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June 29, 2015 CP-L4L-15-00278 -; -. ::·. Long Beach, CA 90807-5309



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U.S. Department ofTransportation Docket Operations M-30 1200 NewJerseyAvenue, SE Room W12-140, West Bldg. Ground Floor Washington DC 20590-0001
Attention: Applicant:

Subject:

References: FAA Transport Airplane Directorate
The Boeing Company Boeing Commercial Airplanes Southern California Engineering Design Center 2401 E. Wardlow Road, Mail Code D800-0022 Long Beach, CA 90807-5309
Contact: Mr. Thomas A. Enyart Email: Thomas.a.Enyart@boeing.com Phone: (562) 797-8956 Seal Beach, CA 90740-1515
Petition for Exemption from 14 CFR 25.901(c) Amendment 25-126 and 14 CFR 25.981 (a)(3) Amendment 25-125 pertaining to planned changes for the 747-400 (Freighters Only), 747-400 BCF CenterWing Tank (CWT) Fuel Quantity Indication System (FQIS) Fuselage Wiring Installation.
a) NPRM 2011-NM-094-AD, The Boeing Company Model 757 airplanes Center Fuel Tank- NPRM proposed to require modifying the fuel quantity indication system (FQIS) wiring b) NTSB report TWA 800 AAR-00-03 c) Service Bulletin 747-28-2340, FUEL- Fuel Quantity Indicating System (FQIS) • FQIS Ground Test and Corrective Action, dated June 06, 2014

Certification Item No: 48206

The Boeing Company respectfully submits the enclosed Petition for Exemption from the Title 14 Code of Federal Regulations §14 CFR 25.901(c) Amendment 25-126 and 14 CFR 25.981(a)(3) Amendment25-125 pertaining to planned changes forthe 747-400 (Freighters Only), 747-400 BCF CenterWing Tank (CWT) Fuel Quantity Indication System (FQIS).

The Extentof ReliefSoughtand Reason(s): 14 CFR 25.901(c) atAmendment 25-126 requires: (c) Foreach power plant and auxiliary power unit installation, it must be established that no single failure or malfunction or probable combination ofPage 2 of6 CP-L4L-15-00278

failures willjeopardize the safe operation ofthe airplane exceptthatthe failure of structural elements need not be considered ifthe probability ofsuch failure is extremely remote.

14 CFR 25.901(c) Amendment 25-126 Boeing relief is necessary because: Direct compliance would require excessive design changes and retrofit ofin-service airplanes. Changes include the following: Further redesign ofthe Airplane Wiring System to ensure FQIS wire separation for numerous airplane configurations. Make new tank penetrations and procure new in-tankwiring harnesses. Modify the Fuel Quantity Processor Unit (FQPU) and associated connectors. The solution would require a FQIS architecture change to relocate the FQPU and consider Remote Data Connectors (RDCs). In-tank component changes (new brackets, potential need for shorter probes, revised in-tankwire harness and retention means). Software changes related to Fuel Tank Gauging Function (to account for capacitance changes ifshorter in-tank probes are required).

14 CFR 25.981(a)(3) at Amendment 25-125 requires: (a) No ignition source may be present at each point in the fuel tank orfuel tank system where catastrophic failure could occurdueto ignition offuel orvapors. This must be shown by: (3) Demonstrating that an ignition source could not result from each single failure, from each single failure in combination with each latent failure condition not shown to be extremely remote, and from all combinations of failures not shown to be extremely improbable. The effects ofmanufacturing variability, aging, wear, corrosion, and likely damage must be considered.

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 NPRM for the 747 similarto the reference a) 757 NPRM which proposes to require modifying the FQIS wiring orfuel tank systems to prevent developmentofan ignition source inside the centerfuel tank. Paragraph (h)(2) ofthe 757 NPRM states: "Within 72 months afterthe effective date ofthis AD, modify the airplane by separating FQIS wiring that runs between the FQIS processor and the centerfuel 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 CWTwiring between the FQIS processor and the centerfuel tank, as well as performing repetitive system check using the FQIS Built in Test Equipment (BITE) check. The reference c) BITE service bulletin 747-28-2340, which includes the instructions to ensure tank circuitwiring integrity, is already approved bythe FAA. The CWT FQIS wiring separation is being prepared with guidance from the FAA's approved standard for retrofit wire separation from FQIS wiring. Butthe combination of BITE and wire separation will not result in the FQIS system being compliant to 25.901(c) [25-126] and 25.981 (a)(3) [25-125]. Since the wiring changes are a change to type design, but will not be compliant, an exemption is being petitioned. The FAA's response to a 757 NPRM commentsuggests that FAA will accept petitionsfor exemption forthe "latentplus-one" requirements ofsections 25.901 (c) and 25.981 (a)(3) ofthe Federal AviationPage 3 of6 CP-L4L-15-00278
Regulations, and there has also been FAA communication thatthis acceptance applies to the 747.

This petition for an exemption is being made since full compliance to these rules forthe 747-400 freighters would require extensive system design/installation changes, but do not substantially improve the safety ofthe current airplane design, and are economically prohibitive given thatthe retrofit 747-400 freighterfleet is small, and so extensive system changes are not in the public's interest. The FQIS system was previously shown compliantto §25.1309 and 25.901 (c) forType Certification (TC); however, both §25.901(c) [25-126] and §25.981(a)(3) [25-125] have additional failure combination requirements. Forsystems that may cause a catastrophic hazard, §25.1309 requires no single failure and no combination offailures greaterthan extremely improbable; §25.901 (c) [25-126] requires no single failure or probable combination offailures; and §25.981 (a)(3) [25-125] requires no single failure, no single plus latent (greaterthan extremely remote}, and no multiple combination greaterthan extremely improbable. This exemption is being soughtfor the no single plus latent (greaterthan extremely remote) as is stated in §25.981 (a)(3) and interpreted by the FAAfor §25.901(c). An exemption is also being soughtfor the non-environmental aspects of§25.901(c) provided by FAA interpretation, and the explicit §25.981(a)(3) requirements of manufacturing variability, aging, wear, corrosion, and likely damage, as these considerations are already covered by airline maintenance ofthe type design ofthe airplane.

Statement of Public Interest: Without exemption reliefforthe FQIS CWTwiring changes, the intent ofthe NPRM and the FAA's previous communication of intentfor airplane design improvementfor the CWT FQIS to address those 747-400 freighters thatdo not have Nitrogen Generating System (NGS) cannot be met. For compliance, airplane changes to the entire Fuel Quantity Indication System (FQIS) (all tanks) would be required forfleet retrofit such as:

• Extensive airplane wiring changes to ensure adequate wire separation throughoutthe fuel quantity indication system.

• In-tankcomponent changes (new brackets] potential need forshorter probes] revised in-tankwire harness and retention means).

• Software changes related to Fuel Tank Gauging Function and Safetyfunction ifshorter probes are required.

The current FQIS system has been thoroughly evaluated for safety aspects as was required per SFAR88for the Fuel Quantity Indicating System, howeverthe FAA determined there were safety issues identified with FQIS wiring connected into a high flammabilitytank, forthe 747-400 it isthe CWT. Thetime needed to successfully design and implement system changes beyond the proposed CWT FQIS wiring separation design changes to comply with the rules would further impactthe availability ofthe wiring change on this out-of-production fleet of747 airplanes These new complete FQIS design changes would not provide any economic benefitto the operators and do not provide any significant benefit or increased level ofsafety.Page 4 of6 CP-l4L-15-00278

The Boeing Company considers that the granting ofthis exemption would negate the need for FAAto evaluate the additional data required to support compliance with these regulations. Therefore, granting this exemption would reduce the burden on FAA resources and consequently public expenditure. Granting this exemption is in the public interestforthe aforementioned reasons and will: 1. Enhance the safety ofthe 747-400 freighter fleet (as has been determined by the FAA) for those airplanes not installing NGS by adding wiring changes forthe CWT FQIS. 2. Enhance the safety ofthe 747-400 freighterfleet, by also including FQIS BITE for the CWT circuit interval tests, so thatwhen done in addition with the CWT FQIS wiring separation, the airplane addresses the single plus latent failure modes for the FQIS which was the probable failure combination indicated bythe reference b) NTSB report.
Statement ofNo Adverse Effect on Safety. The addition ofthe FQIS CWTwiring changes along with a BITE interval check, in lieu ofa fully compliant (all tanks) FQIS (which would have a HSP* FQPU LRU, wire separation forthe tank (total of7) circuitwiring (both outside and inside the tank), and a fault detecting BITE that is annunciated), does not have an adverse effect on safety.

*A HSP is an LRU that is also designed to havethefunction to protect thetank circuitwiring from Electrical Power Sourcethreats that could affectthe airplane circuit wiring ofthe LRU (FQPU).

In the proposed CWT FQIS wire separation design change, the ignition source threat from other airplane systems is reduced since the wiring will have increased separation. There is also Instructions for Continued Airworthiness (ICA) that ensures that any other system changes will continue to maintain the separation provided bythis proposed design change which will be now clearly be visually identified as FQIS wiring. Together, this improves the wiring failure modes, and improves the system probability relative to fuel tank ignition. With the addition ofthe FQIS BITE interval checks for the CWT, the probability is better since the exposure ofwiring failures will be further reduced.

Forthe CWT FQIS, where the changes to the FQIS are being done instead ofthe installation of NGS as determined bythe FAAto be an acceptable substitute safety improvement, the combination ofthe separation, the ICA, and the BITE/circuittest addresses no single failures in combination with latentfailures with an acceptable level ofsafety by ensuring the continued integrity ofprotection features from threats to the tank circuit wiring.

• A- The fault modesofthe in tankwiring have reduced exposure to 750 hours duetothe BITE check and FLSS circuittest. Wiring inside thetank is well protected and has avery lowfailure probabilitywhich is improved bythe lowerexposure.

• Bl- The FQPU is a HSP upto llSVAC. Ifa low probability highervoltage power source short

wereto occur on the airplane side ofthe FQPU, it most likelywould, butforvery high voltage powersources may not stop itfrom propagatingthrough to the tank circuits, butthefailure would atthe least be detectablewhen the BITE interval checkwas done, and in most cases sooner, as itwould most likely affect indication.Page 5 of6 CP-L4L-15-00278

o B2 -Thewiringfrom the FQPU tothetankwill have separation provided bytheAD mandated SB. This wiring has low probabilityfailure modeswhich also have reduced exposure provided by the 750 hour interval BITE check.

Whetherthefailure is A, or Bl, or 82, there is no single failure. Forthe combination offailures, A and Bl, orAand B2, the BITE has reduced the exposure and the latency intervalfor each protection design feature (wiring has less than extremely remote failure rates) and so the probabilityforeach failure mode is betterthan remote. This also addressesthe single plus latent failure requirement with an acceptable level ofsafety as the probabilityofeitherfailure on the flight beforethe next interval check would both be betterthan remote.
The 747-400 FQIS was found to be compliant to §25.901(c) during airplane type certification in 1989. Since then Boeing has completed the SFAR88 safety assessment and has increased the airplane fuel system safety with installation ofa Hot Short Protector (HSP) LRU for the densitometer. Forthe 747-8 project, the FQPU which has the same architecture as the 747-400 FQPU, was also shown to be a HSP LRU and so the fuel level sensing probes/compensator have that same protection. Following the SFAR88 system safety assessments, Boeing assessmentwas that the risks for the 747-400 FQIS installation were extremely improbable, which is the typical industry and CFR §25.1309 standard foran acceptable safetyfor systems. The Boeing approach to incorporate design changes to add centerwing tank FQIS wire separation with visual identification, a CWT FQIS 750 hour BITE check, along with ICA that ensures that added systems wiring will maintain the separation for the life ofthe airplane, the HSP FQPU LRU, and the densitometertank circuit HSP provided by Boeing SB 747-28A2266, will provide for an enhanced safety margin overthe existing, approved FQIS on the in-service fleet. 

### RequesttoWaive Publication and Comment: Since the reference a) NPRM for the 757 is closely related to this change as the 747- 400 issue is the same, and the NPRM makes mention ofa 757 petition for exemption, and has already gone through public commenting process, Boeing respectfully requests that the FAA waive the "publication and comment" step in the process for making afinal decision on this exemption.

In addition to the timeliness concern, it is the Boeing position thatthe safety-associated aspects related to this system have been fully vetted in the publicforum as part ofthe SFAR88 project. 

### Privileges ofthe Exemption Outsidethe United States: Per 14 CFR 11.81(h), Boeing requests that the privileges ofthis exemption be extended outside the United States. This extension ofprivileges is necessaryfor operations based within foreign countries having bilateral agreements with the United States accepting FAA 14 CFR part 25 as their airworthiness standards fortransport category aircraft.


### Justification for Exemption: In accordance to the requirements of 14 CFR §11.81 (e), the Boeing company has provided a means ofcompliance to the FAAto establish an acceptable level ofsafety to that provided by the rules 14 CFR §25.901(c) and 14 CFR §25.981(a)(3) by separating the FQIS wiring from other airplane powerwires thatwill meetthe minimum separationPage 6 of6 CP-L4L-15-00278

requirements for mostofthe wire runs. Forthe areas that minimum separation are not achievable due to space limitation, other positive separation means, such as clamps, spacers and sleeving will be used forthe CWT FQIS and also including FQIS BITE interval checks forthe CWT,. These design changes address the single plus latent failure modes forthe FQIS which was the probable failure combination indicated by the NTSB report, reference b). Therefore, granting this exemption would, in turn, reduce the burden on FAA resources and consequently public expenditure.


### Conclusion: Boeing is petitioning for an exemption from the provisions of 14 CFR 25.901(c)[25-126] and 14 CFR 25.981 (a)(3)[25-125] atthe system level as they applyto the FQIS installed on the 747-400 (Freighters Only), 747-400 BCF airplanes for the FQIS wiring changes described above.
Sincerely,

Tim Hendrix Manager, Certification & Airworthiness Southern California Engineering Design Center Boeing Commercial Airplanes (562) 593-7074, MC 0800-0022 

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