# 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 ofTransportation Docket Operations West Building Ground Floor, Room Wl2-140 1200 NewJersey Avenue, S.E. Washington, DC 20590 

### Subject:
Model: RA ProjectNo.: EASA ProjectNo.: EASALevel: Branch/PanelNo.: Branch/PanelName: Response Due: Reference(s):

SpecialInstructions: This letteris 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 DocketNo. FAA-2009-1058.

N/AFAAExemptionNo. 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 CPR25.981(a)(3)**L~** c:::
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### 9 (}1 (J'l

The Boeing Company hereby petitions for an exemption for relieffrom the fueltank safety provisions of 14 CFR25.981(a)(3) Amendment 25-125 for structural lightning protection ofwing fasteners ofthe Boeing Model 767-2C. To supportthe 767-2C ATC program schedule, The Boeing Company requests that the enclosedinformationbe processed by September 21 5\ 2012. Furthermore, The Boeing Company requests to be notified whenthe enclosed petitionprocessing 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 commentperiod ofthis 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 ifyou 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 informationbeing forwarded to the FAA by or withthis correspondence is for the exclusive purpose ofsupport ofapplications for or amendments toType Certificates.

. . ·

# ·~~ nouglasM. Lane ODADeputy Lead Administrator (425) 237-1383, MC 03-56

. FAX: (425) 294-9340
Enclosures: (A) Petitionfor Exemption from 14 CFR25.981(a)(3) cc Name Jim Cashdollar Angelos Xidias Letter EDT EDT Enclosures EDT EDT Comments ANM-106B ANM-100.8Enclosure 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 CFR25.981 (a)(3) Amendment25-125 Name and Address ofthe Petitioner Doug Lane, Director, Regulatory Administration Deputy Lead Administrator The Boeing Company PO Box 3707 Seattle, Washington, 98124 

### Section(s) oftheRegulations from which Reliefis Sought: Boeing is petitioning for an exemptionto 14 CFR25.981(a)(3) for fuel tank structural lightning protection for the 767-2C (Project No. PS09-0863). The subjectregulation section is unchanged between amendment level 1 02 and 125. The regulation as currently written: (a) No ignition source may be present at eachpointinthe fuel tank orfuel tank system where catastrophic failure could occur due to ignition offuel or vapors. This mustbe shownby: (3) Demonstrating that anignition source could notresult from each single failure, from each single failure incombination with each latent failure conditionnot shownto be extremely remote, and from all combinations offailures not shownto be extremely improbable. The effects ofmanufacturing variability, aging, wear, corrosion, and likely damage mustbe considered. 

### TheExtent ofReliefSought and Reason(s) Regulation Requires: Reliefis Necessary because: 14 CFR 25.981(a)(3) Compliance to 14 CFR Boeinghas 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 currenttechnology to obtaintriple protection would require three redundant means ofprotection 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 onunique structural load requirements. New installations ofsimilar faster types may also be incorporated. The FAApreviously found a grant of exemption was inthe public interest for the same fuel tank fastener issue onthe 747-8/8F (BDCO ProjectNo PS05-0212 & PS05-0211) (ExemptionNo. 10174 was granted).

ECCN 9E991Enclosure 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 exemptionto 14 CFR25.981(a)(3) for fuel tank structural lightning protection for the 767-2C (ProjectNo. PS09-0863). The ANM-112-08-002 FAA policy memorandum provides the following alternate requirements: 1. Instead ofcompliance with the requirements of§ 25.981 (a)(3), the applicant must show that the design includes at leasttwo independent, effective, and reliable lightning protection features (or sets offeatures) suchthat fault tolerance to prevent lightning-related ignition sources is provided for each area ofthe structural design areaproposed to be exempt from the requirements ofthat regulation. Faulttolerance is notrequired for any specific design feature if: a) providing fault tolerance is shownto be impractical for that feature, and b) fuel tank vapor ignitionbecause ofthat feature and all other non-fault tolerant features, whentheir fuel tank vapor ignition eventprobabilities are summed, is shownto be extremely improbable. 2. The applicant mustperform an analysis to showthat the design, manufacturing processes, and airworthiness limitations section ofthe instructions for continued airworthiness include all practical measures to prevent, and detect and correct, failures ofstructural lightning protection features because ofmanufacturing variability, aging, wear, corrosion, and likely damage. Discussion Boeing has concludedthat compliance to 14 CFR 25.981(a)(3) for fuel tank structural fastener lightning protection would require three independent layers ofprotection. For fuel tank fasteners, there are no practical means in current technology to obtaintriple redundant means ofprotection in all locations. Another option would be to apply inspection interval which monitors the health ofeach fastener that penetrates the fuel tanks. With thousands offasteners onthe wing ofthe 767-2C, this option is impractical. Increasing the number ofin-tank inspection intervals could also have a potential unintended consequence ofdamaging the lightning protective features or other components inside the fuel tanks. Proposed Risk Mitigation As discussed inthe FAAPolicy Memo, Boeing will submit detailed proprietary informationto the FAA aboutthe measures taken inthe 767-2C design to provide practical structural lightning protection. In general, the 767-2C lightning protection features are based on state ofthe art industry designpractices for aluminum wing structure including inherently conductive low resistance current paths that have been used in existing in service designs. Further, Boeingproposes to enhance the lightning protection by incorporating additional fault tolerantprotection for fasteners in areas of

ECCN 9E991Enclosure A RA-12-02722 Page 

### 3 of 8 Petition for Exemption from§ 25.981(a)(3) ofTitle 14, Code of Federal Regulations potential swept lightning attachment (referredto as Zone 2) by cap sealing the fasteners to contain a possible spark inthe eventthatthe primary protective features fail, thereby increasing the level of fuel tank safety. Boeing will showthat the structural fastener design for the majority ofthe 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 notproduce 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. Forthe limited areas in which a single failure ofa fastener could result inloss ofbothprotection features, or any other area where a single layer ofprotection is all that canpractically be provided, a safety assessment will be done to showthatthe probability ofa lightning related fuel tank ignition event is extremely improbable. The systems supporting structure will also be analyzed as part ofthe fault tree assessment to ensure that they meet the requirements inthe policy memo. Additionally, Boeing will utilize productionprocedures in orderto minimize the risk ofmis-installedprotective measures, and to identify and repair errors in such a way thatthe lightning protection features will be maintained. The instructions for continued airworthiness and repairprocedures will also be provided to ensure the protection features are retained throughoutthe life ofthe airplane. The FAApreviously found a grant ofexemption was inthe public interest for the same fuel 

### tank fastener issue on the 747-8/SF (BDCO ProjectNo PS05-0212 & PS05-0211) (ExemptionNo. 10174 was granted). Additional Information 1. The 767-2C design will show compliance with 14 CFR25.981(b) and (d) at amendment 25-125. Documentation ofcompliance will be submitted for approval per CP 11633. 2. Boeing has utilized all practical measures to meet the requirements of 14 CFR25.981(a)(3) for fuel tank structural lightning protection. Boeing has designed the 767-2C fuel tank structure to be fault tolerant for all buttwo failure modes (broken bolts and structural cracks). A detailed FMEA will be provided as part ofthe 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), butthese were found either impractical to implement or insufficientto provide any additional lightning protection.

ECCN 9E991Enclosure A RA-12-02722 Page

### 4 of 8 Petition for Exemption from§ 25.981 (a)(3) ofTitle 14, Code of Federal Regulations
Examples ofdesign considerations were:

o Conductive steel fasteners

- widespread use results in higher weight, fuel bumand associated emissions, and higher risk ofcorrosion. 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 skinprotection methods- Not applicable to aluminum design. Note the majority ofthese methods are intendedto**increas~** conductivity ofthe outertank surface inthe area local to the fastener heads, which aluminum structure provides inherently.

o Fuel tankbladders or double walled fuel tanks

- Wouldresult in a new enclosed fuel vapor space, which wouldpose an additional vapor ignitionthreat 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 ofincreased conductivity offeredby the spot bond. The spot bonds would still be subjectto 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. Itis notpossible to produce raw materials large enoughto create monolithic wing panels or spars in dimensions thatthe 767-2C requires and monolithic designs would reduce structural cracktolerance. Using adhesives instead offasteners to bond major -components represents a radical departure from establishedmetallic wing primary structure experience. These types ofdesigns were determined to be impractical due lack ofsafety 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 ofproviding fault tolerantprotectionto conducted currents, which is the only Zone 3 requirement. 4. Boeing will provide a System Safety Assessment(SSA) as part ofcompliance for the 767-2C program. A fault tree analysis will be included inthe SSA which will quantify the single failures, and demonstrate the probability ofa fuel vapor ignition inthe life ofthe 767-2C fleet is

.extremely improbable.

ECCN 9E991Enclosure A RA-12-02722 Page 5 of 8 Petition for Exemption from§ 25.981(a)(3) ofTitle 14, Code of Federal Regulations

The only faults identified for whichthe 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 ofthese 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 ofthese cases sparking due to these failures would only occur ifthere was a direct attachmentto the local area ofthe failure. Boeing will demonstrate sparking does not occur due to these failures by similarity analysis to previously conducted testing orby newtesting for configurations not covered by previous testing. For both ofthe above failure modes, Boeing has been unable to identify a practical alternative to provide a protectionto the failure mode for direct attachment. A numerical assessment will be provided demonstrating the probability ofa fuel vapor ignition due to these failures is extremely improbable (and thus unlikely to occur inthe life ofthe fleet). Service experience onthe 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 ofstructural cracking will be conservatively based on Boeing's structural fatigue methodology. This methodology is based ontest and service experience, and ensures thatthe presence offatigue cracks is minimized during the life ofthe airplane. Althoughnone are anticipated at this time, any additional non-faulttolerant installations identified later (e.g. during the testprogram) which are impractical to preclude will also be included inthe required numerical analysis. 5. Boeing has implemented inthe 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 onthe drawings and are maintained. The repairprocedures will be reviewedto ensure the lightning protection features will bemaintainedthroughout the life ofthe airplane. Instructions for Continued Airworthiness will be developed and included in the certification documentation. A complete analysis ofthe manufacturing process and repair procedure will be part ofthe System Safety Assessment and submitted for compliance per CP 11633.



### Statement ofPublic 

### 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 protectthe fuel tanks from sparking due to a lightning event. All practical measures to address this safety concern have been utilized. Additional features to directly meetthe rule are impractical (as the FAA Policy Memo notes) and wouldpotentially add significant cost,

ECCN 9E991Enclosure A RA-12-02722 Page 

### 6 of 8 Petition for Exemption from§ 25.981 (a)(3) ofTitle 14, Code of Federal Regulations weight, and maintenance to the airplane without a measurable safety benefit. Further, additional lightning protection features could inhibitthe ability to inspectthe 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. Itwould also render the 767-2C to be oflesservalue 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 andthe public. Therefore, Boeing believes that it is inthe public interest for the FAAto grant this exemption 

### Statement ofNo Adverse Effect on Safety With current design practices for lightning protection, Boeing aircraft designs have accumulated in excess of600 million revenue service flight hours with no lightning related events. Priorto these designs and service hours, there were 2 commercialjettransport 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 oflightningprotection 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 eventrepresent over 6 times the hours accumulated with earlier designs through 1976. The accident free fleet history since 1976 shows current Boeing wing designs have sufficientprotection 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 thatthe proposed fuel tank lightning protection design ofthe 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 FAApreviously found a grant of exemption was inthe public interest for the same fuel tank fastener issue onthe 7 4 7-8/8F (BDCO ProjectNo PS05-0212 & PS05-0211) (ExemptionNo. 10174 was granted). 

### Privileges ofthe Exemption Outside the United States Per 14 CFR 11.81(h), Boeing requests that the privileges ofthis exemptionbe extended outside the United States. This extension ofprivileges is necessary for operations based within foreign countries having bilateral agreements withthe United States accepting FAA 14 CFRpart 25 as their airworthiness standards for transport category aircraft. The 767-2C is intended for the global market place.

ECCN 9E991Enclosure A RA-12-02722 Page 7 of 8 Petition for Exemption from§ 25.981(a)(3) ofTitle 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 lightningprotection. The Boeing model 767-2C is nearing the end ofits design cycle. Granting this exemptionwill 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 ofsafety against lightning-induced fuel-tank ignition, and will be shownto.comply with the alternative requirements provided in the FAApolicy memo ANM-112-08-002.

ECCN 9E991Enclosure A RA-12-02722 Page 

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

### ·Summaryto be Published in the FederalRegister
PETITIONER: The Boeing Company
SECTION OF 14 CFRAFFECTED: 14 CFR25.98l(a)(3) DESCRIPTION OFRELIEF SOUGHT: The petitioner seeks relieffrom the requirements offuel-tank structural lightning protection for the Boeing 767-2C model airplane.

ECCN 9E991