AD 2001-22-11

Effective December 6, 2001.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of December 6, 2001.

The service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Stephen S. Oshiro, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2793; fax (425) 227-1181.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 99-08-03, amendment 39-11107 (64 FR 15920, April 2, 1999), which is applicable to all Boeing Model 737-600, -700, and -800 series airplanes, was published in the Federal Register on June 11, 1999 (64 FR 31518). The action proposed to continue to require an inspection of the power distribution panels (PDP) to verify proper installation of the power feeder terminals and associated hardware, corrective actions, if necessary, and repetitive torque checks of the terminal attachment screws. The action proposed to add a requirement for repetitive replacement of the PDP rigid bus assembly with a new assembly.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Two commenters concur with the proposed AD.

Several commenters ask the FAA to revise the proposed AD to specify that replacement of the existing PDP rigid bus assemblies with new, improved assemblies terminates the repetitive torque checks in paragraph (b) and the repetitive replacements of the PDP rigid bus assemblies in paragraph (c) of the proposed AD. Three commenters point out that we have previously approved Boeing Service Bulletin 737-24-1128, dated April 29, 1999, as an alternative method of compliance (AMOC) with the repetitive torque check requirement of AD 99-08-03. That service bulletin describes procedures for replacement of existing rigid bus assemblies on the P91 and P92 PDPs with new, improved assemblies. One of the commenters states that the new, improved PDP rigid bus assemblies incorporate retaining blocks that are integral to the rigid bus cover, surround the termination assemblies, and provide a solid surface for the termination assemblies to bear on during installation and removal of power feeders, thus reducing the load transmitted through the attachment screws. The commenters state that installation of the new, improved PDP rigid bus assemblies addresses the unsafe condition in the proposed AD.

The FAA concurs. As noted by the commenters, replacement of existing rigid bus assemblies with new, improved assemblies eliminates the need for the repetitive replacement of PDP rigid bus assemblies specified in paragraph (c) of the proposed AD. Also, we have previously approved Boeing Service Bulletin 737-24-1128, and have approved that service bulletin as an AMOC for the repetitive torque checks required by AD 99-08-03, which this AD supersedes. Therefore, we have done the following in this final rule:

• Added a new paragraph (d) to this AD to state that replacement of existing PDP rigid bus assemblies with new, improved PDP rigid bus assemblies constitutes terminating action for the requirements of this AD.

• Revised paragraphs (b) and (c) of this AD to state that the requirements of those paragraphs only apply until paragraph (d) of this AD is accomplished.

• Added a new paragraph (e)(2) to this AD to state that AMOCs approved previously in accordance with AD 99-08-03 are approved for the corresponding requirements of this AD. (This provision should have been stated in the proposed rule but was inadvertently omitted.)

In a related issue, two commenters request that we revise the applicability statement of the proposed AD to remove airplanes on which improved PDP rigid bus assemblies have been installed during production.

We partially concur with this request. Airplanes equipped with the improved PDP rigid bus assemblies would not be subject to this AD. However, we must consider the possibility that some airplanes originally delivered with PDPs having the improved rigid bus assemblies may have been changed to be equipped with PDPs having rigid bus assemblies of the original design. This could occur as a result of rotation of spare parts inventories during routine maintenance replacements. Therefore, we have revised the applicability statement of this AD to state that this AD applies only to Boeing Model 737-600, -700, and -800 series airplanes equipped with PDPs bearing any of the Boeing part numbers in the “Existing Part Number” column of the table under paragraph 2.E., “Existing Parts Accountability,” of Boeing Service Bulletin 737-24-1128.

Two commenters ask us to revise paragraph (c) of the proposed AD to clarify appropriate replacement parts. The commenters question whether we intend paragraph (c) to require replacement of existing PDP rigid bus assemblies with identical parts (i.e., parts with the same part number as the existing parts), or with new, improved parts (as described in the previous section above). Both commenters note that replacement of existing PDP rigid bus assemblies with new, improved assemblies should eliminate the need for the repetitive replacement specified in paragraph (c).

We concur that we need to clarify under what circumstances it is necessary to repeat the replacement of the PDP rigid bus assembly required by paragraph (c) of this AD. Therefore, we have revised paragraph (c) of this final rule to require repetitive replacement of the PDP rigid bus assembly with a new assembly having the same part number as the removed part. As stated above, we have also added paragraph (d) to this AD to state that replacement of existing PDP rigid bus assemblies with new, improved rigid bus assemblies terminates the requirements of this AD.

One commenter requests that we confirm the availability of replacement parts from the manufacturer prior to issuance of this final rule. The commenter states that, as of the time of its comment, sufficient replacement parts have not been available to support replacement schedules. We have confirmed that the manufacturer can support replacement according to the schedule required by this AD, and no change to the final rule is necessary in this regard.

One commenter requests that we revise the Extended Twin Engine Operations (ETOPs) coverage in the Boeing 737 CMP Document to be consistent with the provisions of the proposed AD. The commenter notes that, while the proposed AD would require repetitive torque checks of the attachment screws of the power feeder terminals every 1,000 flight hours, and replacement of the PDP rigid bus assembly with a new assembly within 1,000 flight hours after every eighth torque check, the Boeing 737 CMP Document requires repetitive torque checks every 400 flight hours, with replacement of the PDP rigid bus assembly after every fourth check. The commenter notes that revision of the ETOPs information in the Boeing 737 CMP Document would provide consistency for all Boeing 737 “Next Generation” airplanes.

We do not concur. The torque check and replacement at the intervals required by this AD are intended to ensure that an adequate level of safety is maintained. However, the more conservative torque check and replacement intervals specified in the Boeing 737 CMP Document are necessary for airplanes performing ETOPS. No change to the final rule is necessary in this regard.

Paragraph (a) of the proposed AD specifies accomplishment of a “general visual” inspection. To clarify this inspection requirement, we have added a note to this final rule that defines that type of inspection.

Also, the inspection procedure included in paragraph (a) of AD 99-08-03, which is restated in paragraph (a) of this AD, contains several references to Boeing 737-600, -700, -800, -900 Airplane Maintenance Manual (AMM) Section 24-21-71/401, Figure 401. These references have been clarified in this final rule to refer specifically to relevant page numbers in AMM Section 24-21-71, Figure 401.

After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

This is considered to be interim action. The FAA is considering further rulemaking to require accomplishment of the optional terminating action described in this AD. However, the planned compliance time for this action is sufficiently long so that notice and opportunity for prior public comment will be practicable.

There are approximately 153 Model 737-600, -700, and -800 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 56 airplanes of U.S. registry will be affected by this AD.

The actions that are currently required by AD 99-08-03 take approximately 2 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required actions on U.S. operators is estimated to be $6,720, or $120 per airplane.

The new replacement required by this AD will take approximately 6 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will be provided by the manufacturer at no cost to the operators. Based on these figures, the cost impact of the replacement required by this AD on U.S. operators is estimated to be $20,160, or $360 per airplane, per replacement cycle.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this 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.

The regulations adopted herein will 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 final rule does not have federalism implications under Executive Order 13132.

For the reasons discussed above, I certify that this action (1) Is not a “significant regulatory action” under Executive Order 12866; (2) is not a “significant rule” under 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. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption ADDRESSES.

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

1. The authority citation for part 39 continues to read as follows: