71346 Federal Register / Vol. 75, No. 225 / Tuesday, November 23, 2010 / Rules and Regulations 

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Done at Washington, DC, on November 16, 

2010. 

Alfred V. Almanza, 

Administrator. 

[FR Doc. 2010–29492 Filed 11–22–10; 8:45 am] 

BILLING CODE 3410–DM–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. NM415; Special Conditions No. 

25–414–SC] 

Special Conditions: Boeing Model 787– 

8 Airplane; Lightning Protection of 

Fuel Tank Structure To Prevent Fuel 

Tank Vapor Ignition 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final special conditions. 

SUMMARY: These special conditions are 

issued for the Boeing Model 787–8 

airplane. This airplane will have novel 

or unusual design features when 

compared to the state of technology 

envisioned in the airworthiness 

standards for transport category 

airplanes. The Boeing Model 787–8 

airplane will incorporate a fuel tank 

nitrogen generation system (NGS) that 

actively reduces flammability exposure 

within the main fuel tanks significantly 

below that required by the fuel tank 

flammability regulations. Among other 

benefits, this 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 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: Effective Date: December 23, 

2010. 

FOR FURTHER INFORMATION CONTACT: 

Mike Dostert, FAA, ANM–112, 

Transport Airplane Directorate, Aircraft 

Certification Service, 1601 Lind 

Avenue, SW., Renton, Washington 

98057–3356; telephone (425) 227–2132; 

facsimile (425) 227–1149. 

SUPPLEMENTARY INFORMATION: 

Background 

On March 28, 2003, The Boeing 

Company applied for an FAA type 

certificate for its new Boeing Model 

787–8 passenger airplane. The Boeing 

Model 787–8 airplane will be a new 

design, two-engine turbo-jet transport 

category airplane with a two-aisle cabin 

configuration. The maximum takeoff 

weight will be 484,000 pounds, and it 

will carry a maximum of 381 

passengers. 

Type Certification Basis 

Under provisions of Title 14, Code of 

Federal Regulations (14 CFR) 21.17, 

Boeing must show that Boeing Model 

787–8 airplanes (hereafter referred to as 

‘‘the 787’’) meet the applicable 

provisions of 14 CFR part 25, as 

amended by Amendments 25–1 through 

25–117, with three exceptions. Sections 

25.809(a) and 25.812 will remain as 

amended by Amendment 25–115, and 

§ 25.981, which will be as amended by 

Amendment 25–125 in accordance with 

14 CFR 26.37. 

If the Administrator finds that the 

applicable airworthiness regulations 

(i.e., part 25) do not contain adequate or 

appropriate safety standards for the 787 

because of novel or unusual design 

features, special conditions are 

prescribed under provisions of 14 CFR 

21.16. 

In addition to the applicable 

airworthiness regulations and special 

conditions, the 787 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. Finally, the FAA must also 

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, in accordance 

with § 11.38, and they become part of 

the type certification 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 or similar novel 

or unusual design features, the special 

conditions would also apply to the other 

model under § 21.101. 

Novel or Unusual Design Features 

The 787 will have a fuel tank NGS 

that is intended to control fuel tank 

flammability. This NGS is designed to 

provide a level of performance that will 

reduce the warm day fleet average wing 

fuel tank flammability significantly 

below the maximum wing fuel tank 

flammability limits set in § 25.981(b), as 

amended by Amendment 25–125. This 

high level of wing fuel tank NGS 

performance is an unusual design 

feature not envisioned at the time the 

regulations in the 787 certification basis 

were promulgated. 

Existing Regulations 

The certification basis of the 787 

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 the wing fuel 

tanks and new specific limitations on 

flammability of normally emptied fuel 

tanks located within the fuselage 

contour as defined in § 25.981(b), as 

amended by Amendment 25–125. 

(Section 25.981(c) contains an 

alternative to meeting paragraph (b)— 

vapor ignition mitigation—that is not 

applicable to the 787 design.) 

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 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 

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Federal Register / Vol. 75, No. 225 / Tuesday, November 23, 2010 / Rules and Regulations 71347 

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

www.airweb.faa.gov/Regulatory_and

_Guidance_Library/rgPolicy.nsf/0/

12350AE62D393B7A862575C300709CA3?Open

Document&Highlight=anm-112-08-002. 

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 construction 

conventional 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 787 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 787, Boeing 

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. Boeing 

has concluded from this examination 

that providing multiple fault tolerance 

for some structural elements is not 

practical. Boeing has also identified 

some areas of the 787 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 Boeing 

in detail and has agreed that providing 

fault tolerance beyond that in the 

proposed 787 design for these areas 

would be impractical. 

As a result of the 787 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 wing 

main tanks on the 787 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 a 787 

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 787 

design includes a wing tank NGS 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 wing tank NGS on 

the 787 provides performance that 

meets part 25, Appendix M, the FAA 

has determined that the risk reduction 

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71348 Federal Register / Vol. 75, No. 225 / Tuesday, November 23, 2010 / Rules and Regulations 

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 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 performancebased 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 Boeing shows that 

providing fault tolerance is impractical, 

these special conditions would require 

Boeing to show that a fuel tank vapor 

ignition event due to the summed risk 

of all non-fault-tolerant design features 

is extremely improbable. Boeing 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. 

Discussion of the Final Special 

Conditions 

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 787. However, 

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

the remaining applicable regulations in 

the 787 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 

787. These 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 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 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 

special conditions is a prescriptive 

requirement that structural lightning 

protection design features must be fault 

tolerant. (An exception wherein Boeing 

can show that providing fault tolerance 

is impractical, and associated 

requirements, is discussed below.) The 

other core requirement is that Boeing 

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 

small portion of the fleet operational 

life. 

For any non-fault-tolerant features 

proposed in the design, Boeing 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 Boeing 

shows that providing fault tolerant 

structural lighting protection features is 

impractical, non-fault-tolerant features 

will be allowed provided Boeing 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. Boeing 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 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 special conditions only to 

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Federal Register / Vol. 75, No. 225 / Tuesday, November 23, 2010 / Rules and Regulations 71349 

structural lightning protection features 

of fuel systems. We do not intend to 

apply the alternative standards used 

under these 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 787 by applying these 

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 tank. In addition, the level of 

average fuel tank flammability achieved 

by compliance with these 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 

787. Paragraph 2(a) of these 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 the wing tanks of the 

787. 

Because of the more stringent fuel 

tank flammability requirements in these 

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 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 

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 special 

conditions is considered equivalent to 

that which would be required by 

compliance with § 25.981(a)(3) and (b). 

Discussion of Comments 

Notice of proposed special conditions 

No. 25–09–11–SC for the Boeing Model 

787–8 airplanes was published in the 

Federal Register on October 14, 2009 

(74 FR 52698). Several comments were 

received from two commenters (Cessna 

and NATCA). 

Cessna #1 

Cessna requested additional wording 

be added to the discussion of the 

proposed special conditions to clarify 

the fuel tank flammability requirements 

proposed in the special conditions 

would only be applied specifically to 

special conditions. Cessna referred to 

FAA Policy Memo ANM–112–08–002 

and noted the flammability levels of 

Appendix M are not defined as a 

precondition for petitions for 

exemptions. Cessna proposed the 

following text: 

‘‘Since the proposed wing tank NGS on the 

787 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.’’ 

The additional wording proposed by 

the commenter clarifies that the safety 

level provided by the special conditions 

is equivalent to that established in the 

regulation. Part 21 only allows the FAA 

to propose special conditions when 

equivalent safety to the applicable 

airworthiness standards has been 

demonstrated. We agree with the 

accuracy of the commenters proposed 

text and modified the wording of the 

discussion in the special conditions as 

suggested by the commenter. 

As we have already stated in FAA 

Policy Memo ANM–112–08–002 (Policy 

on Issuance of Special Conditions and 

Exemptions Related to Lightning 

Protection of Fuel Tank Structure), for 

traditional airplanes that do not have 

active flammability reduction systems, 

where the applicant shows that full 

compliance with § 25.981 is impractical, 

we intend to allow a similar reduction 

in the number of ignition-prevention 

features using the exemption process. 

Exemptions are needed because 

reducing the number of ignitionprevention features without reducing 

the fuel-tank flammability does not 

provide equivalent safety to § 25.981. 

No change to the proposed special 

conditions was made as a result of this 

comment. 

Cessna #2 

Cessna recommended that the 

alternative requirements for special 

conditions and exemptions to 

§ 25.981(a)(3) include considerations for 

both structure and systems, with regards 

to both lightning and electrostatics 

protection. They supported their 

comment with the rationale that 

electrostatic protection methods rely 

upon bonding techniques similar to 

those employed for lightning protection, 

and pose similar practicality issues. 

Each additional redundant bonding 

provision is itself another potential 

failure mode, and the over-complication 

of increased redundancy presents 

maintenance and operational issues. 

Cessna requested that the proposed 

Special Condition No. 1, Definitions, be 

changed to broaden the applicability of 

the special conditions to include 

‘‘systems internal to the fuel tank.’’ We 

have already addressed this comment in 

developing FAA Policy Memo ANM– 

112–08–002. The public comments to 

FAA Policy Memo ANM–112–08–002 

and our disposition of those comments 

are available at http://rgl.faa.gov. Click 

on ‘‘Policy,’’ then search (By Policy 

Number) for ANM–112–08–002. The 

commenter has provided no new 

information, and no change was made to 

the proposed special conditions as a 

result of this comment. 

Cessna #3 

Cessna recommended the FAA 

include reference to guidance material 

developed by the Society of Automotive 

Engineers (SAE) AE–2 Lightning 

Committee directly in exemptions and 

special conditions. The FAA 

participated on the SAE committee that 

prepared the guidance material. 

However, at this time the FAA has not 

completed its review of the AE–2 

guidance. We will review the proposed 

guidance material and publish it for 

comment if we determine it to be a 

viable means of showing compliance to 

special conditions or exemptions. In the 

mean time, this guidance is not 

necessary for the adoption of, or 

compliance with, these special 

conditions. 

NATCA #1 

The National Air Traffic Controller 

Association (NATCA) requested the 

proposed special conditions be 

withdrawn since they believe the 

information provided in the special 

condition’s Background section does not 

support the FAA finding that the 

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71350 Federal Register / Vol. 75, No. 225 / Tuesday, November 23, 2010 / Rules and Regulations 

proposed special conditions provide 

equivalent safety to the existing part 25 

safety standards for transport airplanes. 

We have already addressed this 

request to not publish the proposed 

special conditions in developing FAA 

Policy Memo ANM–112–08–002. For 

the reasons stated in that policy memo 

and the associated disposition of 

comments, we believe these special 

conditions do establish an equivalent 

level of safety. 

NATCA #2 & #3 

NATCA provided an alternative to the 

proposed special conditions. They 

requested the proposed special 

conditions be withdrawn and revised 

and suggested the following 

requirements replace those proposed by 

the FAA: 

(1) Eliminate the allowance for single 

failures that can result in an ignition 

source, unless the fuel tank is shown to 

have a flammability reduction means 

that prevents the tanks from becoming 

flammable or, 

(2) Do not allow dispatch of any 

airplane with the inerting system that is 

not functioning if the design does not 

have two independent features that will 

prevent an ignition source. 

NATCA provided comments in 

support of its suggested change to the 

special conditions discussed above that 

would not ‘‘allow dispatch of any 

airplane with the inerting system that is 

not functioning if the design does not 

have independent features that will 

prevent an ignition source.’’ They 

suggested a means of meeting their 

proposed special conditions could be 

achieved by ‘‘a combination of 

eliminating the single failures through 

design improvements and limiting 

airplane operation on warmer days with 

the NGS inoperative could essentially 

eliminate the chance of a fuel tank 

explosion due to a lightning strike.’’ 

They supported their comment by 

stating design improvements 

implemented by Boeing have reduced 

the number of ignition sources and 

further design improvements 

implemented on later production 

airplanes could eliminate single 

failures. They proposed that once the 

single failures were eliminated, the 

restriction on dispatch of airplanes with 

the inerting system inoperative could be 

removed. They stated this would be a 

practical way to implement new 

technology because a small number of 

airplane flights could be impacted by 

flight delays caused by an inoperative 

fuel tank inerting system. 

We have already addressed the 

proposal to restrict dispatch with the 

inerting system inoperative in 

developing FAA Policy Memo ANM– 

112–08–002. In short, determining 

appropriate dispatch relief, if any, is the 

function of the Flight Operations 

Evaluation Board and not the function 

of special conditions. 

NATCA #4 

NATCA requested extension of the 

comment period because guidance 

material regarding means of compliance 

with the proposed special conditions 

was not available to the public prior the 

closing of the comment period. We do 

not agree with the request to extend the 

comment period but do agree that 

public comment on future policy should 

be sought. These special conditions are 

specific to the 787 and means of 

compliance are dependent upon specific 

proprietary design details of the 

airplane that cannot be released to the 

public. 

NATCA #5 

NATCA provided comments that the 

number of single failures on the 787 had 

been reduced through design changes 

and that earlier exemptions issued by 

the FAA did not allow single failures. 

They questioned the FAA’s 

determination that it is impractical to 

eliminate single failures in the 787 

design. They offered specific examples 

of possible methods of preventing 

certain single failures discussed in the 

preamble to the proposed special 

conditions, including use of monitoring 

aids consisting of overlays that are on 

the outside the fuel tank where failure 

could be easily detected and therefore 

failure of the features would not be 

latent. 

From this comment the FAA infers 

the commenter believes preventing all 

single failures is practical. While 

NATCA is correct that previously issued 

exemptions did not explicitly allow for 

single failures, at the time those 

exemptions were issued, we were not 

aware of the particular failure modes 

that could result in single failures that 

could create ignition sources. As stated 

in the proposed special conditions and 

in the discussion in FAA Policy Memo 

ANM–112–08–002, we now recognize 

that eliminating all single failures in 

airplane structure using current state-ofthe-art design practices is not always 

practical. 

The FAA therefore does not agree that 

the proposed allowance for single 

failure conditions should be eliminated. 

NATCA #7 

NATCA requested that ‘‘the FAA 

make available to the public all 

documentation supporting the 

impracticality findings for each ignition 

prevention feature that will not be failsafe, as well as why it is impractical 

(costs) to issue special conditions 

requiring the 787 inerting system be 

operating on warmer days on any 

airplane that has been produced with 

known single failures.’’ No change to the 

special conditions was requested in this 

comment. General information 

supporting the impracticality of 

eliminating single failures, as well as 

considerations for operating airplanes 

with the NGS inoperative, was 

previously discussed in FAA Policy 

Memo ANM–112–08–002. The specific 

design issues associated with the design 

of the 787 are likely to be proprietary, 

but that determination can only be made 

in the context of a Freedom of 

Information Act request. The special 

conditions, with clarifications discussed 

above, are adopted as proposed. 

Applicability 

As discussed above, these special 

conditions are applicable to the Boeing 

Model 787–8 airplane. Should Boeing 

apply at a later date for a change to the 

type certificate to include another 

model incorporating the same novel or 

unusual design features, these special 

conditions would apply to that model as 

well. 

Conclusion 

This action affects only certain novel 

or unusual design features of the Boeing 

Model 787–8 airplane. 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 Special Conditions 

Accordingly, pursuant to the 

authority delegated to me by the 

Administrator, the following special 

conditions are issued as part of the type 

certification basis for the Boeing Model 

787–8 airplane. 

1. Definitions 

Most of the terms used in Special 

Condition No. 2, 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 are the only 

terms intended to have a specialized 

meaning when used in Special 

Condition No. 2: 

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Federal Register / Vol. 75, No. 225 / Tuesday, November 23, 2010 / Rules and Regulations 71351 

(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 

Special Condition No. 1, Definitions, for 

which The Boeing Company 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) The Boeing Company 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) The Boeing Company 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 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) The applicant 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, 2010. 

Ali Bahrami, 

Manager, Transport Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. 2010–29409 Filed 11–22–10; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2010–0725; Directorate 

Identifier 2010–NE–18–AD]; Amendment 39– 

16528; AD 2010–24–09] 

RIN 2120–AA64 

Airworthiness Directives; Pratt & 

Whitney PW4000 Series Turbofan 

Engines 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final rule. 

SUMMARY: We are adopting a new 

airworthiness directive (AD) for the 

products listed above. This AD requires 

a one-time visual inspection of the No. 

3 bearing oil pressure tube, part number 

(P/N) 51J041–01, P/N 50J604–01, or 

P/N 50J924–01. Tubes that are found 

cracked or repaired must be removed 

from service. This AD also prohibits 

repaired tubes from being installed. This 

AD results from one report of a repaired 

No. 3 bearing oil tube that caused an 

engine in-flight shutdown, seven reports 

of repaired No. 3 bearing oil pressure 

tubes found cracked that led to 

unscheduled engine removals, and one 

report of a test cell event from a repaired 

tube that cracked. We are issuing this 

AD to prevent cracking of No. 3 bearing 

oil pressure tubes, which could result in 

internal oil fire, failure of the highpressure turbine (HPT) disks, 

uncontained engine failure, and damage 

to the airplane. 

DATES: This AD is effective December 

28, 2010. 

Examining the AD Docket 

You may examine the AD docket on 

the Internet at http:// 

www.regulations.gov; or in person at the 

Docket Management Facility between 

9 a.m. and 5 p.m., Monday through 

Friday, except Federal holidays. The AD 

docket contains this AD, the regulatory 

evaluation, any comments received, and 

other information. The address for the 

Docket Office (phone: 800–647–5527) is 

Document Management Facility, U.S. 

Department of Transportation, Docket 

Operations, M–30, West Building 

Ground Floor, Room W12–140, 1200 

New Jersey Avenue, SE., Washington, 

DC 20590. 

FOR FURTHER INFORMATION CONTACT: 

James Gray, Aerospace Engineer, Engine 

Certification Office, FAA, Engine and 

Propeller Directorate, 12 New England 

Executive Park, Burlington, MA 01803; 

telephone (781) 238–7742; fax (781) 

238–7199; e-mail: james.e.gray@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Discussion 

We issued a notice of proposed 

rulemaking (NPRM) to amend 14 CFR 

part 39 to include an airworthiness 

directive (AD) that would apply to the 

specified products. That NPRM 

published in the Federal Register on 

June 3, 2010 (75 FR 31330). That NPRM 

proposed to require: 

• A one-time visual inspection of the 

No. 3 bearing oil pressure tube, P/N 

51J041–01, P/N 50J604–01, or P/N 

50J924–01; and 

• Removal from service if found 

cracked or repaired, or if suspected that 

the tube was repaired; and 

• A prohibition on installing repaired 

tubes. 

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