Airworthiness Directives; Boeing Model 737-600, -700, and -800 Series Airplanes

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 notice may be changed in light of the comments received. 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 notice must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 99-NM-62-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. 99-NM-62-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On March 29, 1999, the FAA issued AD 99-08-03, amendment 39-11107 (64 FR 15920, April 2, 1999), applicable to all Boeing Model 737-600, - 700, and -800 series airplanes, to require an inspection of the power distribution panels (PDP) to verify proper installation of the power feeder terminals and associated hardware, and corrective actions, if necessary. That action also requires repetitive torque checks of the terminal attachment screws. That action was prompted by reports of loss of electrical power from the engine-driven generators or the auxiliary power unit due to overheating, melting, and subsequent failure of the power feeder terminals. The requirements of that AD are intended to prevent such conditions, which could result in increased risk of fire and the loss of electrical power from the associated alternating current power source.

Actions Since Issuance of Previous Rule

In the preamble to AD 99-08-03, the FAA specified that the actions required by that AD were considered ``interim action'' and that the FAA was considering further rulemaking action to supersede that AD to require repetitive replacement of the PDP rigid bus assembly with a new assembly for all Boeing Model 737-600, -700, and -800 series airplanes. The FAA has determined that further rulemaking is indeed necessary; this proposed AD follows from that determination.

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 supersede AD 99-08-03 to continue to require an inspection of the PDP's to verify proper installation of the power feeder terminals and associated hardware, and corrective actions, if necessary. This action also would continue to require repetitive torque checks of the terminal attachment screws. This proposed AD would add a requirement for repetitive replacement of the PDP rigid bus assembly with a new assembly.

Interim Action

This is considered to be interim action. The manufacturer has advised that it currently is developing a modification that will positively address the unsafe condition addressed by this AD. Once this modification is developed, approved, and available, the FAA may consider additional rulemaking.

Cost Impact

There are approximately 153 airplanes of the affected design in the worldwide fleet. The FAA estimates that 56 airplanes of U.S. registry would be affected by this proposed 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 that is proposed in this AD action would take approximately 6 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts would be provided by the manufacturer at no cost to the operators. Based on these figures, the cost impact of the replacement proposed 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 current or proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.

Regulatory Impact

The regulations proposed herein would not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. 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.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by removing amendment 39-11107 (64 FR 15920, April 2, 1999), and by adding a new airworthiness directive (AD), to read as follows:

Boeing: Docket 99-NM-62-AD. Supersedes AD 99-08-03, Amendment 39- 11107.

Applicability: All Boeing Model 737-600, -700, and -800 series airplanes; certificated in any category.

Note 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent overheating, melting, and subsequent failure of the power feeder terminals, which could result in increased risk of fire and the loss of electrical power from the associated alternating current (AC) power source, accomplish the following:

Restatement of Requirements of AD 99-08-03, Amendment 39-11107:

Initial Inspection

(a) Within 90 days after April 19, 1999 (the effective date of AD 99-08-03, amendment 39-11107): Perform a one-time general visual inspection to verify proper installation of the power feeder terminals and associated hardware located in power distribution panels (PDP) P91 and P92, in accordance with the following procedures: Using a flashlight, inspect each of the six power feeder terminals by looking into the access holes located in the plastic cover of the rigid bus assembly. The holes are located on the aft face of PDP's P91 and P92. [Refer to the Boeing 737-600, -700, -800, -900 Airplane Maintenance Manual (AMM), Section 24-21-71/401, Figure 401 (Sheet 1), for the location of PDP P91 and P92.] On PDP P91, the holes are adjacent to terminal blocks TB5001 and TB5002. On PDP P92, the holes are adjacent to terminal blocks TB5005 and TB5006. There are a total of six holes per PDP. [Refer to the Boeing 737-600, - 700, -800, -900 AMM, Section 24-21-71/401, Figure 401 (Sheet 2), for the location of the access holes on the PDP's.] Note that although each PDP has nine power feeder terminals, only the six terminals adjacent to the access holes require inspection. Verify that the power feeder terminal is properly installed and held in place on the busbar by the No. 8 socket head cap screw, and verify that the cap screw is inserted into the hole in the terminal. For the proper power feeder terminal and screw buildup, refer to the Boeing 737- 600, -700, -800, -900 AMM, Chapter 24-21-71/401, Figure 401 (Sheet 4). The subject power feeder terminal is identified as item [7] and the cap screw as item [12]. This visual inspection does not require loosening or removing any fasteners. The inspection may require looking through the access hole at a slight angle to see the terminal clearly. The terminal can be identified by its shiny metal finish; the current transformer behind the terminal block is made of plastic with a flat black finish. If the power feeder terminal and No. 8 socket head cap screw are not assembled as shown in Boeing 737-600, -700, -800, -900 AMM, Section 24-21-71/401, Figure 401 (Sheet 4): Prior to further flight, replace the rigid bus assembly with a new assembly, in accordance with the procedures specified in Boeing 737-600, -700, -800, -900 AMM, Section 24-21-22.

Repetitive Torque Check

(b) Concurrent with the accomplishment of the requirements of paragraph (a) of this AD: Perform a torque check of the attachment screws of the power feeder terminals in accordance with the procedures specified in Boeing Maintenance Tip 737 MT 24-003, dated May 14, 1998. Repeat the torque check thereafter at intervals not to exceed 1,000 flight hours, in accordance with the maintenance tip.

New Requirements of This AD

Repetitive Replacement

(c) Within 1,000 flight hours after accomplishment of the eighth torque check required by paragraph (b) of this AD: Replace the PDP rigid bus assembly with a new assembly, in accordance with the procedures specified in Boeing 737-600, -700, -800, -900 AMM, Chapter 24-21-22. Repeat the replacement thereafter at intervals not to exceed 1,000 flight hours after every eighth torque check in accordance with the procedures specified in the AMM.

Alternative Methods of Compliance

(d) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.

Note 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

Special Flight Permits

(e) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

Issued in Renton, Washington, on June 4, 1999. Vi L. Lipski, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 99-14817 Filed 6-10-99; 8:45 am] BILLING CODE 4910-13-P