UNITED STATES OF AMERICA DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION RENTON, WASHINGTON 98057-3356

In the matter of the petition of Exemption No.15780

The Boeing Company Regulatory Docket No. FAA-2015-3166 for an exemption from§§ 25 .901(c) and 25.981(a)(3) ofTitle 14, Code of Fed e ra1 Regu lations

GRANT OF EXEMPTION By le tter dated Jun e 29, 2015, Mr. Tim Hendrix, Ce r tific ation & A irworthi ness Manager, The Boeing Company, 240 1 E. Wardlow Road , Lo n g Beach, Ca liforni a, 90807

- 5309, petitioned th e Federa l Av i ation Administration (FAA) for an exemption fro m the requ irements of§§ 25.901(c) and 25.981(a)(3) ofTitle 1 4, Code ofFederal Reg ul ations ( 14 CFR). This exemption , if granted would allow p lanned type-design changes to the Boein g Model 747-400 (freighters o n ly) and 747-400B CF airplane center wing

- tank (CWT) fuel-quantity indication system (FQIS) fuselage wi ring installation

. The petitioner requests relief from the following regulation(s) : Section 25.90l(c), at Amendment 25-126, requires that for eac h powerp lant and auxiliary power unit in stall ation, it must be estab li s hed that no single fa il u re or ma lfunc t ion or probable combination of fai lures w ill jeopardize the safe operation of the airplane except that the fa ilure of structural elements ne ed not be considered i f the probability of such failure is extremel y remote. Section 25.981( a)(3), at Amendment 25

- 125, requires that no ignition source may be present at each point in the fue l tank or fue l tank system where catastrop hic fai lure could occur due to i g nition of fuel or vapors. T hi s mu st be sho wn by demonstrating that an igni t ion source could not result from each sing le failure , from each s in g l e fa ilure in combination with each latent fai lure condit ion not shown to be extre mely remote, and from all combinations of failures not shown to be extreme l y improbable. T he effects of manufacturin g vari abi l ity, aging, wear , corros ion, and likely damage must be con s id e r ed

.

### The petitioner supports its request with the following information: This section quotes the relevant infonnation from the petitioner's request, with minor edits for clarity. The complete petition is available at the Department of Transportation's Federal Docket Management System, on the Internet at http://regu lations.gov, in Docket No. FAA-20 15-3 166. 

### The Extent of Relief So ught and Reasons 14 CFR 25.90 1 (c) Amendment 25 -1 26 Boeing r elief is necessary because direct compliance wou ld requ ire excessive design changes and retrofit of in- service airplanes. Changes include the following: Further redesign of the Airplane Wiring System to ensure FQIS wire separation for numerous airp lane configurations. Make new tank penetrations and procure new in-tank wiring harnesses. Modify the Fuel Quantity Processor Unit (FQPU) and associated connectors. The so lution wou ld require a FQIS architecture change to relo cate the FQPU and consider Remote Data Connectors (RDCs). In-tank component changes (new brackets , potential need for shorter probes , revised in-tank wire harn ess and retention means). Software changes related to Fuel Tank Gauging Function (to account for capacitance chan ges if shorter in-tank probes are required). 14 CFR 25.981 (a)(3) Amendment 25-125 Boeing relief is necessary because: Same as above. 

### Background The FAA is planning to issue a notice of proposed rulemaking (NPRM) for the 747 , similar to the 757 NPRM No. 2011-NM-094-AD , which proposes to require modifying the FQIS w iring or fuel tank systems to prevent development of an ignition SJurce in side the center fuel tank. Paragraph (h)(2) states , " Within 72 months after the effect ive date of this airworthiness directive (AD) , modify the airplane by separating FQI S wiring that runs between the FQIS processor and the center fuel tank, includin g any circuits that might pass through a main fuel tank, from other a irplane wiring that is not intrinsically safe

. " Boein g i s proposing to accomplish the FAA's planned AD requirements by separating the FQIS CWT wirin g between the FQIS processor and the center fuel tank , as well as using the FQIS b uilt in test equ ipment (BITE) check. The BITE service bulletin (SB) 747-28

- 2340, which includes the instruction s to ensure tank circuit wiring integrity , is already approved by the FAA. The CWT FQIS wi rin g separation is bein g prepared with guidance from the FAA's approved standard for retrofit wire separation from FQIS wiring. But the combination of BITE and wire separation will not result in the FQ I S system being compliant to§ 25.901(c) at Amendment 25-126 and§ 25.98 1( a)(3) at Amendment 25- 125. Since the wiring c hanges are a change to type design , but wi ll not be compliant , an exemption is being petitioned. Boeing states that the FAA's response to a 757 NPRM comment suggests that the FAA will accept petitions for exemption for the "latent-plusone" requ irements of§§ 25.90 l (c) and 25.98l(a)(3), and there has a lso been FAA communication that this acceptance app lies to the 747.

2This petition for an exe mption i s being made because fu ll compliance to these rules for the 747-400 freighters would require extensive system design/installation changes , but do not substantially improve the safety of the current airplane design , and are economically prohibitive given that the retrofit 747-400 freighter fleet is small, and so extensive system changes are not in the public's interest. The FQIS system was previous ly shown compliant to§§ 25.1309 and 25.901(c) for type certification (TC); however, both § 25.901(c) at Amendment 25-126 and§ 25.981(a)(3) at Amendment 25 -1 25 have additional fai lu re combination requirement s. For systems that may cause a catastrophic hazard, § 25. 1309 requires no s in g le failure and no combination of fai lu res greater than extremely improbable ;§ 25.901(c) at Amendment 25 -1 26 requires no sing le failure or probable combination of failures; and§ 25.981(a)(3) at Amendment 25 -125 requires no single failure, no single-plus-latent (greater than extremely remote), and no multiple combination greater than extremely improbable. This exemption is being sought for the no single-plus-latent (greater than extreme ly remote) as is stated in§ 25.981(a)(3) and interpreted by the FAA for§ 25.901(c). An exe mption is also being sought for the nonenvironmental aspects of§ 25.90 I (c) provided by FAA interpretation , and the explicit § 25.98 1 (a)(3) requirements ofmanufacturing variab ility , aging , wear , corrosion, and likely damage, as these considerations are already covered by airline maintenance of the type design of the airplane. Statement of Public Interest Without exemption relief for the FQIS CWT wiring changes , the intent ofthe NPRM and the FAA 's previous cornmunicatio11 of intent for airplane desi gn improvement for the CWT FQI S to address those 747-400 freighters that do not have a nitrogen generating system (NOS) cannot be met. For comp li ance , airplane changes to the entire FQIS (all tanks ) would be required for fleet retrofit such as:

• Exte nsive airplane wiring changes to ensure adequate w ire separation throughout the fuel quantity indication system.

• In-tank component changes (new brackets] potential need for s horter probes] revised in-tank wire harnes s and retention means).

• Software c han ges related to Fue l Tank Gauging Function and Safety function if shorter probes are required. The current FQIS system has been thoroughly evaluated for safety aspects as was required per Special Federal Aviation Regulati on No. 88 (SFAR 88) for the FQIS; however , the FAA determined there were safety issues id e ntified with FQIS wiring c01mected into a high flammability tank. For the 747-400 , it is th e CWT. The time needed to successfully design and implement system changes beyond the proposed CWT FQIS wiring separation design changes to comp ly with th e rules wou ld further impact the avai lability of the wiring change on this out-of-production fleet of747 airplanes. These new complete FQIS design changes would not provide any economic benefit to th e operators and do not provide any sign ificant benefit or increased level of safety. The Boeing Company



### 3considers that the granting of this exe mp ti o n would negate the need for th e FAA to e valuat e th e add itional data requir ed to s upp ort co mplianc e with these regulations. Therefore, g rantin g this exemp tion would r e du ce the burden on FAA r es ources and consequently public expenditure. Granting thi s exe mption i s in the public interes t for th e aforementioned reasons and w ill: 1

. Enhance th e safe ty of the 747-400 freighter fleet (as has been determined by the FAA) for those a irplan es not in stalli ng N OS by adding w iring c hanges for th e CWTFQIS. 2. Enhance the safety of the 747-400 freighter fleet by a l so including F QIS BITE for the CWT c ircui t interv a l te s ts , so that w hen don e in a dditi on to the CWT FQIS w irin g se paration , the airp lane ad dresses the single-plu s -l ate nt failure mode s for th e FQ I S, whic h was the probable fai lure combination indicate d by the National Tran spo rtation Safety Board (NTSB) R eport AAR -0 0-03 for th e Trans World Airlines (TWA) flight 800 accident. Statement of No Adverse Effect on Safety T he addition of the FQIS CWT wirin g changes with a BITE interv a l check, in lieu of a fully compliant (all tanks) FQIS (which would have a hot s hort p rotector (HSP 1) FQPU line replacem e nt unit (LRU) , wire separati on for th e tank (to tal of 7 ) ci rc uit wiring (b oth outside and in s ide the tank) , and a fau lt detectin g BITE th at i s ann un c i ated ); does not have an adve rse effec t on safety. In the prop ose d CWT FQIS wire sepa r atio n d es ign c hange , the ign iti on s ource thr eat from other airplane system s is reduced , si nce the wiring will have i nc reased separation. T h ere are a lso airworthiness limitations in the in s tructions for continued airworth iness (IC A) that ensure th at any o ther system c han ge w ill co ntinue to mainta in the sep aration provided by t hi s proposed desig n change which will now clearly b e v i suall y identifi ed as FQIS wiring. Together, this improves th e w iring failure m odes and improves th e syste m probability re l ative to fuel tank ignition

. With the ad dition of th e FQ I S BITE interval checks for th e CWT, th e probability is better s in ce the exposure of w irin g failures wi ll b e furt her r ed uc ed. For the CWT FQIS , w here the c hanges to the FQ I S are be ing do ne instead o f th e install ation of NOS as de termined by the FAA to be an acceptable subst itute safety improveme n t, the combinat i o n of the se p aration , the I CA , and the BITE/circuit te s t a ddresses no s in g le failure s in combination w ith late nt fa ilures wi th an acce p table leve l of s afety by ensuring the continued integrity of protection features fro m threats to the ta nk circuit wiri ng.

1 A HSP is an LR U that is also des igned to have the funct ion to protect the tank circuit wiring from E lectrical Power Source threats that could affect the airplane circu it wr in g of the LRU (FQ P U).

4• A - The fault modes of the in- ta nk wiring have reduced exp os ure to 750 hours due to the BIT E check and FLSS c ircuit tes t. Wirin g inside the tank i s well protecte d and has a very low failure probabi lity w hich is impro ved by the lower exposure.

• B 1 - The FQ PU is an H S P up to 115 V AC. If a lo w -prob ability hi g her v oltage power sour ce s hort were to occ ur on th e airp lan e si de of the FQ P U, it mo st like ly would , but for very high voltage power source s may not stop it from propagating through to th e tank circuit s, but the failure wou ld at the least be detectable wh e n the BITE inte rval check w as done, and in mo st cases sooner, as it would mo st likely affect indication.

• B2- T he wiring from the FQPU to the tank will have separation provided by th e AD-mand a t e d SB. This wirin g has low probability failure mod es which also hav e reduced expos ure provided by the 750-hour interv al BITE check. Whe ther th e f a ilure is A, orB 1 , or B2 , the re is n o s ingle failure. For the combin at ion of f ailure s, A and B 1 , or A and B2 , the BITE has r e du ced the expo s ure and the latency interval for each protection design feature (wiring has less than extreme ly remote fa ilure rates) and so the probability for each failure mode is b ette r than remot e. This a lso addresses the s ingl e -plu s -l atent fa ilure requirement with an acceptable le vel of safety as the probab ili ty of either fai lure o n th e flight b efore the next in terval check would both be better than rem ote. The 747

- 400 FQIS was found to be compliant to§ 25.90 l (c) durin g ai rplan e type certifi cation in 1989. S ince then, Bo e in g has compl ete d the SFAR 88 safety assessment and has increas e d the airp lane fuel sys t e m safety with in s tallation of an HSP LR U for th e densitometer. F or th e 747-8 proj ect , the FQPU , which has the same arc h i t ecture as the 747-400 FQPU , was also s hown to be an HSP LR U and so the fuel leve l sen s ing probes/ compensator have that same p rotection. Following the SFAR 88 system safety assessme nts , Bo e in g's assessment was that the r i sks for the 747-400 FQ IS installation were extremely improbable , which i s the typical indu stry and§ 25.1309 s tandard for an acceptable safety sys te m. The Bo e in g approach to incorporate de s ign c h anges to add CWT FQIS w i re separation with v i sual identification , a CWT FQIS 750 hour B ITE check , alo n g with ICA that e n sures that ad ded sys t e m s w iring wi ll ma intain the separation fo r the lif e o f the a i rp lane, the H SP FQPU L R U, and the densitometer tank c ircui t H SP provi ded by B oei ng S B 747-28A2266 , w ill prov id e for an enhanced safety margin over th e ex is ting approved FQIS on t h e in -servi ce fleet. 

### Request to Waive Publication and Co mment : S in ce the reference a) NPRM for the 757 is cl ose ly rela ted to this change as the 747- 400 issue i s the same, and the NPRM makes mention of a 757 petition for exe mption , and ha s already go n e throu g h public conm1enting process , Boeing respectfully requests that the FAA waive the " publication and com ment" step in the process for making a final decision on this exe mp t io n .

5In addition to the timeliness concern, it is the Boei ng position that the safety

- associated aspects related to th is system have been fully vetted in the pu b li c forum as part of the SFAR 88 project. 

### Pri vil ege s o f th e Exe m ptio n Ou ts id e of th e United Stat es Per 14 CFR 11.81 (h), Boeing reque sts that the privileges of this exemption be extended outside of th e United States. This extensio n of pr i vi leges is necessary for opera t ions based within foreign countries having bilateral agreements with the United States accep ting FAA 14 CFR part 25 a s their airworthiness st andards for transport category airc raft. 

### Ju s tifi cati on fo r Ex em p ti o n In accordance with the requirements of§ 1 1.81(e), The Boeing Company has prov ided a m eans of complianc e to the FAA to establish an acceptable level of safety to that provided by §§ 25.901(c) and 25.981(a)(3) by separating the FQIS wiring from oth er airplane power wires that w ill me et the minimum separation requirements for most of the wire ru n s. For the areas that minimum separation is not achievab le due to space limitation, other positive separat ion means s uc h as c lamps, spacers , and s leeving will be u sed for the CWT FQIS which also includes FQIS BITE interval checks for the CWr. T he se design chan ges address the s in g le-plus-latent failure modes for th e F QIS which was the probable fail ure combinati on indicated by the N TSB TWA fli g ht 800 accident r eport. Therefore, granting this exe mption would, in turn , reduce the burden on FAA reso urces and consequently public ex penditure. 

### Co nclu s ion : B oe ing is petitio ni ng for an exemption from the provisions of 14 CFR 25.90 l (c)[25-126] and 14 CFR 25.981 (a)(3)[25 -1 25] at the system level as they app ly to th e FQI S install e d on the 747-400 (Freighters Only) and 747-400 BCF airplanes for the FQIS wiring changes describ e d above.


### Fe d era l R eg i st er p ubli ca t io n Although th e petitioner requested that action on its petition not be delayed for pub lication in th e Federal Reg ister, the FAA found t hat the petition , if g rante d , would set a precedent. Therefore, to allow an opportunity for the public to comment on the p etition, a summary of it was publi s hed in th e Federal Register on Septe mber 2 , 20 1 5 ( 80 FR 53223). No comments were received. 

### T h e FAA's a n a lys i s We agree with the petitioner 's justifica tio n th at g ranting the petition is in th e pub lic interest, w i th two exceptions. For clari ty, we do not agree with the petiti oner's public-inter es t s tatement s that " The time ne e ded to successfu ll y des i gn a nd implement system changes be yond the proposed CWT FQ I S wiring sep arati on design changes , to co mpl y with the rule s, would furthe r impact the availability of th e

6wiring c ha n ge on thi s out-of-production fleet of 747 aircraft. " The AD worksheet for correctin g this unsafe co ndition was i ss ued in 2004. Boeing has not provided service in structions sinc e th at time. The time need e d to develop a compliant design is minimal w hen compared to t he petitioner 's delay in providing the service ins tru ctions. We did not consider thi s argument in o ur determination that granting the exemption i s in the public inte re st. We also do not agree with the petitioner 's public interest statement that "

... the g ranting of thi s exemption would negate the need for [the] FAA to evaluate the additional data required to support co mpliance with the se regulation s. T herefo re , granting this exemption would reduce the burden on FAA resources and consequently public expenditure. " FAA reso ur ces needed to re view d esig n changes that are needed for full compliance wo uld be minimal , and these re s ources are available to address unsafe conditions. Th ere would be no sav ings in public expenditure and no public interest by not providing a compli ant design, and w e did not consid e r this argume nt in our determination that granting the exemption i s in the public interest. We agree with the peti t ione r 's justification that grantin g th e petition i s in th e publi c inte rest. Modification of existing in

- service 747 airplanes to provide a compliant des ig n wo uld be costly bec ause changi ng the fue l-quantity pro cessor, se paratin g a irpl ane wiring from other high-power wiring, or providing electrical isolating devic es to prevent electrical energy from entering the fuel tank s for th e s mall numb er of c argo airpl a nes is cost prohibiti ve. This exemption will allo w approval of serv ice in struction s needed to address an un safe condition on t he center wing-tank FQIS w irin g. The FAA has detem1in e d that the propo sed modifications represe nt a reaso nab le , cost-e ffective method to achieve a m eanin g ful reduction in the risk due to potential FQIS fuel-tank-ignition sourc es . The FAA's current fuel-tank-safety airworthiness s tan dards rely upon a balanced approach of limiting fuel-tank-flammability expos ure time and precluding i gnition sources that could fo rm in the fu el tanks. Fo r this reaso n ,§ 25.981 include s separate a n d distinct requirements for limiting fu e l-tank fl am mabi li ty and preventing ignition sources in the fu e l tanks. The wing and ce nter wing-tank safety are addressed by co n si derin g flammability and ig nition source mitigation s . T he wing tanks are exposed to outside air , are unheate d, naturally cooled, and are considered low flammability. We do not co ns ider it to be an un sa fe condition for the FQIS wiring entering these wing tank s to be co-routed in wire bundl es with w ires carry in g hi gh e lec trical energies. Because t h e ce nter wi ng tank i s heated and is consider ed a high-flammability tank , additio nal ignition-source mitigations a re provide d. The mod i fications to separate a porti on of the w irin g for the cen ter w in g-tank FQ I S sig nifi can tl y reduces the likelih ood of a failure that could introduc e high powe r onto the FQI S wiring. In addition , mandatory m a inte nance checks for the ce nte r tank FQIS w iring wi ll be required as part of th e petitioner's de s ig n approval. This will significant ly reduce the likelihood of a latent fa ilure in the FQIS w irin g re sulting in an ignition source in the fuel tank s. Grant i ng thi s exemption wi ll allo w FAA approval of serv ice instructions needed to ad dress the unsafe co nd ition and therefore resu lt in a safety improvement that is in the public interes t. SFAR 88 requires the type-design-approval hold er to d evelop all design changes to th e fuel-tank syste m that are nec essary to meet the requirements of§§ 25.90 1 an d 25.981. The peti ti oner did not specifica ll y request exe mption from thi s requirement. H owever , it did request an exemption

7from§§ 25.901 and 25.981. Granting the exemption to these sections results in granting an exemption to the same ignition-source prevention requirements of SF AR 88. Therefore, we have added clarification in the e xemption that states that exemption from SF AR 88 for the service instruction is al so included in thi s exemption. T h e FAA's de ci s i on In consideration of the foregoing, I find that a grant of exemption is in the public interest. Therefore , pursuant to the authority contained in 49 U.S.C. 40113 and 44701 delegated to me by the Administrator , The Boeing Company , is hereby granted an exemption from SFAR 88, and §§ 25.90 l (c) and 25.98l(a)(3) , as they pertain to fuel-tank-ignition prevention associated with the center wing-tank FQIS wiring installation , to allow for FA A-approval of Boeing Service Bulletins to address the unsafe condition in the FQIS that was identified through the SFAR 88 safety analysis. The app l icabi l ity of any service bull etin approved using this exemption must be limited to airplanes with an all-cargo configuration.

Issued in Renton Washington , on 

## M AR 2 9 2 0E

Victor Wick l und Acting Manager, Transport Airplane Directorate Aircraft Certification Service

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