[Federal Register Volume 79, Number 243 (Thursday, December 18, 2014)]
[Proposed Rules]
[Pages 75496-75505]
From the Federal Register Online via the Government Publishing 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 [email protected].
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 [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 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