[Federal Register Volume 64, Number 112 (Friday, June 11, 1999)]
[Proposed Rules]
[Pages 31518-31520]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-14817]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-62-AD]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to all Boeing Model 737-600, -
700, and -800 series airplanes, that currently requires 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 AD also requires repetitive torque checks 
of the terminal attachment screws. This action would add a requirement 
for repetitive replacement of the PDP rigid bus assembly with a new 
assembly. This proposal is 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 actions specified by the proposed 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.

DATES: Comments must be received by July 26, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-62-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.
    Information pertaining to this amendment may be obtained from or 
examined at the FAA, Transport

[[Page 31519]]

Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

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

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 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:

[[Page 31520]]

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