Petition to Amend Exemption No. 10174 from 14 CFR 25.981 (a)(3) Amendment 25-102

Name and Address of the Petitioner

Doug Lane, Director, Regulatory Admi nistration Deputy Lead Administrator The Boeing Company

PO Box 3707 Seattle, Washington, 98124

Section(s) of the Regulations from which Relief is Sought:

Boeing is petitioning to amend Exemption Nu mber 10174 to 14 CFR 25.981( a)(3) at Amendment 102 for fuel tank structural light ning protection for the 747-8/-8F through Certification Project Number PS14-1034 (H igh Performance Program (OZARK) – Wingbox – Revision) based on recently released FAA policy PS-ANM-25.981-02. Exemption Number 10174 was applicable to the wing tanks on both the 747-8 and 747-8F (PS05-0211 and PS05-0212 respectively). The regulation (unchanged between Amendment level 102 and 120) as currentl y written 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 coul d not result from each single failure, from each single failure in combination with each latent failure cond ition not shown to be extremely remote, and from all combinations of failures not show n to be extremely improbable. The effects of manufacturing va riability, aging, wear, corrosion, and likely damage must be considered.

The Extent of Relief Sought and Reason(s)

R egul a tio n R equires: R elief is Necess a ry b ecause: 14 CFR 25.981(a)(3)

Amendment 25-102 Note: Boeing is requesting exemption at this

amendment levels to cover changes that affect lightning protection, which might require compliance to either

amendment level. Compli a nce to 14

CFR 25.981(a)(3) for

fuel tank

structural lightning protection would require dual fault

tolerant or three independent layers of protection. As previously stated in Exemption 10174, Boeing

has concluded that for fuel tank fasteners and structural joints, there are no practical means in current technology to provide three means of protection in all locations.

Boeing has considered changes which might provide additional mitigation, but found these

means: a) Still do not provide a means of direct compliance to 25.981(a)(3), b) Are unnecessary to ensure safety of the fleet c) Would incur a significant cost (e.g. fuel burn due to increased weight) to the public. d) Do not provide a commensurate safety benefitDescription of Issue

Boeing is petitioning to amend Exemption No. 10174 to 14 CFR 25.981(a)(3) for fuel tank structural lightning protection for the 747-8 and 747-8F to remove the requirement of cap sealing wing tank rivets in Lightning Zone 2 (1/4” diameter and larger) based on new FAA Policy. The PS-ANM-25.981-02 FAA policy memorandum provides the following alternate requirements:

(1) The fuel tank structure and systems must be designed and installed to prevent catastrophic fuel vapor ignition due to lightning.

(2) The fuel tank structure and systems lightning protection design must be fault tolerant for failures that result in lightning-related ignition sources.

(3) Fault tolerance is not required for any specific design feature if:

(a) 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 combined, is shown to be extremely improbable.

Note: FAA Policy Memo PS-ANM-25.981-02 defines “Practicality” as a balance of available means, economic viability, and proportional benefit to safety.

(4) Inspections or other procedures must be established to prevent development of lightningrelated ignition sources within the fuel tank structure and systems, for example: (a) Identifying as airworthiness limitations, mandatory maintenance actions (i.e., inspections), or CDCCLs, necessary to preclude the development of unsafe conditions due to non-fault-tolerant lightning protection features;

(b) Including sampling programs, maintenance, and/or inspections for fault-tolerant lightning protection features in the manufacturer’s recommended airplane maintenance program;

Note: If inspections from non-mandatory programs such as Baseline Zonal inspection program, Corrosion Prevention and Control Program (CPCP), etc., are going to be used to support the robustness of the overall inspection program, these programs must become mandatory and must be included in the Airworthiness Limitations section of the airplane’s Instructions for Continued Airworthiness.

(c) Incorporating into applicable airplane maintenance documents, including the manufacturer’s structural repair manual, caution information that identifies the lightning protection features of the fuel system design to minimize the potential for inadvertent damage or disruption of these features.

(5) An analysis must be performed to show that the airplane’s design, its manufacturing processes, and the Airworthiness Limitations section of its Instructions for Continued Airworthiness include all practical measures to prevent, and detect and correct, failures of fuel tank structure and systems lightning protection features because of manufacturing variability, aging, wear, corrosion, and likely damage.The 2009 Policy Memo AMM-112-08-002 did not provide a specific definition of “practical” or “impractical”, however the pol icy stated: “Determinations of practicality are somewhat subjective and can be dependent on the proposed desi gn and the “state of

the art” at the time.” The 2014 PS-ANM- 25.981-02 policy statement provides a specific statement that defines “practicality” as a ba lance of available means, economic viability, and proportional benefit to safety. This definition is consiste nt with the May 2011 recommendations of the Aviation Rulemaking Committee that the FAA formed after release of the initial policy memo release.

Discussion

As stated in Exemption 10174 , Boeing concluded and the FAA concurred that there are no practical means in current technology to obt ain triple redundant means of fuel tank structural fastener lightning pr otection in all locations. Fo r example, one option deemed to be impractical was to apply an inspection interval which monitors the health of each fastener that penetrates the fu el tanks. This was due to th e thousands of fasteners on the wing of the 747-8/-8F and the inability to visually inspect most means of lightning protection. Increasing the number of in-t ank inspection interval s could also have a potential unintended cons equence of damaging the igniti on protective features or other components inside the fuel tanks. As di scussed in Exemption 10174, examples of additional design considerations found to be impractical were: conductive steel fasteners,

additional sealant on l ocations already seal ed, composite skin pr otection methods, fuel tank bladders or double walled fuel tanks, spot bonds, and fastener free wing structure.

During the initial certif ication of the 747-8/8F, while it wa s recognized that cap sealing of wing tank rivets (1/4” diameter) may have been unnecessary to provide a fault tolerant design, the 2008 policy statement required us e of “all practical measures” and equated practicality with “state of the art”. Because cap sealing was within the state of the art, it was implemented for rivets in Zone 2 areas wi thout consideration of the safety benefit to the airplanes, whether it was necessary for fault tolerance, and the impact upon aircraft customers and the flying public of the si gnificant weight added to each aircraft.

Boeing has since done testing to evaluate the safety benefit of sealing 1⁄4” rivets in fuel tank Zone 2 areas. It has been determined by an alysis and testing of all anticipated faults that cap sealing 1⁄4” rivets (and larger) in skin thicknesses used on the 747-8/8F is unnecessary to ensure safe ope ration during lightning strike c onditions, even when faults are present. The use of sealant on rivets in Zone 2 of the 747-8/-8F wing, results in additional weight to the aircra ft. This in turn increases fuel burn, carbon emissions, and reduces inspectability during maintenance

. Further, Boeing has assessed the likelihood of lightning attachment to a faulted rivet dur ing flammable tank conditions, and concluded this combination is not expected to occur in the life of the fleet. Regardless of this probabilistic conclusion, testing (w ill repeat for compliance) de monstrates that even with faults present, the 1⁄4” (and larger) 747-8/8F rivet installations w ill not cause an ignition source during severe direct light ning attachments. Since the design is already safe during

this combination of conditions that are unlikel y to occur in the life of the fleet, Boeing has concluded that further mitigation (i.e. covering 1⁄4” and larger rivets with sealant) does not provide a commensurate sa fety benefit to the public considering the significant weight and associated fuel costs plus carbon emissions, aircraft production costs and operator maintenance cost impact s. Additional detailed prop rietary information has been provided to the FAA via Boeing letter RA-14-05275.Note that cap sealing of bolt in stallations in Zone 2 areas is practical and used for sealing

bolts to ensure fault tolerant protection.

Finally, this impractical conclu sion is only with respect to pr oviding a design that is dual

fault tolerant. The basic re quirement to provide single fault tolerance as defined in Policy Statement PS-ANM-25.981-02, can be met without cap sealing rivets. As discussed in the initial release of Exemption 10174, the two faults which the 747- 8/8F design is not single fault tolerant, remain; 1) attachment to or near a large crack in structure, and 2)

attachment to or near a bolt failure that also caused the fastener nut (or collar) to release

with sufficient force to tear free the asso ciated cap seal. Boeing additionally identified another fault in support of Exemption 10477 which is non-fault tolerant; 3) Three Zone 2 dome nuts for a single tank access door on the 747-8 only.

Proposed Risk Mitigation

To support granting of Exemption No 10174 per FAA Policy Memo ANM-112-08-002 for the 747-8/-8F, Boeing su bmitted detailed proprietary information as compliance

documents to the FAA about the measures taken in the 747-8/-8F design to provide practical structural lightning protec tion (FAA Project Numbers PS05-0211 and PS05-0212). In general, the 747-8/-8F lightning protection features are based on state of the art industry design practic es for aluminum wing structur e including inherent current paths that have been used in existing in se rvice designs. Boeing further enhanced the lightning protection by incorporating fault tolerant protection m eans where practical, thereby increasing the level of fuel tank safety.

FAA Policy Memo ANM-112-08-002 discusses th e need to demonstrate compliance to

14 CFR 25.981 or Part 26 flamma bility requirements as applicable. For the 747-8/-8F, Boeing complied with FAR 26.35 and FAR 26.33, as well as voluntarily stepping up to the requirements of 14 CFR25.981 (b) at amendment 125 for the center tank. 26.33(b) and 26.35(b) require a flammability assessment be conducted for all fuel tanks. The flammability exposure analysis showed that the main wing tanks of the 747-8/-8F have a low fleetwide flammability exposure (inboard and outboard main tanks) as required by 26.33(c). The Center tank of the 747-8 uti lizes an inerting system to meet the flammability exposure criteria of Part 25 Appendix M, for compliance to 14 CFR25.981 (b).

To demonstrate compliance of the 747-8 withou t cap sealing of 1⁄4” rivets in Zone 2 of wing fuel tank areas, Boeing proposes primar ily to use the comp liance documentation originally submitted to fulfill the requirem ents of Exemption No 10174. In addition, Boeing will provide analysis and testing that demonstrates that 747-8/8F rivet

installations are fault tolera nt without sealant. Boei ng notes that the alternate requirements that were the basis of Exemption 10174 were based upon FAA Policy memo ANM-112-08-002, released in 2009. The requirements of the new policy

statement PS-ANM-25.981-02 released in 2014 ar e similar to the 2009 requirements, and differ primarily only in that the new stat ements allows for the determination of practicality to be based upon commensurate sa fety benefit, and allows exemptions for

systems installations (which Boei ng is not requesting for the 747-8/-8F.) Compliance to each of the Policy ANM-25.981-002 requirement s will be as summarized below:Policy Requirement 1 - Prevent catast rophic fuel vapor ignition due to lightning:

The 747-8/8F utilizes all practical measures for fault tolerant structural lightning protection. Boeing utilizes manufacturing pr ocesses to minimize the risk of errors in aircraft manufacturing which could affect the lightning protection features. The Structural Repair Manual procedures are provided to retain the lightning protection features throughout the life of the airplane. Instructions for Continued Airworthiness including CDCCLs are incl uded in the Special Compliance Items Document. A complete anal ysis of the manufactur ing process and repair procedures were provided as part of the original Fuel System Lightning Protection System Safety Assessment.

Policy Requirement 2 – Provide fault tolerant lightning protection: The basic requirement to provide single fault tolerance will be met without cap sealing rivets. Boeing will provide analysis and/or testing that demonstrates that wing fuel tank rivet installati ons are fault tolerant without sealant. The requested Exemption amendment does not change a ny other data previously provided to demonstrate fault tolerant lighting pr otection. The 747-8/-8F provides fault tolerant lightning protection, except for 3 improbable combinations discussed in Requirement 3 below.

Policy Requirement 3 – Fault tolerance is not required for any specific design

feature if fault tolerance is shown to be impractical for that feature

The requested Exemption amendment does not change this means of compliance. The only faults previously identified for wh ich 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 fr ee the associated cap seal. 3) Three Zone 2 dome nuts for a single tank access door on the 747-8 only.

An assessment was provided to support the requirements of existing Exemption 10174 demonstrating that the risk of a fuel vapor ignition due to the sum of these failures is not anticipated in the life of the fleet.

Policy Requirement 4 – Provide li ghtning protection maintenance

information: The requested Exemption amendment does not change this means of compliance. No revision to the existing ALI, mandatory inspections, or CDCCLs for structural lightning protection is anticipated.

The Structural Repair Manual includes in structions to minimize the risk that alterations (repairs) will affect lightning protection. The SRM includes CDCCL references (equivalent to Cautions). Cha nges to the SRM will be made if required to clarify that production rivets ar e not sealed in Lightning Zone 2A.Policy Requirement 5 - Analysis of de sign, manufacturing and maintenance procedures: Boeing has implemented in the design a ll practical measures for structural lightning protection. As disc ussed above, it will be demonstrated by analysis and testing of all anticipated faults that cap sealing 1⁄4” rive ts (and larger) is unnecessary to ensure safe operation dur ing lightning strike conditions, even when faults are present. The use of s ealant on rivets in Zone 2 of the 747-8/-8F wing results in additional weight to the aircraft. This in turn increases fuel burn, carbon emissions, and reduces insp ectability during maintenance

. Further, Boeing has assessed the likelihood of light ning attachment to a faulted rivet during flammable tank conditions, and c oncluded this combination is not expected to occur in the lif e of the fleet. Since the de sign is already safe during

this combination of conditions that are unl ikely to occur in the life of the fleet, Boeing has concluded that further mitigati on (i.e. covering 1⁄4” and larger rivets with sealant) does not provide a comme nsurate safety benefit to the public considering the significant weight an d associated fuel costs plus carbon emissions, aircraft production costs and operator maintenance cost impacts. Additional detailed proprietary informa tion has been provided to the FAA via Boeing letter RA-14-05275.

The manufacturing processes include prac tical means to minimize the risk that lightning protection features are not im plemented as intended on the drawings. CDCCL and the SRM repair procedures ha ve been established to retain the lightning protection features through out the life of the airplane.

Statement of Public Interest

Boeing is working to improve the efficiency of the 747-8/-8F models by a redesign for weight improvement. For lightning protecti on, the 747-8/-8F has sufficient features to enhance safety and protect the fuel tanks from potential ignition sources due to a lightning event. All practical measures have been utilized. Additi onal features (i.e. cap sealing of rivets) to directly meet the rule are impractical and resu lt in significant cost, weight, increased emissions, and maintenan ce to the airplane without a proportional safety benefit. This renders th e 747-8/-8F to be of lesser valu e to the public interest with no commensurate increase in safety. Further, this additional lightning protection reduces the ability to inspect the structure. Therefor e, Boeing believes that it is in the public interest for the FAA to grant this revision to the Exemption.

Statement of No Adverse Effect on Safety

With current design practices for lightni ng protection, Boeing aircraft designs have

accumulated in excess of 800 million revenue service flight hours with no lightning

related events. Prior to th ese 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 / Fuel Tank Safety Level Assessment). The first was in 1963, which led to the de velopment of lightning protection standards for fuel tanks. Thesecond and last event was in 1976 and also resulted in improvements in fuel tank lightning protection. The hours accumulated si nce the last event re present over 8 times

the hours accumulated with earli er designs through 1976. The ac cident free fleet history since 1976 shows current Boeing wing desi gns have sufficient protection against lightning induced fuel tank ignition events.

This safety record for the fuel system de signs upon which the e nhanced Boeing 747-8/-8F design is based, indicates that the proposed fuel tank lightni ng protection design of the

model 747-8 will be safe.

Request to ‘Waive P ublication and Comment

Boeing requests to waive the requirement fo r publication and comment. Boeing believes there is good cause to be granted a waiver du e to the fact that the FAA previously found a grant of exemption was in th e public interest for the same fuel tank lightning protection compliance to 14 CFR 25.981(a)(3) issue on the 747-8/8F (Exemption No. 10174 was granted). Exemption 10477, which was requested to address the structural lightning protection on the Horizontal Stabilizer Tank (HST) of the 747-8 and was based on the same requirements of 10174, was issued wit hout a public comment period. Additionally,Boeing has already submitted a Petition for Exemption based on the revised PS-ANM25.981-02 policy for the 737 MAX (Docket No. FAA-2014-1042).

Privileges of the Exemption Outside the United States

Per 14 CFR 11.81(h), Boeing request s that the privileges of th is exemption be extended

outside the United States. This extension of privileges is necessary for operations based within foreign countries havi ng bilateral agreements with the United States accepting FAA 14 CFR part 25 as their airworthiness stan dards for transport category aircraft. The

747-8/-8F is intended for the global market place.

Conclusion

Boeing is petitioning to amend Exemp tion No 10174 from 14 CFR 25.981(a)(3) at amendment 102 for fuel-tank structural light ning protection. Granting these revisions will allow Boeing to provide a competitive product without compromising safety. Per FAA Policy memo PS-ANM-25.981-02, Boeing has shown that certain existing design

features that are considered impractical add significant cost , weight, increased emissions, and maintenance to the airplane without a proportional safety bene fit. The proposed design for the 747-8/-8F will provide an appr opriate level of safety against lightninginduced fuel-tank ignition and will be shown to comply with the alternative requirements provided in the FAA policy memo PS-ANM-25.981-02.Summary to be Published in the Federal Register

PETITIONER : The Boeing Company

SECTION OF 14 CFR AFFECTED : 14 CFR 25.981(a)(3)

DESCRIPTION OF RELIEF SOUGHT : The petitioner seeks relief from the requirements of fuel tank stru ctural lightning pr otection for the Boeing 747-8/8F model airplane.