04-10433. 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 all Boeing Model 747 series airplanes. This proposal would require repetitive inspections for cracking of the top and side panel webs and panel stiffeners of the nose wheel well (NWW), and corrective actions, if necessary. This action is necessary to detect and correct fatigue cracks in the top and side panel webs and stiffeners of the NWW, which could compromise the structural integrity of the NWW and could lead to the rapid depressurization of the airplane. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by June 21, 2004.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2001-NM-179-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 [phone]. Comments may also be sent via the Internet using the following address: [e-mail]. Comments sent via fax or the Internet must contain “Docket No. 2001-NM-179-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 or 2000 or ASCII text.

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

FOR FURTHER INFORMATION CONTACT:

Nick Kusz, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone [phone]; fax [phone].

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-179-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-179-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

The FAA has received reports indicating that cracks have been found on the top and side panel webs and side panel horizontal stiffeners of the nose wheel well (NWW) on Boeing Model 747 series airplanes. The cause of the cracking is fatigue. If left undetected, fatigue cracks in the top and side panel webs and stiffeners could become large. This condition, if not detected and corrected, could compromise the structural integrity of the NWW and could lead to rapid depressurization of the airplane.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Bulletin 747-53A2465, Revision 1, dated October 16, 2003. The service bulletin describes procedures for performing repetitive detailed and ultrasonic inspections for cracking of the top and side panel webs of the NWW and for performing repetitive detailed and surface high frequency eddy current inspections for cracking of the top and side panel stiffeners of the NWW; replacing cracked stiffeners with new stiffeners; and repair of any cracked panel web. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition.

New Reports Since Issuance of Service Bulletin

Since issuance of the service bulletin, there have been several new reports of cracking in the nose wheel well panels. The reported cracking was as long as 12 inches and, in one case, was discovered within less than 1,200 flight cycles since the previous inspection per the service bulletin.

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 described below.

Differences Between Proposed Rule and Service Bulletin

Operators should note that while the service bulletin, “Planning Information” 1.D. Note 2., specifies that flight cycles with a cabin differential pressure of 2.0 psi or less do not need to be counted as part of the compliance time, this proposed AD counts all flight cycles as part of the compliance time. We have determined that an adjustment of flight cycles due to a lower cabin differential pressure is not substantiated and will not be allowed for use in determining the flight cycle threshold.

It should also be noted that, although the repeat interval listed in Figure 1 of the service bulletin is listed as 6,000 flight cycles, this proposal would require repeat inspections at 1,000 flight cycle intervals due to the severity of the new reports and the relatively short interval since the previous inspection that they were found. This reduced interval has been coordinated with the manufacturer.

Clarification of Service Bulletin

Operators should note that, although the “Action” paragraph in the Summary and paragraph D., “Description,” in the Planning Information of the service bulletin specify that operators may contact the manufacturer for disposition of certain repair conditions, the Accomplishment Instructions of the service bulletin specify to repair web cracks as shown in the Structural Repair Manual. This proposed AD would require the repairs be done per the Accomplishment Instructions of the service bulletin.

Cost Impact

There are approximately 1,127 airplanes of the affected design in the worldwide fleet. The FAA estimates that 255 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 42 work hours per airplane to accomplish the proposed inspection, and that the average labor rate is $65 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $696,150, or $2,730 per airplane, per inspection cycle.

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.

§ 39.13

[Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

Boeing: Docket 2001-NM-179-AD.

Applicability: All Model 747 series airplanes, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To detect and correct fatigue cracks in the top and side panel webs and stiffeners of the nose wheel well (NWW), which could compromise the structural integrity of the NWW and could lead to the rapid depressurization of the airplane, accomplish the following:

Initial and Repetitive Inspections

(a) Prior to the accumulation of 16,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever is later, do the inspections specified in paragraphs (a)(1) and (a)(2) of this AD, per the Accomplishment Instructions of Boeing Service Bulletin 747-53A2465, Revision 1, dated October 16, 2003. Repeat the inspections thereafter at intervals not to exceed 1,000 flight cycles.

(1) Do detailed and ultrasonic inspections of the top and side panel webs of the NWW for cracks.

(2) Do detailed and surface high frequency eddy current inspections of the top and side panel stiffeners of the NWW for cracks.

Note 1:

For the purposes of this AD, a detailed inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirrors, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”

Corrective Actions

(b) If any crack is found during any inspection required by paragraph (a) of this AD: Prior to further flight, do the repair specified in paragraph (b)(1) and/or (b)(2) of this AD, as applicable, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 747-53A2465, Revision 1, dated October 16, 2003. Thereafter, repeat the inspections required by paragraph (a) of this AD.

(1) Repair web cracks.

(2) Replace cracked stiffeners with new stiffeners.

Inspections Accomplished Per Previous Issue of Service Bulletin

(c) Inspections accomplished before the effective date of this AD per Boeing Alert Service Bulletin 747-53A2465, dated April 5, 2001, are considered acceptable for compliance with the corresponding inspection specified in this AD.

Alternative Methods of Compliance

(d) In accordance with 14 CFR 39.19, the Manager, Seattle Aircraft Certification Office, FAA, is authorized to approve alternative methods of compliance for this AD.

Issued in Renton, Washington, on April 29, 2004.

Kevin M. Mullin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.