Document ID: FAA-2014-1027-0001
Agency: faa
Document Type: Proposed Rule
Title: Transport Airplane Fuel Tank and System Lightning Protection
Posted Date: 2014-12-18T05:00Z

[Federal Register Volume 79, Number 243 (Thursday, December 18, 2014)]
[Proposed Rules]
[Pages 75496-75505]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-29385]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No.: FAA-2014-1027; Notice No. 14-09]
RIN 2120-AK24

Transport Airplane Fuel Tank and System Lightning Protection

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to amend certain airworthiness regulations 
for transport category airplanes regarding lightning protection of fuel 
tanks and

[[Page 75497]]

systems. This action would establish design requirements for both 
normal conditions and possible failures of fuel tank structure and 
systems that could lead to fuel tank explosions, add new maintenance 
requirements related to lightning protection features, and impose 
specific requirements for airworthiness limitations in the instructions 
for continued airworthiness. We would create performance-based 
standards for prevention of catastrophic fuel vapor ignition caused by 
lightning by regulating the risk due to both ignition sources and fuel 
tank flammability. This change would allow designers to take advantage 
of flammability reduction technologies whose effectiveness was not 
foreseen when earlier revisions to these rules were written. This 
change would also relieve some of the administrative burdens created by 
the current regulations. These proposed amendments are based on 
recommendations from the Large Airplane Fuel System Lightning 
Protection Aviation Rulemaking Committee (Lightning ARC).

DATES: Send comments on or before March 18, 2015.

ADDRESSES: Send comments identified by docket number FAA-2014-1027 
using any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov and follow the online instructions for sending your 
comments electronically.
     Mail: Send comments to Docket Operations, M-30; U.S. 
Department of Transportation (DOT), 1200 New Jersey Avenue SE., Room 
W12-140, West Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Take comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://www.regulations.gov, including any personal 
information the commenter provides. Using the search function of the 
docket Web site, anyone can find and read the electronic form of all 
comments received into any FAA docket, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov at any time. Follow the online instructions 
for accessing the docket or go to the Docket Operations in Room W12-140 
of the West Building Ground Floor at 1200 New Jersey Avenue SE., 
Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except federal holidays.

FOR FURTHER INFORMATION CONTACT: For technical questions concerning 
this action, contact Massoud Sadeghi, Airplane and Flight Crew 
Interface Branch, ANM-111, Transport Airplane Directorate, Aircraft 
Certification Service, Federal Aviation Administration, 1601 Lind 
Avenue SW., Renton, WA 98057-3356; telephone (425) 227-2117; facsimile 
(425) 227-1149; email massoud.sadeghi@faa.gov.
    For legal questions concerning this action, contact Sean Howe, 
Office of the Regional Counsel, ANM-7, Federal Aviation Administration, 
1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone (425) 
227-2591; facsimile (425) 227-1007; email Sean.Howe@faa.gov.

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 new safety standards for the design and operation of 
transport category airplanes.

I. Overview of Proposed Rule

    The FAA proposes to amend the airworthiness regulations in Title 
14, Code of Federal Regulations (14 CFR) part 25 related to lightning 
protection for fuel systems \1\ (including fuel tank structure \2\ and 
systems.\3\) This action would remove the requirement for the 
prevention of lightning ignition sources from Sec.  25.981(a)(3) at 
Amendment 25-102 and add a new requirement to Sec.  25.954 for the 
prevention of ignition due to lightning.
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    \1\ Fuel system, in the context of this NPRM, includes any 
component within either the fuel tank structure or the fuel tank 
systems and any other airplane structure or system components that 
are penetrating, located within, or connected to the fuel tanks.
    \2\ Fuel tank structure, in the context of this NPRM, 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 NPRM, 
include tubing, components, and wiring that are penetrating, located 
within, or connected to the fuel tanks.
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    We propose to revise Sec.  25.954 to expand and clarify its 
objective and to modify it to meet current knowledge about lightning 
and state-of-the-art airplane design. This new requirement would reduce 
the risk of fuel tank ignition by requiring applicants to account for 
both ignition sources and fuel tank flammability limits established by 
existing regulations. The proposed amendments would adopt a 
performance-based standard to prevent catastrophic fuel tank vapor 
ignition due to lightning, rather than focus solely on the prevention 
of ignition sources.
    We propose to insert an exception into Sec.  25.981(a)(3) to remove 
its applicability to lightning protection. Inclusion of lightning in 
that section has resulted in recurring cases where applicants showed 
that compliance was impractical, leading them to seek exemptions to 
compliance with Sec.  25.981 for fuel tank structural aspects. We have 
not issued exemptions for systems-related lightning protection, but we 
believe common treatment of structure- and systems-related lightning 
protection in the fuel system is appropriate.
    To maintain the integrity of lightning protection features of 
airplanes certificated under the amended rules, we propose to amend 
part 25 appendix H to create a new requirement for applicants to 
establish airworthiness limitations specific to the airworthiness of 
fuel tank structure and systems lightning protection features.
    This proposed rule would affect manufacturers who apply for type 
certification of new or significantly modified transport category 
airplanes, specifically, the airplanes' fuel tank structures and 
systems. It would also apply to applicants for supplemental type 
certificates for such modifications. This proposal would revise the 
part 25 regulations for design and maintenance of lightning protection 
features for fuel tank structure and systems.

[[Page 75498]]

II. Background

A. Statement of the Problem

    We have found that compliance with Sec.  25.981(a)(3), as it is 
currently written, is not always practical. The impracticality has led 
applicants to petition for exemptions and the FAA to impose special 
conditions to achieve the intended level of safety of the rule, which 
has created an administrative burden on industry and the FAA.

B. History of Lightning-Related Fuel Tank Explosion Events

    Lightning strikes to airplanes do occur, particularly when 
operating in instrument meteorological conditions. When lightning 
strikes an airplane, high transient current is conducted in the 
airplane structure. The transient current can melt, burn, and deform 
airplane parts and structure where the lightning attaches to the 
airplane. This current is also conducted through the airplane structure 
between the lightning attachment points on the airplane. The conducted 
lightning transient current can also induce voltage and current on 
airplane wiring, tubes, and control mechanisms. Melting, burning, 
arcing, or sparking due to conducted lightning current or voltage can 
result in fuel vapor ignition if they occur in a flammable environment.
    On June 26, 1959, a Lockheed L-1649A Constellation was struck by 
lightning, which caused explosions in two of its fuel tanks, resulting 
in a crash. This airplane was fueled with aviation gasoline. Prior to 
this accident, government and industry had conducted research into the 
possible effects of lightning on airplane fuel tanks, but the scope of 
this research had been limited to the melting of integral fuel tank 
skin, and hot-spot formation.
    Fuel vapor ignition due to lightning was the probable cause of a 
Boeing 707 accident that occurred near Elkton, Maryland on December 8, 
1963. At the time of its certification, the 707 was not required to 
demonstrate effective lightning protection for fuel systems. Following 
the 707 accident, government and industry performed substantial 
research to determine the factors that could result in lightning-
related fuel vapor ignition. However, most of this research focused on 
lightning burn-through for metal fuel tank structure, and lightning-
related ignition of fuel vapor in fuel vents.
    On December 23, 1971, lightning struck a Lockheed L-188A Electra, 
which led to a fire and separation of the right wing. Since the L-188A 
was certified by the FAA in 1958, the type did not benefit from the 
additional attention given to airplane fuel tanks after Sec.  25.954 
was published in 1967.
    On May 9, 1976, a Boeing 747 crashed during descent into Madrid, 
Spain following a lightning strike to the airplane. The investigation 
of this accident found evidence that fuel vapor ignition could have 
been caused by lightning-induced sparking at a motor-driven fuel valve.
    In three of the four accidents noted above, investigations found 
that the airplane fuel tanks contained either aviation gasoline or a 
mixture of Jet A kerosene-type fuels and higher volatility Jet B/JP-4 
fuels. The fuel type involved in the 1971 Electra accident was not 
identified. The investigations for the other three accidents determined 
that the fuel mixtures would be flammable at the temperatures and 
altitudes that the airplanes were flying at the time of the lightning 
strikes. During the 1980s the use of Jet B/JP-4 fuels began to decline 
and those fuels became nearly obsolete in the 1990s.
    Since the last lightning-related airplane fuel tank explosion 
(1976), the understanding of lightning effects on airplane fuel tanks 
and systems has increased significantly, and no further events have 
occurred even though the number of flight hours since the 1976 accident 
(approaching 1 billion) is more than 8 times that which preceded that 
event (less than 120 million).
    Methods for preventing ignition sources due to lightning strikes 
are mature and are based on years of research into natural lightning 
characteristics and effects on airplane structure and systems. The 
results have been documented in a large body of literature and 
formalized into SAE standards such as ARP5412,\4\ ARP5414,\5\ and 
ARP5416.\6\ The FAA has accepted use of these standards through 
Advisory Circulars (AC) 20-53B, Protection of Aircraft Fuel Systems 
Against Fuel Vapor Ignition Caused by Lightning, and AC 20-155, SAE 
Documents to Support Aircraft Lightning Protection Certifications. The 
International Conference on Lightning and Static Electricity (ICOLSE), 
National Aeronautics and Space Administration (NASA), the European 
Organization on Commercial Aircraft Equipment (EUROCAE), and other 
industry forums have published much of the supporting research. A high 
level of communication among airplane lightning specialists worldwide 
ensures that designers and certification authorities are continually 
informed of advances in lightning protection technology and application 
of this technology to new designs.
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    \4\ ARP5412, Aircraft Lightning Environment and Related Test 
Waveforms, SAE International, November 1999.
    \5\ ARP5414, Aircraft Lightning Zoning, SAE International, 
December 1999.
    \6\ ARP5416, Aircraft Lightning Test Methods, SAE International, 
March 2005.
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C. Advancement of Current Regulations and Associated Guidance

    Following the 1963 Boeing 707 Elkton accident, the FAA adopted new 
fuel system lightning protection regulations. These regulations were 
implemented for transport category airplanes in Sec.  25.954 at 
Amendment 25-14, Fuel system lightning protection. Section 25.954 
states:
    The fuel system must be designed and arranged to prevent the 
ignition of fuel vapor within the system by--
    (a) Direct lightning strikes to areas having a high probability of 
stroke attachment;
    (b) Swept lightning strokes to areas where swept strokes are highly 
probable; and
    (c) Corona and streamering at fuel vent outlets.
    This regulation requires lightning protection regardless of the 
likelihood that lightning would strike the airplane. This regulation 
does not acknowledge that lightning protection features could fail or 
become ineffective. The regulation contains no requirement for fault-
tolerant fuel system lightning protection or for any evaluation of 
probabilities of failures related to the lightning protection features.
    Following the 1976 Madrid Boeing 747 accident, the FAA issued a 
number of airworthiness directives to address possible sources of 
ignition that were found during the investigation. The FAA subsequently 
developed further guidance for airplane fuel system lightning 
protection. Specifically, the FAA revised AC 20-53, Protection of 
Airplane Fuel Systems Against Fuel Vapor Ignition Due to Lightning. 
This AC has been revised twice since its original issue. These 
documents added emphasis regarding lightning protection of fuel system 
components such as fuel tubes, fuel quantity systems, and fuel filler 
caps.
    On July 17, 1996, a Boeing 747 operating as TWA Flight 800 was 
involved in an in-flight breakup after takeoff. The ensuing 
investigation determined that the center wing fuel tank exploded due to 
an unknown ignition source. Following the Flight 800 accident, the FAA 
reviewed the transport airplane fleet history and determined that fail-
safe design principles had not been properly applied to prevent 
ignition sources in fuel tanks and application of the existing rules 
had not been adequate to

[[Page 75499]]

prevent fuel tank explosions. The FAA also found that preventing 
ignition sources throughout the life cycle of a transport category 
airplane was an extremely difficult task and agreed with National 
Transportation Safety Board (NTSB) recommendations to also reduce or 
eliminate fuel tank flammability.
1. Amendment 25-102
    In January 1998 the FAA tasked \7\ an Aviation Rulemaking Advisory 
Committee (ARAC) to provide specific recommendations and propose 
regulatory text that would eliminate or significantly reduce the 
hazards associated with explosive vapors in transport category airplane 
fuel tanks. Under the tasking, the proposed regulatory text was to 
ensure that new type designs of transport category airplanes are 
designed and operated so that during normal operation (up to maximum 
certified operating temperatures) the presence of explosive fuel vapor 
in all tanks is eliminated, significantly reduced, or controlled to the 
extent that there could not be a catastrophic event. The ARAC concluded 
\8\ it was not practical to eliminate fuel tank flammability. They 
determined that the safety level of unheated aluminum main fuel tanks 
on airplanes using Jet A type fuel was adequate, and recommended that 
fuel tank flammability be limited to that level.
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    \7\ Aviation Rulemaking Advisory Committee--New Task: 
``Prevention of Fuel Tank Explosions;'' published in the Federal 
Register January 23, 1998 (63 FR 3614-3615).
    \8\ Aviation Rulemaking Advisory Committee: ``Fuel Tank 
Harmonization Working Group--Final Report;'' July 1998. Available in 
the docket.
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    In May 2001 the FAA adopted Amendment 25-102 (66 FR 23086-23131) 
revising Sec.  25.981, Fuel tank ignition prevention, which was 
intended to prevent future fuel tank explosions. This amendment adopted 
a new Sec.  25.981(a)(3), which eliminated ambiguity as to the 
necessary methods of compliance with the previously established 
requirements of Sec. Sec.  25.901 and 25.1309. As stated in AC 25.981-
1C, ``. . . in order to eliminate any ambiguity as to the restrictions 
on latent failures, Sec.  25.981(a)(3) explicitly requires that any 
anticipated latent failure condition not result in the airplane being 
one failure away from a catastrophic fuel tank ignition.''
    This new paragraph added the requirement that the fuel tank design 
address potential failures that could cause ignition sources within the 
fuel system. Section 25.981(a)(3) requires consideration of factors 
such as aging, wear, and maintenance errors as well as the existence of 
single failures, combinations of failures not shown to be extremely 
improbable, and single failures in combination with latent failures to 
account for the cause of many ignition sources in fuel tanks and 
deficiencies in the existing regulations.
    Section 25.981(a)(3) states that no ignition source may be present 
at each point in the fuel tank or fuel tank system where catastrophic 
failure could occur due to ignition of fuel or vapors. This must be 
shown by 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. The 
effects of manufacturing variability, aging, wear, corrosion, and 
likely damage must be considered.
    While lightning was not listed as a probable cause of the Flight 
800 accident, the FAA's accident and incident historical review of fuel 
tank explosions resulted in our finding that improving fuel tank safety 
required preventing ignition from all sources, including lightning. 
Potential ignition sources due to lightning must be considered as part 
of compliance with this regulation, as discussed in the rulemaking 
preamble for Sec.  25.981(a)(3) and the associated AC 25.981-1. This 
regulation effectively requires fail-safe ignition prevention means, 
like redundant features, or monitoring and indication of failures, be 
provided. However, in applying this rule to recent certification 
programs, we found that for the purpose of lightning protection, 
providing redundant features is not always practical. For example, 
failures of lightning protection features could remain latent for years 
between inspections, thereby exposing the fuel tank to the risk of 
ignition due to lightning. Typically these latent failures cannot be 
shown to be extremely remote considering the long inspection intervals.
    The preamble to Amendment 25-102 stated the FAA's assumption that 
environmental conditions such as lightning are present when failures of 
systems occur. Consistent with this approach, AC 25.981-1C also states 
that applicants should assume that a lightning attachment could occur 
at any time (probability of lightning = 1). In addition, industry and 
FAA practice had been to assume that a defined set of severe lightning 
current components would be associated with every lightning strike to 
the aircraft. AC 25.981-1C, as well as the user's manual \9\ associated 
with AC 20-53 that defines guidance for compliance to Sec.  25.954, 
also states that applicants should assume that the fuel tank is always 
flammable (probability = 1).
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    \9\ DOT/FAA/CT-83/3. User's manual for AC-20-53A Protection of 
Airplane Fuel Systems Against Fuel Vapor Ignition Due to Lightning; 
FAA Technical Center and SAE-AE4L Lightning Subcommittee, October 
1984.
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    Amendment 25-102 also introduced Sec.  25.981(b) requirements to 
identify critical design configuration control limitations (CDCCLs) to 
prevent development of ignition sources within the fuel tank systems.
    When Amendment 25-102 was adopted, the FAA considered it practical 
to limit fuel tank flammability to that of an unheated aluminum fuel 
tank. As recommended by the ARAC, the amendment adopted Sec.  25.981(c) 
that required minimizing the flammability of airplane fuel tanks, or 
mitigating the effects of an explosion such that any damage from a fire 
or explosion would not prevent continued safe flight and landing. The 
FAA considered flammability control, through the use of fuel tank 
designs that provided cooling of the tanks using ventilation, as well 
as locating heat sources away from fuel tanks, to be practical means of 
minimizing fuel tank flammability. The FAA explained in the preamble to 
the rule that the intent was to limit fuel tank flammability to that of 
an unheated aluminum wing fuel tank. This regulation did not 
specifically require fuel tank inerting, nor did the regulation state 
specific fuel tank flammability limits. The preamble to Amendment 25-
102 stated:

    As noted previously in this preamble, we tasked the ARAC on July 
14, 2000 (65 FR 43800), to evaluate both on-board and ground-based 
fuel tank inerting systems. If further improvement is found to be 
practicable, we may consider initiating further rulemaking to 
address such improvements.

    At the time we developed Amendment 25-102 (i.e., 1998-2001), the 
FAA and industry were still exploring the dynamics of tank flammability 
and the fleet average flammability exposure for transport airplane fuel 
tanks. Evaluation of the technical and economic viability of fuel tank 
inerting systems for commercial transport airplanes was also in its 
early stages at that time. After promulgation of Amendment 25-102, the 
FAA and industry continued research and discussion of the measurement 
and modeling of fuel tank flammability and development of practical 
means to reduce or eliminate flammability in transport airplane fuel 
tanks. This

[[Page 75500]]

eventually led to the certification of practical retrofit designs for 
center wing fuel tank nitrogen generating systems on existing transport 
airplane models.\10\ Those systems use nitrogen-enriched air that is 
generated onboard the airplane to displace oxygen in the fuel tank. 
This results in inerting the fuel tank throughout most of the flight 
and ground operations. Some applicants for new type certificates 
involving composite wing structure have included flammability reduction 
means, such as an ullage inerting system, for all fuel tanks, including 
the main fuel tanks located in the wing.
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    \10\ Inerting systems are approved for Boeing Models 737, 747, 
757, 767, and 777 and for Airbus Models A320, A330, and A340.
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2. Amendment 25-125
    Amendment 25-125 (73 FR 42444-42504), which was part of the fuel 
tank flammability reduction (FTFR) rule adopted in 2008, revised Sec.  
25.981(b) and (c) to introduce specific performance-based standards for 
the maximum flammability allowed in various fuel tanks. Amendment 25-
125 maintained the alternative adopted by Amendment 25-102 allowing 
ignition mitigation means. Amendment 25-125 established a new fleet 
average flammability exposure limit of 3 percent for all fuel tanks, or 
that of an equivalent conventional unheated aluminum fuel tank. Fuel 
tanks that are not main fuel tanks and that have any portion located 
within the fuselage contour must be limited to 3 percent fleet average 
exposure and 3 percent warm day exposure. Amendment 25-125 did not 
change the ignition prevention standards of Sec.  25.981(a), and it 
moved the CDCCL requirements created by Amendment 25-102 to Sec.  
25.981(d).
    Introduction of airplane designs with composite fuel tanks that 
cannot be shown to meet the flammability requirements of Sec.  25.981 
has resulted in the need to provide active fuel tank flammability 
control systems in all fuel tanks. For main tanks that were only 
required to be equivalent to unheated aluminum wing tanks, these 
systems reduce fuel tank flammability well below that required by Sec.  
25.981(c). The FAA has issued special conditions for new airplane 
designs that allow consideration of these fuel tank flammability 
control systems when showing that fuel tank ignition will not result 
from structural ignition sources following a lightning strike.

D. Related Actions Following the Adoption of Amendment 25-102

    Several applicants found that it was impractical to achieve dual 
fault tolerance for fuel tank structure lightning protection. The FAA 
agreed that applying Sec.  25.981(a)(3) for fuel tank structure was 
impractical in certain cases. The FAA required the safety assessment 
associated with the fuel tank system to include the assumptions that 
the fuel tank was always flammable and lightning was continuously 
present. However, when evaluating where lightning attaches to the 
airplane and considering the lightning protection features, the 
probability of strikes that could cause an ignition source is 
significantly less than the required assumptions. We have defined 
strikes that could cause an ignition source as ``critical lightning 
strikes.'' Critical lightning strikes occur on the order of once every 
100,000 hours of airplane operation. In addition, for airplanes with 
the fuel tank flammability reduction means required by Sec.  25.981, 
the likelihood of a fuel tank being flammable is less than one hour for 
every hundred hours of operation. For airplanes without fuel tank 
flammability reduction means (i.e., with unheated aluminum wing tanks), 
the flammability range is one to five hours for every one hundred hours 
of operation. Consideration of these factors in combination with fail-
safe ignition required by Sec.  25.981, which typically resulted in the 
need for triple-redundant lightning ignition prevention features, led 
the FAA to conclude that the required assumptions were overly 
conservative.
    As a result, 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 requirements that were to be applied through special conditions 
or exemptions. This policy allowed the consideration of the likelihood 
of both the occurrence of a critical lightning strike and the tank 
being flammable. The policy contained detailed information that 
explained the design goal of Sec.  25.981(a)(3) for fuel tank structure 
and provided guidance for alternatives to compliance that still 
achieved that design goal.
    In 2009 the FAA chartered the Lightning ARC to re-examine 
Sec. Sec.  25.954 and 25.981 at Amendments 25-102 and 25-125 for fuel 
tank lightning protection. The Lightning ARC included industry members 
that were the leading aircraft lightning protection design experts in 
the world, along with the leading regulatory experts working in the 
lightning area. To address structure-specific issues, such as the 
occurrence of cracks and fastener failures, the Lightning ARC 
established a subcommittee made up of airplane manufacturer structural 
experts. The ARC also commissioned a specific study of lightning 
current distribution at structural cracks and fasteners, including the 
evaluation of lightning-related sparks at these cracks and fasteners. 
In May 2011 the Lightning ARC issued a final report \11\ that included 
the results of these special studies and their findings and 
recommendations. They proposed new rulemaking on the following topics:
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    \11\ FAA Large Airplane Fuel System Lightning Protection ARC, 
Final Report, May 2011. http://www.faa.gov/regulations_policies/rulemaking/committees/documents/media/LAFSLP.ARC.RR.20110518.pdf.
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    1. Lightning-specific requirements that focused on ignition source 
prevention;
    2. Inclusion of both structure and systems in the same fuel system 
lightning protection rule with the same requirements;
    3. Single fault-tolerant designs, or if impractical, a qualitative 
assessment to ensure the combination of non-fault-tolerant failures 
resulting in an ignition source, is remote;
    4. Design, manufacturing processes, and instructions for continued 
airworthiness (ICA) to address manufacturing variability, aging, wear, 
corrosion, and likely damage;
    5. ICA to include caution information for critical lightning 
protection features to minimize accidental damage during maintenance, 
alteration, or repairs;
    6. Inclusion of inspections and procedures required for non-fault-
tolerant designs in the Airworthiness Limitations Section of the ICA;
    7. Addition of a new section in the ICA specific to fuel tank 
lightning protection;
    8. No requirement for lower flammability in the lightning 
regulations (i.e., retain existing flammability requirements); and
    9. Development of new guidance material and revision of existing 
guidance material to ensure a consistent approach to fuel system 
lightning protection.
    To address these recommendations, the FAA issued a new policy 
statement that superseded Policy Memorandum ANM-112-08-002 as an 
interim

[[Page 75501]]

approach until new rulemaking could be accomplished. 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, issued June 24, 2014, expands the scope of the previous policy 
to include systems and provides guidance for special conditions and 
exemptions that are applicable to the design of lightning protection 
features in fuel tank structure and systems with respect to compliance 
with Sec.  25.981(a)(3).
    The proposed revisions to Sec.  25.981(a)(3) would eliminate the 
need to issue special conditions and exemptions; however, the detailed 
information provided in that policy statement addresses the design goal 
of the proposed Sec.  25.954 for fuel tank structure and systems and 
provides valuable information about means of compliance. Therefore, a 
copy of that policy statement has been added to the docket for this 
rule.

III. Discussion of the Proposal

A. General

    In order to comply with the latent failure criterion of Sec.  
25.981(a)(3), systems with potentially catastrophic failure conditions 
resulting from a lightning strike typically need at least triple-
redundancy in their protective features, or dual-redundancy with 
continuous system monitoring to reduce the latency period. Dual-
redundant designs could only be shown to comply with Sec.  25.981(a)(3) 
when combined with either regular inspections at very short intervals 
or with a monitoring device to verify the functionality of the 
protective features. Inspection of the various design features might be 
difficult or impossible if, for example, the feature is covered by 
airframe structure. This level of redundancy has been shown to be 
impractical for certain areas of airplane structure, such as airplane 
skins, joints, ribs, spars, stringers, and associated fasteners, 
brackets, and coatings.
    Lightning protection features are typically an integral part of the 
fuel tank structure or inside the fuel tanks. Due to the frequency of 
inspections that would be required to sufficiently limit exposure to 
latent failures, it would be impractical to use inspections of 
lightning protection features by themselves to eliminate the 
requirement for triple redundancy. Therefore, the FAA proposes to amend 
the requirements of Sec. Sec.  25.954 and 25.981(a)(3) to address these 
and other issues related to fuel tank lightning protection design. The 
FAA's intent is to establish a balanced approach to ensure that 
airplane designs provide an acceptable level of safety, while allowing 
manufacturers to develop an economically viable design, economical 
manufacturing methods, and effective maintenance programs considering 
the limitations in preventing or managing failures inside the fuel 
tanks. To preclude a catastrophic event, the proposed standards would 
require the applicant to develop structural and system component 
designs that are free of ignition sources. In addition, the applicant 
must still account for fuel vapor flammability as required in Sec.  
25.981(b). This proposal would also allow applicants to take credit for 
providing reduced flammability exposure below what is required by Sec.  
25.981(b).
    Practicality is a balance of available means, economic viability, 
and proportional benefit to safety. A means to provide fault tolerance 
against potential ignition sources that is possible with little 
economic impact is practical even if the potential ignition source 
conditions would be remote without them. In general, applicants have 
found fault tolerance to be practical for systems lightning protection 
features. However, in several cases, applicants found that providing 
fault tolerance was impractical because the means had a significant 
economic impact on production, operational, or maintenance costs. In 
these cases, it is not necessary that the applicants use these means if 
it can be determined that the probability of a potential ignition 
source, combined with a critical lightning strike and flammable fuel 
tank conditions is such that catastrophic failure is not anticipated 
over the life of the fleet.

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

    The current rule specifies the primary lightning threats to the 
fuel system and requires designs that prevent ignition of fuel vapor 
within the system. The original intent was to prevent ignition of fuel 
vapor in the fuel tank structure and system due to lightning.
    As written, the current rule does not address failures or 
deterioration of the lightning protection features.
    In lieu of regulating fuel tank lightning protection by Sec. Sec.  
25.954 and 25.981, we propose to consolidate requirements for the 
prevention of fuel vapor ignition solely in Sec.  25.954. We propose to 
retain (and renumber) the existing rule text of Sec.  25.954, add a 
clarification of the existing requirements regarding lightning-induced 
or conducted electrical transients, and add two new performance-based 
requirements to regulate the risk of failures and to maintain the 
integrity of the lightning protection features during the airplane 
service life.
    The addition of a clarification regarding lightning-induced or 
conducted electrical transients is needed to make it clear that this 
regulation addresses these effects. Lightning strikes to airplanes 
result in significant current conducted through airplane structure and 
equipment, and can induce voltage and current on wires, tubes, and 
equipment. The use of composite structure can increase these induced 
and conducted electrical transients. Therefore, this proposed rule 
would require that the design and arrangement of the fuel system 
prevent the ignition of fuel vapor within the system by lightning-
induced and conducted electrical transients.
    A new paragraph (b) would require that catastrophic ignition caused 
by lightning be extremely improbable, placing that risk in line with 
that of all other potentially catastrophic hazards. The proposed rule 
would require the type design to take into account the likelihood of a 
critical lightning strike, the fuel tank being flammable, and creation 
of an ignition source due to the failure of fuel system or structural 
lightning protection features. The purpose of the proposed rule is to 
ensure that a catastrophic fuel vapor ignition will not occur due to 
any single failure when lightning attaches to the airplane. In 
addition, the combination of the probabilities of a critical lightning 
strike, a flammable fuel tank condition, and the exposure time of all 
specified failures of structural features that are not fault-tolerant 
(and that can occur within the fuel tank) must, under the proposed 
rule, be such that catastrophic failure from ignition due to lightning 
would not be anticipated over the life of that airplane fleet. For 
example, for each structural discrepancy identified, the applicant 
would be required to demonstrate that mandated structural inspection 
procedures would reliably detect cracks or failed fasteners/cap-seals 
(where the gap size required to create arcing is exceeded) before the 
combined probability of the occurrence of a flammable fuel tank 
condition and a critical lightning strike was exceeded.
    The proposed rule would also require that the type design take into 
account the failure of other system components that may run into and/or 
through the fuel tank and can be an ignition source in the event of a 
critical lightning strike. Lightning-related ignition of flammable 
fluids and vapors due to leakage outside the fuel system and the 
resultant

[[Page 75502]]

hazards will continue to be covered in Sec.  25.863.
    The proposed rule would use ``taking into account,'' rather than 
``consider,'' \12\ a term the FAA has previously used. We intend no 
substantive effect by this change.
---------------------------------------------------------------------------

    \12\ See Legal Interpretation to William Szendrey from Rebecca 
MacPherson (Apr. 28, 2005).
---------------------------------------------------------------------------

    We propose to add a new paragraph (c) that would require applicants 
to develop CDCCLs that identify lightning protection design features, 
instructions on how to protect them, and inspection and test procedures 
specific to lightning protection features within fuel tank structure 
and systems to detect and correct any anomalies or failures during the 
life of the airplane. Section 25.954 as written in 1967 required 
applicants to design lightning protection features into fuel tank 
structure and systems, but it does not account for the deterioration of 
those features during the life of the airplane. During inspections and 
accident investigations, we found damage and deterioration of fuel tank 
lightning protection features such as bonding straps, brackets, and 
sealants that could present gaps or other electrical discontinuities 
that could become ignition sources in the presence of lightning 
strikes.
    CDCCLs are one type of fuel system airworthiness limitation that 
define critical features of the design that must be maintained. CDCCLs 
were originally required by the fuel tank explosion prevention 
standards of Sec.  25.981 and appendix H to 14 CFR part 25 at Amendment 
25-102. Fuel system airworthiness limitations include mandatory 
replacement times, inspection intervals, related inspection procedures, 
and CDCCLs. As explained in the FTFR final rule, Amendment 25-125, 
``The intent of the CDCCL requirement is to define the critical 
features of the design that could be unintentionally altered in a way 
that could cause reduction in fuel system safety.'' CDCCLs are distinct 
from mandatory replacement times, inspection intervals, and inspections 
and other procedures.
    This proposed new paragraph will require applicants to identify the 
lightning protection design features of the airplane, as well as to 
prepare instructions on how to protect those features. Identification 
of a feature refers to listing the feature in the CDCCL. The FAA has 
determined that during airplane operations, modifications, and 
unrelated maintenance actions, these features can be unintentionally 
damaged or inappropriately repaired or altered. Instructions on 
protection are meant to address this safety concern. An example of a 
common design feature to prevent catastrophic ignition caused by 
lightning is wire separation so that wires cannot chafe against one 
another. An example of an instruction on how to protect this design 
feature would be, ``When performing maintenance or alterations in the 
vicinity of these wires, ensure a minimum of 6-inch wire separation is 
maintained.''
    Addressing the effects of aging, wear, and corrosion as both a 
design and continuing airworthiness consideration is necessary to 
ensure reliable protection over the life of the airplane. The proposed 
rule would require applicants to establish necessary inspection and 
test procedures to prevent development of lightning-related ignition 
sources within the fuel tank structure and systems. One example of an 
inspection procedure would be to examine a structural element for 
cracks. An example of a test procedure would be a functional test to 
ensure a ground fault interrupter continues to function. The FAA would 
require these inspection and test procedures to include airworthiness 
limitations for non-fault-tolerant features and caution information for 
lightning protection features that may be altered by maintenance and 
repairs. For non-fault-tolerant lightning protection features that are 
identified in support of certification, the rule would require 
applicants to develop and identify inspection and test procedures as 
airworthiness limitations in the instructions for continued 
airworthiness, approved by the FAA, in order to preclude the 
development of unsafe conditions.
    We also propose to add a new paragraph (d) to define ``critical 
lightning strike'' and ``fuel system'' for the purpose of this section.

C. ``Fuel Tank Ignition Prevention'' (Sec.  25.981(a)(3))

    Section 25.954 provides requirements for protection from ignition 
due to lightning, and Sec.  25.981 provides requirements for protection 
against ignition from all sources, including lightning. The redundancy 
of the rule coverage has caused confusion regarding which regulation 
applies to fuel tank lightning protection.
    To consolidate lightning protection requirements into one rule, 
Sec.  25.954, we propose to add an exception to Sec.  25.981(a)(3) 
removing lightning as an ignition source from the scope of this section 
and referring applicants to Sec.  25.954 for lightning protection 
requirements.
    Section 25.981(d) at Amendment 25-125 requires CDCCLs, inspections, 
or other procedures to be established to ensure fuel tank safety. The 
FAA intended that CDCCLs would be required to identify critical design 
features, and that inspections or other procedures would also be 
provided where it was determined necessary. However, some have 
misunderstood the wording to allow inspections or other procedures, for 
example adhering to component maintenance manuals alone, instead of 
maintaining the original design details of the critical feature. We are 
proposing to revise this rule text to clarify that CDCCLs must be 
provided to identify critical design features, in addition to 
inspections or other procedures.

    Note: The title of Sec.  25.981 would be corrected in this 
rulemaking from ``Fuel Tank Ignition Prevention'' to ``Fuel Tank 
Explosion Prevention.'' We intended this change with Amendment 25-
125, but the change was not accomplished.

D. Instructions for Continued Airworthiness (Appendix H to Part 25)

1. Airworthiness Limitations Section (H25.4)
    Currently, section H25.4 does not expressly mention instructions 
about lightning protection features. We propose to add a new paragraph 
H25.4(5) that will make mandatory any inspection and test procedures 
that are needed to sustain the integrity of the lightning protection 
features that are used to show compliance with Sec.  25.954.
2. Lightning Protection Features Instructions for Continued 
Airworthiness (H25.X)
    We propose to add a new section to appendix H to require applicants 
to develop instructions for continued airworthiness that are approved 
by the FAA, and that are specific to the lightning protection features 
for fuel tank structure and systems required by Sec.  25.954.

E. Advisory Circular

    The FAA would develop one new proposed AC and would propose 
revisions to two other ACs to be published concurrently with the 
proposed regulations contained in this NPRM. The proposed new AC would 
provide guidance material for acceptable means, but not the only means, 
of demonstrating compliance with proposed Sec.  25.954. The revisions 
to the existing ACs would update them to reflect the revised rules.

[[Page 75503]]

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 proposed or 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 proposed 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 proposed 
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) would not have a 
significant economic impact on a substantial number of small entities; 
(5) would not create unnecessary obstacles to the foreign commerce of 
the United States; and (6) would 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 rule is a retrospective regulatory review rulemaking under 
Executive Order 13563. This rule would be relieving for both government 
and industries with the estimated net benefits. We assess regulatory 
benefits based on resources saved for reducing regulatory burden on 
both industry and the FAA. The total combined savings would be about 
$610 million or $450 million present value at a 7% discount rate. The 
lower and the higher estimates of the total combined regulatory savings 
range from $384 million to $836 million (see table). The proposed rule 
would maintain a level of safety for fuel tank structure and system 
lightning protection consistent with that provided for other airplane 
hazards.

----------------------------------------------------------------------------------------------------------------
                                        Value in 2014 dollar                       Present value at 7%
    Benefits (1 x million    -----------------------------------------------------------------------------------
           dollar)               Average     Lower bound   Upper bound     Average     Lower bound   Upper bound
----------------------------------------------------------------------------------------------------------------
Government benefits (sub-             $0.1          $0.1          $0.2          $0.1          $0.1          $0.1
 total).....................
Industries benefits (sub-            610           384           836           450           283           618
 total).....................
    Exemptions and special            30            17            44            21            12            30
     conditions.............
    Productions.............         570           361           779           423           267           579
    Operations..............          10             6            13             6             4             9
                             -----------------------------------------------------------------------------------
        Total Societal               610           384           836           451           283           618
         Benefits...........
----------------------------------------------------------------------------------------------------------------

2. Parties Potentially Affected by This Rulemaking
     Part 25 airplane manufacturers.
     Operators of part 25 airplanes.
     The Federal Aviation Administration.
3. 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 source and the agency's experts 
judgments.
     The FAA would process four special conditions and seven 
exemptions in the next ten years in the absence of this rule.
     Domestic airplane manufacturers would petition for two 
special conditions and three exemptions before reaching their cost-
benefit steady-state.\13\
---------------------------------------------------------------------------

    \13\ Ibid.
---------------------------------------------------------------------------

     Approximately 184 airplanes would be produced per year for 
ten years based on airplane models being approved for exemptions and 
special conditions for lightning protection.\14\
---------------------------------------------------------------------------

    \14\ ``Fleet Discovery'' 2000-2004 Penton, provided by Aviation 
Week Intelligence Network, data through the end of April 2014 Ibid.
---------------------------------------------------------------------------

     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.\15\
---------------------------------------------------------------------------

    \15\ Ibid.
---------------------------------------------------------------------------

     Airplanes have service life-span for 30 years.\16\
---------------------------------------------------------------------------

    \16\ Ibid 1 and 2.
---------------------------------------------------------------------------

     Projected impacts on manufacturers and the government are 
for a ten-year period from 2015 to 2024.
     All monetary values are expressed in 2014 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

[[Page 75504]]

not required. The certification must include a statement providing the 
factual basis for this determination, and the reasoning should be 
clear.
    The proposed rule would amend certain airworthiness regulations 
that are not always practical for transport category airplanes 
regarding lightning protection of fuel tanks and systems. While the 
largest benefiters of this proposed rule would be airplane 
manufacturers, who are large entities, many small airline operators 
would also benefit from this proposed rule due to fuel savings. 
Therefore, as provided in section 605(b), the Administrator of the FAA 
certifies that the proposed rule would not have a significant economic 
impact on a substantial number of small entities and also certify that 
a regulatory flexibility analysis is not required.

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 proposed rule and determined that 
it could result in the same benefits or costs 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 $151 million in lieu of $100 
million. This proposed 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 would be no new requirement for information collection associated 
with this proposed rule.

F. International Compatibility and Cooperation

    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 
reviewed the corresponding ICAO Standards and Recommended Practices and 
has identified no differences with these proposed regulations.

G. Environmental Analysis

    FAA Order 1050.1E 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 Section 312f of Order 1050.1E and involves no 
extraordinary circumstances.

V. Executive Order Determinations

A. Executive Order 13132, Federalism

    The FAA has analyzed this proposed rule under the principles and 
criteria of Executive Order 13132, Federalism. The agency has 
determined that this action would 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, would not have 
Federalism implications.

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

    The FAA analyzed this proposed 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 
would not be a ``significant energy action'' under the executive order 
and would not be likely to have a significant adverse effect on the 
supply, distribution, or use of energy.

VI. Additional Information

A. Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. The agency 
also invites comments relating to the economic, environmental, energy, 
or federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, and 
include supporting data. To ensure the docket does not contain 
duplicate comments, commenters should send only one copy of written 
comments, or if comments are filed electronically, commenters should 
submit only one time.
    The FAA will file in the docket all comments it receives, as well 
as a report summarizing each substantive public contact with FAA 
personnel concerning this proposed rulemaking. Before acting on this 
proposal, the FAA will consider all comments it receives on or before 
the closing date for comments. The FAA will consider comments filed 
after the comment period has closed if it is possible to do so without 
incurring expense or delay. The agency may change this proposal in 
light of the comments it receives.
    Proprietary or Confidential Business Information: Commenters should 
not file proprietary or confidential business information in the 
docket. Such information must be sent or delivered directly to the 
person identified in the FOR FURTHER INFORMATION CONTACT section of 
this document and marked as proprietary or confidential. If submitting 
information on a disk or CD ROM, mark the outside of the disk or CD ROM 
and identify electronically within the disk or CD ROM the specific 
information that is proprietary or confidential.
    Under 14 CFR 11.35(b), if the FAA is aware of proprietary 
information filed with a comment, the agency does not place it in the 
docket. It is held in a separate file to which the public does not have 
access, and the FAA places a note in the docket that it has received 
it. If the FAA receives a request to examine or copy this information, 
it treats it as any other request under the Freedom of Information Act 
(5 U.S.C. 552). The FAA processes such a request under Department of 
Transportation procedures found in 49 CFR part 7.

[[Page 75505]]

B. Availability of Rulemaking Documents

    An electronic copy of rulemaking documents 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 to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue SW., Washington, DC 20591, or by calling (202) 267-9680. 
Commenters must identify the docket or notice number of this 
rulemaking.
    All documents the FAA considered in developing this proposed rule, 
including economic analyses and technical reports, may be accessed from 
the Internet through the Federal eRulemaking Portal referenced in item 
(1) above.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Life-limited parts, Reporting and record 
keeping requirements.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend 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(g), 40113, 44701, 44702 and 44704.

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

Sec.  25.954  Fuel system lightning protection.

    (a) The design and arrangement of a fuel system must prevent the 
ignition of fuel vapor within the system by--
    (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;
    (3) Lightning-induced or conducted electrical transients; and
    (4) Corona and streamering at fuel vent outlets.
    (b) The design and arrangement of a fuel system must ensure that 
catastrophic fuel vapor ignition is extremely improbable, taking into 
account flammability, critical lightning strikes, and failures within 
the fuel system.
    (c) 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 on how 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. The applicant must include the information 
required by this paragraph in the Airworthiness Limitations section of 
the instructions for continued airworthiness required by Sec. Sec.  
25.1529 and 25.1729.
    (d) For purposes of this section, a critical lightning strike is 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. 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.
0
3. Amend Sec.  25.981 by revising the title of the section 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, 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) 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. Sec.  25.1529 and 25.1729. 
The type design must also include the placement of 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 (e.g., color-coding of wire to identify 
separation limitation). The type design must identify these visible 
means as CDCCLs.
0
4. In appendix H to part 25, section H25.4, add new paragraph (a)(5) 
and new section H25.X to read as follows:

Appendix H to Part 25--Instructions for Continued Airworthiness

    H25.4 Airworthiness Limitations section.
    (a) * * *
* * * * *
    (5) Mandatory replacement times, inspection intervals, and 
related inspection and test procedures for each lightning protection 
feature approved under Sec.  25.954.
* * * * *
    H25.X Lightning Protection Features Instructions for Continued 
Airworthiness.
    The applicant must prepare instructions for continued 
airworthiness (ICA) applicable to lightning protection features for 
fuel tank structure and systems as required by Sec.  25.954 that are 
approved by the FAA and include sampling programs, maintenance, or 
inspections necessary for lightning protection features.

    Issued under authority provided by 49 U.S.C. 106(f) and 44701(a) 
in Washington, DC, on December 9, 2014.
Chris Carter,
Acting Deputy Director, Aircraft Certification Office.
[FR Doc. 2014-29385 Filed 12-17-14; 8:45 am]
BILLING CODE 4910-13-P