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Federal Register / Vol. 86, No. 37 / Friday, February 26, 2021 / Proposed Rules
11.35, the FAA will post all comments received, without change, to https
www.regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this proposed AD.

khammond on DSKJM1Z7X2PROD with PROPOSALS

Confidential Business Information CBI is commercial or financial information that is both customarily and actually treated as private by its owner.
Under the Freedom of Information Act FOIA 5 U.S.C. 552, CBI is exempt from public disclosure. If your comments responsive to this NPRM
contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI
as PROPIN. The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI
should be sent to Rebel Nichols, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 2200
South 216th St., Des Moines, WA 98198;
phone and fax: 2062313556; email:
rebel.nichols@faa.gov. Any commentary that the FAA receives which is not specifically designated as CBI will be placed in the public docket for this rulemaking.
Background The FAA has examined the underlying safety issues involved in fuel tank explosions on several large transport airplanes, including the adequacy of existing regulations, the service history of airplanes subject to those regulations, and existing maintenance practices for fuel tank systems. As a result of those findings, the FAA issued a final rule titled Transport Airplane Fuel Tank System Design Review, Flammability Reduction and Maintenance and Inspection Requirements 66 FR 23086, May 7, 2001. In addition to new airworthiness standards for transport airplanes and new maintenance requirements that rule included Amendment 2178, which established Special Federal Aviation Regulation No. 88 SFAR 88 at 14 CFR
part 21. Subsequently, SFAR 88 was amended by Amendment 2182 67 FR
57490, September 10, 2002; corrected at 67 FR 70809, November 26, 2002, Amendment 2183 67 FR 72830, December 9, 2002; corrected at 68 FR
37735, June 25, 2003, to change 2182

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to 2183, and Amendment 21101
83 FR 9162, March 5, 2018.
Among other actions, SFAR 88
requires certain type design i.e., type certificate TC and supplemental type certificate STC holders to substantiate that their fuel tank systems can prevent ignition sources in the fuel tanks. This requirement applies to type design holders for large turbine-powered transport airplanes and for subsequent modifications to those airplanes. It requires them to perform design reviews and to develop design changes and maintenance procedures if their designs do not meet the new fuel tank safety standards. As explained in the preamble to the final rule published on May 7, 2001, the FAA intended to adopt airworthiness directives to mandate any changes found necessary to address unsafe conditions identified as a result of these reviews.
In evaluating these design reviews, the FAA has established four criteria intended to define the unsafe conditions associated with fuel tank systems that require corrective actions. The percentage of operating time during which fuel tanks are exposed to flammable conditions is one of these criteria. The other three criteria address the failure types under evaluation:
Single failures, single failures in combination with another latent conditions, and in-service failure experience. For all four criteria, the evaluations included consideration of previous actions taken that may mitigate the need for further action.
This proposed AD was prompted by significant changes made to the AWL
related to fuel tank ignition prevention and the nitrogen generation system.
This condition, if not addressed, could result in the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, or maintenance actions, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.
The FAA has determined that accomplishing the revision required by paragraph g of this proposed AD
would terminate the following requirements for that airplane:
The revision required by paragraphs g and h of AD 20081101 R1, Amendment 3916145 74 FR 68515, December 28, 2009.
The revision required by paragraph h of AD 20100610, Amendment 39
16234 75 FR 15322, March 29, 2010
AD 20100610.
The revision required by paragraph k of AD 20112505, Amendment 39

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16881 77 FR 2442, January 18, 2012
AD 20112505.
The revision required by paragraph n of AD 20132502, Amendment 39
17698 79 FR 24541, May 1, 2014 AD
20132502.
The revision required by paragraph g of AD 20140809, Amendment 39
17833 79 FR 24546, May 1, 2014 AD
20140809.
The revision required by paragraph h of AD 20142002, Amendment 39
17975 79 FR 59102, October 1, 2014
AD 20142002.
The revision required by paragraphs i3i and ii of AD 20182013, Amendment 3919447 83 FR 52305, October 17, 2018 AD 20182013.
Related Service Information Under 1
CFR Part 51
The FAA reviewed Boeing 767200/
300/300F/400ER Special Compliance Items/Airworthiness Limitations, D622T001904, dated January 2020.
This service information describes AWLs that include airworthiness limitation instructions ALIs and critical design configuration control limitations CDCCLs tasks related to fuel tank ignition prevention and the nitrogen generation system. 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.
FAAs Determination The FAA is proposing this AD
because the agency evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.
Proposed AD Requirements This proposed AD would require revising the existing maintenance or inspection program, as applicable, to incorporate the latest revision of the AWLs.
This proposed AD would require revisions to certain operator maintenance documents to include new actions e.g., inspections and CDCCLs.
Compliance with these actions and CDCCLs is required by 14 CFR
91.403c. For airplanes that have been previously modified, altered, or repaired in the areas addressed by this proposed AD, the operator may not be able to accomplish the actions described in the revisions. In this situation, to comply with 14 CFR 91.403c, the operator must request approval for an alternative method of compliance according to paragraph k of this proposed AD.

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