Airworthiness Directives; Boeing Model 747 Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747 airplanes. This proposed AD would require repetitive tests to detect hot air leaking from the trim air diffuser ducts or sidewall riser duct assemblies (collectively referred to in this proposed AD as “TADDs”), related investigative actions, and corrective actions if necessary. This proposed AD also would provide an optional terminating action for the repetitive tests. This proposed AD is prompted by reports of deteriorating sealants both inside and outside the center wing fuel tank due to heat damage from leaking TADDs. We are proposing this AD to prevent leakage of fuel or fuel vapors into areas where ignition sources may be present, which could result in a fire or explosion.

DATES:

We must receive comments on this proposed AD by January 18, 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 Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

You can examine the contents of this AD docket on the Internet at http://dms.dot.gov , or 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.

FOR FURTHER INFORMATION CONTACT:

Technical information: Dan Kinney, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6499; fax (425) 917-6590.

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-2004-19755; Directorate Identifier 2004-NM-23-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 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

We have received a report indicating that inspections have revealed deteriorating sealants both inside and outside the center wing fuel tank on certain Boeing Model 747 airplanes. The deterioration is attributed to damage caused by hot air leaking from the trim air diffuser ducts or sidewall riser duct assemblies (collectively referred to in this proposed AD as “TADDs”), which are part of the cabin air distribution system that is located between the top of the center wing fuel tank and the floor of the passenger cabin. These hot air leaks occur when the fiberglass diffuser ducts are damaged by the hot bleed air that they carry, leading the fiberglass diffuser ducts to leak or disconnect from the titanium trim air manifold. The release of hot air can damage the upper skin of the center wing section, the longitudinal floor beams, and the fuselage frame intercostals, as well as the sealants of the center wing fuel tank. Damage to the sealants inside or outside the center wing fuel tank could allow fuel or fuel vapors to leak into an area where ignition sources may be present. This condition, if not corrected, could result in a fire or explosion.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 747-21A2418, Revision 2, dated March 4, 2004; including Information Notice (IN) 747-21A2418 IN 01, dated March 11, 2004. The service bulletin describes procedures for repetitive tests to detect hot air leaking from the TADDs, related investigative actions, and corrective actions if necessary. The related investigative actions are repetitive general visual inspections for discrepancies or damage of the TADDs; and, if necessary, for damage of adjacent structure, the primary and secondary fuel barriers of the center wing fuel tank, control cables, and cable pulleys, and for raised cable seals. The corrective actions, if any damage is found, consist of replacing any damaged TADD with a new TADD having the same part number, or a new, improved TADD that has a higher temperature tolerance; and repairing any damage to adjacent structure, the primary and secondary fuel barriers of the center wing fuel tank, control cables, cable pulleys, or raised cable seals. After a TADD is replaced with a new TADD having the same part number, there is no need to test or inspect the replaced TADD until 21,200 flight hours after the replacement. After a TADD is replaced with a new, improved TADD, the repetitive inspections are no longer needed for that TADD. Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

IN 747-21A2418 IN 01 identifies some headings that were inadvertently omitted from the Accomplishment Instructions of Boeing Alert Service Bulletin 747-21A2418, Revision 2. These headings clarify what procedures apply to which airplane configuration.

The service bulletin refers to Chapter 21-61-20 of the 747 Airplane Maintenance Manual as an additional source for service information for the test and inspection of the TADDs. Chapter 21-61-20 contains, among other things, detailed procedures for the general visual inspection of the TADDs for damage or discrepancies, including detachment of the trim air duct from the diffuser duct, delamination, missing or softened surface material, or blackened material. For any discrepant TADD, Chapter 21-61-20 also describes procedures for a general visual inspection for damage of the primary and secondary fuel barriers of the center wing tank; structure adjacent to the discrepant TADD; and cables, cable pulleys, and raised cable seals in the over-wing area.

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 doing the actions specified in the service information described previously, except as discussed under “Differences Between the Proposed AD and Service Information.”

This proposed AD also provides an optional terminating action for the repetitive inspections, which is replacing the existing TADDs with new, improved TADDs. We have determined that it is acceptable to allow you to continue doing repetitive tests and inspections in lieu of requiring that you do the terminating action. In making this determination, we considered that long-term continued operational safety in this case will be adequately ensured by repetitive inspections to detect hot air leaking from the TADDs or discrepancies of the TADDs before these conditions are a hazard to the airplane.

Clarification of Proposed Requirements

This proposed AD would require that any replacement TADD must be new. Used TADDs are not acceptable replacement parts. Because the material of the TADDs deteriorates at a known rate, an operator would have to know how many total flight hours had been accumulated on a serviceable TADD, and would have to test and inspect that TADD at appropriate intervals. We find that it is unlikely that operators will have all of the data that would be needed for a serviceable TADD to be an acceptable replacement. Therefore, this proposed AD would allow replacement only with new parts.

Differences Between the Proposed AD and Service Information

For the hot air leak test, the service bulletin provides a compliance time of the earlier of 180 days or 2,000 flight hours after the release date of Revision 2 of the service bulletin, once the airplane has accumulated 20,000 total flight hours. For this test, this proposed AD would require the initial test to be done prior to the accumulation of 21,200 flight hours, or within 1,200 flight hours after the effective date of this AD, whichever is later. This compliance time is the equivalent of the inspection threshold of 20,000 total flight hours, plus a grace period of 1,200 flight hours (which is equivalent to one repetitive interval, as specified in the service bulletin). In developing an appropriate compliance time for this AD, we considered the manufacturer's recommendation, and the degree of urgency associated with the subject unsafe condition. In light of these factors, we find that a 1,200-flight-hour grace period represents an appropriate interval of time for affected airplanes (with close to or more than 20,000 total flight hours as of the effective date of the AD) to continue to operate without compromising safety.

Costs of Compliance

This proposed AD would affect about 1,305 airplanes worldwide. The following table provides the estimated costs for U.S. operators to comply with this proposed 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.