Document ID: FAA-2014-1027-0017
Agency: faa
Document Type: Rule
Title: Transport Airplane Fuel Tank and System Lightning Protection
Posted Date: 2018-09-20T04:00Z

[Federal Register Volume 83, Number 183 (Thursday, September 20, 2018)]
[Rules and Regulations]
[Pages 47548-47557]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-20174]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No.: FAA-2014-1027; Amdt. No. 25-146]
RIN 2120-AK24

Transport Airplane Fuel Tank and System Lightning Protection

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is amending certain airworthiness regulations for 
transport category airplanes regarding lightning protection of fuel 
systems. This action is relieving in several ways. It removes the 
requirement for manufacturers to provide triple-redundant fault 
tolerance in lightning protection. It removes regulatory inconsistency 
by establishing a single standard for lightning protection of both fuel 
tank structure and fuel tank systems. It establishes a performance-
based standard that the design and installation of fuel systems prevent 
catastrophic fuel vapor ignition caused by lightning and its effects. 
This performance-based standard allows applicants to choose how to 
provide the required level of safety. This action requires 
airworthiness limitations to preclude the degradation of design 
features that prevent catastrophic fuel vapor ignition caused by 
lightning. Its intended effects are to align airworthiness standards 
with industry's and the FAA's understanding of lightning, and to 
address issues of inconsistency and impracticality that applicants 
experienced with previous lightning protection regulations.

DATES: Effective November 19, 2018.

ADDRESSES: For information on where to obtain copies of rulemaking 
documents and other information related to this final rule, see ``How 
To Obtain Additional Information'' in the SUPPLEMENTARY INFORMATION 
section of this document.

FOR FURTHER INFORMATION CONTACT: For questions concerning this action, 
contact Stephen Slotte, Airplane and Flight Crew Interface Section, 
AIR-671, Transport Standards Branch, Policy and Innovation Division, 
Aircraft Certification Service, Federal Aviation Administration, 2200 
South 216th Street, Des Moines, WA 98198; telephone and fax (206) 231-
3163; email [email protected].

SUPPLEMENTARY INFORMATION: 

Authority for This Rulemaking

    The FAA's authority to issue rules on aviation safety is found in 
Title 49 of the United States Code. 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.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
Requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing 
regulations and minimum standards for the design and performance of 
aircraft that the Administrator finds necessary for safety in air 
commerce. This regulation is within the scope of that authority. It 
prescribes revised safety standards for the design and operation of 
transport category airplanes.

I. Overview of Final Rule

    The FAA is amending the airworthiness regulations in title 14, Code 
of Federal Regulations (14 CFR) part 25 related to the lightning 
protection of fuel systems \1\ (including fuel tank structure \2\ and 
fuel tank systems \3\). This amendment removes the requirement for 
prevention of lightning ignition sources from Sec.  25.981(a)(3), 
``Fuel tank ignition prevention,'' at amendment 25-102 and modifies 
Sec.  25.954, ``Fuel system lightning protection.'' The modification to 
Sec.  25.954 creates a performance-based standard that provides 
definitions for ``critical lightning strike'' and ``fuel systems;'' 
requires catastrophic fuel vapor ignition due to lightning and its 
effects to be extremely improbable; and requires applicants to add 
airworthiness limitations to the airplane's Instructions for Continued 
Airworthiness (ICA) to prevent catastrophic fuel vapor ignition caused 
by lightning. These changes align the rule with the current 
understanding of lightning-related risk, fuel tank flammability 
exposure, and current airplane design practices. It also revises the 
title of Sec.  25.981 to ``Fuel tank explosion prevention.''
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    \1\ Fuel system, in the context of this final rule, includes any 
component within either the fuel tank structure or the fuel tank 
systems and any airplane structure or system components that 
penetrate, connect to, or are located within a fuel tank.
    \2\ Fuel tank structure, in the context of this final rule, 
includes structural members of the fuel tank such as airplane skins, 
access panels, joints, ribs, spars, stringers, and associated 
fasteners, brackets, coatings, and sealant.
    \3\ Fuel tank systems, or systems, in the context of this final 
rule, include tubing, components, and wiring that penetrate, connect 
to, or are located within a fuel tank.
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    This amendment removes lightning from the ignition sources 
regulated by Sec.  25.981(a)(3). Inclusion of lightning in that section 
has resulted in applicants showing that compliance was impractical, 
leading them to seek exemptions to compliance with Sec.  25.981 for 
fuel tank structure and systems. The FAA has granted several exemptions 
for fuel tank structure and systems. The FAA agrees, however, with the 
Large Airplane Fuel System Lightning Protection Aviation Rulemaking 
Committee (Lightning ARC) \4\ that common regulatory treatment of 
structure- and systems-related lightning protection in the fuel system 
is appropriate. Applicants have also requested that the FAA develop 
special conditions to allow the consideration of fuel tank flammability 
and the probability of lightning strikes when meeting the requirement 
that a fuel tank explosion caused by lightning be extremely improbable. 
This amendment removes the necessity for such special conditions by 
incorporating such considerations into the rule.
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    \4\ See the ``Large Airplane Fuel System Lightning Protection 
Rulemaking Recommendations'' report, May 2011, available in the 
docket.
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    To maintain the integrity of lightning protection features of 
airplanes, this amendment adds a new paragraph (d) to Sec.  25.954 and 
amends part 25, appendix H, section H25.4(a) to require applicants to 
establish airworthiness limitations to protect the continued function 
of the lightning protection features of fuel tank structure and fuel 
systems.
    This rule applies to applications for new type certificates, and 
applications for amended or supplemental type certificates on 
significant product-level change projects in which Sec.  25.954, ``Fuel 
system lightning protection,'' is applicable to the changed area.

II. Background

A. Statement of the Problem

    Section 25.954, adopted in 1967, required protection of the 
airplane from the effects of lightning, regardless of the likelihood 
that lightning would strike the airplane. The regulation did not 
acknowledge that lightning protection

[[Page 47549]]

features, or other features, could fail or become ineffective. The 
regulation also did not require evaluation of probabilities of failures 
affecting lightning protection features, nor did it require maintenance 
actions to ensure the continued effectiveness of design features that 
prevent catastrophic fuel vapor ignition.
    Compliance with Sec.  25.981(a)(3), at amendment 25-102,\5\ 
required the assumption that lightning would strike the airplane (i.e., 
that the probability of lightning was one) and that the design provide 
fail-safe ignition prevention means to preclude ignition sources from 
being present in fuel tanks when component failures, malfunctions, or 
lightning strikes occur. This typically resulted in the need for 
triple-redundant lightning ignition protection features because some 
structural failures may have long latency periods.\6\ The FAA found, 
however, that for lightning protection, providing triple-redundant 
features is not always practical. This impracticality has led 
applicants to apply for exemptions and special conditions to ensure the 
design and maintenance actions provide for, and maintain, an acceptable 
level of safety. However, the processing and issuance of these 
exemptions and special conditions has created an administrative burden 
on industry and the FAA.
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    \5\ See 66 FR 23086 (May 7, 2001), ``Transport Airplane Fuel 
Tank System Design Review, Flammability Reduction, and Maintenance 
and Inspection Requirements.''
    \6\ In this context, latency period means the time interval 
between a failure and the discovery of that failure.
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B. Related Actions

    On May 26, 2009, the FAA issued a policy memorandum to standardize 
the process for granting exemptions and issuing special conditions for 
fuel tank structure lightning protection. FAA Policy Memorandum ANM-
112-08-002, ``Policy on Issuance of Special Conditions and Exemptions 
Related to Lightning Protection of Fuel Tank Structure,'' defined 
alternative methods that could be applied through special conditions or 
exemptions to some areas of structural designs where compliance with 
Sec.  25.981(a)(3) was impractical. This policy allowed the applicant's 
risk assessment to account for the reduced likelihood of the 
simultaneous occurrence of a critical lightning strike and a fuel tank 
being flammable. The policy explained the level of safety intended by 
Sec.  25.981(a)(3) for fuel tank structure, and provided guidance for 
alternatives to compliance that still achieve that level of safety.
    On June 24, 2014, the FAA superseded that policy memorandum with 
Policy Statement PS-ANM-25.981-02, ``Policy on Issuance of Special 
Conditions and Exemptions Related to Lightning Protection of Fuel Tank 
Structure and Systems,'' expanding the scope of the policy to include 
systems. The policy statement provided guidance for approval of special 
conditions and exemptions for lightning protection features in fuel 
tank structure and fuel systems with respect to Sec.  25.981(a)(3).
    The revisions to Sec.  25.981(a)(3) in this amendment should 
eliminate the need to issue such special conditions and exemptions. 
However, some of the information in that policy statement will remain 
in Advisory Circular (AC) 25.981-1D, ``Fuel Tank Ignition Source 
Prevention Guidelines,'' \7\ for this rule because the FAA expects that 
the information will continue to be useful in ensuring the level of 
safety required by the amended Sec.  25.954 for fuel tank structure and 
systems.
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    \7\ AC 25.981-1D is available in the docket and on the internet 
at http://www.faa.gov/regulations_policies/advisory_circulars/.
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    The final rule will maintain the level of safety established by 
these policies. It codifies these policies into a performance-based 
rule that allows the applicant to choose the means of compliance.

C. Summary of the NPRM

    On December 9, 2014, the FAA issued a notice of proposed rulemaking 
(NPRM) to amend Sec. Sec.  25.954 and 25.981 and appendix H to part 25. 
The Federal Register published NPRM Notice No. 14-09, Docket No. FAA-
2014-1027, on December 18, 2014. In the NPRM, the FAA proposed the 
following changes:
1. ``Fuel System Lightning Protection,'' (Sec.  25.954)
     Consolidate the requirements for the prevention of fuel 
vapor ignition due to lightning, currently in Sec. Sec.  25.954 and 
25.981, into Sec.  25.954;
     Retain and renumber the existing rule text;
     Add lightning-induced or conducted electrical transients 
\8\ to the lightning effects that applicants must consider;
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    \8\ As used in this discussion, a transient is a brief 
electrical disturbance on wiring and equipment caused by the intense 
voltage, current, and electromagnetic fields associate with 
lightning.
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     Add a new performance-based standard to require that a 
catastrophic fuel tank explosion be extremely improbable when taking 
into account the risk of failures, probability of a critical lightning 
strike, and fuel tank flammability exposure;
     Add maintenance requirements to maintain the integrity of 
lightning protection features during the airplane service life; and
     Define critical lightning strike and fuel system.
2. ``Fuel Tank Ignition Prevention,'' (Sec.  25.981)
     Remove the requirement to prevent lightning ignition 
sources and instead refer applicants to Sec.  25.954 for lightning 
protection requirements;
     Clarify that the applicant must provide critical design 
control configuration limitations (CDCCLs) to identify critical design 
features in addition to inspections or other procedures; and
     Change the title to ``Fuel tank explosion prevention.''
3. ``Instructions for Continued Airworthiness,'' Appendix H to Part 25
     Add a new paragraph to make mandatory any inspection and 
test procedures that are needed to sustain the integrity of the 
lightning protection design features used to show compliance with Sec.  
25.954; and
     Add a new section to require applicants to develop ICA 
that protect the lightning protection features required by Sec.  
25.954.
    The FAA proposed these changes based on recommendations from the 
Lightning ARC. The comment period closed on March 18, 2015.

III. Discussion of the Final Rule and Public Comments

    The FAA received comments from eight (8) manufacturers and one (1) 
industry group. All of the commenters generally supported the proposed 
amendments. Some of the comments suggested changes.
    In the discussion below, some comments identify paragraph 
designations of the rules as proposed in the NPRM. In this final rule, 
the FAA is revising and reorganizing some of those paragraphs, so 
paragraph references in the comments may be different from their 
designation in the final rule. This section references each paragraph 
according to its designation in this final rule, with the NPRM 
paragraph designation noted in brackets when there has been a change.

A. ``Fuel System Lightning Protection'' (Sec.  25.954)

    With some differences from what the FAA proposed in the NPRM, this 
amendment requires that the design and installation of the airplane 
fuel system

[[Page 47550]]

prevent catastrophic fuel vapor ignition due to lightning and its 
effects. This final rule removes ``corona and streamering at fuel vent 
outlets'' as a lightning effect that applicants must consider, and adds 
``lightning-induced or conducted electrical transients'' to the non-
exclusive list of lightning effects against which the fuel system must 
be protected. This amendment adds definitions for ``critical lightning 
strike'' and ``fuel system'' to ensure common understanding and 
consistent application of those terms.
    To comply with the revised Sec.  25.954, this amendment requires 
applicants to show that catastrophic fuel vapor ignition is extremely 
improbable, taking into account flammability, critical lightning 
strikes, and failures within the fuel system.
    To protect those features of the airplane that prevent catastrophic 
fuel vapor ignition due to lightning, this amendment adds a requirement 
that the type design include CDCCLs identifying those features and 
providing information to protect them. To ensure the continued 
effectiveness of those features, the rule requires that the type design 
specify necessary inspections and test procedures, intervals between 
repetitive inspections and tests, and mandatory replacement times. The 
rule also requires the applicant to include information regarding 
CDCCLs and methods for ensuring continued effectiveness of lightning 
protection features in the Airworthiness Limitations section (ALS) of 
the ICA.
    The following is a discussion of comments the FAA received on the 
changes to Sec.  25.954 as they were proposed in the NPRM.
1. Definitions
    The NPRM proposed adding definitions of ``critical lightning 
strike'' and ``fuel system'' to Sec.  25.954(d). This final rule 
revises these definitions and moves them to paragraph (a) of the 
section.
    The AE-2 and WG-31 Lightning Committees (SAE Lightning Group) 
supported the proposed definition of ``fuel system.'' However, the FAA 
determined that the inclusion of the word ``other'' in the definition, 
``A fuel system includes any component within either the fuel tank 
structure or the fuel tank systems, and any other airplane structure or 
system components that penetrate, connect to, or are located within a 
fuel tank,'' could be misinterpreted to exclude basic structure, such 
as wings, in the context of the definition. Therefore, the definition 
of fuel system in the final rule does not include ``other.''
    The proposed definition of a ``critical lightning strike'' was ``. 
. . a lightning strike that attaches to the airplane in a location that 
affects a failed feature or a structural failure, and the amplitude of 
the strike is sufficient to create an ignition source when combined 
with that failure.'' The SAE Lightning Group requested changes to this 
definition for clarity. The commenter requested that the term ``failed 
feature'' be changed to ``failed protection feature,'' but did not 
provide a rationale. The commenter also stated that it is unnecessary 
to list structural failures separately. The commenter further stated 
that the inclusion of ``a failed [protection] feature'' already 
includes structural failures, which otherwise could result in an 
ignition source. The commenter also suggested revising the definition 
to, ``A critical lightning strike is a lightning strike that attaches 
to the airplane in a location that affects a failed protection feature 
with characteristics that could create an ignition source when combined 
with that failure.''
    The FAA partially agrees with the SAE Lightning Group's requests. 
The FAA modified the definition of critical lightning strike by 
deleting ``the amplitude of the strike is sufficient,'' but did not 
replace that text with ``characteristics that could,'' as the commenter 
recommended. The definition is clear without either of those phrases. 
The FAA also did not replace ``failed feature'' with ``failed 
protection feature,'' or delete the phrase ``structural failure.'' To 
address the comments, we have revised the definition by removing the 
phrase ``failed feature'' and stating instead that, ``A critical 
lightning strike is a lightning strike that attaches to the airplane in 
a location that, when combined with the failure of any design feature 
or structure, could create an ignition source.''
    In this revised definition, a ``design feature'' means any feature 
specifically designed for lightning protection or any other design 
feature whose failure, when combined with a lightning strike, could 
cause ignition. An example of a design feature that is specifically 
designed for lightning protection is a metal foil layer installed 
between the laminate layers of a composite wing. An example of a design 
feature that is not specifically designed for lightning protection but 
whose failure, when combined with a lightning strike, could cause 
ignition is a swaged fitting on a hydraulic tube located within the 
fuel tank. Structural failures that could create an ignition source in 
the event of a lightning strike must also be addressed and, therefore, 
the final definition includes ``any design feature or structure.''
    Related to the definition of critical lightning strike, the NPRM 
stated that a critical lightning strike occurs ``on the order of once 
every 100,000 hours of airplane operation.'' The SAE Lightning Group 
commented that the location of the lightning's attachment to the 
airplane, whether the strike's amplitude is sufficient to create an 
ignition source, and the effect of a failed feature or structural 
failure are all design-dependent. The SAE Lightning Group also 
commented that compliance with Sec.  25.954 would require use of a 
strike rate of 1 in 100,000 hours. The commenter suggested that the FAA 
should allow applicants to identify how often a critical lightning 
strike might occur relative to their designs.
    The intent of the statement in the NPRM that a critical lightning 
strike occurs once per 100,000 hours was to provide a general 
understanding of their average rate of occurrence. It was not intended 
as a rate to be used in demonstrating compliance. The FAA agrees with 
the SAE Lightning Group that the actual rate of a critical strike would 
be based on an applicant's analysis of the specific airplane design 
features, which include additional factors such as location of the 
strike, characteristics of the lightning strike, failure of design 
features and structure, and specific ignition source thresholds for 
each feature failure and failure mode.
    Related to this same discussion in the NPRM, Parker Aerospace 
(``Parker'') requested that the FAA add a paragraph to Sec.  25.954 
that describes all of the conditions and guidance regarding 
probabilities that the applicant must consider, such as flammability 
exposure and failure latency of inerting systems. The FAA disagrees 
with Parker's request. Rather than make such conditions and guidance on 
probabilities mandatory via a new paragraph in Sec.  25.954, such 
guidance is included in AC 25.954-1, ``Transport Airplane Fuel System 
Lightning Protection.'' \9\ The AC discusses the probability for 
different airplane composite tank structures and threat levels.
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    \9\ AC 25.954-1 is available in the docket and on the internet 
at http://www.faa.gov/regulations_policies/advisory_circulars/.
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2. Relationship of Sec.  25.954 to Sec. Sec.  25.901 and 25.1309
    The SAE Lightning Group suggested that the FAA clearly state that 
the revised Sec.  25.954 takes precedence over the general requirements 
of Sec. Sec.  25.901,

[[Page 47551]]

``Installation'' (``Subpart E--Powerplant''), and 25.1309, ``Equipment, 
systems, and installations.'' The FAA disagrees. Section 25.954 does 
not supersede the requirements of Sec.  25.901 or Sec.  25.1309. 
However, compliance with Sec.  25.954 may assist applicants in showing 
compliance with other regulations.
3. Lightning Effects
    The NPRM proposed adding ``lightning-induced or conducted 
electrical transients'' to the lightning effects in Sec.  25.954(b) 
[paragraph (a) in the NPRM] that applicants must ensure will not cause 
ignition of fuel vapor within the fuel system. The SAE Lightning Group 
recommended that, rather than adding to the existing list of lightning 
threats in the rule, the FAA delete the list of lightning effects. 
Instead, the SAE Lightning Group recommended that the rule include a 
more general and inclusive reference to lightning that requires that 
the airplane be protected against catastrophic effects from lightning. 
The SAE Lightning Group suggested that the list may not be complete and 
may be inconsistent with lightning environments defined in the industry 
documents accepted by the FAA in AC 20-155A, ``Industry Documents to 
Support Aircraft Lightning Protection Certification.'' In contrast, 
Parker supported keeping the text as proposed, including ``lightning-
induced or conducted electrical transients.''
    The FAA disagrees with the SAE Lightning Group's suggestion to 
include only a general lightning requirement. Relying on guidance 
material to detail the lightning effects that applicants must consider 
could result in some applicants not addressing all effects. However, 
the FAA recognizes that the list of effects, as proposed, could be 
misinterpreted as an exhaustive list. Therefore, the FAA added 
``including'' to the text that introduces the list to clarify that the 
list is not exhaustive. The FAA agrees to limit, in Sec.  25.954(b), 
the type of fuel vapor ignition that must be prevented to 
``catastrophic'' events. This change will make the requirement 
consistent with Policy Statement PS-ANM-25.981-02, which states that 
``the fuel tank structure and systems must be designed and installed to 
prevent catastrophic fuel vapor ignition due to lightning.'' This 
change also makes Sec.  25.954(b) consistent with Sec.  25.581, which 
requires that the airplane be protected against ``catastrophic'' 
effects from lightning. Thus, Sec.  25.954(b) now states, ``The design 
and installation of a fuel system must prevent catastrophic fuel vapor 
ignition due to lightning and its effects, including . . . .''
    The SAE Lightning Group recommended the removal of ``corona and 
streamering at fuel vent outlets'' from the list of lightning effects 
because that term is inconsistent with the terminology in the industry 
guidance material recommended by AC 20-155A. The FAA agrees and has 
removed this term from the final rule.
4. Fault-Tolerant Design
    Regarding Sec.  25.954(c) [paragraph (b) in the NPRM], the SAE 
Lightning Group requested that the FAA require that catastrophic fuel 
vapor ignition due to lightning be prevented by demonstrating that the 
fuel system ignition source protection design is fault tolerant, or for 
designs that are not fault tolerant, by showing catastrophic fuel vapor 
ignition to be extremely improbable, taking into account flammability, 
critical lightning strikes, and failures in the fuel system. The SAE 
Lightning Group argued that the proposed broader requirement to show 
that catastrophic ignition is extremely improbable, without requiring a 
fault tolerant design, would be costly and would negate the savings to 
industry stated in the regulatory evaluation. In a related comment, 
Bombardier S.A. (Bombardier) requested that ``fault tolerant'' be 
defined to clarify if it is equivalent to single fault tolerance and 
the type of compliance that the FAA would expect, numerical analysis or 
qualitative. Although the term was not used in the proposed rule (and 
is not in the final rule), Bombardier suggested more clarity was needed 
in the rule and supporting guidance.
    The FAA agrees that fuel systems designed with reliable fault-
tolerant ignition source protection features should comply with the 
requirement that catastrophic fuel vapor ignition be extremely 
improbable. As used in this context, a fault-tolerant fuel system 
design is a design that precludes ignition sources in the fuel system 
even when a fault is present; ``reliable'' means the ability to 
maintain the effectiveness of the protection features over the service 
life of the individual airplane.
    However, the FAA disagrees that fault tolerance should be required 
because fault tolerance is only one possible means of compliance with 
the requirement that catastrophic fuel vapor ignition be extremely 
improbable. The use of a full-time flammability control system (e.g., 
fuel system inerting) exceeding the current part 25 flammability 
reduction means (FRM) performance standard could be another means of 
compliance. If the FAA limited the requirement to fault tolerance as 
requested by the SAE Lightning Group, such a design approach, or others 
as technology progresses, would not be allowed.
    Regardless of the design approach chosen by the applicant to 
prevent lightning-induced catastrophic fuel vapor ignition, a safety 
analysis will be necessary to demonstrate extreme improbability. The 
complexity of the analysis can range from a relatively simple 
assessment to establish any maintenance requirements for reliable 
fault-tolerant ignition protection features, to a more in-depth 
analysis if non-fault-tolerant design features are used. For reliable 
fault-tolerant features, this analysis would be substantially less 
costly than traditional methods for showing that catastrophic failures 
are extremely improbable. The supporting AC 25.954-1 provides guidance 
on methods for both fault-tolerant and FRM compliance approaches, 
including the necessary safety assessment, which could be numerical, 
qualitative, or a combination of the two.
    The FAA disagrees with Bombardier's request to define fault-
tolerant in Sec.  25.954. Since a fault-tolerant design is not a 
requirement for compliance with this rule, there is no need to provide 
a regulatory definition. However, the supporting AC 25.954-1 includes 
the definition for fault-tolerant design noted earlier in this section 
(4. Fault-Tolerant Design), ``A fault-tolerant fuel system design is a 
design that precludes ignition sources in the fuel system even when a 
fault is present.''
    Therefore, this amendment retains the requirement in Sec.  
25.954(c) that catastrophic fuel vapor ignition be extremely 
improbable, and clarifies its relationship with paragraph (b). The 
revised Sec.  25.954(c) states, ``To comply with paragraph (b) of this 
section, catastrophic fuel vapor ignition must be extremely improbable, 
taking into account flammability, critical lightning strikes, and 
failures within the fuel system.''
    The SAE Lightning Group also commented that the FAA should revise 
the regulatory evaluation if the FAA does not adopt the SAE Lightning 
Group's recommendation to replace the requirement of extreme 
improbability with fault tolerance. The commenter argued that the 
requirement to show that fuel tank ignition is extremely improbable 
would be costly and negate the savings to industry shown in the 
regulatory evaluation. The SAE Lightning Group did not submit any 
supporting financial data.
    The FAA does not agree that the requirement to show that fuel tank

[[Page 47552]]

ignition is extremely improbable would be costly and negate the savings 
to industry. In general, an applicant that can show its design is 
reliably fault-tolerant will not need to conduct an extensive safety 
analysis. The requirement to develop airworthiness limitations for 
critical lightning protection features will result in the need for the 
applicant to assess the reliability of the features and provide 
appropriate maintenance tasks to achieve an acceptable level of 
reliability.
    In addition, this rule allows both fault-tolerant and non-fault-
tolerant design approaches. Under the rule, the fuel system must 
prevent catastrophic fuel vapor ignition due to lightning. To comply 
with this requirement, catastrophic fuel vapor ignition must be 
extremely improbable. If an applicant's design achieves this 
requirement through the use of fault-tolerant design, the safety 
analysis (Sec.  25.1309) to support the design will not have to be as 
extensive as one that would be necessary to support a non-fault-
tolerant design. As a result, the rule allows industry the flexibility 
to select the means of compliance based on design approach, safety 
analysis, and costs. Therefore, the FAA determined that the regulatory 
evaluation did not need to be revised as a result of this comment.
5. Flammability Reduction Means (FRM) as a Means of Compliance
    The SAE Lightning Group, Bombardier, and Parker all commented on 
the discussion of fuel tank flammability reduction in the NPRM and 
asked for clarification of how flammability reduction could be used as 
a means of compliance with Sec.  25.954.
    Boeing stated that the majority of the NPRM discussion of fuel tank 
FRM was unnecessary because applicants could infer that the FAA would 
relax the requirement for providing fault tolerance if the FAA allowed 
FRM as a sole means of compliance. Boeing did not agree that the FAA 
should accept controlling fuel tank flammability as the primary means 
for preventing a fuel tank explosion without providing fault-tolerant 
lightning protection features.
    As discussed in the previous section (4. Fault-Tolerant Design), 
the FAA does not agree that the lightning protection requirement in 
Sec.  25.954 should dictate the use of fault-tolerant ignition 
protection features in the design without allowing the use of 
flammability control means. As explained in the NPRM, the intent of the 
amendment to Sec.  25.954 is to require the design to take into account 
the likelihood of a critical lightning strike, the fuel tank being 
flammable, and the creation of an ignition source due to the failure of 
fuel system or structural lightning protection features. If designers 
develop a full-time fuel tank flammability control system that prevents 
the fuel tanks from being flammable during all foreseeable operating 
conditions and all phases of airplane operation (including descent), 
resulting in the probability of a fuel tank explosion being extremely 
improbable, this could achieve the level of safety that Sec.  25.954 
requires, and could be used as a means of compliance without the need 
for fault-tolerant lightning protection features. While fuel tank 
flammability control system technology has not evolved to a state where 
flammability control can replace the need for fault-tolerant ignition 
prevention, the FAA's goal is to develop rules that are performance-
based, and in this case, to allow designers to comply via the use of 
flammability control when the technology is adequately developed. 
Allowing the use of fuel tank FRM for demonstrating compliance with the 
rule could offer designers the opportunity to reduce the number of 
fault-tolerant features and mandatory maintenance actions.
6. CDCCLs
    Section 25.954(d) [paragraph (c) in the NPRM] requires that the 
type design include CDCCLs identifying those design features that 
prevent catastrophic fuel vapor ignition caused by lightning and 
providing information to protect them. To ensure the continued 
effectiveness of those features, paragraph (d) also requires that the 
type design include inspections and test procedures, intervals between 
repetitive inspections and tests, and mandatory replacement times. This 
paragraph also requires applicants to place all this information in the 
ALS of the ICA.
    The SAE Lightning Group proposed that CDCCLs be included as 
cautions \10\ in the airplane maintenance manual, not as airworthiness 
limitations in the ALS of the ICA. The SAE Lightning Group suggested 
that, as proposed, the requirement would create a burden on the 
airlines because the ALS documents are not used by the airline 
mechanics, and therefore the CDCCL information must be duplicated and 
links created for the information in both the ALS documents and the 
maintenance documents used by the mechanics. The commenter stated that 
if the FAA does not agree with this approach, then only critical 
information necessary to demonstrate compliance, along with CDCCLs, 
should be included as airworthiness limitations, and proposed that the 
regulatory text be amended to reflect this request. The SAE Lightning 
Group did not define what it considered critical information.
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    \10\ Cautions in an airplane maintenance manual call attention 
to methods and procedures that must be followed to avoid damage to 
equipment (ATA iSpec 2200, Information Standards for Aviation 
Maintenance, published by Airlines for America, 2014).
---------------------------------------------------------------------------

    The FAA disagrees with the SAE Lightning Group's request to move 
the CDCCLs from the ALS of the ICA to the Cautions section of the 
maintenance manual. CDCCLs provide information that is essential for 
protecting the design features that are critical for preventing fuel 
tank explosions. The Caution section of the maintenance manual is not 
mandatory for U.S. operators, and therefore CDCCLs need to be included 
in the ALS of the ICA, which is mandatory.
    The SAE Lightning Group commented that, since the Lightning ARC 
study and report in 2011, the use of Air Transport Association (ATA) 
Maintenance Steering Group (MSG)-3 \11\ processes has not been 
effective in establishing maintenance requirements for lightning 
protection features and does not take into consideration the many 
factors that are critical for certification. This can create 
conflicting or duplicate fuel tank entry requirements. To eliminate 
this potential duplication, the SAE Lightning Group stated that 
industry now recommends that maintenance practices for both fault-
tolerant and non-fault-tolerant protection features be established via 
the type certification process only, and that the ATA MSG-3 process 
should not be used for this purpose.
---------------------------------------------------------------------------

    \11\ ATA MSG-3 is a maintenance steering group composed of 
regulatory authorities, operators, and manufacturers that, through a 
process, develop documents that present a methodology for developing 
scheduled maintenance tasks and intervals for aircraft structure, 
systems, and components.
---------------------------------------------------------------------------

    Airbus and Airlines for America disagreed with the request to 
establish maintenance practices for both fault-tolerant and non-fault-
tolerant protection features via the type certification process. Both 
commenters proposed that the FAA require airworthiness limitations and 
CDCCLs for only non-fault-tolerant design features. Both commenters 
stated that an airworthiness limitation requirement for fault-tolerant 
design features could be a disincentive to develop fault-tolerant 
designs and may increase the burden on operators unnecessarily. As an 
alternative, they proposed reliance on the current ATA MSG-3 process 
for establishing maintenance programs for

[[Page 47553]]

fault-tolerant design features. Airbus also suggested that operational 
rules and guidance could be established to prevent tasks identified 
through the ATA MSG-3 process from being deleted in service.
    The FAA agrees with the SAE Lightning Group that all maintenance 
practices for both fault-tolerant and non-fault-tolerant protection 
features be established via the type certification process and not 
through the ATA MSG-3 process. Using the certification process will 
ensure that applicants develop necessary maintenance actions to 
maintain the integrity of lightning ignition source protection 
features. As all maintenance actions necessary to ensure the integrity 
of lightning ignition source protection features will be addressed by 
compliance with section H25.4(a)(5), the ICA requirement in the 
proposed section H25.X is not necessary and has been deleted from the 
final rule. This is discussed further in the discussion regarding 
appendix H.
    The FAA disagrees with Airbus' and Airlines for America's proposal 
to rely on the ATA MSG-3 process for development of maintenance actions 
for fault-tolerant design features. U.S. operators are not required to 
adopt the ATA MSG-3 developed maintenance program, but they are 
required to include all airworthiness limitations in their maintenance 
program.\12\ Therefore, airworthiness limitations are needed to ensure 
an operator's maintenance program includes all tasks determined by the 
safety analysis, performed as part of the system's certification 
activity, to be critical. The safety analysis may show that some fault-
tolerant features are life-limited or require periodic inspection, so 
mandatory maintenance tasks established through engineering review and 
approval would be needed. Therefore, the FAA did not change this rule 
as a result of these comments.
---------------------------------------------------------------------------

    \12\ Section H25.4(a) and 14 CFR 91.403(c).
---------------------------------------------------------------------------

    The SAE Lightning Group also stated that the reference to Sec.  
25.1729 in Sec.  25.954(d) is not within the scope of this rule and 
requested that it be removed. The FAA agrees and removed that reference 
from the final rule.
    Embraer suggested that Sec.  25.954(d) include the same requirement 
that is in Sec.  25.981(d). Section 25.981(d) requires the type design 
to include visible means for identifying critical features in areas 
where foreseeable maintenance actions, repairs, or alterations may 
compromise the CDCCLs. Embraer stated that this would harmonize both 
requirements.
    The FAA does not agree. Because of the large number and multiple 
types of bonding features used for fuel tank and system lightning 
protection, it is not practical to require installation of visible 
means of identification for all lightning-related CDCCLs. However, all 
critical lightning protection features identified as CDCCLs must be 
included in the ALS of the ICA. Although the FAA made minor editorial 
changes \13\ to the final Sec.  25.954(d), the requirement that the 
type design include CDCCLs is adopted as proposed.
---------------------------------------------------------------------------

    \13\ The FAA deleted ``on how'' in the first sentence of the 
paragraph, ``. . . (CDCCLs) identifying those features and providing 
information on how to protect them,'' and added ``used in 
demonstrating compliance to paragraph (b) of this section'' in the 
second sentence, ``. . . and mandatory replacement times for those 
design features used in demonstrating compliance to paragraph (b) of 
this section.''
---------------------------------------------------------------------------

B. ``Fuel Tank Explosion Protection'' (Sec.  25.981)

    Section 25.981 requires that the airplane design protect the fuel 
tank and fuel tank system against ignition from all sources. This 
amendment adds an exception to Sec.  25.981(a)(3) to remove lightning 
as an ignition source from the scope of this section and refers 
applicants to Sec.  25.954 for lightning protection requirements.
    Paragraph (d) of Sec.  25.981 requires applicants to establish 
CDCCLs, inspections, or other procedures to ensure fuel tank safety. 
This amendment revises paragraph (d) to clarify that applicants must 
provide CDCCLs to identify critical design features, in addition to 
inspections or other procedures. The FAA received the following 
comments on the proposed changes to this section.
1. Consistency of Language
    Boeing suggested that the FAA expand the applicability of Sec.  
25.981(d) to include the fuel tank system, in addition to the fuel 
tank, to be consistent with Sec.  25.981(a). Paragraph (a) of Sec.  
25.981 requires ignition source prevention in the ``fuel tank or fuel 
tank system.''
    The FAA agrees and revised the final rule to add, ``. . . or fuel 
tank system according to paragraph (a) of this section. . . .'' This 
addition makes it consistent with Sec.  25.981(a).
    Boeing proposed that Sec.  25.981(d) refer to paragraph (b) of that 
section in addition to the references to paragraphs (a) and (c) of that 
section because mandatory maintenance required by paragraph (d) should 
also apply to flammability reduction means.
    The FAA agrees, and this amendment includes a reference to 
paragraph (b) in Sec.  25.981(d).
2. CDCCL Visible Means
    Boeing requested that the FAA revise Sec.  25.981(d) to delete the 
requirement for placement of visible means, limit that placement to 
areas where the means would be ``practical and meaningful,'' or provide 
more clear guidance. Boeing stated that, as proposed, the regulation 
provides no practical way to fully comply with the requirement to 
provide visible means of identifying CDCCL. Boeing argued that, ``While 
it may be easy to pick the color of external fuel quantity wiring, much 
of the fuel tank design for ignition prevention is basic to airplane 
design, such as bonding, grounding, sealing, etc. There is no practical 
way to color code or otherwise identify these design features.''
    The FAA partially agrees. The intent is not to require markings in 
all locations--only in those locations where foreseeable errors due to 
maintenance actions, repairs, or alterations may compromise critical 
features. This is not a new requirement with this amendment. However, 
this amendment deletes the example of visible means (color coding of 
wire to identify separation limitation), and it removes the requirement 
of identifying visible means as CDCCLs, both of which had been added at 
amendment 25-125. AC 25.981-1D provides additional guidance.

C. ``Instructions for Continued Airworthiness'' (Appendix H to Part 25)

    With some differences from what the FAA proposed in the NPRM, this 
amendment adds a new paragraph, (a)(5), to section H25.4 of appendix H 
to part 25. This paragraph requires any mandatory replacement times, 
inspection intervals, related inspection and test procedures, and 
CDCCLs for lightning protection features approved under Sec.  25.954 to 
be included in the ALS of the ICA.
    The SAE Lightning Group proposed revisions to the airworthiness 
limitation requirements of section H25.4(a)(5) by adding the phrases 
``critical design configuration control limitations'' and ``fault 
tolerant and non-fault tolerant.'' The commenter stated that the 
revisions would align this paragraph with the SAE Lightning Group's 
requested changes to Sec.  25.954 regarding fault-tolerant and non-
fault tolerant designs. The commenter also requested deletion of the 
proposed section H25.X, stating that the MSG-3 process has been shown 
to be ineffective for maintenance inspections and procedures that are 
critical to fuel tank systems lightning protection.

[[Page 47554]]

    Although Airbus was a participant in the SAE Lightning Group, it 
disagreed with the above comments on section H25.4(a)(5) because it 
makes reference to the ALS as being the only means to develop the ICA 
for both fault-tolerant and non-fault tolerant lightning protection 
features. Airbus suggested instead that the FAA limit the applicability 
of section H25.4(a)(5) to non-fault-tolerant lightning protection 
features rather than to all lightning protection features. Airbus also 
asked that the FAA delete the reference to sampling programs in section 
H25.X. Airbus stated that sampling programs are typically managed by 
the type certificate applicant, not the operator of the airplane that 
uses the ICA to develop their maintenance programs.
    The FAA partially agrees with the SAE Lightning Group's proposed 
changes. The FAA does not agree to the proposed changes to section 
H25.4(a)(5) as the FAA did not adopt the SAE Lightning Group's 
requested changes to Sec.  25.954, with the exception of deleting 
reference to Sec.  25.1729. However, the FAA did add the term 
``critical design configuration control limitations'' to the final 
section H25.4(a)(5). Thus, section H25.4(a)(5) now states, ``Each 
mandatory replacement time, inspection interval, and related inspection 
and test procedure, and each critical design configuration control 
limitation for each lightning protection feature approved under Sec.  
25.954.''
    The FAA agrees with the request to delete the proposed new section 
H25.X because all necessary maintenance actions for ensuring the 
integrity of lightning ignition source protection features will be 
addressed by compliance with section H25.4(a)(5). Therefore, the ICA 
requirement in the proposed section H25.X is not necessary, so that 
section is not included in the final rule. This also addresses Airbus's 
request to delete the reference to sampling programs in section H25.X. 
The FAA disagrees with Airbus's request to add the phrase ``non-fault-
tolerant'' to section H25.4(a)(5) because all necessary maintenance 
actions, both fault-tolerant and non-fault-tolerant, must be included 
in the ALS as required by section H25.4(a)(5).

D. Miscellaneous Comments

1. Hazards of Electrostatic Charge
    An individual suggested that the FAA revise Sec. Sec.  25.954 and 
25.981 to include a requirement for fuel system design features to 
mitigate the hazards of electrostatic charge. The commenter stated that 
these design features would also have a role in lightning protection.
    Section 25.899 specifically addresses electrostatic charge, and 
Sec.  25.981 addresses all ignition sources, which would include 
electrostatic charge. Lightning is the only exception, and it is now 
addressed by Sec.  25.954. Adding a specific requirement for 
electrostatic charge to Sec. Sec.  25.954 and 25.981 would be redundant 
and may cause confusion. Therefore, the FAA did not revise the rules 
because of this comment.
2. Regulatory Evaluation
    Boeing requested that the FAA explain the assumption made in 
paragraph IV.A.3 of the NPRM preamble, ``Regulatory Notices and 
Analyses, Regulatory Evaluation, Assumptions and Data Sources,'' that 
computational weights of composite wing airplanes would change from 
current approximate 15%-25% level linearly increasing to 50% level for 
a ten-year production cycle.
    The FAA clarified the information with the major manufacturer that 
had provided the data during the development of the NPRM regulatory 
evaluation. The assumption is more correctly stated that the weighted 
production rate of composite wing airplanes is estimated at 15%-25% of 
total production at the beginning of the 10-year production cycle, 
increasing linearly to 50% at the end of the cycle.

IV. Regulatory Notices and Analyses

A. Regulatory Evaluation

    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 and Executive Order 13563 direct 
that each Federal agency shall propose or adopt a regulation only upon 
a reasoned determination that the benefits of the intended regulation 
justify its costs. Second, the Regulatory Flexibility Act of 1980 (Pub. 
L. 96-354) requires agencies to analyze the economic impact of 
regulatory changes on small entities. Third, the Trade Agreements Act 
(Pub. L. 96-39) prohibits agencies from setting standards that create 
unnecessary obstacles to the foreign commerce of the United States. In 
developing U.S. standards, this Trade Act requires agencies to consider 
international standards and, where appropriate, that they be the basis 
of U.S. standards. Fourth, the Unfunded Mandates Reform Act of 1995 
(Pub. L. 104-4) requires agencies to prepare a written assessment of 
the costs, benefits, and other effects of final rules that include a 
Federal mandate likely to result in the expenditure by State, local, or 
tribal governments, in the aggregate, or by the private sector, of $100 
million or more annually (adjusted for inflation with base year of 
1995). This portion of the preamble summarizes the FAA's analysis of 
the economic impacts of this final rule. We suggest readers seeking 
greater detail read the full regulatory evaluation, a copy of which we 
have placed in the docket for this rulemaking.
    In conducting these analyses, FAA has determined that this final 
rule: (1) Has benefits that justify its costs; (2) is not an 
economically ``significant regulatory action'' as defined in section 
3(f) of Executive Order 12866; (3) is not ``significant'' as defined in 
DOT's Regulatory Policies and Procedures; (4) will not have a 
significant economic impact on a substantial number of small entities; 
(5) will not create unnecessary obstacles to the foreign commerce of 
the United States; and (6) will not impose an unfunded mandate on 
state, local, or tribal governments, or on the private sector by 
exceeding the threshold identified above. These analyses are summarized 
below.
1. Total Benefits and Costs of This Rule
    This final rule will be relieving for both government and 
industries with the estimated net benefits. The FAA assesses cost 
savings based on resources saved for reducing regulatory burden on both 
industry and the FAA. This rule results in cost savings by reducing the 
number of exemptions and special conditions.
    Over a 10-year period, the average total present value savings to 
manufacturers and the FAA are about $29.03 million at a 7% discount 
rate with annualized savings of about $4.13 million. The lower and the 
higher estimates of the total present value savings are $16.17 million 
and $41.93 million at a 7% discount rate, with annualized savings of 
$2.30 million and $5.97 million, respectively. The final rule will 
maintain achieved safety levels related to fuel tank structure and 
system lightning protection commensurate with the current requirements.
    Parties Potentially Affected by this Rulemaking will be:
     Part 25 airplane manufacturers.
     Operators of part 25 airplanes.
     The Federal Aviation Administration.
    Assumptions and Data Sources.
     Data related to industry savings mainly come from airplane 
manufacturers.
     Data related to requests for exemptions and special 
conditions come from FAA internal data sources and the judgments of 
agency subject matter experts.

[[Page 47555]]

     The FAA would process 4 special conditions and 7 
exemptions in the next 10 years in the absence of this rule.\14\
---------------------------------------------------------------------------

    \14\ FAA internal data source and the judgment of agency subject 
matter experts.
---------------------------------------------------------------------------

     Domestic airplane manufacturers would petition for two 
special conditions and three exemptions before reaching their cost-
benefit steady-state.\15\
---------------------------------------------------------------------------

    \15\ See footnote 14.
---------------------------------------------------------------------------

     While foreign manufacturers may benefit also from this 
final rule, cost savings directly attributable to foreign entities are 
not included in this analysis.
     For the final rule, the FAA estimates cost savings from 
avoided petitions for exemption and special conditions occur at the 
beginning of a 10-year production cycle.
     Projected impacts on manufacturers and the government are 
for a 10-year period associated with one production cycle.
     All monetary values are expressed in 2016 dollars.

B. Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes ``as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of applicable 
statutes, to fit regulatory and informational requirements to the scale 
of the businesses, organizations, and governmental jurisdictions 
subject to regulation.'' To achieve this principle, agencies are 
required to solicit and consider flexible regulatory proposals and to 
explain the rationale for their actions to assure that such proposals 
are given serious consideration.'' The RFA covers a wide-range of small 
entities, including small businesses, not-for-profit organizations, and 
small governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    However, if an agency determines that a rule is not expected to 
have a significant economic impact on a substantial number of small 
entities, section 605(b) of the RFA provides that the head of the 
agency may so certify and a regulatory flexibility analysis is not 
required. The certification must include a statement providing the 
factual basis for this determination, and the reasoning should be 
clear.
    This final rule amends certain airworthiness regulations that were 
not always practical for transport category airplanes regarding 
lightning protection of fuel tanks and systems. This final rule 
provides burden relief and savings to airplane manufacturers, who are 
large entities. Therefore, as provided in section 605(b), the head of 
the FAA certifies that this final rule will not have a significant 
economic impact on a substantial number of small entities and also 
certifies that a regulatory flexibility analysis is not required. The 
FAA solicited comments in the NPRM and did not receive comments with 
regard to this certification. Therefore, the FAA Administrator 
certifies that this rule does not have a significant economic impact on 
a substantial number of small entities.

C. International Trade Impact Assessment

    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the 
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal 
agencies from establishing standards or engaging in related activities 
that create unnecessary obstacles to the foreign commerce of the United 
States. Pursuant to these Acts, the establishment of standards is not 
considered an unnecessary obstacle to the foreign commerce of the 
United States, so long as the standard has a legitimate domestic 
objective, such as the protection of safety, and does not operate in a 
manner that excludes imports that meet this objective. The statute also 
requires consideration of international standards and, where 
appropriate, that they be the basis for U.S. standards. The FAA has 
assessed the potential effect of this final rule and determined that it 
could result in the same benefits to domestic and international 
entities in accord with the Trade Agreements Act.

D. Unfunded Mandates Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4) requires each Federal agency to prepare a written statement 
assessing the effects of any Federal mandate in a proposed or final 
agency rule that may result in an expenditure of $100 million or more 
(in 1995 dollars) in any one year by State, local, and tribal 
governments, in the aggregate, or by the private sector; such a mandate 
is deemed to be a ``significant regulatory action.'' The FAA currently 
uses an inflation-adjusted value of $155 million in lieu of $100 
million. This final rule does not contain such a mandate; therefore, 
the requirements of Title II of the Act do not apply.

E. Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA consider the impact of paperwork and other information 
collection burdens imposed on the public. The FAA has determined that 
there is no new requirement for information collection associated with 
this final rule.

F. International Compatibility

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to conform to 
International Civil Aviation Organization (ICAO) Standards and 
Recommended Practices to the maximum extent practicable. The FAA has 
determined that there are no ICAO Standards and Recommended Practices 
that correspond to these regulations.

G. Environmental Analysis

    FAA Order 1050.1F identifies FAA actions that are categorically 
excluded from preparation of an environmental assessment or 
environmental impact statement under the National Environmental Policy 
Act in the absence of extraordinary circumstances. The FAA has 
determined this rulemaking action qualifies for the categorical 
exclusion identified in paragraph 5-6.6 and involves no extraordinary 
circumstances.

V. Executive Order Determinations

A. Executive Order 13132, Federalism

    The FAA has analyzed this final rule under the principles and 
criteria of Executive Order 13132, Federalism. The agency determined 
that this action will not have a substantial direct effect on the 
States, or the relationship between the Federal Government and the 
States, or on the distribution of power and responsibilities among the 
various levels of government, and, therefore, does not have Federalism 
implications.

B. Executive Order 13211, Regulations That Significantly Affect Energy 
Supply, Distribution, or Use

    The FAA analyzed this final rule under Executive Order 13211, 
Actions Concerning Regulations that Significantly Affect Energy Supply, 
Distribution, or Use (May 18, 2001). The agency has determined that it 
is not a ``significant energy action'' under the executive order and it 
is not likely to have a significant adverse effect on the supply, 
distribution, or use of energy.

[[Page 47556]]

C. Executive Order 13609, International Cooperation

    Executive Order 13609, Promoting International Regulatory 
Cooperation, promotes international regulatory cooperation to meet 
shared challenges involving health, safety, labor, security, 
environmental, and other issues and to reduce, eliminate, or prevent 
unnecessary differences in regulatory requirements. The FAA has 
analyzed this action under the policies and agency responsibilities of 
Executive Order 13609, and has determined that this action would have 
no effect on international regulatory cooperation.

D. Executive Order 13771, Reducing Regulation and Controlling 
Regulatory Costs

    This final rule is considered an E.O. 13771 deregulatory action. 
Details on the estimated cost savings of this rule can be found in the 
rule's economic analysis.

VI. How To Obtain Additional Information

A. Rulemaking Documents

    An electronic copy of a rulemaking document may be obtained from 
the internet by--
    1. Searching the Federal eRulemaking Portal (http://www.regulations.gov);
    2. Visiting the FAA's Regulations and Policies web page at http://www.faa.gov/regulations_policies/; or
    3. Accessing the Government Printing Office's web page at http://www.gpo.gov/fdsys/.
    Copies may also be obtained by sending a request (identified by 
notice, amendment, or docket number of this rulemaking) to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue SW, Washington, DC 20591, or by calling (202) 267-9680.

B. Comments Submitted to the Docket

    Comments received may be viewed by going to http://www.regulations.gov and following the online instructions to search the 
docket number for this action. Anyone is able to search the electronic 
form of all comments received into any of the FAA's dockets by the name 
of the individual submitting the comment (or signing the comment, if 
submitted on behalf of an association, business, labor union, etc.).

C. Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SBREFA) of 
1996 requires FAA to comply with small entity requests for information 
or advice about compliance with statutes and regulations within its 
jurisdiction. A small entity with questions regarding this document, 
may contact its local FAA official, or the person listed under the FOR 
FURTHER INFORMATION CONTACT heading at the beginning of the preamble. 
To find out more about SBREFA on the internet, visit http://www.faa.gov/regulations_policies/rulemaking/sbre_act/.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

The Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration amends chapter I of title 14, Code of Federal 
Regulations as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

0
1. The authority citation for part 25 continues to read as follows:

    Authority:  49 U.S.C. 106(f), 106(g), 40113, 44701, 44702 and 
44704.

0
2. Revise Sec.  25.954 to read as follows:

Sec.  25.954  Fuel system lightning protection.

    (a) For purposes of this section--
    (1) A critical lightning strike is a lightning strike that attaches 
to the airplane in a location that, when combined with the failure of 
any design feature or structure, could create an ignition source.
    (2) A fuel system includes any component within either the fuel 
tank structure or the fuel tank systems, and any airplane structure or 
system components that penetrate, connect to, or are located within a 
fuel tank.
    (b) The design and installation of a fuel system must prevent 
catastrophic fuel vapor ignition due to lightning and its effects, 
including:
    (1) Direct lightning strikes to areas having a high probability of 
stroke attachment;
    (2) Swept lightning strokes to areas where swept strokes are highly 
probable; and
    (3) Lightning-induced or conducted electrical transients.
    (c) To comply with paragraph (b) of this section, catastrophic fuel 
vapor ignition must be extremely improbable, taking into account 
flammability, critical lightning strikes, and failures within the fuel 
system.
    (d) To protect design features that prevent catastrophic fuel vapor 
ignition caused by lightning, the type design must include critical 
design configuration control limitations (CDCCLs) identifying those 
features and providing information to protect them. To ensure the 
continued effectiveness of those design features, the type design must 
also include inspection and test procedures, intervals between 
repetitive inspections and tests, and mandatory replacement times for 
those design features used in demonstrating compliance to paragraph (b) 
of this section. The applicant must include the information required by 
this paragraph in the Airworthiness Limitations section of the 
Instructions for Continued Airworthiness required by Sec.  25.1529.

0
3. Amend Sec.  25.981 by revising the section heading and paragraphs 
(a)(3) and (d) to read as follows:

Sec.  25.981  Fuel tank explosion prevention.

    (a) * * *
    (3) Except for ignition sources due to lightning addressed by Sec.  
25.954, demonstrating that an ignition source could not result from 
each single failure, from each single failure in combination with each 
latent failure condition not shown to be extremely remote, and from all 
combinations of failures not shown to be extremely improbable, taking 
into account the effects of manufacturing variability, aging, wear, 
corrosion, and likely damage.
* * * * *
    (d) To protect design features that prevent catastrophic ignition 
sources within the fuel tank or fuel tank system according to paragraph 
(a) of this section, and to prevent increasing the flammability 
exposure of the tanks above that permitted in paragraph (b) of this 
section, the type design must include critical design configuration 
control limitations (CDCCLs) identifying those features and providing 
instructions on how to protect them. To ensure the continued 
effectiveness of those features, and prevent degradation of the 
performance and reliability of any means provided according to 
paragraphs (a), (b), or (c) of this section, the type design must also 
include necessary inspection and test procedures, intervals between 
repetitive inspections and tests, and mandatory replacement times for 
those features. The applicant must include information required by this 
paragraph in the Airworthiness Limitations section of the Instructions 
for Continued Airworthiness required by Sec.  25.1529. The type design 
must also include visible means of identifying critical features of the 
design in areas of the airplane where foreseeable maintenance actions, 
repairs, or alterations may compromise the CDCCLs.

[[Page 47557]]

0
4. In appendix H to part 25, section H25.4, add new paragraph (a)(5) to 
read as follows:

Appendix H to Part 25--Instructions for Continued Airworthiness

* * * * *

H25.4 Airworthiness Limitations section.

    (a) * * *
    (5) Each mandatory replacement time, inspection interval, and 
related inspection and test procedure, and each critical design 
configuration control limitation for each lightning protection 
feature approved under Sec.  25.954.
* * * * *

    Issued under authority provided by 49 U.S.C. 106(f), 44701(a), 
and 44703 in Washington, DC, on September 6, 2018.
Carl Burleson,
Acting Deputy Administrator.
[FR Doc. 2018-20174 Filed 9-19-18; 8:45 am]
BILLING CODE 4910-13-P