Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126 pertaining to planned changes for the 767-300 and 

767-300F Fuel Quantity Indication System (FQIS) 

Reference: Limited Time Partial Exemption number 10767 

Name and Address of the Petitioner 

Douglas Lane, Director, Regulatory Administration 

The Boeing Company 

PO Box 3707 

Seattle, Washington, 98124 

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

14 CFR 25.901(c) at Amendment 25-126 requires: 

(c) For each power plant and auxiliary power unit installation, it must be established that 

no single failure or malfunction or probable combination of failures will jeopardize the 

safe operation of the airplane except that the failure of structural elements need not be 

considered if the probability of such failure is extremely remote. 

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 or fuel tank system 

where catastrophic failure could occur due to ignition of fuel or vapors. This must be 

shown by: 

(3) Demonstrating that an ignition source 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, 

aging, wear, corrosion, and likely damage must be considered. 

The Extent of Relief Sought and Reason(s): 

Regulation Compliance requires: Relief is Necessary because: 

14 CFR 25.901(c) 

Amendment 25-

126 

No single failure or 

malfunction or probable 

combination of failures 

will jeopardize safe 

operation

Direct compliance would require 

excessive design changes to incorporate 

FQPU modifications and Remote 

Electronic Units that result in investment 

not commensurate with level of safety 

improvement. 

Changes include the following: 

Enclosure to RA-14-05050 

Page 1 of 7
Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

- Redesign of the Airplane Wiring 

System to ensure FQIS wire 

separation for numerous airplane 

configurations. 

- Modification of the Fuel Quantity 

Processor Unit (FQPU) and 

associated connectors. 

- FQIS architecture change and to 

locate Remote Electronic Units 

(REU) on the E5 shelf. 

- 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 (to 

account for capacitance changes if 

shorter in-tank probes are 

required). 

14 CFR 

25.981(a)(3) 

Amendment 25-

125

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, aging, wear, 

corrosion, and likely 

damage must be 

considered.

Same as above 

Enclosure to RA-14-05050 

Page 2 of 7
Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

Description of Issue: 

Background: 

The 767 Fuel Quantity Processer Unit (FQPU) uses digital ARINC 429 busses to 

receive/transmit data to the flight deck, EICAS and refueling panels through two 

redundant Input/Output Channel (IOC) circuit cards. The current production IOC card 

utilizes many integrated electronic microchips to transmit and receive the ARINC 429 

data. One of the microchip components, which is involved with communication to the 

flight deck and refueling panel, has been out of production for several years, and the 

supply has now become exhausted. 

In February 2012 the FQPU supplier informed Boeing that the supply of this particular 

ARINC 429 chip used on the two IOC cards and also on the BITE card would run out in 

late 2012 and that there were no sources for procurement of the current chip. The supplier 

initiated a contract with another chip manufacturer to develop a replacement chip to the 

unchanged requirements of the original chip as defined by the supplier’s Specification 

Control Document. The new chip, by requirement, is an identical form-fit-function 

replacement to the current production chip. In August, 2012, Boeing and the supplier 

reviewed the existing stores of parts and determined the existing supply would support 

production through January 2013 with a possible extension into March 2013. 

In the previous exemption application for this subject, The Boeing Company 

communicated that if showing full compliance to 25.901(c) Amendment Level 25-126 

and 25.981(a)(3) Amendment Level 25-125 for the FQIS at the system level was required 

due to replacing this obsolescent chip with an identical form-fit-function chip, then a 

significant number of changes would be required to the FQIS intrinsically safe side 

wiring. The previous exemption was granted as a time-limited exemption (reference 

exemption number 10767), expiring in 2016, after which full compliance of the FQIS 

would be required. Since the issuance of the time limited exemption, The Boeing 

Company has been working on a FQIS that would meet the requirements and has 

quantified the design change required and the cost of the new design. Based on these 

findings The Boeing Company is petitioning for a new time limited exemption to address 

the remaining production of the 767-300 and -300F. 

Discussion: 

This new petition for a time limited exemption is being made since full compliance to 

these rules for the 767 would require extensive system design changes which do not 

substantially improve the safety of the current airplane design, are economically 

prohibitive given the remaining production of the 767-300 and -300F and are not in the 

public’s interest. In conjunction with this petition The Boeing Company is proposing to 

incorporate significant improvements to newly produced 767 airplanes that will increase 

the level of safety by addressing both ignition sources and exposure time. 

Enclosure to RA-14-05050 

Page 3 of 7
Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

Boeing proposes that all new production airplanes incorporate design changes similar to 

the center fuel tank wire separation being developed by SB 767-28-XXXX which will be 

required by AD for all 767 freighters that do not have NGS. These wire separation 

changes would be implemented on all new production airplanes one year after the 

exemption is granted. Boeing will further address ignition sources by requiring a three 

tank, 750 hour BITE check, similar to instructions for the center wing tank provided in a 

SB 767-28-0118 for freighters without NGS, and being required by AD. The proposed 

BITE instructions would apply to all tanks. 

All newly produced 767 airplanes, since line number 993 in July 2010, address 

flammability exposure time with the incorporation of a center tank fuel tank flammability 

reduction system, the Nitrogen Generation System (NGS). This addresses exposure time 

as required for all 767 in-service passenger airplanes and adds flammability reduction 

systems for all freighter airplanes since line number 993. 

In the previously granted time limited exemption, the FAA stated that current fuel tank 

safety airworthiness standards rely upon a balanced approach of precluding ignition 

sources that could form in the fuel tanks and limiting fuel tank flammability exposure 

time. The aforementioned fuel tank wire separation, BITE check and flammability 

reduction system will address both exposure time and ignition sources for all newly 

produced 767 airplanes, both passenger and freighter. 

This time limited exemption is being sought for the no single plus latent (greater than 

extremely remote) as is stated in §25.981(a)(3) and interpreted by the FAA for 

§25.901(c). Exemption is also being sought for 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 factory manufacturing processes, and airline 

maintenance of the type design of airplane. Exemption is requested to apply through the 

end of 2019 to provide coverage through the end of the currently committed 767-300 and 

-300F production activity and potential incremental sales. The 767-2C, which will be 

produced beyond 2019, will be fully compliant to these requirements. 

Statement of Public Interest: 

In support of this petition, Boeing is proposing to address both ignition sources and 

exposure time in the center tank (NGS on all newly produced airplanes). In-service 

airplanes are currently required to address either exposure time (passenger airplanes) or 

ignition sources (freighter airplanes) but not both. This approach addresses both aspects, 

incorporating improvements to address both ignition sources and exposure time. 

All new production airplanes will incorporate design changes similar to the center fuel 

tank wire separation being developed by SB 767-28-XXXX which will be required by 

AD for all 767 freighters that do not have NGS. These wire separation changes will be 

Enclosure to RA-14-05050 

Page 4 of 7
Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

implemented on all new production airplanes one year after the exemption is granted and 

will be made with the guidance of 28-AWL-09. In addition, Boeing is proposing a three 

tank, 750 hour BITE check, similar to instructions for the center tank provided in SB 

767-28-0118 for freighters without NGS, and being required by AD. These changes will 

address ignition sources on all newly produced 767 airplanes. 

All newly produced 767 airplanes, since line number 993 in July 2010, address 

flammability exposure time with the incorporation of a center tank fuel tank flammability 

reduction system, the Nitrogen Generation System (NGS). This addresses exposure time 

as required for all 767 in-service passenger airplanes and adds flammability reduction 

systems for all freighter airplanes since line number 993. 

By addressing both exposure time and ignition sources, newly produced 767 airplanes 

will use a balanced approach and achieve a higher level of safety than any in-service 767 

airplane. Design changes that would be required to be fully compliant would not provide 

a significant benefit or increased level of safety for new production airplanes that 

incorporate the proposed wire separation, BITE check, and have the Nitrogen Generation 

System (NGS) installed. Additionally, the costs associated with these changes would not 

be commensurate with the increased level of safety and would be economically 

prohibitive given the relatively small number of additional production aircraft that would 

be burdened with these costs. These changes would include the following: 

 New system architecture and extensive airplane wiring changes to ensure 

adequate wire separation throughout the fuel quantity indication system. 

 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. 

Release of new Boeing design architecture requirements, supplier development and 

qualification of new software and hardware to be fully compliant would negatively affect 

offerability of the 767-300 and 300F airplanes. These design changes would also affect 

only one customer and result in an undesirable configuration mix for that customer, 

driving maintenance complexity and increased operational costs. 

Finally, the associated design proposal in support of this petition for exemption will 

implement center tank FQIS limited wire separation and a three tank FQIS BITE check 

earlier than other alternatives, approximately one year after grant of the petition. This 

will provide important enhancements to airplane safety earlier, and on more production 

airplanes. Please note, relief is not being sought for the 767-2C, which will be fully 

compliant with a new FQIS, and is anticipated to be the only minor model produced for 

the next several decades. 

Enclosure to RA-14-05050 

Page 5 of 7
Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

Granting this time limited exemption is in the public interest for the aforementioned 

reasons and will: 

1. Promote continued production of the 767 airplane after May 17, 2016, currently 

forecasted to end in 2019. All production airplanes will address fuel tank safety 

with incorporation of wire separation, scheduled health checks, and a fuel tank 

inerting system (NGS). A grant of exemption will also provide significant 

economic benefit to the public in the form of continued 767 production and 

support efficient, safe operation by our customers by providing a consistent fleet 

configuration. 

2. The proposal for this exemption request of implementing the center tank FQIS 

limited wire separation and three tank FQIS BITE check can be accomplished on 

an earlier schedule, (proposed to be one year after the exemption is granted) 

enhancing safety earlier on more airplanes. 

Statement of No Adverse Effect on Safety: 

The replacement of the existing ARINC 429 chip with the new replacement chip does not 

adversely affect the safety of the current system. There is no threat to fuel tank ignition 

from the IOCs within the FQPU because there is no electrical conductor connection 

between the boards with the obsolete chip and the fuel tank. Hence, the change has no 

relation to fuel tank ignition prevention, does not impact line replaceable unit (LRU) or 

system level failure modes, effects, or probabilities relative to fuel tank ignition and 

therefore has no affect on the safety of the system and has no impact to airplane safety. 

The 767 FQIS was found to be compliant to §25.901(c) during airplane type certification 

for the FQIS change in 1992 and since then Boeing has completed the SFAR88 safety 

assessment and has increased the airplane fuel system safety with installation of a hot 

short protector for the densitometer and with installation of a NGS for the center fuel 

tanks. The proposed change to address the previous time limited exemption has no impact 

on any of the SFAR88 related assessments. 

Even prior to the implementation of NGS which further reduces any risk, the Boeing 

assessment was that the risks for the 767 FQIS installation were extremely improbable, 

which is the typical industry and CFR §25.1309 standard for an acceptable safety for 

systems. 

The Boeing approach to incorporate design changes to add center fuel tank fuel wire 

separation, a three tank 750 hour BITE check, and installation of NGS on all newly 

produced 767 airplanes will provide for an improved safety margin over the existing, 

approved in-service fleet. These changes are also proposed to be done one year after 

grant of exemption, thereby incorporating changes to more airplanes than possible under 

the existing time limited exemption. 

Enclosure to RA-14-05050 

Page 6 of 7
Petition for Exemption from 14 CFR 25.981(a)(3) Amendment 25-125 and 14 CFR 

25.901(c) Amendment 25-126, Code of Federal Regulations

Request to Waive Publication and Comment: 

Given the time-sensitive nature of this request for exemption, Boeing respectfully 

requests that the FAA waive the “publication and comment” step in the process for 

making a final decision on this exemption. In addition to the timeliness concern, it is the 

Boeing position that the safety-associated aspects related to this system have been fully 

vetted in the public forum as part of the SFAR88 project and the previous time-limited 

partial exemption (reference exemption number 10767). Expedited treatment is necessary 

to prevent interruption to 767 production deliveries. 

Privileges of the Exemption Outside the United States: 

Per 14 CFR 11.81(h), Boeing requests that the privileges of this exemption be extended 

outside the United States. This extension of privileges is necessary for operations based 

within foreign countries having bilateral agreements with the United States accepting 

FAA 14 CFR part 25 as their airworthiness standards for transport category aircraft. 

Conclusion: 

Boeing is petitioning for a time-limited exemption from the provisions of 14 CFR 

25.901(c)[25-126] and 14 CFR 25.981(a)(3)[25-125] at the system level as they apply to 

the FQIS installed on the 767-300 and 767-300F airplanes for the FQPU parts 

obsolescence change described above. The proposed center fuel tank wire separation, 

FQIS three tank, 750 hour BITE check, and incorporation of NGS for all 767 production 

airplanes will further improve fuel tank safety and reduce fleet safety risks. Exemption is 

requested to apply through the end of 2019 to provide coverage through the end of the 

currently committed 767-300 and -300F production activity. The 767-2C, which will be 

produced beyond 2019, will be fully compliant to these requirements. 

Summary to be published in the Federal Register: 

PETITIONER: Boeing Commercial Airplanes 

SECTION OF 14 CFR AFFECTED: 14 CFR 25.981(a)(3) Amendment 25-125 

and 14 CFR 25.901(c) Amendment 25-126 

DESCRIPTION OF RELIEF SOUGHT:

The Boeing Company is petitioning for a time limited exemption from the provisions of 

14 CFR 25.901(c)[25-126] and 14 CFR 25.981(a)(3)[25-125] at the system level as they 

apply to the FQIS installed on the 767-300 and 767-300F airplanes through the end of 

2019, thereby providing relief through the end of the currently anticipated 767-300 and 

767-300F production. 

Enclosure to RA-14-05050 

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