Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes. This proposal would require an initial inspection to identify all H-11 steel bolts on the outer chord of the body station (BS) 2360 aft pressure bulkhead between stringers 12L and 12R; follow-on repetitive inspections to identify all remaining H-11 steel bolts on the entire outer chord of the BS 2360 aft pressure bulkhead; and follow-on and corrective actions, if necessary. This proposal also would require eventual replacement of all H-11 steel bolts with Inconel bolts. This action is necessary to prevent broken bolts, which could result in progressive failure of the remaining bolts and consequent structural damage and rapid depressurization of the airplane. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by November 12, 2002.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2001-NM-394-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2001-NM-394-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

The service information referenced in the proposed rule may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT:

Technical Information: Rick Kawaguchi, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-1153; fax (425) 227-1181.

Other Information: Sandi Carli, Airworthiness Directive Technical Editor/Writer; telephone (425) 687-4243, fax (425) 687-4248. Questions or comments may also be sent via the Internet using the following address: sandi.carli@faa.gov. Questions or comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this action may be changed in light of the comments received. Submit comments using the following format:

• Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
• For each issue, state what specific change to the proposed AD is being requested.
• Include justification (e.g., reasons or data) for each request.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2001-NM-394-AD.” The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2001-NM-394-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received several reports of numerous broken H-11 steel bolts found on the outer chord of the aft pressure bulkhead on certain Boeing Model 747 series airplanes. The broken bolts have been attributed to the steel material being susceptible to corrosion and subsequent stress corrosion cracking. If multiple adjacent H-11 steel bolts are broken, a progressive failure of the remaining bolts may occur. Such failure could result in structural damage and consequent rapid depressurization of the airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2474, dated October 25, 2001, which describes procedures for an initial inspection to identify all H-11 steel bolts on the outer chord of the body station (BS) 2360 aft pressure bulkhead between stringers 12L and 12R. The inspection procedures include checking the bolt part number stamped on the top, the outside diameter, or the sloped surface of the bolt head; or verifying the bolt is steel by using a magnet.

The service bulletin also describes procedures for follow-on repetitive inspections to identify all remaining H-11 steel bolts on the entire outer chord of the BS 2360 aft pressure bulkhead.

The follow-on and corrective action procedures include doing either an ultrasonic inspection or a torque check for cracked or broken bolts if any H-11 steel bolt is found, or replacing the H-11 steel bolt with an Inconel bolt; and, if the H-11 steel bolt is replaced, visually inspecting the bolt hole for corrosion, oversizing the hole up to 1/32-inch to remove any corrosion, and, after installation of a new Inconel bolt, coating the bolt with corrosion inhibitor compound. The procedures also recommend replacing any cracked or broken bolt with an Inconel bolt before further flight.

The service bulletin also specifies contacting the manufacturer if additional oversizing of the bolt holes is necessary. Replacing all H-11 steel bolts with Inconel bolts would eliminate the need for the repetitive inspections. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition.

Explanation of Requirements of Proposed Rule

Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would require accomplishment of the actions specified in the service bulletin described previously, except as discussed below.

Differences Between This Proposed Rule and the Service Information

The service bulletin does not specify the type of initial and follow-on inspections to be used to find H-11 steel bolts on the outer chord of the body station 2360 aft pressure bulkhead. For the purposes of this AD, we have determined that the procedures in the service bulletin constitute a “detailed inspection.” Note 2 of this proposed AD defines such an inspection.

Although the service bulletin specifies that the manufacturer may be contacted for disposition of certain repairs, this proposed AD would require such repairs to be accomplished per a method approved by us, or per data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle Aircraft Certification Office, to make such findings.

Cost Impact

There are approximately 487 airplanes of the affected design in the worldwide fleet. The FAA estimates that 165 airplanes of U.S. registry would be affected by this proposed AD.

It would take approximately 9 work hours per airplane to accomplish the proposed initial inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the initial inspection on U.S. operators is estimated to be $89,100, or $540 per airplane.

It would take approximately 35 work hours per airplane to accomplish the proposed follow-on inspection to identify all remaining H-11 steel bolts on the entire outer chord, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the follow-on inspection on U.S. operators is estimated to be $346,500, or $2,100 per airplane, per inspection cycle.

Should an operator be required to replace the H-11 steel bolts, it would take approximately 108 work hours per airplane to accomplish the proposed replacement, at an average labor rate of $60 per work hour. Required parts would cost approximately $3,233 per airplane. Based on these figures, the cost impact is estimated to be $9,713 per airplane.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

Regulatory Impact

The regulations proposed herein 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. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132.

For the reasons discussed above, I certify that 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); and (3) if promulgated, 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. A copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (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.