U.S. Department 

of Transportation 

Federal Aviation 

Administration 

JUN 0 2 2015 

Mr. Jeremy Taylor 

Transport Airplane Directorate 

1601 Lind Avenue, S.W. 

Renton, Washington 98057-3356 

Re: Exemption No. l 0174 

Regulatory Docket No. F AA-2009-1 058 

BCA Regulatory Administration 747/767 Program Manager 

The Boeing Company 

P.O. Box 3707, MC 03-56 

Seattle, W A 98124-2207 

Dear Mr. Taylor: 

We have reviewed Boeing's request, received in letter RA-15-01 067, dated March 13,2015, 

for amendment to exemption I 0174. That letter requests an amendment to the original 

exemption to " .. . remove the requirement of cap sealing the wing tank rivets in Lightning 

Zone 2 (l/4''diameter and larger) based on new FAA policy." The new policy Boeing cites is 

Policy Statement PS-ANM-25.981-02. 

We have considered your request and determined that an amendment to the original exemption 

is not necessary because the original exemption included consideration of the need for fault 

tolerance of the wing fasteners in Zone 2, through the use of features that included cap-sealing 

the fasteners, as follows: 

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. 

Your request for amendment states that Boeing will demonstrate fault tolerance of the 0.25-in. 

and larger fasteners in Zone 2, through testing of various failure scenarios, without the need 

for cap sealant. Provided fault tolerance can be demonstrated and the FAA approves the data, 

this approach meets provision 1 of the criteria in the original exemption, which reads as 

follows: 

1. Instead of compliance with the requirements of§ 25.981 (a)(3), Boeing must show that 

the design includes at least two independent. effective, and reliable lightningprotectionfeatures (or sets offeatures) such that fault tolerance to prevent lightningrelated ignition sources is providedfor the structural:fastener design and systemssupporting structure of the wing. Fault tolerance is not required for a latent crack in 

structure, or a bolt failure that also causes the fastener nut (or collar) to release with 

sufficient force to tear free the associated cap seal, if: 
a. Boeing shows that providing fault tolerance is impractical, and 

b. Boeing shows that fuel-tank vapor ignition, because of each of these features 

and all other non-fault-tolerant features, when their fuel-tank vapor-ignition 

event probabilities are summed, is extremely improbable. 

In summary, the original exemption allows modifications to the design, provided that the 

provisions of the exemption are satisfied. The new policy Boeing references does not change 

the provisions of the original exemption. Therefore, amendment to the exemption, due to 

specific design modifications that the original exemption addresses, is not necessary. 

Sincerely, 

Victor Wicklund 

Manager, Propulsion and Mechanical Systems Branch 

Transport Airplane Directorate 

Federal Aviation Administration 

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