07-3712. Airworthiness Directives; Boeing Model 707 Airplanes and Model 720 and 720B Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for all Boeing Model 707 airplanes and Model 720 and 720B series airplanes. This proposed AD would require accomplishing an airplane survey to define the configuration of certain system installations, and repair of any discrepancy found. This proposed AD would also require modifying the fuel system by installing lightning protection for the fuel quantity indication system (FQIS), ground fault relays for the fuel boost pumps, and additional power relays for the center tank fuel pumps and uncommanded on-indication lights at the flight engineer's panel. This proposed AD results from fuel system reviews conducted by the manufacturer. We are proposing this AD to prevent certain failures of the fuel pumps or FQIS, which could result in a potential ignition source inside the fuel tank, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.

DATES:

We must receive comments on this proposed AD by September 17, 2007.

ADDRESSES:

Use one of the following addresses to submit comments on this proposed AD.

• DOT Docket Web site: Go to http://dms.dot.gov and follow the instructions for sending your comments electronically.
• Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
• 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.
• Fax: [phone].
• Hand Delivery: Room W12-140 on the ground floor of the West Building, 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207, for the service information identified in this proposed AD.

FOR FURTHER INFORMATION CONTACT:

Kathrine Rask, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to submit any relevant written data, views, or arguments regarding this proposed AD. Send your comments to an address listed in the ADDRESSES section. Include the docket number “FAA-2007-28828; Directorate Identifier 2007-NM-010-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://dms.dot.gov,, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of that Web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov.

Examining the Docket

You may examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Operations office (telephone [phone]) is located on the ground floor of the West Building at the street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them.

Discussion

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 regulation 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, this rule included Special Federal Aviation Regulation No. 88 (“SFAR 88,” Amendment 21-78, and subsequent Amendments 21-82 and 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, single failures in combination with a latent condition(s), and in-service failure experience. For all four criteria, the evaluations included consideration of previous actions taken that may mitigate the need for further action.

Results from the SFAR 88 analysis show that potential ignition sources include:

• Fuel pump electrical failures that burn through the pump end cap or case.
• Fuel pump electrical failures that burn through the wire and cause electrical arcing through the conduit.
• Mechanical failure of center tank fuel pumps due to uncommanded operation that causes an ignition source and an arc in a wing tank due to a latent in-tank degradation of the fuel quantity indication system (FQIS) and a lightning strike.

We have determined that the actions identified in this AD are necessary to prevent certain failures of the fuel pumps or FQIS, which could result in a potential ignition source inside the fuel tank, which, in combination with flammable fuel vapors, could result in fuel tank explosion and consequent loss of the airplane.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other airplanes of this same type design. For this reason, we are proposing this AD, which would require modifying the fuel system by installing lightning protection for the fuel quantity indication system (FQIS), ground fault relays for the fuel boost pumps, and additional power relays for the center tank fuel pumps and uncommanded on-indication lights at the flight engineer's panel.

To date, the airframe manufacturer has not developed service information for the modifications proposed by this AD. Due to the age of the subject airplane models, the operator needs to conduct an airplane survey to define the configuration of system installations for the wing leading edges, wing-to-body area, electrical equipment bay, flight deck, and FQIS to facilitate development of the required service information. The survey would identify locations where new components and wire bundles could be installed, as well as the configuration of affected systems.

Therefore, to ensure that service information is available within a reasonable time to allow modification of the airplane; this proposed AD would also require conducting an airplane survey, and reporting the results to the FAA. The report would include photographs and sketches, part numbers of certain components, and the actual configuration of certain systems.

Due to the age of these airplanes, it is possible that discrepancies (i.e., wear or deterioration) might be detected during the survey. This proposed AD would also require repair of those discrepancies.

Ensuring Compliance with Airplane Survey

Appendix 1 of this proposed AD contains the 707 SFAR 88 survey areas. The appendix is for informational use and provides highlights of the general content of the required survey to assist operators in developing an acceptable survey plan. Operators may wish to use the appendix as an aid to implement the airplane survey.

Costs of Compliance

There are about 185 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 52 airplanes of U.S. registry.

The proposed survey would take about 20 work hours per airplane, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the proposed survey for U.S. operators is $83,200, or $1,600 per airplane.

Because the manufacturer has not yet developed a modification commensurate with the actions specified by this proposed AD, we cannot provide specific information regarding the required number of work hours or the cost of parts to do the proposed modification. In addition, modification costs will likely vary depending on the operator and the airplane configuration. The proposed compliance time of 72 months should provide ample time for the development, approval, and installation of an appropriate modification.

Based on similar modifications accomplished previously on other airplane models, however, we can reasonably estimate that the proposed modification may require as many as 420 work hours per airplane, at an average labor rate of $80 per work hour. Required parts may cost up to $185,000 per airplane. Based on these figures, the estimated cost of the proposed modification for U.S. operators is $11,367,200, or $218,600 per airplane.

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 have 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 that the 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); and

3. 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.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• 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:

PART 39—AIRWORTHINESS DIRECTIVES

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

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

§ 39.13

[Amended]

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

Boeing: Docket No. FAA-2007-28828; Directorate Identifier 2007-NM-010-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by September 17, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to all Boeing Model 707-100 long body, -200, -100B long body, and -100B short body series airplanes; and Model 707-300, -300B, -300C, and -400 series airplanes; and Model 720 and 720B series airplanes; certificated in any category.

Unsafe Condition

(d) This AD results from fuel system reviews conducted by the manufacturer. We are issuing this AD to prevent certain failures of the fuel pumps or fuel quantity indication system (FQIS), which could result in a potential ignition source inside the fuel tank, which, in combination with flammable fuel vapors, could result in fuel tank explosion and consequent loss of the airplane.

Compliance

(e) You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.

Airplane Survey

(f) Within 12 months after the effective date of this AD: Conduct an airplane survey that defines the configuration of system installations for the wing leading edges, wing-to-body area, electrical equipment bay, flight deck, and FQIS using a method approved in accordance with the procedures specified in paragraph (h)(1) of this AD. If any discrepancy is detected, repair before further flight using a method approved in accordance with the procedures specified in paragraph (h)(1) of this AD. Submit the survey results to the Manager, Seattle Aircraft Certification Office (ACO), FAA, 1601 Lind Avenue SW., Renton, Washington 98057-3356, at the applicable time specified in paragraph (f)(1) or (f)(2) of this AD. The report must include the survey results (e.g., photographs and sketches, part numbers of FQIS components and fuel pumps, and the actual configuration of FQIS and the fuel pump control systems), a description of any discrepancy found, the airplane serial number, and the number of landings and flight hours on the airplane. Under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.), the Office of Management and Budget (OMB) has approved the information collection requirements contained in this AD and has assigned OMB Control Number 2120-0056.

(1) If the survey was done after the effective date of this AD: Submit the report within 30 days after the survey.

(2) If the survey was done before the effective date of this AD: Submit the report within 30 days after the effective date of this AD.

Note 1:

For the purposes of this AD, “discrepancy” is defined as any wear or deterioration (e.g., damage, fluid leaks, corrosion, cracking, or system failures) that might prevent the airplane from being in an airworthy condition.

Modification of Fuel System

(g) Within 72 months after the effective date of this AD: Modify the fuel system as specified in paragraphs (g)(1), (g)(2), and (g)(3) of this AD, using a method approved in accordance with the procedures specified in paragraph (h)(1) of this AD.

(1) Replace the FQIS wire bundle along the leading edge of the left and right wings with a new wire bundle that has a lightning shield that is separated from other wiring.

(2) Replace each fuel pump relay with a ground fault interrupter relay.

(3) Install redundant power relays for the center tank fuel pumps and uncommanded on-indication lights at the flight engineer's panel.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Seattle ACO has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.

(2) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO.

Issued in Renton, Washington, on July 18, 2007.

Stephen P. Boyd,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.