( ^ . 

Ronald J. Hinderberger 

Lead Administrator 

Regulatory Administration 

Commercial Airplanes 

The Boeing Company 

P.O. Box 3707 MC 03-56 

Seattle. WA 98124-2207 

JAN 2 6 2012 

RA-12-00367 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor, Room W12-140 

1200 New Jersey Avenue, SE 

Washington, D.C. 20590 

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Subject: 

Model: 

RA Project No.: 

EASA Project No. 

EASA Level: 

Response Due: 

Reference(s): 

Petition for Exemption from 14 CFR 25.981(a)(3) for the 747-8 

Horizontal Stabilizer Tank (HST) Fuel Tank Structural Lightning 

Protection 

747-8 

PS11-0863 

N/A 

N/A 

February 23, 2012 

(a) Teleconference between Boeing (James Wilkinson and others) 

and F AA (Sue Lucier and others), December 21, 2011. 

(b) FAA Exemption No. 10174 "hi the matter of the petition of The 

Boeing Company Regulatory Docket No. FAA-2009-1058 for 

an exemption from § 25.981(a)(3) at Amendment 25-102 of 

Title 14, Code of Federal Regulations" dated December 14, 

2010. 

(c) FAA Policy Memo ANM-112-08-002 (Policy on Issuance of 

Special Condition and Exemptions Related to Lightning 

Protection of Fuel Tank Structure), dated May 26, 2009. 

Special Instructions: This project is for RC003 

This letter submits: 

The first production incorporation of the change will occur on 747-8 

(BBJ) RC003 which is scheduled to AC-E on April 1, 2012. 

Retained compliance to FAA, that is dependent on this petition 

request, is scheduled for February 23, 2012. 

(X) Petition for an Exemption 

Enclosed, please find the Boeing Petition for Exemption from 14 CFR 25.981(a)(3) for the 747-8 

Horizontal Stabilizer Tank (HST) Fuel Tank Structural Lightning Protection. 

During the reference (a) meeting, the applicability of reference (b) to the HST was discussed. 

Boeing stated that the intent was to include the HST tank and its structural fasteners in the 

petition wording for the exemption, as the petition was based on reference (c) which addressed 
0-^ Page 2 

Mr. A. Xidias 

RA-12-00367 

the lightning protection requirements of friel tank structure (The 747-8 has fuel tanks both in the 

wing and the horizontal stabilizer). 

The FAA, after consulting with legal counsel, stated that the wording of reference (b) did not 

cover the 747-8 HST and that Boeing needed to petition for a separate exemption to cover the 

HST. 

Waiver from Public Comment 

During the reference (a) meeting, the FAA felt that such an exemption, based on reference (a), 

can forgo the public comment process, as allowed by 14 CFR 11.87, and be issued to support the 

schedule of RC003 certification activities. 

This letter is sent for: 

(X) Posting to the Federal Docket 

Please contact this office or the following individuals if you have any questions: 

(X) Project Administrator (PA); James Wilkinson at (425) 717-3736 

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, is considered 

proprietary to The Boeing Company and/or its suppliers, and is provided on a confidential basis. 

The data provided should be returned to Boeing immediately following use by the FAA, 

including any copies thereof that the FAA may be required to make in the course of its review. 

Boeing does not authorize the FAA to retain any portion of the materials being supplied. 

Very truly yours, 

bald J. Hinderberger 

^ead Program Administrator 

(425) 237-1355, MC 03-56 

FAX: (425) 294-9340 

Enclosures 

cc: 

Name Sharepoint Comments 

G. Oltman (747-8/8F) Yes (FAA) 6Y-01 

D. Tsuji (747-8/8F) Yes (FAA) 6Y-01 
Enclosure to RA-12-00367 

Exemption Petition from 14 CFR 25.981(a)(3) for 

the Horizontal Stabilizer Fuel Tank Structural Lightning Protection 

Introduction 

The Boeing Company is petitioning for an exemption for 14 CFR 25.981(a)(3) at 

amendment 25-102 for fuel tank structural lightning protection for the horizontal 

stabilizer fuel tank (HST). Only the 747-8 passenger airplane is equipped with the HST. 

A similar petition for exemption for the 747-8F/-8 wing fiiel tanks was submitted to the 

FAA in 2009 and granted in Exemption No. 10174 in 2010. 

The FAA has issued Policy Memorandum ANM-112-08-002 to address the impracticality 

of compliance to 14 CFR 25,981(a)(3) at amendment 25-102 with regards to structural 

lightning protection. 14 CFR 25.981(a)(3) at amendment 25-102 requires: 

(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. 

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

lightning protection. 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 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-faulttolerant 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. 

Page 1 of4 
Enclosure to RA-12-00367 

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 an 

inspection interval which monitors the health of each fastener that penetrates the fuel 

tanks. With thousands of fasteners on the wing and the horizontal stabilizer of the 747-8, 

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 tank. 

Proposed Risk Mitigation 

As discussed m the FAA Policy Memo, Boeing will submit detailed Proprietary 

information to the FAA about the measures taken in the 747-8 design to provide practical 

structural lightning protection. In general, the 747-8 lightning protection features are 

based on state of the art industry design practices for aluminimi wing structure including 

inherently conductive low-resistance current paths that have been used in existing inservice designs. Further, Boeing proposes to enhance the lightning protection by 

incorporating additional fault tolerant protection for fasteners in areas of 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 747-8 

horizontal stabilizer will have two reliable and effective features for lightning protection. 

Testing has shown that the fastener installation will be safe for applicable Ughtnmg zone 

requirements and will not produce any sparks inside the fuel tanks. Additionally, Boeing 

has shown 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 maintained throughout the life of the airplane. 

Page 2 of4 
Enclosure to RA-12-00367 

Issue of Public Interest 

Boeing is working to improve the efficiency of the 747 model by a redesign. The 747-8 

has additional capability and capacity over the 747-400 model. For lightning protection, 

the 747-8 has additional features to enhance safety and protect the fuel tanks from 

sparking due to a lightning event. All practical measures have been utilized. Additional 

features to directly meet the rule are impractical (as the FAA Policy Memo notes) and 

would potentially add significant cost, 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 747-8 to attempt to directly comply with this rule would significantly 

inhibit Boeing's ability to certify the HST so that the 747-8 could be fueled for extended 

range benefit of the operator. This additional range capability of the 747-8 is critical to 

its operational mission. If the 747-8 with the HST were not able to be fueled, it would 

render the 747-8 to be of lesser value to the public interest with no commensurate 

increase in safety. Many Boeing customers are depending on the range of the 747-8 to 

meet their business needs. New 747-8 aircraft will typically replace older less fuel 

efficient models, thus reducing the public expense for fuel consumed in air travel. 

Therefore, it is the position of The Boeing Company that the public interest would be best 

served if the FAA were to grant this exemption. 

Effect of Exemption 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 lightningrelated events. Prior to these designs and service hours, there were two 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 / Fuel Tank Safety Level Assessment). The first was in 

1963, which led to the development of lightning protection standards for fuel tanks. The 

second and last event was in 1976 which also resulted in improvements in fuel tank 

lightning protection. In addition, both events utilized JP-4, which is a wide cut, higher 

volatility fuel rarely used today. The 747-8 airplanes will not be certified for use with JP4 or other wide cut fuels. The hours accumulated since the last event represent over six 

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 enhanced Boeing 747-8 

design is based indicates that the proposed fuel tank lightning protection design of the 

model 747-8 will be safe. 

Page 3 of4 
Enclosure to RA-12-00367 

Conclusion 

Boeing is petitioning for an exemption for 14 CFR 25.981(a)(3) at amendment 25-102 for 

fijel tank structural lightning protection for the horizonted stabilizer fiiel tank. The 

Boeing model 747-8 received an Amended Type Certificate in December 2011 without 

certification for the horizontal stabilizer fuel tank. Granting this exemption will allow 

Boeing to certify the HST for structural lightning protection. The design for the 747-8 

provides 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. 

Page 4 of 4