Airworthiness Directives; Boeing Model 737-600, -700, -700C, -800 and -900 Series Airplanes; and Model 757-200, -200PF, -200CB, and -300 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 certain Boeing airplanes, identified above. This proposed AD would require inspecting to determine if certain motor-operated shutoff valve actuators for the fuel tanks are installed, and related investigative and corrective actions if necessary. This proposed AD would also require revising the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-21, No. 28-AWL-22, and No. 28-AWL-24 (for Model 737-600, -700, -700C, -800 and -900 series airplanes), and No. 28-AWL-23, No. 28-AWL-24, and No. 28-AWL-25 (for Model 757-200, -200PF, -200CB, and -300). This proposed AD results from a design review of the fuel tank systems. We are proposing this AD to prevent electrical energy from lightning, hot shorts, or fault current from entering the fuel tank through the actuator shaft, which could result in fuel tank explosions and consequent loss of the airplane.

DATES:

We must receive comments on this proposed AD by August 24, 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: (202) 493-2251.
• 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:

Judy Coyle, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 917-6497; fax (425) 917-6590.

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-2007-28662; Directorate Identifier 2007-NM-014-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 (800) 647-5527) 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.

We have determined that the actions identified in this AD are necessary to reduce the potential for ignition sources inside fuel tanks caused by latent failures, alterations, repairs, or maintenance actions, which, in combination with flammable fuel vapors, could result in fuel tank explosions and consequent loss of the airplane.

Boeing has found that, under specific conditions, it was possible for electrical current to flow through certain motor operated shutoff valve actuators in the fuel tank. Boeing has developed a new valve actuator to replace those actuators. A motor-operated shutoff valve actuator that does not have sufficient protection against electrical energy from lightning, hot shorts, and fault current, could allow electrical energy to enter the fuel tank through the actuator drive shaft, which could result in fuel tank explosions and consequent loss of the airplane.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletins 737-28A1207, dated February 15, 2007, and 757-28A0088, dated January 25, 2007. Boeing Alert Service Bulletin 757-28A0088 describes procedures for inspecting to determine the part number (P/N) of motor-operated valve (MOV) actuators for the fuel tanks; Boeing Alert Service Bulletin 737-28A1207 also specifies removing MOV actuators having a certain P/N. The service bulletins specify that no more work is necessary if the P/N is acceptable.

For Boeing Model 737-600, -700, -700C, -800 and -900 series airplanes, the affected MOVs are at 3 locations: The left engine fuel shutoff (spar) valve, the right engine fuel shutoff (spar) valve, and the fuel crossfeed valve. For Boeing Model 757-200, -200PF, -200CB, and -300 series airplanes, the affected MOVs are at 6 locations for airplanes in the single crossfeed configuration, or at 7 locations for airplanes in the dual crossfeed configuration.

If the P/N is not acceptable, the service bulletins specify related investigative and corrective actions as follows:

For all airplanes: Reworking the index plate; reworking the adapter plate if necessary; installing the adapter/shaft plate with sealant; installing the index plate with sealant; installing a new MOV actuator on the index plate with sealant; installing bonding jumpers with sealant. For Boeing Model 737-600, -700, -700C, -800 and -900 series airplanes the actions also include installing shield ground terminals using sealed fay surface bonding for the main tank fuel quantity indicating system (FQIS). All of these actions include steps that specify measuring the electrical bonding resistance between various components and reworking the bonding if necessary.

We have also reviewed Subsection F, “AIRWORTHINESS LIMITATIONS—FUEL SYSTEM AWLs,” of Boeing 737-600/700/700C/700IGW/800/900 Maintenance Planning Data (MPD) Document D626A001-CMR, Section 9, Revision May 2006; and Subsection G, “AIRWORTHINESS LIMITATIONS—FUEL SYSTEM AWLs,” of Boeing 757 MPD Document D622N001, Section 9, Revision October 2006 (hereafter referred to as Revisions May 2006 and October 2006 of the MPDs). These sections of the MPDs describe the critical design configuration control limitations (CDCCL) and inspections applicable to the MOV installation. CDCCLs are limitation requirements to preserve a critical ignition source prevention feature of the fuel tank system design that is necessary to prevent the occurrence of an unsafe condition. The purpose of a CDCCL is to provide instruction to retain the critical ignition source prevention feature during configuration change that may be caused by alterations, repairs, or maintenance actions. A CDCCL is not a periodic inspection.

Subsection F of Revision May 2006 of the Boeing 737-600/700/700C/700IGW/800/900 MPD adds new fuel system AWLs 28-AWL-21 (lightning and fault current protection—MOV actuator), No. 28-AWL-22 (repair of the MOV actuator), and 28-AWL-24 (lightning and fault current protection—MOV actuator).

Subsection G of Revision October 2006 of the Boeing 757 MPD adds new fuel system AWLs No. 28-AWL-23 (lightning and fault current protection—MOV actuator), No. 28-AWL-24 (repair of the MOV actuator), and No. 28-AWL-25 (lightning and fault current protection—MOV actuator).

Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

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 the following actions:

• Inspecting to determine if certain motor-operated shutoff valve actuators for the fuel tanks are installed, and related investigative and corrective actions if necessary.
• Revising the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-21, No. 28-AWL-22, and No. 28-AWL-24 (for 737-600, -700, -700C, -800 and -900 series airplanes).
• Revising the Airworthiness Limitations (AWLs) section of the Instructions for Continued Airworthiness to incorporate AWL No. 28-AWL-23, No. 28-AWL-24, and No. 28-AWL-25 (for Model 757-200, -200PF, -200CB, and -300).

This proposed AD would also allow accomplishing the revision to the AWLs section of the Instructions for Continued Airworthiness in accordance with later revisions of the MPD as an acceptable method of compliance if they are approved by the Manager, Seattle Aircraft Certification Office, FAA.

Costs of Compliance

There are about 2,916 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 1,406 airplanes of U.S. registry. The average labor rate is $80 per work hour.

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.