Federal Register / Vol. 78, No. 244 / Thursday, December 19, 2013 / Proposed Rules 76775 

the replacement of batteries with 

batteries that have experienced 

degraded charge-retention ability or 

other damage due to prolonged storage 

at a low state of charge. Replacement 

batteries must be of the same 

manufacturer and part number as 

approved by the FAA. Precautions 

should be included in the Instructions 

for Continued Airworthiness 

maintenance instructions to prevent 

mishandling of the rechargeable 

lithium-ion batteries and battery 

systems, which could result in shortcircuit or other unintentional impact 

damage caused by dropping or other 

destructive means. 

Note 1: The term ‘‘sufficiently charged’’ 

means that the battery will retain enough of 

a charge, expressed in ampere-hours, to 

ensure that the battery cells will not be 

damaged. A battery cell may be damaged by 

lowering the charge below a point where the 

battery experiences a reduction in the ability 

to charge and retain a full charge. This 

reduction would be greater than the 

reduction that may result from normal 

operational degradation. 

Note 2: These special conditions are not 

intended to replace § 25.1353(b) at 

Amendment 25–113 in the certification basis 

for Airbus Model A350–900 airplanes. These 

special conditions apply only to rechargeable 

lithium-ion batteries and battery systems and 

their installations. The requirements of 

§ 25.1353(b) at Amendment 25–113 remain in 

effect for batteries and battery installations 

on Airbus Model A350–900 airplanes that do 

not use rechargeable lithium-ion batteries. 

Issued in Renton, Washington, on 

December 10, 2013. 

John P. Piccola, Jr., 

Acting Manager, Transport Airplane 

Directorate, Aircraft Certification Service. 

[FR Doc. 2013–30231 Filed 12–18–13; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. FAA–2013–1002; Notice No. 25– 

13–36–SC] 

Special Conditions: Airbus, Model 

A350–900 Series Airplane; Lightning 

Protection of Fuel Tank Structure To 

Prevent Fuel Tank Vapor Ignition 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed special 

conditions. 

SUMMARY: This action proposes special 

conditions for the Airbus Model A350– 

900 series airplanes. These airplanes 

will have a novel or unusual design 

feature(s) that will incorporate a 

nitrogen generation system (NGS) for all 

fuel tanks that actively reduce 

flammability exposure within the fuel 

tanks significantly below that required 

by the fuel tank flammability 

regulations. Among other benefits, the 

NGS significantly reduces the potential 

for fuel vapor ignition caused by 

lightning strikes. The applicable 

airworthiness regulations do not contain 

adequate or appropriate safety standards 

for this design feature. These proposed 

special conditions contain the 

additional safety standards that the 

Administrator considers necessary to 

establish a level of safety equivalent to 

that established by the existing 

airworthiness standards. 

DATES: Send your comments on or 

before February 3, 2014. 

ADDRESSES: Send comments identified 

by docket number FAA–2013–1002 

using any of the following methods: 

• Federal eRegulations 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 8 

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: 

Doug Bryant, Propulsion/Mechanical 

Systems, ANM–112, Transport Airplane 

Directorate, Aircraft Certification 

Service, 1601 Lind Avenue SW., 

Renton, Washington, 98057–3356; 

telephone (425) 227–2384; facsimile 

(425) 227–1320. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

We invite interested people to take 

part in this rulemaking by sending 

written comments, data, or views. The 

most helpful comments reference a 

specific portion of the special 

conditions, explain the reason for any 

recommended change, and include 

supporting data. 

We will consider all comments we 

receive on or before the closing date for 

comments. We may change these special 

conditions based on the comments we 

receive. 

Background 

On August 25, 2008, Airbus applied 

for a type certificate for their new 

Airbus Model A350–900 series airplane. 

Later, Airbus requested and the FAA 

approved an extension to the 

application for FAA type certification to 

June 28, 2009. The Model A350–900 

series has a conventional layout with 

twin wing-mounted Rolls-Royce Trent 

XWB engines. It features a twin aisle 9- 

abreast economy class layout, and 

accommodates side-by-side placement 

of LD–3 containers in the cargo 

compartment. The basic Model A350– 

900 series configuration will 

accommodate 315 passengers in a 

standard two-class arrangement. The 

design cruise speed is Mach 0.85 with 

a Maximum Take-Off Weight of 602,000 

lbs. Airbus proposes the Model A350– 

900 series to be certified for extended 

operations (ETOPS) beyond 180 minutes 

at entry into service for up to a 420- 

minute maximum diversion time. 

Type Certification Basis 

Under Title 14, Code of Federal 

Regulations (14 CFR) 21.17, Airbus must 

show that the Model A350–900 series 

meets the applicable provisions of 14 

CFR part 25, as amended by 

Amendments 25–1 through 25–129. 

If the Administrator finds that the 

applicable airworthiness regulations 

(i.e., 14 CFR part 25) do not contain 

adequate or appropriate safety standards 

for the Model A350–900 series because 

of a novel or unusual design feature, 

special conditions are prescribed under 

§ 21.16. 


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In addition to the applicable 

airworthiness regulations and special 

conditions, the Model A350–900 series 

must comply with the fuel vent and 

exhaust emission requirements of 14 

CFR part 34 and the noise certification 

requirements of 14 CFR part 36 and the 

FAA must issue a finding of regulatory 

adequacy under § 611 of Public Law 92– 

574, the ‘‘Noise Control Act of 1972.’’ 

The FAA issues special conditions, as 

defined in 14 CFR 11.19, under § 11.38, 

and they become part of the typecertification basis under § 21.17(a)(2). 

Special conditions are initially 

applicable to the model for which they 

are issued. Should the type certificate 

for that model be amended later to 

include any other model that 

incorporates the same novel or unusual 

design feature, the special conditions 

would also apply to the other model 

under § 21.101. 

Novel or Unusual Design Features 

The Airbus Model A350–900 series 

will incorporate the following novel or 

unusual design features: fuel tank NGS 

that is intended to control fuel tank 

flammability for all fuel tanks. This NGS 

is designed to provide a level of 

performance that applies the more 

stringent standard for warm day 

flammability performance applicable to 

normally emptied tanks within the 

fuselage contour from § 25.981(b) and 14 

CFR part 25 appendix M, to all fuel 

tanks of the Model A350–900 series. 

This high level of NGS performance for 

all fuel tanks is an unusual design 

feature not envisioned at the time the 

regulations in the Model A350–900 

series certification basis were 

promulgated. 

Discussion 

The certification basis of the Airbus 

Model A350–900 series includes 

§ 25.981, as amended by Amendment 

25–125, as required by 14 CFR 26.37. 

This amendment includes the ignition 

prevention requirements in § 25.981(a), 

as amended by Amendment 25–102, 

and it includes revised flammability 

limits for all fuel tanks and new specific 

limitations on flammability for all fuel 

tanks as defined in § 25.981(b), as 

amended by Amendment 25–125. 

Ignition Source Prevention 

Section 25.981(a)(3) requires 

applicants to show that an ignition 

source in the fuel tank system could not 

result from any single failure, from any 

single failure in combination with any 

latent failure condition not shown to be 

extremely remote, or from any 

combination of failures not shown to be 

extremely improbable. This requirement 

was originally adopted in Amendment 

25–102 and it requires the assumption 

that the fuel tanks are always flammable 

when showing that the probability of an 

ignition source being present is 

extremely remote. (Amendment 25–102 

included § 25.981(c) that required 

minimizing fuel tank flammability and 

this was defined in the preamble as 

being equivalent to unheated aluminum 

fuel tanks located in the wing.) This 

requirement defines three types of 

scenarios that must be addressed in 

order to show compliance with 

§ 25.981(a)(3). The first scenario is that 

any single failure, regardless of the 

probability of occurrence of the failure, 

must not cause an ignition source. The 

second scenario is that any single 

failure, regardless of the probability of 

occurrence, in combination with any 

latent failure condition not shown to be 

at least extremely remote, must not 

cause an ignition source. The third 

scenario is that any combination of 

failures not shown to be extremely 

improbable must not cause an ignition 

source. Demonstration of compliance 

with this requirement would typically 

require a structured, quantitative safety 

analysis. Design areas that have latent 

failure conditions typically would be 

driven by these requirements to have 

multiple fault tolerance, or ‘‘triple 

redundancy.’’ This means that ignition 

sources are still prevented even after 

two independent failures. 

Flammability Limits 

Section 25.981(b) states that no fuel 

tank fleet average flammability exposure 

may exceed 3 percent of the 

flammability exposure evaluation time 

calculated using the method in part 25, 

Appendix N, or the fleet average 

flammability of a fuel tank within the 

wing of the airplane being evaluated, 

whichever is greater. If the wing is not 

a conventional unheated aluminum 

wing, the analysis must be based on an 

assumed equivalent conventional 

construction unheated aluminum wing. 

In addition, for fuel tanks that are 

normally emptied during operation and 

that have any part of the tank located 

within the fuselage contour, the fleet 

average flammability for warm days 

(above 80 °F) must be limited to 3 

percent as calculated using the method 

in part 25, Appendix M. 

Application of Existing Regulations 

Inappropriate Due to Impracticality 

Since the issuance of § 25.981(a)(3), as 

amended by Amendment 25–102, the 

FAA has conducted certification 

projects in which applicants found it 

impractical to meet the requirements of 

that regulation for some areas of 

lightning protection for fuel tank 

structure. Partial exemptions were 

issued for these projects. These same 

difficulties exist for the Airbus Model 

A350–900 series project. 

The difficulty of designing multiplefault-tolerant structure, and the 

difficulty of detecting failures of hidden 

structural design features in general, 

makes compliance with § 25.981(a)(3) 

uniquely challenging and impractical 

for certain aspects of the electrical 

bonding of structural elements. Such 

bonding is needed to prevent 

occurrence of fuel tank ignition sources 

from lightning strikes. The effectiveness 

and fault tolerance of electrical bonding 

features for structural joints and 

fasteners is partially dependent on 

design features that cannot be 

effectively inspected or tested after 

assembly without damaging the 

structure, joint, or fastener. Examples of 

such features include a required 

interference fit between the shank of a 

fastener and the hole in which the 

fastener is installed, metal foil or mesh 

imbedded in composite material, a 

required clamping force provided by a 

fastener to pull two structural parts 

together, and a required faying surface 

bond between the flush surfaces of 

adjacent pieces of structural material 

such as in a wing skin joint or a 

mounting bracket installation. In 

addition, other features that can be 

physically inspected or tested may be 

located within the fuel tanks; therefore, 

it is not practical to inspect for failures 

of those features at short intervals. 

Examples of such failures include 

separation or loosening of cap seals over 

fastener ends and actual structural 

failures of internal fasteners. This 

inability to practically detect 

manufacturing errors and failures of 

structural design features critical to 

lightning protection results in degraded 

conditions that occur and remain in 

place for a very long time, possibly for 

the remaining life of the airplane. 

Accounting for such long failure 

latency periods in the system safety 

analysis required by § 25.981(a)(3) 

would require multiple fault tolerance 

in the structural lightning protection 

design. As part of the design 

development activity for the Model 

A350–900 series, Airbus has examined 

possible design provisions to provide 

multiple fault tolerance in the structural 

design to prevent ignition sources from 

occurring in the event of lightning 

attachment to the airplane in critical 

locations. Airbus has concluded from 

this examination that providing 

multiple fault tolerance for some 

structural elements is not practical. 

Airbus has also identified some areas of 


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1The memorandum may be viewed at: http://

www.airweb.faa.gov/Regulatory_and_Guidance_

Library/rgPolicy.nsf/0/12350AE62D393B7A8

62575C300709CA3?OpenDocument&

Highlight=anm-112-08-002. 

the Model A350–900 series design 

where it is impractical to provide even 

single fault tolerance in the structural 

design to prevent ignition sources from 

occurring in the event of lightning 

attachment after a single failure. The 

FAA has reviewed this examination 

with Airbus in detail and has agreed 

that providing fault tolerance beyond 

that in the proposed Model A350–900 

series design for these areas would be 

impractical. 

As a result of the Airbus Model A350– 

900 series and other certifications 

projects, the FAA has now determined 

that compliance with § 25.981(a)(3) is 

impractical for some areas of lightning 

protection for fuel tank structure, and 

that application of § 25.981(a)(3) to 

those design areas is therefore 

inappropriate. The FAA plans further 

rulemaking to revise § 25.981(a)(3). As 

appropriate, the FAA plans to issue 

special conditions or exemptions, for 

certification projects progressing before 

the revision is complete. This is 

discussed in FAA Memorandum ANM– 

112–08–002, Policy on Issuance of 

Special Conditions and Exemptions 

Related to Lightning Protection of Fuel 

Tank Structure, dated May 26, 2009.1

Application of Existing Regulations 

Inappropriate Due to Compensating 

Feature That Provides Equivalent Level 

of Safety 

Section 25.981(b) sets specific 

standards for fuel tank flammability as 

discussed above under ‘‘Flammability 

Limits.’’ Under that regulation, the fleet 

average flammability exposure of all 

fuel tanks on the Model A350–900 

series may not exceed 3 percent of the 

flammability exposure evaluation time 

calculated using the method in part 25, 

Appendix N, or the fleet average 

flammability of a wing main tank within 

an equivalent construction conventional 

unheated aluminum wing fuel tank, 

whichever is greater. The typical fleet 

average fuel tank flammability of fuel 

tanks located in the wing ranges 

between 1 and 5 percent. If it is 

assumed that an Model A350–900 series 

equivalent conventional unheated 

aluminum wing fuel tank would not 

exceed a fleet average flammability time 

of 3 percent, the actual composite 

airplane wing fuel tank design would be 

required to comply with the 3 percent 

fleet average flammability standard and 

therefore a means to reduce the 

flammability to 3 percent would be 

required. However, the proposed Model 

A350–900 series design includes NGS 

for all fuel tanks that will also be shown 

to meet the additional, more stringent 

warm day average flammability 

standard in part 25, Appendix M, which 

is only required for normally emptied 

fuel tanks with some part of the tank 

within the fuselage contour. Fuel tanks 

that meet this requirement typically 

have average fuel tank flammability 

levels well below the required 3 

percent. 

Since the proposed NGS for all fuel 

tanks on the Model A350–900 series 

provides performance that meets part 

25, Appendix M, the FAA has 

determined that the risk reduction 

provided by this additional performance 

will provide compensation for some 

relief from the ignition prevention 

requirements of § 25.981(a)(3) while still 

establishing a level of safety equivalent 

to that established in the regulations. 

In determining the appropriate 

amount of relief from the ignition 

prevention requirements of § 25.981(a), 

the FAA considered the original overall 

intent of Amendment 25–102, which 

was to ensure the prevention of 

catastrophic events due to fuel tank 

vapor explosion. These proposed 

special conditions are intended to 

achieve that objective through a 

prescriptive requirement that fault 

tolerance (with respect to the creation of 

an ignition source) be provided for all 

structural lightning protection design 

features where providing such fault 

tolerance is practical, and through a 

performance-based standard for the risk 

due to any single failure vulnerability 

that exists in the design. In addition, for 

any structural lightning protection 

design features for which Airbus shows 

that providing fault tolerance is 

impractical, these proposed special 

conditions would require Airbus to 

show that a fuel tank vapor ignition 

event due to the summed risk of all nonfault-tolerant design features is 

extremely improbable. Airbus would be 

required to show that this safety 

objective is met by the proposed design 

using a structured system safety 

assessment similar to that currently 

used for demonstrating compliance with 

§§ 25.901 and 25.1309. 

Given these novel design features, and 

the compliance challenges noted earlier 

in this document, the FAA has 

determined that application of 

§ 25.981(a)(3) is inappropriate in that it 

is neither practical nor necessary to 

apply the ignition source prevention 

provisions of § 25.981(a)(3) to the 

specific fuel tank structural lightning 

protection features of the Airbus Model 

A350–900 series airplanes. However, 

without the § 25.981(a)(3) provisions, 

the remaining applicable regulations in 

the Model A350–900 series certification 

basis would be inadequate to set an 

appropriate standard for fuel tank 

ignition prevention. Therefore, in 

accordance with provisions of § 21.16, 

the FAA has determined that, instead of 

§ 25.981(a)(3), alternative fuel tank 

structural lighting protection 

requirements be applied to fuel tank 

lightning protection features that are 

integral to the airframe structure of the 

Model A350–900 series. These proposed 

alternative requirements are intended to 

provide the level of safety intended by 

§ 25.981(a)(3), based on our recognition, 

as discussed above, that a highly 

effective NGS for the fuel tanks makes 

it unnecessary to assume that the fuel 

tank is always flammable. As discussed 

previously, the assumption that the fuel 

tanks are always flammable was 

required when demonstrating 

compliance to the ignition prevention 

requirements of § 25.981(a)(3). 

One resulting difference between 

these proposed special conditions and 

the § 25.981(a)(3) provisions they are 

meant to replace is the outcome being 

prevented—fuel vapor ignition versus 

an ignition source. These proposed 

special conditions acknowledge that the 

application of fuel tank flammability 

performance standards will reduce fuel 

tank flammability to an extent that it is 

appropriate to consider the beneficial 

effects of flammability reduction when 

considering design areas where it is 

impractical to comply with 

§ 25.981(a)(3). 

One of the core requirements of these 

proposed special conditions is a 

prescriptive requirement that structural 

lightning protection design features 

must be fault tolerant. (An exception 

wherein Airbus can show that providing 

fault tolerance is impractical, and 

associated requirements, is discussed 

below.) The other core requirement is 

that Airbus must show that the design, 

manufacturing processes, and 

airworthiness limitations section of the 

instructions for continued airworthiness 

include all practical measures to 

prevent, and detect and correct, failures 

of structural lightning protection 

features due to manufacturing 

variability, aging, wear, corrosion, and 

likely damage. The FAA has determined 

that, if these core requirements are met, 

a fuel tank vapor ignition event due to 

lightning is not anticipated to occur in 

the life of the airplane fleet. This 

conclusion is based on the fact that a 

critical lightning strike to any given 

airplane is itself a remote event, and on 

the fact that fuel tanks must be shown 

to be flammable for only a relatively 


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small portion of the fleet operational 

life. 

For any non-fault-tolerant features 

proposed in the design, Airbus must 

show that eliminating these features or 

making them fault tolerant is 

impractical. The requirements and 

considerations for showing it is 

impractical to provide fault tolerance 

are described in FAA Memorandum 

ANM–112–08–002. This requirement is 

intended to minimize the number of 

non-fault tolerant features in the design. 

For areas of the design where Airbus 

shows that providing fault tolerant 

structural lighting protection features is 

impractical, non-fault-tolerant features 

will be allowed provided Airbus can 

show that a fuel tank vapor ignition 

event due to the non-fault-tolerant 

features is extremely improbable when 

the sum of probabilities of those events 

due to all non-fault-tolerant features is 

considered. Airbus will be required to 

submit a structured, quantitative 

assessment of fleet average risk for a fuel 

tank vapor ignition event due to all nonfault-tolerant design features included 

in the design. This will require 

determination of the number of nonfault tolerant design features, estimates 

of the probability of the failure of each 

non-fault-tolerant design feature, and 

estimates of the exposure time for those 

failures. This analysis must include 

failures due to manufacturing 

variability, aging, wear, corrosion, and 

likely damage. 

It is acceptable to consider the 

probability of fuel tank flammability, 

the probability of a lightning strike to 

the airplane, the probability of a 

lightning strike to specific zones of the 

airplane (for example, Zone 2 behind 

the nacelle, but not a specific location 

or feature), and a distribution of 

lightning strike amplitude in performing 

the assessment provided the associated 

assumptions are acceptable to the FAA. 

The analysis must account for any 

dependencies among these factors, if 

they are used. The assessment must also 

account for operation with inoperative 

features and systems, including any 

proposed or anticipated dispatch relief. 

This risk assessment requirement is 

intended to ensure that an acceptable 

level of safety is provided given the 

non-fault-tolerant features in the 

proposed design. 

Part 25, Appendix N, as adopted in 

Amendment 25–125, in conjunction 

with these proposed special conditions, 

constitutes the standard for how to 

determine flammability probability. In 

performing the safety analysis required 

by these special conditions, relevant 

§ 25.981(a)(3) compliance guidance is 

still applicable. Appropriate credit for 

the conditional probability of 

environmental or operational conditions 

occurring is normally limited to those 

provisions involving multiple failures, 

and this type of credit is not normally 

allowed in evaluation of single failures. 

However, these special conditions 

would allow consideration of the 

probability of occurrence of lightning 

attachment and flammable conditions 

when assessing the probability of 

structural failures resulting in a fuel 

tank vapor ignition event. 

The FAA understands that lightning 

protection safety for airplane structure 

is inherently different from lightning 

protection for systems. We intend to 

apply these proposed special conditions 

only to structural lightning protection 

features of fuel systems. We do not 

intend to apply the alternative standards 

used under these proposed special 

conditions to other areas of the airplane 

design evaluation. 

Requirements Provide Equivalent Level 

of Safety 

In recognition of the unusual design 

feature discussed above, and the 

impracticality of requiring multiple 

fault tolerance for lightning protection 

of certain aspects of fuel tank structure, 

the FAA has determined that an 

equivalent level of safety to direct 

compliance with § 25.981(a)(3) will be 

achieved for the Model A350–900 series 

by applying these proposed 

requirements. The FAA considers that, 

instead of only concentrating on fault 

tolerance for ignition source prevention, 

significantly reducing fuel tank 

flammability exposure in addition to 

preventing ignition sources is a better 

approach to lightning protection for the 

fuel tanks. In addition, the level of 

average fuel tank flammability achieved 

by compliance with these proposed 

special conditions is low enough that it 

is not appropriate or accurate to assume 

in a safety analysis that the fuel tanks 

may always be flammable. 

Section 25.981(b), as amended by 

Amendment 25–125, sets limits on the 

allowable fuel tank flammability for the 

Model A350–900 series. Paragraph 2(a) 

of these proposed special conditions 

applies the more stringent standard for 

warm day flammability performance 

applicable to normally emptied tanks 

within the fuselage contour from 

§ 25.981(b) and part 25, Appendix M, to 

all of the fuel tanks of the Model A350– 

900 series. 

Because of the more stringent fuel 

tank flammability requirements in these 

proposed special conditions, and 

because the flammability state of a fuel 

tank is independent of the various 

failures of structural elements that could 

lead to an ignition source in the event 

of lightning attachment, the FAA has 

agreed that it is appropriate in this case 

to allow treatment of flammability as an 

independent factor in the safety 

analysis. The positive control of 

flammability and the lower flammability 

that is required by these proposed 

special conditions exceeds the 

minimum requirements of § 25.981(b). 

This offsets a reduction of the stringent 

standard for ignition source prevention 

in § 25.981(a)(3), which assumes that 

the fuel tank is flammable at all times. 

Given the stringent requirements for 

fuel tank flammability, the fuel vapor 

ignition prevention and the ignition 

source prevention requirements in these 

proposed special conditions will 

prevent ‘‘ . . . catastrophic failure . . . 

due to ignition of fuel or vapors’’ as 

stated in § 25.981(a). Thus, the overall 

level of safety achieved by these 

proposed special conditions is 

considered equivalent to that which 

would be required by compliance with 

§ 25.981(a)(3) and (b). 

Applicability 

As discussed above, these proposed 

special conditions apply to Airbus 

Model A350–900 series airplanes. 

Should Airbus apply later for a change 

to the type certificate to include another 

model incorporating the same novel or 

unusual design feature, the special 

conditions would apply to that model as 

well. 

Conclusion 

This action affects only certain novel 

or unusual design features on the Airbus 

Model A350–900 series airplanes. It is 

not a rule of general applicability. 

List of Subjects in 14 CFR Part 25 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

The authority citation for these 

special conditions is as follows: 

Authority: 49 U.S.C. 106(g), 40113, 44701, 

44702, 44704. 

The Proposed Special Conditions 

Accordingly, the Federal Aviation 

Administration (FAA) proposes the 

following special conditions as part of 

the type certification basis for Airbus 

Model A350–900 series airplanes. 

1. Definitions 

Most of the terms used in these 

proposed special conditions, Alternative 

Fuel Tank Structural Lightning 

Protection Requirements, either have 

the common dictionary meaning or are 

defined in Advisory Circular 25.1309– 

1A, System Design and Analysis, dated 

June 21, 1988. The following definitions 


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are the only terms intended to have a 

specialized meaning when used in these 

proposed special conditions: 

(a) Basic Airframe Structure. Includes 

design elements such as structural 

members, structural joint features, and 

fastener systems including airplane 

skins, ribs, spars, stringers, etc., and 

associated fasteners, joints, coatings, 

and sealant. Basic airframe structure 

may also include those structural 

elements that are expected to be 

removed for maintenance, such as 

exterior fuel tank access panels and 

fairing attachment features, provided 

maintenance errors that could 

compromise associated lightning 

protection features would be evident 

upon an exterior preflight inspection of 

the airplane and would be corrected 

prior to flight. 

(b) Permanent Systems Supporting 

Structure. Includes static, permanently 

attached structural parts (such as 

brackets) that are used to support 

system elements. It does not include any 

part intended to be removed, or any 

joint intended to be separated, to 

maintain or replace system elements or 

other parts, unless that part removal or 

joint separation is accepted by the FAA 

as being extremely remote. 

(c) Manufacturing Variability. 

Includes tolerances and variability 

allowed by the design and production 

specifications as well as anticipated 

errors or escapes from the 

manufacturing and inspection 

processes. 

(d) Extremely Remote. Conditions that 

are not anticipated to occur to each 

airplane during its total life, but which 

may occur a few times when 

considering the total operational life of 

all airplanes of one type. Extremely 

remote conditions are those having an 

average probability per flight hour on 

the order of 1 × 10¥7 or less, but greater 

than on the order of 1 × 10¥9. 

(e) Extremely Improbable. Conditions 

that are so unlikely that they are not 

anticipated to occur during the entire 

operational life of all airplanes of one 

type. Extremely improbable conditions 

are those having an average probability 

per flight hour of the order of 1 × 10¥9

or less. 

2. Alternative Fuel Tank Structural 

Lightning Protection Requirements 

For lightning protection features that 

are integral to fuel tank basic airframe 

structure or permanent systems 

supporting structure, as defined in this 

these proposed special conditions, 

Definitions, for which Airbus shows and 

the FAA finds compliance with 

§ 25.981(a)(3) to be impractical, the 

following requirements may be applied 

in lieu of the requirements of 

§ 25.981(a)(3): 

(a) Airbus must show that the airplane 

design meets the requirements of part 

25, Appendix M, as amended by 

Amendment 25–125, for all fuel tanks 

installed on the airplane. 

(b) Airbus must show that the design 

includes at least two independent, 

effective, and reliable lightning 

protection features (or sets of features) 

such that fault tolerance to prevent 

lightning-related ignition sources is 

provided for each area of the structural 

design proposed to be shown compliant 

with these proposed special conditions 

in lieu of compliance with the 

requirements of § 25.981(a)(3). Fault 

tolerance is not required for any specific 

design feature if: 

(1) For that feature, providing fault 

tolerance is shown to be impractical, 

and 

(2) Fuel tank vapor ignition due to 

that feature and all other non-faulttolerant features, when their fuel tank 

vapor ignition event probabilities are 

summed, is shown to be extremely 

improbable. 

(c) Airbus must perform an analysis to 

show that the design, manufacturing 

processes, and airworthiness limitations 

section of the instructions for continued 

airworthiness include all practical 

measures to prevent, and detect and 

correct, failures of structural lightning 

protection features due to 

manufacturing variability, aging, wear, 

corrosion, and likely damage. 

Issued in Renton, Washington, on 

November 15, 2013. 

John P. Piccola, Jr., 

Manager, Transport Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. 2013–30236 Filed 12–18–13; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 71 

[Docket No. FAA–2013–0922; Airspace 

Docket No. 13–AWA–5] 

RIN 2120–AA66 

Proposed Modification of the 

Philadelphia, PA, Class B Airspace 

Area 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: This action proposes to 

amend the description of Area G of the 

Philadelphia Class B airspace area to 

correct a design error that resulted in 

the Class B airspace being published 2.1 

nautical miles (NM) larger on the 

southeast side of the area than intended. 

No other changes to the Philadelphia 

Class B airspace are being proposed. 

DATES: Comments must be received on 

or before February 3, 2014. 

ADDRESSES: Send comments on this 

proposal to the U.S. Department of 

Transportation, Docket Operations, M– 

30, 1200 New Jersey Avenue SE., West 

Building Ground Floor, Room W12–140, 

Washington, DC 20590–0001; telephone: 

(202) 366–9826. You must identify FAA 

Docket No. FAA–2013–0922 and 

Airspace Docket No. 13–AWA–5 at the 

beginning of your comments. You may 

also submit comments through the 

Internet at http://www.regulations.gov. 

FOR FURTHER INFORMATION CONTACT: Paul 

Gallant, Airspace Policy and 

Regulations Group, Office of Airspace 

Services, Federal Aviation 

Administration, 800 Independence 

Avenue SW., Washington, DC 20591; 

telephone: (202) 267–8783. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

Interested parties are invited to 

participate in this proposed rulemaking 

by submitting such written data, views, 

or arguments as they may desire. 

Comments that provide the factual basis 

supporting the views and suggestions 

presented are particularly helpful in 

developing reasoned regulatory 

decisions on the proposal. Comments 

are specifically invited on the overall 

regulatory, aeronautical, economic, 

environmental, and energy-related 

aspects of the proposal. 

Communications should identify both 

docket numbers (FAA Docket No. FAA– 

2013–0922 and Airspace Docket No. 13– 

AWA–5) and be submitted in triplicate 

to the Docket Management Facility (see 

ADDRESSES section for address and 

phone number). You may also submit 

comments through the internet at http:// 

www.regulations.gov. 

Commenters wishing the FAA to 

acknowledge receipt of their comments 

on this action must submit with those 

comments a self-addressed, stamped 

postcard on which the following 

statement is made: ‘‘Comments to 

Docket Nos. FAA–2013–0922 and 

Airspace Docket No. 13–AWA–5.’’ The 

postcard will be date/time stamped and 

returned to the commenter. 

All communications received on or 

before the specified closing date for 

comments will be considered before 

taking action on the proposed rule. The 

proposal contained in this action may 


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