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

[Federal Register Volume 64, Number 63 (Friday, April 2, 1999)]
[Rules and Regulations]
[Pages 15920-15922]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-8133]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-38-AD; Amendment 39-11107; AD 99-08-03]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that 
is applicable to all Boeing Model 737-600, -700, and -800 series 
airplanes. This action 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. This action also requires repetitive torque checks of the 
terminal attachment screws. This amendment is prompted by reports 
indicating the 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 
in this 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: Effective April 19, 1999.
    Comments for inclusion in the Rules Docket must be received on or 
before June 1, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-38-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056.
    Information pertaining to this amendment may be obtained from or 
examined at the FAA, Transport 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: The FAA has recently received several 
reports indicating the loss of electrical power from the engine-driven 
generators or the auxiliary power unit on Boeing Model 737 series 
airplanes, due to failure of the power feeder terminals located in 
power distribution panels (PDP) P91 and P92. This failure is attributed 
to an overheat condition caused by loosening of the screws that fasten 
the power feeder terminals to the PDP rigid bus assembly. Investigation 
revealed that inadequate support of the power feeder terminal allows 
movement of the terminal during the power feeder wire installation and 
removal procedures. The consequent loosening of the screws may result 
in increased electrical resistance and the generation of heat between 
the power feeder terminal and the rigid busbar at the terminal-to-
busbar interface. This condition, if not corrected, may cause 
overheating and melting 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.

Explanation of the Requirements of the Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other Boeing Model 737-600, -700, and -800 series 
airplanes of the same type design, this AD is being issued 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 AC power source. This AD requires 
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 requires repetitive torque checks of the 
terminal attachment screws.

[[Page 15921]]

Interim Action

    This is considered to be interim action. The FAA is currently 
considering further rulemaking action to supersede this AD to require 
repetitive replacement of the PDP rigid bus assembly for all Boeing 
Model 737-600, -700, and -800 series airplanes. However, the planned 
compliance time for the repetitive replacement is sufficiently long so 
that notice and opportunity for prior public comment will be 
practicable.

Determination of Rule's Effective Date

    Since a situation exists that requires the immediate adoption of 
this regulation, it is found that notice and opportunity for prior 
public comment hereon are impracticable, and that good cause exists for 
making this amendment effective in less than 30 days.

Comments Invited

    Although this action is in the form of a final rule that involves 
requirements affecting flight safety and, thus, was not preceded by 
notice and an opportunity for public comment, comments are invited on 
this rule. Interested persons are invited to comment on this 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 under the caption ADDRESSES. All 
communications received on or before the closing date for comments will 
be considered, and this rule may be amended in light of the comments 
received. Factual information that supports the commenter's ideas and 
suggestions is extremely helpful in evaluating the effectiveness of the 
AD action and determining whether additional rulemaking action would be 
needed.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the rule that might 
suggest a need to modify the 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 that 
summarizes each FAA-public contact concerned with the substance of this 
AD will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this rule must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-38-AD.'' The postcard will be date stamped and 
returned to the commenter.

Regulatory Impact

    The regulations adopted herein will 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 final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    The FAA has determined that this regulation is an emergency 
regulation that must be issued immediately to correct an unsafe 
condition in aircraft, and that it is not a ``significant regulatory 
action'' under Executive Order 12866. It has been determined further 
that this action involves an emergency regulation under DOT Regulatory 
Policies and Procedures (44 FR 11034, February 26, 1979). If it is 
determined that this emergency regulation otherwise would be 
significant under DOT Regulatory Policies and Procedures, a final 
regulatory evaluation will be prepared and placed in the Rules Docket. 
A copy of it, if filed, may be obtained from the Rules Docket at the 
location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety.

Adoption of the Amendment

    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:

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 adding the following new 
airworthiness directive:

99-08-03  Boeing: Amendment 39-11107. Docket 99-NM-38-AD.

    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 (c) 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:

Initial Inspection

    (a) Within 90 days after the effective date of this AD: 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.

[[Page 15922]]

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.

Alternative Methods of Compliance

    (c) 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

    (d) 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.
    (e) This amendment becomes effective on April 19, 1999.

    Issued in Renton, Washington, on March 29, 1999.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-8133 Filed 4-1-99; 8:45 am]
BILLING CODE 4910-13-P

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