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Proposed Rule

Airworthiness Directives; The Boeing Company Airplanes

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Federal Aviation Administration (FAA), DOT.


Notice of proposed rulemaking (NPRM).


We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 707 airplanes and Model 720 and 720B series airplanes. This proposed AD was prompted by fuel system reviews conducted by the manufacturer. This proposed AD would require modifying the fuel quantity indicating system (FQIS) to prevent development of an ignition source inside the center fuel tank due to electrical fault conditions. We are proposing this AD to prevent ignition sources inside the center fuel tank, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.


We must receive comments on this proposed AD by November 7, 2016.


You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:

  • Federal eRulemaking Portal: Go to Follow the instructions for submitting comments.
  • Fax: 202-493-2251.
  • Mail: U.S. Department of Transportation, Docket Operations,M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE., Washington, DC 20590.
  • Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Examining the AD Docket

You may examine the AD docket on the Internet at by searching for and locating Docket No. FAA-2016-9073; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (phone: 800-647-5527) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

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Jon Regimbal, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office (ACO), 1601 Lind Avenue SW., Renton, WA 98057-3356; phone: 425-917-6506; fax: 425-917-6590; email:

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Comments Invited

We invite you to send any written relevant data, views, or arguments about this proposal. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2016-9073; Directorate Identifier 2015-NM-062-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.

We will post all comments we receive, without change, to, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.


The FAA has examined the underlying safety issues involved in fuel tank explosions on several large transport airplanes, including the adequacy of existing regulations, the service history of airplanes subject to those regulations, and existing maintenance practices for fuel tank systems. As a result of those findings, we issued a final rule titled “Transport Airplane Fuel Tank System Design Review, Flammability Reduction, and Maintenance and Inspection Requirements” (66 FR 23086, May 7, 2001). In addition to new airworthiness standards for transport airplanes and new maintenance requirements, that rule included Amendment 21-78, which established Special Federal Aviation Regulation No. 88 (“SFAR 88”) at 14 CFR part 21. Subsequently, SFAR 88 was amended by: Amendment 21-82 (67 FR 57490, September 10, 2002; corrected at 67 FR 70809, November 26, 2002) and Amendment 21-83 (67 FR 72830, December 9, 2002; corrected at 68 FR 37735, June 25, 2003, to change “21-82” to “21-83”).

Among other actions, SFAR 88 requires certain type design (i.e., type certificate (TC) and supplemental type certificate (STC)) holders to substantiate that their fuel tank systems can prevent ignition sources in the fuel tanks. This requirement applies to type design holders for large turbine-powered transport airplanes and for subsequent modifications to those airplanes. It requires them to perform design reviews and to develop design changes and maintenance procedures if their designs do not meet the new fuel tank safety standards. As explained in the preamble to the rule, we intended to adopt airworthiness directives to mandate any changes found necessary to address unsafe conditions identified as a result of these reviews.

In evaluating these design reviews, we have established four criteria intended to define the unsafe conditions associated with fuel tank systems that require corrective actions. The percentage of operating time during which fuel tanks are exposed to flammable conditions is one of these criteria. The other three criteria address the failure types under evaluation: Single failures, combination of failures, and unacceptable (failure) experience. For all three failure criteria, the evaluations included consideration of previous actions taken that may mitigate the need for further action.

We have determined that the actions identified in this proposed AD are necessary to reduce the potential of ignition sources inside fuel tanks, which, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.Start Printed Page 65578

Model 707/720 FQIS Design

The design of the in-tank FQIS components and wiring has the potential for a latent FQIS electrical fault condition inside the fuel tank combined with an electrical hot short condition connecting a high power source to the FQIS wiring to cause an ignition source in a fuel tank.

Under the policy contained in FAA Policy Memo PS-ANM100-2003-112-15, SFAR 88—Mandatory Action Decision Criteria, dated February 25, 2003 (​Regulatory_​and_​Guidance_​Library/​rgPolicy.nsf/​0/​dc94c3a46396950386256d5e006aed11/​$FILE/​Feb2503.pdf), the FAA determined that this ignition source risk combined with the fleet average flammability for the center wing tank on Model 707 airplanes and Model 720 and 720B series airplanes created an unsafe condition for the center fuel tank. Applying that same policy, the FAA determined that due to a lower fleet average flammability, that same unsafe condition does not exist in the main and reserve (wing) tanks of these airplanes.

Related Rulemaking

On March 21, 2016, we issued AD 2016-07-07, Amendment 39-18452 (81 FR 19472, April 5, 2016), for certain Boeing Model 757-200, -200PF, -200CB, and -300 series airplanes. AD 2016-07-07 requires similar actions to those proposed in this NPRM. AD 2016-07-07 addressed the numerous public comments that were submitted on the proposal.

FAA's Determination

We are proposing this AD because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of these same type designs.

Proposed AD Requirements

This proposed AD would require modifying the FQIS to prevent development of an ignition source inside the center fuel tank due to electrical fault conditions. It is likely that operators or modifiers would develop transient suppression devices to be installed in the FQIS circuitry at the fuel tank entry point rather than physically separating FQIS wiring throughout the airplane. If this occurs the costs would be significantly lower than the estimate below.

Costs of Compliance

We estimate that this proposed AD affects 4 airplanes of U.S. registry. This estimate includes 2 cargo/tanker airplanes and 1 non-air-carrier passenger airplane, and 1 experimental airplane. We estimate the following costs to comply with this proposed AD:

Estimated Costs: Required Actions

ActionLabor costParts costCost per productCost on U.S. operators
Modification600 work-hours × $85 per hour = $51,000$150,000$201,000$804,000

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Regulatory Findings

We determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify this proposed regulation:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979),

(3) Will not affect intrastate aviation in Alaska, and

(4) Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

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List of Subjects in 14 CFR Part 39

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Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

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1. The authority citation for part 39 continues to read as follows:

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Authority: 49 U.S.C. 106(g), 40113, 44701.

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2. The FAA amends § 39.13 by adding the following new airworthiness directive (AD):

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The Boeing Company: Docket No. FAA-2016-9073; Directorate Identifier 2015-NM-062-AD.

(a) Comments Due Date

We must receive comments by November 7, 2016.

(b) Affected ADs


(c) Applicability

This AD applies to The Boeing Company Model 707 100 long body, 200, 100B long body, 100B short body, 300, 300B, 300C, and 400 series airplanes; and Model 720 and 720B series airplanes; certificated in any category; excluding airplanes equipped with a flammability reduction means (FRM) approved by the FAA as compliant with the requirements of 14 CFR 25.981(b), as amended on September 19, 2008, or 14 CFR 26.33(c)(1), as amended on September 19, 2008.

(d) Subject

Air Transport Association (ATA) of America Code 28, Fuel.

(e) Unsafe Condition

This AD was prompted by fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent ignition sources inside the center fuel tank, which, in combination with flammable fuel vapors, Start Printed Page 65579could result in a fuel tank explosion and consequent loss of the airplane.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Modification

Within 60 months after the effective date of this AD, modify the FQIS to prevent development of an ignition source inside the center fuel tank due to electrical fault conditions, using a method approved in accordance with the procedures specified in paragraph (h) of this AD.

(h) Alternative Methods of Compliance (AMOCs)

(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the ACO, send it to the attention of the person identified in paragraph (j) of this AD. Information may be emailed to:

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local flight standards district office/certificate holding district office.

(3) An AMOC that provides an acceptable level of safety may be used for any repair, modification, or alteration required by this AD if it is approved by the Boeing Commercial Airplanes Organization Designation Authorization (ODA) that has been authorized by the Manager, Seattle ACO, to make those findings. To be approved, the repair method, modification deviation, or alteration deviation must meet the certification basis of the airplane, and the approval must specifically refer to this AD.

(i) Related Information

For more information about this AD, contact Jon Regimbal, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle ACO, 1601 Lind Avenue SW., Renton, WA 98057-3356; phone: 425-917-6506; fax: 425-917-6590; email:

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Issued in Renton, Washington, on August 30, 2016.

Michael Kaszycki,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 2016-21396 Filed 9-22-16; 8:45 am]