Enclosure to RA-12-04444 

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

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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 767-200, 767-300, 767-300F, 767-

400ER Fuel Quantity Indication System (FQIS) 

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 powerplant 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 for production 

and retrofit of in-service airplanes using 

the redesigned FQPU for replacement or 

repair. Changes include the following: 
Enclosure to RA-12-04444 

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

2

Redesign of the Airplane Wiring System 

to ensure FQIS wire separation for 

numerous airplane configurations. 

Make new tank penetrations and procure 

new in-tank wiring 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-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 

Description of Issue: 

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 
Enclosure to RA-12-04444 

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

3

(IOC) circuit cards. The current production IOC card utilizes many integrated electronic microchips 

to transmit and receive the ARINC 429 data. One of the microchips, a programmable logic device 

(PLD), which is involved with communication to the flight deck and refueling panel, has been out of 

production for several years, and the supply is now becoming 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 will run out in late 2012 and that it is not 

possible to find alternate 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, Boeing and the supplier reviewed the existing stores of parts and were able to 

extend the supply through January 2013 with a possible extension into March 2013. 

There is concern on the part of The Boeing Company that replacing this obsolescent chip with an 

identical form-fit-function chip could result in a requirement to show full compliance to 25.901(c) 

Amendment Level 126 and 25.981(a)(3) Amendment Level 125 for the FQIS at the system level. If 

this were indeed the case, this would require a significant number of changes associated with the 

FQIS intrinsically safe side wiring. 

The reasons for this exemption petition is that full compliance to these rules for the 767 would 

require extensive system design changes which are not in the public’s interest, do not substantially 

improve the safety of the current airplane design, and cannot be accomplished in the very short time 

prior to exhaustion of the parts necessary to deliver airplanes. 

The system has been shown compliant to §25.1309; however, presently both §25.901(c) and 

§25.981(a)(3) have additional failure combination requirements. For systems that may cause a 

catastrophic hazard, §25.1309 requires no single failure and no combination of failures greater than 

extremely improbable; §25.901(c) requires no single failure or probable combination of failures; and 

§25.981(a)(3) 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 extremely remote) as is 

stated in §25.981(a)(3) and interpreted by the FAA for §25.901(c). And 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. 

 

Statement of Public Interest: 
Enclosure to RA-12-04444 

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

4

Without exemption relief the following airplane changes would be required for production and fleet 

retrofit so that the changed FQPU could be used for production airplanes and repair or replacement 

in the existing fleet. 

 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. 

The time needed to successfully design and implement the system changes to comply would 

seriously impact the continued production of the 767 and could result in cancellation of significant 

customer airplane orders. To release new Boeing design architecture requirements and to have a 

supplier develop and qualify new software and hardware to these new requirements would take 

years, and no 767 airplane deliveries could be completed during that time. Also, if these changes are 

required to airplanes that are in the delivered fleet, operators would need to remove the airplanes 

from service for lengthy and expensive modifications whenever existing FQPUs needed to be 

replaced. These new design changes would not provide any economic benefit to the operators or 

public and do not provide any significant benefit or increased level of safety over new production 

airplanes or in-service airplanes which have the Nitrogen Generation System (NGS) installed. The 

current FQIS system has been thoroughly evaluated for safety aspects as was required per SFAR88 

for the Fuel Quantity Indicating System, and no significant safety issues were identified. 

The granting of this exemption is in the public interest for the following reasons: 

1. Denial of this petition for exemption will result in an estimated 3-year delay in the delivery 

of 767 airplanes due to the redesign of the FQIS system to be fully compliant to 

§25.981(a)(3). This would result in subsequent impact to airline operations, as the 767 

would no longer be available. Further, there will be no significant change to the safety of 

production airplanes which are equipped with NGS. 

2. Denial of this petition for exemption would result in the airlines having to perform 

extraordinary work which would result in disruption of operations and would pose significant 

burden on the airlines to make the airplane changes outlined for installation of a §25.901(c) 

and §25.981(a)(3) compliant FQIS whenever an in-service FQPU fails within their fleet. 

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 IOC or the 

BITE card within the FQPU because there is no electrical conductor connection between the boards 
Enclosure to RA-12-04444 

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

5

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 impact to airplane safety. 

 

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

then Boeing has done 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 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 systems installation. 

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. 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 an 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 767-200, 

767-300, 767-300F, 767-400ER airplanes for the FQPU parts obsolescence change described above. 

Replacement of the ARINC 429 chip within the IOC cards and the BITE card of the current FQPU is 

necessary due to obsolescence of the current chip. The re-designed chip will not impact the FQIS 

safety. Incorporation of the NGS for all 767 production airplanes and retrofit of passenger models 

has further improved fuel tank safety and reduced fleet safety risks. 

Granting this exemption will allow use of this replacement chip within the IOC card and BITE card 

of the current production FQPU for repairs without extensive rework to in-service aircraft. 
Enclosure to RA-12-04444 

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

6

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 an 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 767-200, 767-300, 767-300F, 767-400ER airplanes for an FQPU parts 

obsolescence modification.