) specified in Boeing Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. DAL commented that a review of the ''Compliance'' paragraph in the service information indicates that the FAA will possibly release an AD for airplanes in Groups 1, 2, and 4. \n\tWe agree with the commenter's request to clarify the applicability of this AD. This AD applies to all Model 777-200, -200LR, -300, and - 300ER series airplanes as specified in paragraph (c) of this AD. The description of Groups 1, 2, and 4 airplanes in section 1.A., ''Effectivity,'' of Boeing Special Attention Service Bulletin 777-57- 0094, Revision 1, dated November 5, 2014, specifies Model 777-200, - 200LR, -300, and -300ER series airplanes. Additionally, as noted in the service information, the table of variable numbers given in section 1.A., ''Effectivity,'' only reflects up to line number 1322, and affected airplanes after line number 1322 will be added to the profile page of MyBoeingFleet.com. Therefore, this AD applies to all Model 777- 200, -200LR, -300, and -300ER series airplanes. We have not changed this AD in this regard. \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\n((Page 21718)) \n\n\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 Boeing Special Attention Service Bulletin 777-57-0094, Revision 1, dated November 5, 2014. The service information describes procedures for an inspection for the affected part number and serial number of the main flap; various additional repetitive inspections of the fitting, if necessary; and replacement of the fitting or nested bushing installation, if necessary, which would terminate the inspections. The service information also describes an optional terminating action for the repetitive inspections. 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 148 airplanes of U.S. registry. \n\tWe estimate the following costs to comply with this AD: \n\n\n\tEstimated Costs ---------------------------------------------------------------------------------------------------------------- \n\tCost on U.S. \n\tAction Labor cost Parts cost Cost per product operators ---------------------------------------------------------------------------------------------------------------- Inspection to determine the part 3 work-hours x $85 $0 $255................ $37,740. \n\tnumber. per hour = $255. Additional Inspections........... Up to 7 0 Up to $595, per Up to $88,060, per \n\twork(dash)hours x cycle. cycle. \n\t$85 per hour = \n\t$595, per cycle. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tWe estimate the following costs to do any necessary replacements that will be required based on the results of the inspection. The nested bushing installation of the attach fitting and the fitting replacement are also optional terminating actions. We have no way of determining the number of aircraft on which these actions might be done. \n\n\n\tOn-Condition Costs ---------------------------------------------------------------------------------------------------------------- \n\tAction Labor cost Parts cost Cost per product ---------------------------------------------------------------------------------------------------------------- Nested bushing installation of the attach 40 work-hours x $85 per hour = $45 $3,445. \n\tfitting. $3,400. Fitting replacement........................... 73 work-hours x $85 per hour = 7,400 13,605. \n\t$6,205. ---------------------------------------------------------------------------------------------------------------- \n\n\n\tAccording to the manufacturer, all of the costs of this AD may be covered under warranty, thereby reducing the cost impact on affected individuals. We do not control warranty coverage for affected individuals. As a result, we have included all costs in our cost estimate. \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 AD will not have federalism implications under Executive Order 13132. This AD will not havea 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.