rtJ-aoEING John A. Hamilton 

Lead Administrator 

Regulatory Administration 

Commercial Airplanes 

The Boeing Company 

P.O. Box 3707 MC 03-56 

Seattle, WA 98124-2207 

JUN 2'2 2012 

RA-12-02722 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor, Room Wl2-140 

1200 New Jersey Avenue, S.E. 

Washington, DC 20590 

Subject: 

Model: 

RA Project No.: 

EASA Project No.: 

EASALevel: 

Branch/Panel No.: 

Branch/Panel Name: 

Response Due: 

Reference(s): 

Special Instructions: 

This letter is to submit: 

Petition for Exemption from 14 CFR 

25.981(a)(3), Amendment 25..:125, Fuel Tank 

Structural Lightning Protection· 

767-2C 

PS09-086J 

N/A 

N/A 

ANM-106B 

Certification Services 

September 21st, 2012 

(a) Regulatory Docket No. FAA-2009-1058. 

N/A 

FAA Exemption No. 10174, December 14, 

2010, Boeing 747-8F Fuel Tank Structural 

Lightning Protection, Exemption from FAR 

25.981(a)(3) 

(X) Other: Petition for Exemption from 14 CPR 25.981(a)(3) 

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The Boeing Company hereby petitions for an exemption for relief from the fueltank safety provisions of 14 CFR 25.981(a)(3) Amendment 25-125 for structural 

lightning protection of wing fasteners ofthe Boeing Model 767-2C. 

To support the 767-2C ATC program schedule, The Boeing Company requests 

that the enclosed information be processed by September 21 5

\ 2012. 

Furthermore, The Boeing Company requests to be notified when the enclosed 

petition processing has completed. 

Waiver from Public Comment 

An exemption for this subject has previously been granted for the 747-8F as 

documented in Reference (a). Therefore, this petition will not set a precedent 

and accordingly, The Boeing Company respectfully requests a waiver from the 

publication and public comment period of this exemption. The Boeing Company 

believes that good cause exists to waive the publication and comment 

requirements of 14 CPR 11.85, 11.87, and 11.89. 
This letter is being sent for: 

(X) Posting to the Federal Docket 

Page2 

RA-12-02722 

Please contact this office or the following individuals if you have further 

questions: 

Project Administrator (PA): 

Program Manager 

Certification Lead/Specialist: 

P. Guilford 

S. Gordon 

J. Flower 

A. Telesca 

425'-237-5981 . 

425-237-6068 

206-715-1768 

425-266-7445 

The information being forwarded to the FAA by or with this correspondence is 

for the exclusive purpose of support of applications for or amendments to Type 

Certificates. . . · 

·~~ 

nouglas M. Lane 

ODA Deputy Lead Administrator 

(425) 237-1383, MC 03-56 . 

FAX: ( 425) 294-9340 

Enclosures: (A) Petition for Exemption from 14 CFR 25.981(a)(3) 

cc 

Name 

Jim Cashdollar 

Angelos Xidias 

Letter 

EDT 

EDT 

Enclosures 

EDT 

EDT 

Comments 

ANM-106B 

ANM-100.8 
Enclosure A 

RA-12-02722 

Page 1 of 8 

Petition for Exemption from§ 25.981 (a)(3) of Title 14, Code of Federal Regulations 

Petition for Exemption from 14 CFR 25.981 (a)(3) Amendment 25-125 

Name and Address of the Petitioner 

Doug Lane, Director, Regulatory Administration Deputy Lead Administrator 

The Boeing Company 

PO Box 3707 

Seattle, Washington, 98124 

Section(s) ofthe Regulations from which Relief is Sought: 

Boeing is petitioning for an exemption to 14 CFR 25.981(a)(3) for fuel tank structural lightning 

protection for the 767-2C (Project No. PS09-0863). The subject regulation section is unchanged 

between amendment level 1 02 and 125. The regulation as currently written: 

(a) 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: 

(3) 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. 

The Extent of Relief Sought and Reason( s) 

Regulation Requires: Relief is Necessary because: 

14 CFR 25.981(a)(3) Compliance to 14 CFR Boeing has concluded that for fuel tank 

Amendment 25-125 25:981(a)(3) for fuel tank fasteners, there are no practical means in 

structural fastener lightning current technology to obtain triple 

protection would require three redundant means of protection in all 

independent layers of locations. 

protection. The fuel tank fastener types utilized are 

unchanged from the baseline 767;..200 

airplane. In some locations, the sizes and 

grip lengths may change based on unique 

structural load requirements. New 

installations of similar faster types may 

also be incorporated. 

The FAA previously found a grant of 

exemption was in the public interest for 

the same fuel tank fastener issue on the 

747-8/8F (BDCO Project No PS05-0212 

& PS05-0211) (Exemption No. 10174 was 

granted). 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 2 of 8 

Petition for Exemption from§ 25.981 (a)(3) of Title 14, Code of Federal Regulations 

Description of Issue 

Boeing is petitioning for an exemption to 14 CFR 25.981(a)(3) for fuel tank structural lightning 

protection for the 767-2C (Project No. PS09-0863). The ANM-112-08-002 FAA policy 

memorandum provides the following alternate requirements: 

1. Instead of compliance with the requirements of§ 25.981 (a)(3), the applicant 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 area proposed to be exempt from the 

requirements of that regulation. Fault tolerance is not required for any specific design feature 

if: 

a) providing fault tolerance is shown to be impractical for that feature, and 

b) fuel tank vapor ignition because of that feature and all other non-fault tolerant features, 

when their fuel tank vapor ignition event probabilities are summed, is shown to be 

extremely improbable. 

2. 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 because of manufacturing variability, aging, wear, corrosion, and likely 

damage. 

Discussion 

Boeing has concluded that compliance to 14 CFR 25.981(a)(3) for fuel tank structural fastener 

lightning protection would require three independent layers of protection. For fuel tank fasteners, 

there are no practical means in current technology to obtain triple redundant means of protection in 

all locations. Another option would be to apply inspection interval which monitors the health of each 

fastener that penetrates the fuel tanks. With thousands of fasteners on the wing ofthe 767-2C, this 

option is impractical. Increasing the number of in-tank inspection intervals could also have a 

potential unintended consequence of damaging the lightning protective features or other components 

inside the fuel tanks. 

Proposed Risk Mitigation 

As discussed in the FAA Policy Memo, Boeing will submit detailed proprietary information to the 

FAA about the measures taken in the 767-2C design to provide practical structural lightning 

protection. In general, the 767-2C lightning protection features are based on state of the art industry 

design practices for aluminum wing structure including inherently conductive low resistance current 

paths that have been used in existing in service designs. Further, Boeing proposes to enhance the 

lightning protection by incorporating additional fault tolerant protection for fasteners in areas of 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 3 of 8 

Petition for Exemption from§ 25.981(a)(3) of Title 14, Code of Federal Regulations 

potential swept lightning attachment (referred to as Zone 2) by cap sealing the fasteners to contain a 

possible spark in the event that the primary protective features fail, thereby increasing the level of 

fuel tank safety. 

Boeing will show that the structural fastener design for the majority of the model 767-2C wing will 

have two reliable and effective features for lightning protection. Testing will show that the fastener 

installation will be safe for applicable lightning zone requirements and will not produce any sparks 

inside the fuel tanks. Additionally, Boeing will show by test that a cap seal, as a second layer of 

protection, will contain a spark should one occur from a failed fastener. For the limited areas in 

which a single failure of a fastener could result in loss of both protection features, or any other area 

where a single layer of protection is all that can practically be provided, a safety assessment will be 

done to show that the probability of a lightning related fuel tank ignition event is extremely 

improbable. The systems supporting structure will also be analyzed as part of the fault tree 

assessment to ensure that they meet the requirements in the policy memo. Additionally, Boeing will 

utilize production procedures in order to minimize the risk of mis-installed protective measures, and 

to identify and repair errors in such a way that the lightning protection features will be maintained. 

The instructions for continued airworthiness and repair procedures will also be provided to ensure 

the protection features are retained throughout the life of the airplane. 

The FAA previously found a grant of exemption was in the public interest for the same fuel tank 

fastener issue on the 747-8/SF (BDCO Project No PS05-0212 & PS05-0211) (Exemption No. 10174 

was granted). 

Additional Information 

1. The 767-2C design will show compliance with 14 CFR 25.981(b) and (d) at amendment 25-125. 

Documentation of compliance will be submitted for approval per CP 11633. 

2. Boeing has utilized all practical measures to meet the requirements of 14 CFR 25.981(a)(3) for 

fuel tank structural lightning protection. Boeing has designed the 767-2C fuel tank structure to 

be fault tolerant for all but two failure modes (broken bolts and structural cracks). A detailed 

FMEA will be provided as part of the compliance documentation. Analysis will be the primary 

means to demonstrate fault tolerance. Where analysis cannot be shown effective, a test program 

will be considered. 

As described, the 767-2C design utilizes properly installed structural fasteners and cap sealing to 

provide fault tolerant structural lightning protection. Boeing considered additional design 

features to the fuel tank structure to achieve dual fault tolerance for compliance to 14 CFR 

25.981(a)(3), but these were found either impractical to implement or insufficient to provide any 

additional lightning protection. 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 4 of 8 

Petition for Exemption from§ 25.981 (a)(3) of Title 14, Code of Federal Regulations 

Examples of design considerations were: 

o Conductive steel fasteners - widespread use results in higher weight, fuel bum and associated 

emissions, and higher risk of corrosion. Design with all steel fasteners is still not dual fault 

tolerant. 

o Additional sealant - Reduces structural inspectability for cracks and corrosion, potentially 

reducing overall fleet safety. Would result in additional weight, fuel bum and emissions. 

o Composite skin protection methods- Not applicable to aluminum design. Note the majority 

of these methods are intended to increas~ conductivity of the outer tank surface in the area 

local to the fastener heads, which aluminum structure provides inherently. 

o Fuel tank bladders or double walled fuel tanks - Would result in a new enclosed fuel vapor 

space, which would pose an additional vapor ignition threat during a lightning attachment 

and thus does not increase safety. This would also increase weight which increases fuel bum 

and emissions, plus reduces usable fuel tank volume which reduces range. The bladders also 

inhibit structural inspectability inside the tank. 

o Spot Bonds - Spot bond is a local bond in which the primer is removed at the internal 

fastener interface with structure. Removing primer increases corrosion risk, detracting from 

any benefit of increased conductivity offered by the spot bond. The spot bonds would still be 

subject to faults and does not result in a dual fault tolerant design. 

o Fastener Free Wing Structure- Structure that does not have any fasteners would not be 

susceptible to lightning protection faults associated with fasteners but is not necessarily dual 

fault tolerant. It is not possible to produce raw materials large enough to create monolithic 

wing panels or spars in dimensions that the 767-2C requires and monolithic designs would 

reduce structural crack tolerance. Using adhesives instead of fasteners to bond major 

-components represents a radical departure from established metallic wing primary structure 

experience. 

These types of designs were determined to be impractical due lack of safety benefit, increased 

weight, increased fuel bum, increased emissions, and reduced inspectability during maintenance. 

3. Boeing will demonstrate that the structure in Zone 3 (and Zone 2) is capable of providing fault 

tolerant protection to conducted currents, which is the only Zone 3 requirement. 

4. Boeing will provide a System Safety Assessment (SSA) as part of compliance for the 767 -2C 

program. A fault tree analysis will be included in the SSA which will quantify the single 

failures, and demonstrate the probability of a fuel vapor ignition in the life ofthe 767-2C fleet is 

. extremely improbable. 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 5 of 8 

Petition for Exemption from§ 25.981(a)(3) of Title 14, Code of Federal Regulations 

The only faults identified for which the design is not fault tolerant are: 

1. The potential for a latent crack in structure, or 

2. A bolt failure that also causes the fastener nut (or collar) to release with sufficient force to 

tear free the associated cap seal. 

Both of these failure modes are identified in the FAA Policy Memo as typical situations where 

applicants have been unable to identify practical means for fault tolerance. In each of these cases 

sparking due to these failures would only occur if there was a direct attachment to the local area 

of the failure. Boeing will demonstrate sparking does not occur due to these failures by 

similarity analysis to previously conducted testing or by new testing for configurations not 

covered by previous testing. 

For both of the above failure modes, Boeing has been unable to identify a practical alternative to 

provide a protection to the failure mode for direct attachment. A numerical assessment will be 

provided demonstrating the probability of a fuel vapor ignition due to these failures is extremely 

improbable (and thus unlikely to occur in the life of the fleet). Service experience on the existing 

commercial 767 fleet shows each ofthese failures to be rare. The failure rate for fasteners will 

be established using in-service data for fasteners on Boeing airplanes. The expected rate of 

occurrence of structural cracking will be conservatively based on Boeing's structural fatigue 

methodology. This methodology is based on test and service experience, and ensures that the 

presence of fatigue cracks is minimized during the life of the airplane. Although none are 

anticipated at this time, any additional non-fault tolerant installations identified later (e.g. during 

the test program) which are impractical to preclude will also be included in the required 

numerical analysis. 

5. Boeing has implemented in the design all practical measures for structural lighting protection. 

Boeing is currently reviewing the manufacturing processes to ensure the lightning protection 

features are implemented as intended on the drawings and are maintained. The repair procedures 

will be reviewed to ensure the lightning protection features will be maintained throughout the life 

of the airplane. Instructions for Continued Airworthiness will be developed and included in the 

certification documentation. A complete analysis of the manufacturing process and repair 

procedure will be part of the System Safety Assessment and submitted for compliance per CP 

11633. 

Statement of Public Interest 

The 767-2C is a commercial freighter aircraft that will also serve as the baseline for military 

commercial derivative aircraft. For lightning protection, the 767-2C has additional features to 

enhance safety and protect the fuel tanks from sparking due to a lightning event. All practical 

measures to address this safety concern have been utilized. Additional features to directly meet the 

rule are impractical (as the FAA Policy Memo notes) and would potentially add significant cost, 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 6 of 8 

Petition for Exemption from§ 25.981 (a)(3) of Title 14, Code of Federal Regulations 

weight, and maintenance to the airplane without a measurable safety benefit. Further, additional 

lightning protection features could inhibit the ability to inspect the structure (reducing safety). 

Requiring the 767-2C to attempt to directly comply with this rule would significantly increase the 

costs incurred by The Boeing Company to design and certify the airplane. It would also render the 

767-2C to be oflesser value to the public interest with no commensurate increase in safety. The new 

767-2C will replace older, less fuel efficient aircraft reducing costs to their operators and the public. 

Therefore, Boeing believes that it is in the public interest for the FAA to grant this exemption 

Statement of No Adverse Effect on Safety 

With current design practices for lightning protection, Boeing aircraft designs have accumulated in 

excess of 600 million revenue service flight hours with no lightning related events. Prior to these 

designs and service hours, there were 2 commercial jet transport hull loss events which are believed 

to have been caused by lightning strikes (reference ARAC Report: 1998 ARAC Fuel tank 

Harmonization Working Group report. Task Group 1 Service History I Fuel Tank Safety Level 

Assessment). The first was in 1963, which led to the development oflightning protection standards 

for fuel tanks. The second and last event was in 1976 and also resulted in improvements in fuel tank 

lightning protection. The hours accumulated since the last event represent over 6 times the hours 

accumulated with earlier designs through 1976. The accident free fleet history since 1976 shows 

current Boeing wing designs have sufficient protection against lightning induced fuel tank ignition 

events. 

This safety record for the fuel system designs upon which the Boeing 767-2C design is based 

indicates that the proposed fuel tank lightning protection design of the model 767-2C will be safe. 

Request to 'Waive Publication and Comment' 

Boeing requests to waive the requirement for publication and comment. Boeing believes there is 

good cause to be granted a waiver due to the fact that the FAA previously found a grant of 

exemption was in the public interest for the same fuel tank fastener issue on the 7 4 7 -8/8F (BDCO 

Project No PS05-0212 & PS05-0211) (Exemption No. 10174 was granted). 

Privileges of the Exemption Outside the United States 

Per 14 CFR 11.81(h), Boeing requests that the privileges of this exemption be extended outside the 

United States. This extension of privileges is necessary for operations based within foreign countries 

having bilateral agreements with the United States accepting FAA 14 CFR part 25 as their 

airworthiness standards for transport category aircraft. The 767-2C is intended for the global market 

place. 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 7 of 8 

Petition for Exemption from§ 25.981(a)(3) of Title 14, Code of Federal Regulations 

Conclusion 

Boeing is petitioning for an exemption from 14 CFR 25.981(a)(3) at amendment 125 for fuel-tank 

structural lightning protection. The Boeing model 767-2C is nearing the end of its design cycle. 

Granting this exemption will allow Boeing to complete its design and certify the 767-2C for 

delivery. The proposed design for the 767-2C will provide an appropriate level of safety against 

lightning-induced fuel-tank ignition, and will be shown to.comply with the alternative requirements 

provided in the FAA policy memo ANM-112-08-002. 

ECCN 9E991 
Enclosure A 

RA-12-02722 

Page 8 of 8 

Petition for Exemption from§ 25.981 (a)(3) of Title 14, Code of Federal Regulations 

·Summary to be Published in the Federal Register 

PETITIONER: The Boeing Company 

SECTION OF 14 CFR AFFECTED: 14 CFR 25.98l(a)(3) 

DESCRIPTION OF RELIEF SOUGHT: The petitioner seeks relief from the requirements of fuel-tank 

structural lightning protection for the Boeing 767-2C model airplane. 

ECCN 9E991