Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes Modified in Accordance With Supplemental Type Certificate (STC) ST00127BO

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for Boeing Model 737-300, -400, and -500 series airplanes modified in accordance with STC ST00127BO. This proposed AD would require installation of bonding straps to the safe side harnesses of the digital transient suppression device of the fuel quantity indicating system. This proposed AD is prompted by the results of fuel system reviews conducted by the STC holder. We are proposing this AD to prevent unsafe levels of current or energy from entering the fuel tank, due to hot short faults or threat conditions associated with the safe side harness assembly, which could result in a fire or explosion of the fuel tank.

DATES:

We must receive comments on this proposed AD by January 31, 2005.

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: Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW., Nassif Building, room PL-401, Washington, DC 20590.
• By fax: (202) 493-2251.
• Hand Delivery: Room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this proposed AD, contact Goodrich Fuel & Utility Systems, Goodrich Corporation, 100 Panton Road, Vergennes, Vermont 05491.

You can examine the contents of this AD docket on the Internet at http://dms.dot.gov , or in person at the Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street, SW., Room PL-401, on the plaza level of the Nassif Building, Washington, DC. This docket number is FAA-2004-19891; the directorate identifier for this docket is 2004-NM-136-AD.

FOR FURTHER INFORMATION CONTACT:

Technical information: Richard Spencer, Aerospace Engineer, Boston Aircraft Certification Office, ANE-150, FAA, Engine and Propeller Directorate, 12 New England Executive Park, Burlington, Massachusetts 01803; telephone (781) 238-7184; fax (781) 238-7170.

Plain language information: Marcia Walters, marcia.walters@faa.gov.

SUPPLEMENTARY INFORMATION:

Docket Management System (DMS)

The FAA has implemented new procedures for maintaining AD dockets electronically. As of May 17, 2004, new AD actions are posted on DMS and assigned a docket number. We track each action and assign a corresponding directorate identifier. The DMS AD docket number is in the form “Docket No. FAA-2004-99999.” The Transport Airplane Directorate identifier is in the form “Directorate Identifier 2004-NM-999-AD.” Each DMS AD docket also lists the directorate identifier (“Old Docket Number”) as a cross-reference for searching purposes.

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 under ADDRESSES. Include “Docket No. FAA-2004-19891; Directorate Identifier 2004-NM-136-AD” in the subject line 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 submitted 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 can review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you can visit http://dms.dot.gov.

We are reviewing the writing style we currently use in regulatory documents. We are interested in your comments on whether the style of this document is clear, and your suggestions to improve the clarity of our communications that affect you. You can get more information about plain language at http://www.faa.gov/language and http://www.plainlanguage.gov.

Examining the Docket

You can examine the AD docket on the Internet at http://dms.dot.gov,, or in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647-5227) is located on the plaza level of the Nassif Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the DMS receives them.

Discussion

The FAA has examined the underlying safety issues involved in recent 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” (67 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 another 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 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.

As a result of fuel system reviews associated with SFAR 88, the STC holder determined that the existing design of the safe side harness for the digital transient suppression device (DTSD) does not incorporate a method of positively bonding the harness shields to the airframe on certain Boeing transport category airplanes that have been modified in accordance with STC ST00127BO. The DTSD is designed to limit current and energy present during external threat (lightning/electromagnetic interference (EMI)) conditions from being introduced to the fuel quantity indicating system (FQIS) wiring. Bonding of the shielded safe side wire harnesses that extend from the DTSD to the fuel tank entry is essential to ensure that any induced threats or hot short faults are limited to safe levels. Unsafe levels of current or energy entering the fuel tank, due to hot short faults or threat conditions associated with the safe side harness assembly, if not corrected, could result in a fire or explosion of the fuel tank.

Relevant Service Information

We have reviewed Goodrich Service Bulletin 737-300766-28-2, Revision 2, dated July 28, 2004. The service bulletin describes procedures for:

1. Installing bonding straps on each safe side harness.

2. Modifying each safe side harness connector backshell at the tank penetrations and at the DTSDs.

3. Replacing only the backshell for all circular tank and center tank penetrations and DTSD connections that use a short 90 degree connector backshell.

4. Replacing the whole backshell for all rectangular wing tank penetrations that use a long 90 degree connector backshell.

5. Installing ground bracket(s) at the wing tank penetration(s).

6. Installing a ground bracket at the center tank penetration.

7. Installing a ground bracket at wing station DTSD locations.

8. Installing a ground bracket at center tank DTSD location.

9. Installing fuel quantity warning labels of the safe side harnesses.

10. Modifying part number labels for the safe side harness.

11. Bonding verification.

12. Ensuring each safe side harness meets the requirements for minimum clearances from other airplane equipment.

Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition. The Goodrich service bulletin specifies that the actions must be accomplished within the “applicable AD compliance period.”

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. Therefore, we are proposing this AD, which would require accomplishing the actions specified in the service information described previously.

Costs of Compliance

There are about 404 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 2 airplanes of U.S. registry. The proposed actions would take about 9 work hours per airplane, at an average labor rate of $65 per work hour. For airplanes equipped with a Cinch rectangular connector, required parts would cost about $1,650 per airplane. For all other airplanes, required parts would cost about $1,500 per airplane. Based on these figures, the estimated cost of the proposed AD for U.S. operators is between $2,085 and $2,235 per airplane.

Authority for This Rulemaking

The FAA's authority to issue rules regarding aviation safety is found in Title 49 of the United States Code. 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.

This rulemaking is promulgated under the authority described in subtitle VII, part A, subpart III, section 44701, “General requirements.” Under that section, the FAA is charged with promoting safety 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 AD.

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. 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.