Enclosure A to RA-21-03455

Enclosure A to RA-21-03455

Petition for Exemption from §25.901(c) and §25.981(a)(3) of Title 14, Code of Federal Regulations

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Petition for Exemption from 14 Code of Federal Regulations (CFR) §25.901(c) and §25.981(a)(3) for Boeing Model 727, 727-100, 727C, 727-100C, 727-200, 727-200F Airplanes.

Name and Address of the Petitioner

David C. Busby Out Of Production and 747-8 Chief Program Engineer The Boeing Company 2201 Seal Beach Blvd., MC 110-SA46 Seal Beach, CA 90740

Section(s) of the Regulations from which Relief is Sought

Boeing is requesting relief from the design and performance requirements of 14 CFR §25.901(c) Amendment 25-126 and §25.981(a)(3) Amendment 25-146 pertaining to planned changes for the 727 body-mounted auxiliary fuel tank deactivation.

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 25-146 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) Except for ignition sources due to lightning addressed by §25.954, 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, taking into account the effects of manufacturing variability, aging, wear, corrosion, and likely damage.



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The Extent of Relief Sought and Reason(s)

Relief from 14 CFR §25.901(c) Amendment 25-126 is necessary because direct compliance would require excessive design changes and retrofit of 58-year old, in-service airplanes. The changes that would be required to comply with this regulation include the following: extensive redesign of the airplane wiring system to ensure FQIS wire separation for numerous airplane configurations; development and implementation of a hot short protector (HSP) device for the fuel quantity indicating system (FQIS) wiring; and in-tank component changes (new brackets, potential new probes, revised in-tank wire harness and retention means, revised tank structure which includes enhanced electrical bonding and grounding design features).

Relief from 14 CFR §25.981(a)(3) Amendment 25-146 is necessary based on the same statement provided for 14 CFR §25.901(c) above.

Description of Issue

The FAA has issued AD 2019-23-04, which requires either modifying the FQIS to prevent development of an ignition source inside the body-mounted auxiliary fuel tanks, or deactivating the body-mounted auxiliary fuel tanks. Paragraph (g) states: “Within 12 months after the effective date of this AD, do the actions specified in either paragraph (g)(1) or (2) of this AD, using a method approved in accordance with the procedures specified in paragraph (h) of this AD.

(1) Modify the fuel quantity indicating system (FQIS) to prevent development of an ignition source inside the body-mounted auxiliary fuel tanks due to electrical fault conditions.

(2) Deactivate the body-mounted auxiliary fuel tanks.”

Boeing is proposing to accomplish the FAA’s AD-mandated change by generating a service bulletin to deactivate the body-mounted auxiliary fuel tanks in the remaining active affected airplanes. The auxiliary fuel tanks will be physically disconnected from the main tank fuel system to prevent fuel transfer and all electrical wiring to auxiliary tank components will be disconnected. However, the auxiliary fuel tank deactivation will not result in the FQIS system being compliant to 14 CFR §25.901(c) [25-126] and §25.981(a)(3) [25-146]. Since the auxiliary tank deactivation is a change to type design, but will not be compliant, Boeing is respectfully petitioning for an exemption to these regulations.

This petition for an exemption is being made since full compliance to these rules for the 727 would require extensive system design/installation changes, but do not substantially



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improve the safety of the current airplane design, and are economically prohibitive given that the 727 fleet with body-mounted auxiliary fuel tanks is small and diminishing, and so is not in the public’s interest.

The FQIS system was previously shown compliant to 14 CFR §25.1309 and §25.901(c) for type certificate and amended type certificate 727 aircraft. However, both 14 CFR §25.901(c) [25-126] and §25.981(a)(3) [25-146] have additional failure combination requirements. For systems that may cause a catastrophic hazard, 14 CFR §25.1309 requires no single failure and no combination of failures greater than extremely improbable, while 14 CFR §25.901(c) [25-126] requires no single failure or probable combination of failures, and 14 CFR §25.981(a)(3) [25-146] 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) provision as stated in 14 CFR §25.981(a)(3) and interpreted by the FAA for 14 CFR §25.901(c). An exemption is also being sought for the non-environmental aspects of 14 CFR §25.901(c) provided by FAA interpretation, and the explicit 14 CFR §25.981(a)(3) requirements of manufacturing variability, aging, wear, corrosion, and likely damage, as these considerations are already covered by airline maintenance of the type design of the airplane.

In accordance to the requirements of 14 CFR §11.81(e), the Boeing company has provided a means of compliance to the FAA to establish an acceptable level of safety to that provided by the rules 14 CFR §25.901(c) and 14 CFR §25.981(a)(3) by deactivating the body-mounted auxiliary fuel tanks.

These design changes address the single plus latent failure modes for the auxiliary fuel tank FQIS that were the unsafe conditions indicated by the AD. Boeing is following the AD-mandated direction to deactivate the body-mounted auxiliary fuel tanks on the 727 model. Therefore, granting this exemption would, in turn, reduce the burden on FAA resources and consequently public expenditure.



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Statement of Public Interest

The AD to address those 727 airplanes with body-mounted auxiliary fuel tanks cannot be met without exemption relief for the auxiliary fuel tank deactivation option. For compliance, airplane changes to the entire FQIS (all tanks) would be required for fleet retrofit such as:

• New system architecture to design and implement a Hot Short Protector (HSP*) Line Replaceable Unit (LRU) for the FQIS.

• 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, revised tank structure which includes enhanced electrical bonding and grounding design features).

NOTE: Disturbing 58-year aged wire bundles to affect wire separation and/or add new components could introduce additional safety consequences * A HSP is an LRU that is also designed to function as protection of the tank circuit wiring from electrical power source threats that could affect the airplane FQIS circuit wiring.

The current FQIS system has been evaluated for safety aspects as was required per SFAR88 for the Fuel Quantity Indicating System. The FAA determined, however, that there were safety issues identified with FQIS wiring connected into a high flammability tank, which for the 727 is the body-mounted auxiliary fuel tanks. The time needed to successfully design and implement system changes beyond the proposed auxiliary fuel tank deactivation design change to comply with the rules would further impact the availability of the auxiliary fuel tank deactivation design change on this out-of-production fleet of 727 aircraft with body-mounted auxiliary fuel tanks.

Requiring completely new FQIS design changes in addition to complete auxiliary tank deactivation would not contribute any significant benefit or measurable increase to the level of safety to the flying public, and would impart no economic benefit to the operators. Furthermore, The Boeing Company considers that without this exemption, redesigning the FQIS would entail a significant certification effort for both the FAA and Boeing, as many of the regulations, design philosophies, component specifications and design requirements have evolved since the original 727 certification in 1963. Therefore, granting this exemption would reduce the burden on FAA resources and consequently public expenditure.



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Granting this exemption is in the public interest for the aforementioned reasons and will enhance the safety of the affected 727 fleet by deactivating the body-mounted auxiliary fuel tanks per the AD, thus mitigating the unsafe condition.

Statement of No Adverse Effect on Safety

The Boeing change proposal to deactivate the body-mounted auxiliary fuel tanks does not have an adverse effect on safety.

In the proposed auxiliary fuel tank deactivation design change, the ignition source threat from an electrical fault condition in the auxiliary fuel tanks is eliminated since there is no longer any electrical current in the wiring or components inside the auxiliary fuel tank, as all the auxiliary fuel tank wiring connections have been disconnected, capped, and stowed. Additionally, there is no potential of fuel ingress into the auxiliary fuel tanks since the fuel lines connecting the auxiliary fuel tanks to the main fuel tanks will be disconnected. The auxiliary fuel tanks will be completely drained, sumped, and purged of any fuel. The auxiliary tank structure and internal components will not be removed, but will continue to be electrically bonded and grounded to aircraft structure per existing type design methods.

The changes above address no single failures in combination with latent failures with an acceptable level of safety by effectively removing ignition sources due to the FQIS in the body-mounted auxiliary fuel tanks.

The 727 FQIS was found to be compliant to 14 CFR §25.901(c) during airplane type certification and since then Boeing has completed the SFAR88 safety assessment and has increased the airplane fuel system safety with installation of lightning shielding on the FQIS out-tank wiring and ground fault interrupters on the boost pumps.

Following the SFAR88 system safety assessments, the Boeing safety assessment determined that the risks for the 727 FQIS installation were extremely improbable, which is the typical industry and CFR 14 CFR §25.1309 standard for an acceptable safety for systems.

Request to Waive Publication and Comment

Given that the FAA has granted similar exemptions for the 757, 747-400, and 767, and those exemptions have already gone through the public commenting process, Boeing respectfully requests that the FAA waive the “publication and comment” step in the process for making a final decision on this exemption.

Additionally, Boeing has been granted an extension to the compliance time of AD 2019-23-04, but are still managing a schedule-sensitive project, and further requests that the



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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.

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)[25-146] at the system level as they apply to the FQIS for the deactivation of the body-mounted auxiliary fuel tanks for the 727 model. Such a grant would allow for the noted auxiliary fuel tank deactivation design change to be certified for use by the affected 727 fleet to be compliant to AD 2019-23-04.

Summary to be Published in the Federal Register

DESCRIPTION OF RELIEF SOUGHT: Exemption for the 727 body-mounted auxiliary fuel tank deactivation design change for AD 2019-23-04 to allow for the earliest possible incorporation of these safety-related fleet modifications.

PETITIONER: Boeing Commercial Airplanes

SECTION OF 14 CFR AFFECTED: 14 CFR §25.901(c), §25.981(a)(3)

DESCRIPTION OF RELIEF SOUGHT: Exemption for the 727 series aircraft to deactivate the body-mounted auxiliary fuel tanks to comply with AD 2013-23-04.

Enclosure A to RA-21-03455

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Transcript of Enclosure A to RA-21-03455