### UNITED STA TES OF AMERICA DEPARTME NT OF TR AN SPORTATION FEDERAL AVIAT ION ADMINISTRATIO N RE NTON , W AS HI NGTON 98057- 3356

In the ma tter of the petition of
T he Boeing Company E xemption N o . 14593

Re gul a to ry Docket N o. FAA-2015-3086 for an exemption from§§ 25

. 90 l (c) and 25.98l(a)(3) ofTitle 14 , Code of Federal Regu lations

GRAN T O F E XEMPTIO N By letter no
. CP -L4L -1 5-00233, dated Ju ne 22, 2015, 

### Mr. Tim He nd ri x , Manager, Certi ficat ion & 

### Ai rworthiness, The Boeing Company, Boe ing Commerc i al Airp lanes , Southern Ca li fornia Engineering Des i gn Center, 2401 E

. Wardlow Road , Mai l Code D800

- 0022 , Lo n g B each, CA 90807

- 5309, petitioned the Federal Aviation Adminis trati on ( FAA) for an exemption from the requirements of§§ 25.90l(c) and 25.981(a)(3) ofTitle 14, Code of Federal Regu lati on s (14 CFR). Thi s exe mptio n , if granted wo ul d a ll ow planned changes to the 767-200/3 00 (fre ighters only) and 767

- 300F center-wi n g
- tank (CWT) fuel-quantity ind ication sys t em (FQIS) and fuelover fill- s hutoff surge tank fuse lage
- wiri n g installation. The petitioner re que s ts relief from the follow in g re gul ation(s) : Section 2 5 .9 01 (c ) at A mendment 2 5 -12 6- In s tallation
. Fo r each powerplant and auxiliary power unit i n sta ll ati on, it must be estab l ished that no single failure or malfunction or probable combination of fai lures wi ll jeopardi ze the safe operation of the airplane except that the failure of structura l elements need not be considered if the probability of such fai lure is extreme ly remote. Section 25
. 98l(a)(3)- Fuel ta nk ig nition pre vention
. (a) No ign ition source may be present at each po i nt i n the fue l tank or fue l tank system where catastrophic failure cou ld occ ur due to ignition of fuel o r vapors. This must be shown by: (3) Demon strating that an i gnit ion so urce could not result f rom each single failure , from each single fai lure in com bi nat ion with each latent failure condi tion not s hown to be ext remely remote, and from all combinations of failures not s hown to be extremelyimprobable. The effects of manufacturing variability , aging, wear, corrosion, and likely damage must be considered. 

### Related sections of 14 CFR: Section 25.1309- Equipment, systems, and installations, states that required equipment, systems, and installations be designed to ensure that they perform their intended functions under any foreseeable operating condition, and that the occurrence of any failure condition that would prevent the continued safe flight and landing of the airplane be extremely improbable. 

### The petitioner supports its request with the following information: This section quotes the relevant information 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://regulations.gov, in docket no. FAA-2015-3086. 

### Background: The FAA is planning to issue a NPRM for the 767 similar to the 757 NPRM 2011

- NM

094-AD [a proposed airworthiness directive (AD)], which proposes to require modifying the FQIS wiring or fuel tank systems to prevent development of an ignition source inside the center fuel tank. Paragraph (h)(2) states: "Within 72 months after the effective date of this AD, modify the airplane by separating FQIS wiring that runs between the FQIS processor and the center fuel tank, including any circuits that might pass through a main fuel tank, from other airplane wiring that is not intrinsically safe." Boeing is proposing to accomplish the FAA's planned AD-mandated changes to separate the FQIS CWT wiring between the FQIS processor and the center fuel tank, as well as using the FQIS Built-In Test Equipment (BITE) check. In addition, changes to separate the Fuel Overfill Shutoff Surge Tank wiring from the Fuel Level Sensor Control assembly to the center fuel tank , along with its wiring integrity checks, will be done. The BITE service bulletin 767-28-0118, which includes the instructions to ensure tank circuitwiring integrity, is already approved by the FAA. The CWT FQIS wiring separation is being 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 FQIS system being comp li ant to 25.901 (c) [25-126] and§ 25.981 (a)(3) [25- 125]. S inc e the wiring changes are a change to type design, but w ill not be compliant , an exemption is being petitioned. The FAA ' s response to a 757 NPRM comment suggests that FAA will accept petitions for exe mption for the "latent-plus -on e " requirements of sections 25.90 1 (c) and 25.981 (a)(3) of the Federal Aviation Regulations , and there has al so been FAA communication that this acceptance app lie s to the 767. Th is petition for an exemption is being made s i nce full compliance to these rules for the 767 wou ld 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 767 freighter fleet is limited (with some freighters delivered with NGS), and so extensive system changes are not in the public's interest.

2The FQIS sys t em was previously shown compliant to§§ 25.1309 and 25.901(c) for TC [type certificate] and ATC [amended type certificate]; however, both§ 25.901(c) [25- 126] and§ 25.98 1(a)(3) [25

- 125] have additional failure-combination requirements. For systems that may cause a catastrophic ha zard , § 25.1309 requires no single failure and no combination of failures greater than extreme ly improbable;§ 25.901(c) (25-126] require s no s in g le failure or probable combination of failures; and § 25.98 1 (a)(3) [25-125] requires no sing le fai lure, no single plus latent (greater than extremely remote), and no multiple combination greater than extreme ly improbable. This exemption is being sought for the no sing le p lus late nt (greater than extremely remote) [f ai lure condition], as is stated in§ 25.981(a)(3) and interpreted by the FAA for 

### § 25.901(c). An exemption is also being sought for the non-en vi ronmental aspects of 

### § 25.901(c) provided by FAA interpretatio n , and the explicit § 25.981(a)(3) requirements of manufacturin g variabi lit y, aging , wear, corrosion, and li ke ly damage, as these considerations are already covered by airline maintenance of the type design of the airplane. 

### Statement of Public Interest: Without exemptio n relief for the FQIS 

### & [Fuel Leve l Sensor System] FLSS CWT wiring changes, the intent of the NPRM and the FAA's previous communication of intent for airplane design improvement for the CWT FQIS, to address those 767 freighters that do not have Nitrogen Generati ng System (NOS), cannot be met. For compliance, airplane c h anges to the entire FQ IS (all tanks) and FLSS (all tanks are affected) would be required for fleet retrofit such as: FQIS:

• New system architecture to redesign the FQPU [Fuel Quantity Processing Un it] to function as a Hot Short Protector (HSP 1) Line

- Replaceable Unit (LRU) and relocate the FQPU to enab le wire separatio n. Other architectures could be u sed such as providing a HSP LRU c lo ser to the tank, but it would be a more extensive and new architecture.

• Extensive airplane wiring changes to ens ure adequate wire separation throu gh out the FQIS.

• In -tank component changes (new brackets, potential need for shorter probes, revised in-tank wire harness and retention means).

• Software changes related to Fuel Tank Gauging Function and safety function if shorter probes are required. FLSS:

• New system architecture to move the Fue l Level Sensor Control assembly into a new relocated card file.

1 A HSP is an LRU that is also designed to have the function to protect the tank circuit wiring from electrical-powersource threats that could affect the airplane circuit wiring of the LRU (FQPU).

3• The Fuel Leve l Sensor Contro l assem bl y has not been eva lu ated t o function as a H SP , but due to si milari ty of d esign to the 747-8 FLSS Single Point Sensor Card that has been shown to be a HSP, it al so may meet th e r equ ireme nt s for its part in th e syste m , but it also may no t be shown to be a H SP due to the circuit diff erenc es.

• Extens ive changes for the new card fi le and the wiring changes in all 3 tank s to ens ure adequate wire separation throughout the fuel-l eve l se nsi ng system.

• In-tank compone nt changes (new brackets, new pro bes , revised in-tank wire harness and retention means). Th e current FQIS sys te m and FLSS [have] been thoroughly evaluated for safety aspects as was req uired per SFAR 88 for the FQIS, however, the FAA determined there were safety is s ues identified with FQIS wiring connected into a high-fl a mmability tank, for the 767 it is the CWT

. The time needed to success fully design and implement system changes beyond the proposed CWT FQI S w iring separation de s i gn changes, to comply w ith the rules, would further impact the avail ability of the wiring change on this out-ofpr oduction fl eet o f 767 airplanes. These new , co mplete , FQIS and FLSS d es ign cha nges would not provide an y economic benefit to the operators and do no t pro vi de any s ignificant benefit or increased level of safety. The Boeing Co mp any considers that the grantin g of thi s exemption would negate t he need for [the] FAA to eva luate the additiona l data require d to s upport compliance with th ese re gulations. Therefore , granti ng t his exe mption wou ld reduce t he burden on FAA resources and consequently public expenditure. Granting this exe mption is in the publ ic interest for the aforementioned reasons and will:

• Enhance the saf ety of the 767 fleet (as has bee n determined by the FAA) for th ose airp lanes not installing NGS by adding w iring changes for th e CWT FQI S.

• Enhance the safety of the 767 fleet by also including FQ IS BITE for the CWT a nd FLSS circuit interval te s ts, so that when done 

### in addition with the CWT FQIS and FLSS wiring separation , the airp lane addresses the sing l e- plu s- late nt failure mod es fo r the FQIS , which was the probable fai lure combination indicated by the NTSB report. 

### S tatement of No Adverse Effec t on Safety: Th e ad dition of the FQ I S CWT wiring changes , along wit h a BITE interval check, and with t h e FLSS wiring changes an d circuit interval tes ts, 

### in lieu of (a) a fully compl iant (all tanks) FQ I S (w hich would have a HSP FQ PU LRU, wire separa tion for the tank circuit wiring (both outside and inside the tank), and a fault detecting BITE that is annunci a t ed); and (b) a full y comp liant FLSS, which mo st lik ely wi ll need a red es ig ne d Fuel Level Sensor Control assembly , a new card file, and wire separation inside and outside the tank with new probes, does not have an adverse effect on safety. In the proposed CWT FQ IS and FLSS wire

- sep aratio n design c hange , the i gni ti o n- source threat from other airplane system s is reduced s ince the wi rin g will have increased sep aration. There are also In str uctions fo r Continued Airworthiness (ICA) that en s ure that

4any other syste m changes will continue to m ai ntain the separatio n pro v ided by this proposed design change, which will now clearly be visually identifi ed as FQIS wiring. Together, this improves the wiring failure modes , and improves the system probability relative to fue l-t ank ignition. With the addition of the FQIS BITE interval checks for the CWT and FLSS circuit interval tes ts, the probability is better since the exposure of wiring failure s will be further reduced. For the CWT FQIS , where the changes to the FQ IS and FLSS are being done instead of the install at ion ofNGS as determined by the FAA to be an acceptabl e s ubstitute safety improvement, the combination of the separation , the ICA , and the BITE /ci rcuit test addresses no s ingle fai lures in combination w ith latent failures with an acceptable le ve l of safety by ensuring the continued integrity of protection features from threats to the tank circuit wiring. A: The fau lt modes of the in-tank wiring have reduced exposure to 750 hours due to the BITE check and FLSS circuit test. Wiring inside the tank is well protected , and has a very low fai lure probability , which is improved by the lower expo sure. Bl: The FQPU/FLS S is a HSP up to 28V. If a low-probability , higher-voltage power source short were to occur on the airplane side of the FQPU/FLSS Fuel Level Sensor Control assembly or wi thin the FQPU/FLSS Fuel Level Sensor Control assembly, it most li kely would, but for specific failures may not stop it from propagating through to th e tank circuits, but the failure would at least be detec table whe n the BITE interval check was done , and in most cases sooner , as it would most likely affect indication. B2: The wiring from the FQPU/FLSS Fuel Le ve l Sensor Control assembly (card file ) to the tank w ill have sep aration pro v ided by the AD-mandated service bulletin. T his wiring ha s low pro b abili ty failure modes w hi ch a lso have reduced exposure provided by the 750 hour interval BITE check. Whether th e failure is A, orB I , or B2 , th ere is no single failure. For the combination of failures, A and B I , or A and B2 , the BITE has reduced the exposure and the latency interval for each protection-design feature (wiring has le ss than extremely remote failure rates) , and so th e probability for each fai lure mode is better than remote. This also addresses the s ingle-plus-latent failure requirement, with an accep table level of safety , as the probability of either fai lur e on the flight before the next interval c heck wo uld both b e better than remote. The 767 FQI S / FLSS was found to be comp liant to § 25.901(c) during airplane type certification for the FQIS change in 1992. S ince th en, Boeing has com pleted the SFAR 88 safety assessment and has increased the a irplane fuel- sys te m safety with installation of a HSP LRU for the densitometer. Following the SFAR 88 system-safety assess ments , Boeing assessment was that the ri sk s for the 767 FQIS in stal lati o n we re extre mely improbable, which i s the typical industry and CFR 

### § 25.1309 s tandard for an accep tabl e safety for systems. T h e Boeing approach to incorporate design changes to add center wing-tank FQ I S wire separation with visual identification , a CWT FQ IS 750 -hour BITE check, along w ith ICA that ensures that added systems wiring w ill maintain the separation for the life of th e

5

### airplane , and th e densitometer tank- circu it HSP provided by Bo ei ng S B 767-28A0094 , w ill provide f or an enhanced safety margin over the existing , approved FQIS on the inservice fl ee t.
R eq u est to W a ive P ub li cati on and Co mm en t: Since the NPRM 20 11-NM-094-AD for th e 757 is closely related to thi s change as the 767 issu e i s th e same , and the N PRM makes mention of a 7 57 p etition for exemption , and has already go ne through public-commenting process , Bo ein g respec tfull y requests that the FAA waive th e "p ub lication and comment" step i n th e process for maki ng a fmal decision o n thi s exempt ion. Additionally , g iven that the FAA has g ranted a s imilar exemption for the 767 pr oduction airp lanes tha t [ar e ] dependent on compl eting the submitta l by December 2015 of the retrofit type-de s ign change, and the FAA and Boeing h ave made a rapid schedu le for thi s project ; and so due to the schedule- se ns itive nature of this reque s t for exemption, Boeing respectfu ll y requests that the FAA waive the " publication and comment" step in the proces s for making a fina l deci s i on on this exemption. 

### In addition to the time li ness co ncern , it is th e Boeing po si tion th at the safety-as soc iated aspects re lated to this system h ave been full y ve tted in the public forum as part of the SFAR 88 project. Priv ileges of t h e Exe mpti on Ou ts ide t h e Unite d S t a t es: Per 14 CFR 11.81 (h), Boeing reque sts that the privi leges of this exemption be extended outside th e United States. This extension of privileges is neces sary for operations based within foreign countries having bil atera l agree ments with the United States accepting FAA 14 CFR part 25 as their airworthiness standard s for transport catego ry aircraft. Conclu s ion: 

### In accordance to the requirements of 14 CFR 

### § 11.81 (e), the Boein g co mpany has provided a means of compliance to the FAA to establish an acceptable level of safety to that provide d by th e ru les 14 CFR § 25.90l(c) and 14 CFR § 25.981(a)(3) by separatin g t h e FQ I S wiring from ot her airplan e powe r wires that will meet the m inimum separation requirement s for m ost of the wire run s. For the areas [in which] minimum separation [is] not achievable due to space limitation , other positive separation means , such as clamps , spacers and sleevei ng will be used for the CWT F QIS and also including FQIS BITE interval c hecks fo r the CWT. T he FLSS w ill include the sa me type of wiring changes· and in cl ud e the circuit test. Th ese design c ha n ges address the s in gle -plu s -lat ent failure modes for th e FQ IS , which was the probable fa ilure combination indicated by the NTSB report. Therefore , g ranting thi s exemption wo uld , in turn , redu ce the burde n on FAA resourc es and consequently public expe nditure. Federa l R eg is t e r p u b li cat i o n A lthough the petitioner requested that action o n its petition not be d el ayed f o r publication 

### in the Federa l R egi ster , the FAA found that the pe tit io n , if granted, wou ld set a preced ent. Therefo re, to a llo w an oppo rtunity for the public to comme n t o n the petiti o n , a s ummary of it was p ubli s hed in the Federa l Register o n August 20 , 2015 (80 FR 50709)

. Comments were received from th e

6Nat ional A ir Traffic Con tro l Assoc iation (NA TCA) Natio nal Safety Committee. The following quotes the NA TCA comments. NATCA recommends that the FAA deny the p eti tion for exemption publi s hed for public comments on August 20 ,2 015 in Dock et Ite m No. FAA-2015 -3086. This petition requests an exemption "from 14 CFR 25.90l(c) Amendment 25-126 and 14 CFR 25.98l(a)(3) Amendment 25- 1 25 pertaining to planned changes for the 767-200/300 (freighters o nl y) and 767-300F Center Wing Tank (CWT) Fuel Quantity Indication System (FQIS) Fuselage Wiring In stallation. " In the Background it also sta tes "An exemption is a lso being so ught for the nonenvir onme ntal aspects of §25.901 (c) provided by FAA interpretati on , and the explic it §25.98 1 (a)(3) requirements of manufacturing va riability, ag in g, wear, corrosion, and li ke l y damage, a s these considerations are already co ve red by airlin e maintenance of th e typ e design of the airplane." The petition also states the following: The FAA is planning to issue a NPRM for the 767 similar to the 757 NPRM 2011

- NM

- 094-AD w hi ch proposes to require modifying the FQ IS wiring or fue l tank systems to p revent development of an ignition source inside the center fuel tank. P aragraph (h)(2) s tates: " Within 72 months afte r the effective date of this AD , modify the airplane by separat in g FQIS wi rin g that ru ns between the FQIS processor and the center fuel tank , including any c ircuits that might pass through a main fuel tank, from other airplane wiring that is not intrin s icall y safe." The 757 S uppl e me ntal NPRM (SNPRM) was published as the result of unsafe condi ti o n s identified in d esign reviews p erfom1 ed by Design Approval Holders that were required by 14 CFR part 21 Spec ial Federal Airworthin ess Regulation No. 88 (SFAR 88) that was iss ued by the FAA in 200 1

. However, the action proposed in the SNPRM and in this pe tition for exempti o n wo uld not e limin ate the known unsafe con dition re sult ing fro m ig n ition so urces caused by shorts wit hin wi ring and fuel gaug in g e quipme nt on the s ubje ct airp lane models. The National Transportation Safety Board identified thi s ignition sour ce as the most likel y cause of the catastrop hic loss of all li ves o n the TWA Flight 800 airplan e. Thi s known fuel tank ig ni t i o n sou r ce i s required to b e e limin ated in all fu e l tanks of a irp la ne mod e ls affected by SFAR 88 and th e FAA's own SFAR 88 Policy, published as Mandatory Corrective Action c riteri a in FAA Policy Statemen t No. 2003- 112-15. Comment 1 : SFAR 88 Exemption Required Section 2.(a) of SFAR 88 requires th e affected Design Approval Holders: Conduct a safety review of the a irp lane fue l tank syste m to detem1ine th at the des ign mee ts the requirements ofSecs. 25.901 and 25.98 1 (a) an d (b) of thi s chapter
. I f the c urrent d es ign does not meet these re quire men ts, deve lop all design changes to the fuel tank system that are necessary to meet these req uiremen ts. T herefore , all design c hanges re qu ired to comply w ith S FA R 88 must comply with Titl e 14 Code of Federal Regulations sect ion 25.901 at Amendment 25

- 46 and section 25.981 at Amendment 25-102 (the amendment levels in effect on the effective date of SF AR 88). The petition for exemption d id not include a request for an exemption from thi s

7requirement of SFAR 88, and thi s requirement of SFAR 88 still r equires the design change comply with the above sec tion s. NATCA submitted comments to the 757 SNPRM that recommended the means of compliance for paragraph (b) clearly state in th e final rule that the FQ I S design chang es must include all fue l tanks and modifications must comply with th e fail safe requirement s of 14 CFR 25.901, Amendment 25-46, and 14 CFR 25.981(a) and (b) , Amendment 25

- 102. Comp li ance w ith those re gulations i s cl early required by SFA R 88 for all design c hanges requ ired b y SFAR 88. T he same applie s to the Model 767 and thi s petition for exemption. Comment 2: Lack of Public Interest Durin g NATCA 's re view of the petition w e believe that the petition does not meet the requirements for granting an exemption in 14 CFR 11.81 (e) and is not in the public interest. Section 11.8l(e) requires the p e tition for exemption in clude " The reasons why g ranting the exe mption wou ld not adversely affect safety, or how the exe mption would provide a leve l o f s afety at least equal to that pro v ided by the rule from w hich you seek th e exe mption

. " The petitioner ' s ju st ificati on for granting an exe mption is based primarily o n the cost of de ve loping a co mpli ant design and a s tate ment of no ad verse effect on safety beca use of features r e quired by separate regulation s
. This argument o f cost avoidance and no adverse e ffec t on safety does not meet e ither of these two regulatory requirements for the FAA to g rant an exemption. The petitioner al so justifies the exemption by stating: Granting of this exemption wo uld negate the need fo r FAA to evaluate th e additional d ata re quired to supp ort co mpliance w ith these regulations. There fore , grant in g this exemption would reduce the burden on FAA resources and consequently public expenditur e. The costs associated with compliance are no t a consideration for m ee ting the condition s in §I 1.81(e) for g ranting an exemption. Under the regulatory requirements fo r the FAA to adopt a rule , costs for a design approval holder to demon strate comp liance to the regulation s wa s evalu ated by the FAA when th e subject regulati o n s were adopted. The rulemakin g for both the subject regulations and SFAR 88 public records show that th e FAA determ ined the safety benefits outwe ig h the costs of comp lyi ng with th ese regulation s
. The s tateme n t in the petition for exemption of no adverse effect on p ub li c s afe ty is no t supported by safety s tandards established by the FAA 

### in rulernaking. Following the TWA 800 accident resu lting from a fuel tank exp losion, the FAA amended§ 25.98 1 to include require m ents that address precluding creation of ignition sources as well as separate requireme nts to limit fue l tank flammabili ty. All manufacturers are re quired to in corporate flammability reduction systems into airplanes operating in passenger service , includin g the 757 , by the FAA ' s separate and subse quent 2008 Fue l Tank Flammability Reduc tion rulemaking. Ho wever, they are not required to pro v ide flammability redu ction sys t ems f or the ce nte r w ing tank 

### in ca r go a irplanes. In addition, the FAA d etermined th at a lack of separation between wiring that e nters th e fuel tank s and w irin g carrying high power could re su lt in ignition so ur ces in s ide the fuel tanks.



### 8

### The exemption wo uld clearly have " an adverse effect on public safety" compared to a design that complies with the minimum safety standard established by the subject Federal Airworthiness Regulations, including the requirements of SFAR 88 and it's the policy published by the FAA for determinin g mandatory corrective action ( " unsafe conditions). See our Comment No. 5 for further discussion on the requirements of SFAR 88 and its policy as it relates to this petition for exemption. Granting the petition for exemption wou ld not " provide a leve l of safety at least equal to that pro v ided by the rule from which you seek the exemption " since, as the petition states, 1 4 CFR 25.98 1 (a)(3) at Amendment 25- 1 25 requires: (a) No ignition source may be present at each point in the fuel tank or fuel tank system where catastrophic failur e could occur due to ignition of fuel or vapors. Thi s mu s t 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, ag ing , wear , corrosio n , and like ly damage must be cons ide red. As stated by the petitioner, full compliance w ith § 25.901(c) , which i s in the original certification basi s of the 767, and §25.98 1 (a)(3) at Amendment 25-102 or later, would result in redesign of the FQPU , wire separation inside and outside of all 3 fuel tanks. The petitioner's proposal to only separate wiring to r a portion of the wiring outside of one fuel tank , the center wing fuel tank , is a significant reduction in the sa fety level provided by full separation for the wiring of all fuel tanks. The petitioners claim that proposed maintenanc e checks of airplane wiring will be effecti ve as a way to detect damaged wiring ha s not been proven. Isolating fault s in airplane w irin g, which are commonly intermittent , is very difficult. Thi s has been shown when airplane wiring faults were found to be common, but were only detected when new fuel gauging system indicators were retrofitted into existing in service a ir planes. NATCA do es not believe that granting th e amendment to allow only partial wire separation for one of the three fuel tank s (the center wing fuel tank) , and a periodic BITE check of the ce nter wi n g fuel tank , is an overall safety improvement relative to a compliant design that would be require d to h ave wire separation for all fuel tanks together w ith separation of circuits in the FQ IS processor. Th e pet ition states the proposed design fo r the CWT would not meet the s ubject requirements and does not offer a des ign that provides a level of safety at l east equal to that provided by the rule from which the petitioner seeks the exemption , which is required by section 11.8l(e). In addition , no design changes are proposed to the FQIS for th e two main fue l tanks , which SF AR 88 a l so requires comply with the re g ulations that are the s ubj ect of the petition for exemption. The petitioner's argument of cost avo idanc e and no adverse effect on safety should not be a consideration in th e FAA analysis of the exemption request. Th e following additional comments are provided on the justification s in the petition for exemption from the Title 14 Code ofFederal Regulations § 14 CFR 25.90l(c) Amendment 25-126 and 14 CFR 25.981 (a)(3) Amendment 25

- 125 pertaining to planned changes for the 767-200 /3 00 (freighters o nly) and 767-300F Center Wing Tank (CWT)

9

### Fuel Quantity Indication System (FQ J S) Fuselage Wiring Insta ll ation , Docket No. FAA2015-3086. The Petitioner states the planned changes are to support a 767 AD that will be based on the 757 SNPRM. Therefore , some of these comments relate to the 757 SNPRM , as the petitioner states that the FAA ha s said it will apply to the 767. Comment 3
. 

### The FQIS syste m was previously s ho wn compl iant to§§ 25.1309 and 25.901 (c) for TC and ATC; however, both§§ 25.901(c) [25-126] and 25.981(a)(3) [25-125 ] have additional failure combination requirements. NA TCA Co mm ent: 

### The FAA Typ e Certificate Data Sheet A2NM states that the original certification basis for the Model767 airplane s includes§ 25.90l(c) Amendment 25-40. The amendments to § 25.901 s inc e Amendment 25-40 have not changed requirements of§ 25.90 l(c ) trom the requirements of Amendment 25-40. As stated in the preamble discussion to SFAR 88, lessons learn ed from the safety reviews conducted following the TWA 800 accident resulted in the discovery of failure modes th at had not been foreseen at the time of ea rlier type desi gn approvals. Co-routing of high power airplane w iring w ith FQIS wiring without considerat ion of the possibi li ty of a latent arc gap in the system components 

### in the fuel tank was identified as one of the erroneous approvals and as an unsafe condition resulting in AD actions. Therefore , the claim of the petitioner that the design was previously fo und comp liant does not support their statement granting the exemption would provide an adequate level of safety. Based upon the FAA rulemaking actions, the 767 FQIS was not properly shown to be comp liant to§§ 25.901(c) and 25.1309 and should be red es ig ned to properly s how comp liance to the original certification basis of the Model 767. Comment4. 

### This exemption i s being sought for the no s ingle-plus-la tent failure (greater than extremely remote) as is stated in§ 25.981 (a)(3) and interpreted by the FAA for § 25.90l(c). An exemption is also being so ught for the non-environmental aspects of§ 25.901(c) provided by FAA interpretation , and the explicit §25.98l(a)(3) requirements of manufacturing variab ility , aging , wear, corrosio n, and likel y d amage , as these considerations are already covered by airlin e maintenance of the type design of the airplane. NA TCA Comment: 

### Section 2.(a) ofSFAR 88 require s the affected Design Approval Holders "Co nduct a safety revi ew of the airplane fue l tank sys tem to determine that the des ign meets the requirements ofSecs. 25.901 and 25.98l(a) and (b) of thi s chapter
. If th e current des ign does not meet these requirements , develop a ll design changes to the fuel tank system that are necessary to meet these requirements. " Ther efo re , all design changes required to comp ly with SFAR 88 must comply w ith Titl e 14 Code of Federa l Regu l ations sec ti on 25

. 901 at Amendment 25-46 and sect ion 25.981 at Amendment 25-1 02 (the amendment levels in effect on the effective date of SF AR 88).

1 0The petition for exe mption did not in clu de a request for an exemption from this requirem e nt of S FAR 88 , so this r eq uire me nt of SFAR still requires th e d es ig n change comply with the above section s eve n if th e FAA were to grant th e re quested petition for exemption. 

### CommentS

. The petition states that the reque st is re lated to the FAA Supplemental Notice of Proposed Rul e making (SN PRM ) 2011-NM-094-AD, 

### as the FAA ha s told th e petitioner it w ill be appli ed to th e 767. NATCA s ubmitted comments to the SNPRM that are identified as F AA Docket No. F AA-2012 -0187-0027. NATCA R eco mmendation No.1 to the SNPRM equally applies to the p e tition for exemption and we have rep e ate d that here as NATCA Comment 5 to the petition for exemption. 

### NATCA Comment: NATCA recommends this mean s of co mpliance for paragraph (b) of the proposed AD (SNPRM ) clearly state in the final rul e that the FQ IS design changes mu st include all fuel tank s and m odi fi ca tions must comply wi th the fail safe requirement s of 14 CFR 25.901 , Amendment 25

- 46, and 14 CFR 25.981 (a) and ( b), Amendment 25

- 102

. Compliance w ith those regu lations is clearly requir ed by SF AR 88 for all de s ign c han ges required b y SFAR 88

. 

### Require Design Changes for All Fuel Tanks: Paragraph (h ) of the proposed AD, "Op tional Actions for Cargo Airp lan es," provides th e followin g options as alternatives from th e requirements of parag raph (g) for airplan es used e x clu sive ly for cargo operation s: ( 1) Withi n 6 month s after th e effect ive date ofthis AD , record th e existing fault codes s tored in the FQIS p rocessor and th en do a BITE check (check ofbu ilt-in test equ ipment ) of the FQIS , in acco rdance with the Accomp li s hment Instructions of Bo eing Se rvice Bulle tin 757- 2 8-0136 , dated Jun e 5 , 2014. If any fault codes are r eco rded prior to the BITE c hec k or as a result of the BITE check, before furth e r flight , do all app li cable repairs an d repeat the BITE c heck until a s ucc essf ul test i s perfo rm ed with no faults found , in accordance with Boeing Service Bulletin 757-28-01 36 , dated June 5, 20 1 4. Rep eat these actions th ereafter at intervals not to excee d 750 fl ig ht hours, and (2) Within 72 months a fter the effect ive date of thi s A D , modify the a irplane by sep aratin g FQ IS wir in g that run s between the FQIS processor and the center fuel tank , in cl uding any circuits that might pass through a main fue l tank , from other a irpl ane w iring that i s no t intrin sica ll y safe. Nei th er of th ese a lternate actions would brin g the FQI S for th e ce nter tank or the main fu e l tank s into compliance with the fail safe requi r ements of 14 CFR 25.9 01 , Amendment 25

- 45, and 14 CF R 25.98 l(a) and (b) , Ame ndmen t 25 -1 02 , as requi re d by SFAR 88 and the SF AR 88 Po licy publi she d by th e FAA as Mandatory Corrective Action criteria in FAA Policy Statement No. 2003-112-15. The SN PRM references analyses perfonned by the FAA using the FAA Transport Airp lan e R isk Assess ment Methodology (T ARAM) Handb ook, an attachment to FAA

IIPolicy Statement No. PSANM-25-05 , Risk Assessment Methodology for Transport Category Airplanes. However, the T ARAM Handbook requires following specific policy for higher leve l regulations if they exist, and li sts SFAR 88 as an examp le of regulations with specific hi gher level policy. Therefore , TARAM requires that the FAA follow the higher level SFAR 88 policy published by the FAA as Policy Statement No. 2003-112- 15

. As stated in the Polic y Statement: The purpose of this memorandum is to provide standardized po li cy for determining the need for mandatory action relative to the findings f r om the fue l system safety review required by Special Federal Aviation Regulation Number 88 (SFAR 88). The combination of fail ures identified in the proposed 757 AD clearly meets the criteria for an unsafe condition requiring corrective action mandated by AD in Element 2.a of the SF AR 88 memorandum. Element 2.a defines " known combinations " of fai lure s as fai lure s that " must be addressed by corrective action" for low-flammability exposure fuel tanks: Element 2. Combination of failure s 

### a) Fuel tanks with low flammability expos ure time For fuel tanks with low flammability expos ure time , known combinations of fa ilures are considered an unsafe cond ition and must be addressed by corrective action (i.e. A D )

. Known combinations of failure s includes combinations of fai lure s which have occurred in-serv ice and are likely to occur on other products of s imilar type desi g n (i.e. products w i th a si milar design of t h e fuel system) , and combination s of fai lures which have been s ubject to mandatory corrective actions, following in-service fmdings, on products with similar fuel system designs. N ATCA is concerned that our comment to the 20 12 NPRM was not correctly understood because the FAA response provid ed in the SNPRM did not address our concern. Our comment to the 2012 NPRM was that the FAA was not following Element 2.a of FAA SFAR 88 Policy Statement No. 2003-112-15. Instead of responding to Element 2.a , the FAA response in the SNPRM focused on Eleme nt 2.b of the SFAR 88 policy. The proposed action in the SNPRM is st ill not following the policy in Element 2.a ofF AA SF AR 88 Policy Statement No. 2003-112- 15. The failure mode that is the subject of the 2012 NPRM and this 2014 SNPRM is a known combination of fai lure s that was first subject to mandatory corrective action by the FAA over fifteen years ago when, on September 30, 1998 , the FAA published an AD to correct this same unsafe design feature for all fuel tanks o n certain "class ic" model Boeing 747 airplanes. 2 The unsafe cond it ion was described in the preamb l e to the 1997 NPRM for the 747 AD: In support of the subsequent accident investigation, the FAA participated in testing of the fuel quantity indicati o n system (FQIS). Re s ults of that testing

2 AD 98-20-40 , Federal Register Vol. 63 , No. 189 , page 52147 , September 30 , 1998. Boeing Model 747-100 , - 200,

- 300, SP , and SR series airplanes

12revealed that excessive energy could be induced by high transient voltage levels i n the electrical wiring and probes of the fuel system. These excessive levels occurred when the wiring of the FQIS was subjected to electrical transient testing. These electrical transients may be caused in the airplane when switc hing electrical lo ads in the wiring adjacent to the FQIS wiring. The FQIS was tested to determine its performance in accordance with airplane e lectromagnetic interference (EMI) requirements. 

### In this test , conductive debris, such as steel woo l and lockwire , was used to bridge the FQIS probes to sim ulate debris that has been found during in spectio n s of transport category airplanes. Results of this test indicated that tran sient vo ltage l evels induced in the FQI S wiring and probes could be in excess of 800 vo lts, and the resulting energy levels in the FQ IS wiring and probes cou ld be g rea ter than the energy req uired to ignite fuel vapor inside a fuel tank. In addition, recent inspections of the fuel probe wiring in Model 747 fuel tanks revealed damaged wiring insulation, which exposed the conductors inside the fuel tank. This condition, together with the introduction of induced transients or short circuit conditions, increases the likelihood for potential ignition sources in the fuel tank. The conditions described above , if not corrected, could result in excessive levels of energy in the FQIS wiring and a consequent potential source of ig nition in the fuel tank. The FAA SNPRM disposition ofNATCA comments says: The FQIS latent-plus-one vulnerability for Model 757 airplanes was classified as a theoretical vu lnerab ility and not as a condition known to have occurred, the SF AR 88 corrective action policy does not require corrective action for th at condition in low-flammability fuel tanks. The installation of an FRM [Flammability Reduction Means, such as a nitro gen inerting system] causes the center fuel tank to meet the criteria for classification as a low-flammability fuel tank, and therefore FRM installation was considered to be acceptab le mitigating action. However, under " Unsafe Condition ," in the AD proposed by the SNPRM, the FAA states: T his AD was prompted by fue l s ystem reviews conducted by the manufacturer. We are issuing this AD to p revent deve lopment of an ignition source inside the center fue l tank caused by a latent in-tank failure combined with electrical energy transmitted into the center fuel tank via the fue l quantity indicating system (FQIS) wiring due to a single out-tank failure. The Unsafe Condition in the AD proposed by the SNPRM describes the same failure mode that is described in the 1997 NPRM for the 1998 Model 747 AD that required design changes to e li minate the failure mode in all fuel tanks ; low flammability exposure time and high flammability exposure time. Therefore , the unsafe condition described in the SNPRM is a " Known Combination of Failur es " as defined in Criteria 2.a as:

13

### ... combinations of failures which have been subject to mandatory corrective actions, following in-s ervice findings, on products with a similar fuel system designs. 

### Comment6: The petition makes statements that indicate that the FAA may have had ex parte 

### communications with the petitioner. For example, in the Background the petition states: The FAA is planning to issue a NPRM for the 767 similar to the 757 NPRM 2011-NM-094-AD which proposes to require modifying the FQIS wiring or fuel tank systems to prevent development of an ignition source inside the center fuel tank. Paragraph (h)(2) states: Within 72 months after the effective date of this AD, modify the airplane by separating FQIS wiring that runs between the FQIS processor and the center fuel tank, including any circuits that might pass through a main fuel tank , from other airplane wiring that is not intrinsically safe. Since the FAA has not published the final rule AD for that SNPRM, such communications from the FAA of its decision would be exparte 

### communications. The petition also states: Without exemption relief for the FQIS & 

### FLSS CWT wiring changes, the intent ofthe NPRM and the FAA ' s previous communication of intent for airplane design improvement for the CWT FQIS to address those 767 freighters that do not have Nitrogen Generating System (NOS) cannot be met. 

### NATCA Comment: NATCA recommends the FAA document all ex parte 

### communications with the petitioner in the public docket for this petition for exemption as required by Appendix I to 14 CFR Part 11 , titled , " Oral Communications With the Public During Rulemaking." The preamble to Amendment 11-46, 

### Eff. 9/20/2000, which adopted the appendix, clearly states such communication is ex parte, 

### and if ex parte 

### communications do occur, they must be documented and published in the public docket. 

### The FAA's analysis We agree with the petitioner ' s justification that granting the petition is in the public interest, with two exceptions. For clarity , we do not agree with the petitioner's public-interest statements that " The time needed to successfu lly design and implement system changes beyond the proposed CWT FQIS wiring separation design changes, to comply with th e rules , would further impact the availability of the wiring change on this out-of-production fleet of767 aircraft." The AD worksheet for correcting this unsafe condition was issued in 2004. Boeing has not provided service instructions since that time. The time needed to develop a compliant design is minimal when compared to the petitioner's delay in providing the service instructions. We did not consider this argument in our determination that granting the exemption is in the public interest.

14We also do not agree w ith the petitioner ' s public interest s t atement that "

... the granting of this exemption would negate the need for [the] FAA to evaluate the additional data required to su pport compliance with th ese regulations. Therefore, granting this exemption would reduce the burden on FAA resources and consequently public expenditure." FAA resources needed to review design changes that are needed for full compliance would be minimal , and these resources are available to address unsafe conditions. There would be no savings in public expenditure and no public interest by not pro v iding a compliant design , and we did not consider this argument in our determinat ion that granting th e exemption is in the public interest. Modification of existing in-service 767 airplanes to provide a comp li ant design would be costprohibitive because extens ive changes, including modifying the fuel -qu antity processor , separating airplane wiring from other high-power wiring, or providing electrical isolating devices to prevent electrical e nergy from entering the fuel tanks , would be r equire d for this limited number of 767 freighter airp lanes. This exemption will allow approval of serv ic e instructions needed to address an un safe condition on the 767 center wing tank FQIS wiring for freighter airplanes that do not incorporate flammability-reduction systems. We received comments on the propos e d exemption from NA TCA. Regarding NA TCA comments 1 and 4: Section 2.(a) of SF

### AR 88 requires that the affected Design Approval Holders "Conduct a safety review of the airpl ane fuel tank system to determine that the design meets the requirements of Sees. 25.90 1 and 25.981 (a) and (b) of this chapter. If the current design does not mee t these requirements , develop all design changes to the fue l tank system that are necessary to meet these requirements." Therefore, all design changes required to comply with SF

### AR 88 must comply with Title 14, Code ofFederal Regulations 25.901 at Amendment 25-46, and 25.981 at Amendment 25-102 (the amendment levels 

### in effect on the effective date of SFAR 88). The petition for exemption did not include a request for an exemption from this requirement of SFAR 88, so this requirement ofSFAR still requires the design change comp ly with the above sections even if the FAA were to grant the re quested petition for exemption. We agree with the NATCA comment that SFAR 88 requires the typ e -design-approval hold er to develop all design changes to the fuel-tank system that are necessary to meet the requirements of §§ 25.901 and 25.981. The petitioner did not specifica lly request exemption from this requirement. However they did request an exemption from§§ 25.901 and 25.98 1. Granting the exemptio n to these sections results 

### in granting an exem pti on to the same ignition-source prevention requirements of SF AR 88. Therefore, we have added clarification in the exemption that states that exemption from SF A R 88 fo r the service instruction is also included in this exemption. Regarding NATCA comments 2, 3, and 5: NA TCA comment 3 pointed out that the petitioner had stated that the 767 FQIS design had previously been shown to be compliant with§§ 25.90 1 , 25.981, and 25.1309 as justification for the safety of the design. N ATCA stated:

... the FQIS [desig n] must not have been properly shown to be compliant to§§ 25.90 1(c) and 25.1309 , and s hould be redesigned to properly show comp li ance to the original certification basis of the Model 757.

1 5NATCA further stated, in comments 2 and 5, that granting the exemption would not be in the public interest, and that t he action proposed in the SNPRM and in this petition for exemption would not e liminate the known unsafe condition resulting from ignition sources caused by shorts within wir in g and fuel-gauging equipment on the subject airplane models. NA TCA s tated th at the National Transportation Safety Board identifi ed this igni tion source as the most likel y cause of the catastrophic los s of all lives on the TWA Flight 800 airplane. NA TCA believes that thi s known fuel-tank ignition source is required to be eliminated in all fuel tanks of airp l ane model s affected by SFAR 88, and the FAA's own SFAR 88 Policy , published as Mandatory Correctiv e Action criteria in FAA Policy Statement No. 2003-112-15. NATCA does not believe that granting the exemption to allow only partial wi re separation for one of the three fuel tanks (the center w in g fuel tank) is an overa ll safety improvement, relative to a compliant design, that woul d be required to have wire separation for all fuel tank s together, with separatio n of circuits in the FQIS processor. The FAA disagrees with the request to deny the exemption request and require modification of the FQ IS in a ll fuel tank s. We agree that the Model 767 airplane F QIS has the same high-level syste m a rchi tecture and operating principles as those of the Model 747 airplane FQIS, resulting in vul nerability to the same theoretical latent-plu s
- one failure scena rio. Th ere are, however, significant differences in the details of the Mode l 767 airp l ane FQIS design that reduce the likelihood of the individual contributing failures. Those differences include the following:

• Improved FQIS probe-terminal connector-block design.

• The use of wiring that i s not silver plated and th e refore does not create s ilver sulfide deposits on the terminal blocks.

• The use of improved wire types and wiring installation practices outside of the fuel tanks.
• The use of a system processor that sig nificantly iso late s the tank-prob e circuits from the FQIS indication and power circuits. We therefore did not consider that the FQIS designs for Model 747 and Model 767 airplanes were so si milar that the Model 767 airplane FQIS design s hould be considered to have a "know n " latent-plus-one- fa ilure condition vulnerability as defined in the po li cy memorandum. Service hi sto ry of conventional, unheated , a luminum wing tanks that contain Jet A fuel indicates little safety benefit i s gained by further limiting the flammability of the these tanks. Our review of nine wing-tank ignition events shows that 5 of the 9 airplanes were using JP-4 fuel, which is no longer used except on an emergency basis in the U.S. Externa l heating of the wing due to engine fires caused three of the remaining fou r eve nts , and the fourth event occ urred on the ground during maintenance. To date, ignitions in conventional, unheated, aluminum wing tanks fueled with Jet A fuel have not resulted in fata lities. The flammability characteristics of JP-4 fue l result in the fuel tanks be ing flammable a significant portion of the time when an airplane is in flight. T hi s is not the case for wing tanks containing Jet A fuel? We do not consider it to be an unsafe cond i tion for the FQIS wir ing entering these tanks to be co -rout ed in w ir e bundles with wires carrying high electrical energies.

3 See " Reduction of fuel Tank Flammability in Transport Category Airplanes ; Final R ule ", Federal Register, Volume 73 , No 140 , Monday July 21 , 2008 , page 42456.

16In su mmary , the F AA does not agree with th e NA TCA comment that changes to the fuelquantity system proposed by Boeing will not addre ss the unsafe condition , and that granting th e exemptio n is not in the pub li c interest. The FAA has d etermined that th e proposed modification s r ep resent a reasonab le, cost-effective method to ach i eve a meanin gfu l reduction in the ri sk due to potential FQIS f u e l- tank-i gnition sources. Th e FAA's curre nt fuel-tank

- safety airworthine ss s tandards rely upon a balanced approac h of limitin g fuel-tank-flammabilit y ex posure t ime and p recluding ignition sou rce s that could form in the fu e l tanks. For t h is reason ,§ 25.981 include s separa t e and distinct requ ireme nts for limitin g fuel -tank flammability and preventing ignition so urces in the fue l tank s. The w i ng and center wing tank s afety are addressed by c onsidering flamma bility and ignition-source miti gatio n s
. The wing tanks are exposed to outside air , are unheated, naturally cool , and are consid e red low flammability. We do not cons ide r it to be an unsafe condition for the FQIS wiri n g enterin g these tanks to be co-r outed in w ire bundles with w ires carrying hi gh e lectrical energies. Becau se the ce nter wing tank is heated and is considere d a hi g h -flamm ab ilit y tank , additional igni ti on
- so urc e mitigations are provided. T he modificati o n s to separate a portion of the wiri ng fo r the center wing tank FQIS s i gn ificant ly reduces the li kel ih ood of a failure th at could introduc e hi g h power o n to the FQ IS wi ring. In addition, mandatory mai ntenan ce c hecks for the center tan k FQIS wiring w ill be req ui red as p art of the pet itione r 's design approval. T his w ill signifi cant l y red uce the lik e liho o d of a la t e nt fai l ure in the FQI S wir in g resulti ng in an ignition source in th e fu e l tanks. Granting this exe mption allows FAA approval of serv ic e instructions needed to ad dress the unsafe condition and , therefore , res ults in a safety improvement that i s in the public interest. NATC A comment 6 requested th at record s of ex parle communications between the FAA a nd the petitioner, regardin g Model 767 airplane airworthiness directive (AD) act iv i ty or the exemption time- limit e xte n s ion , be included in the docket fi le
. The ite m s NATCA no ted regarding the peti tioner 's request concern a planned A D

. Any contact that occurs durin g AD rulemaking i s documented in the d ocke t a s an ex par te contact. Note that the FAA communic ates w ith the des ign-approval ho lder , in advance of A D rulemaking, in part to receive necessary serv ice informati on. This t ype of contact is not ex parle in that it occurs prior to the AD rul e making.

17

### T h e F AA's dec i s ion In co ns ideration of the forego in g, I fi nd that a grant of exempti o n is in the public interest. Therefore, purs uant to t he authority contained in 49 U.S.C. 40113 and 44701 de legated to me by th e Adm in i strator, The Boeing Company , is hereby granted an exemptio n from SFAR 88 , and 

### §§ 25 .90l (c) and 25.981(a)(3) , as the y pertain t o fuel-t ank-ignition prevention ass ociated w ith the fuel-quantity i ndication system and fue l- overfi ll -shutoff surge tank w iring installation , limited to in

- service 767-200 (freighter only), 767

- 300 (freighter only), and 767-300F airplanes

.

I ssue d in Re nton Washington , on 

## JAN 2 5 2016



# ~~
Mi chae l Ka szyck i Acting Manager, Transport Airp lane Directorate Aircraft Certification Service

18