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

[Federal Register Volume 66, Number 212 (Thursday, November 1, 2001)]
[Rules and Regulations]
[Pages 55072-55075]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-27187]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-62-AD; Amendment 39-12490; AD 2001-22-11]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment supersedes 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. The existing AD also requires repetitive torque checks of 
the terminal attachment screws. This amendment adds a requirement for 
repetitive replacement of the PDP rigid bus assembly with a new 
assembly and provides an optional terminating action for the repetitive 
torque checks and the repetitive replacement of the PDP rigid bus 
assembly. This amendment 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 at the PDPs. The actions specified by 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 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.

ADDRESSES: 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.

FOR FURTHER INFORMATION CONTACT: 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.

SUPPLEMENTARY INFORMATION: 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.

Comments

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

Support for the Proposed Rule

    Two commenters concur with the proposed AD.

Provide Terminating Action

    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

[[Page 55073]]

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:
    <bullet> 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.
    <bullet> 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.
    <bullet> 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.

Clarify Appropriate Replacement Parts

    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.

Ascertain Parts Availability

    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.

Revise Boeing 737 Configuration Maintenance and Procedures (CMP) 
Document

    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.

Explanation of Changes Made to Proposed Rule

    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.

Conclusion

    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.

[[Page 55074]]

Interim Action

    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.

Cost Impact

    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.

Regulatory Impact

    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.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, 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 removing amendment 39-11107 (64 FR 
15920, April 2, 1999), and by adding a new airworthiness directive 
(AD), amendment 39-12490, to read as follows:

2001-22-11  Boeing: Amendment 39-12490. Docket 99-NM-62-AD. 
Supersedes AD 99-08-03, Amendment 39-11107.

    Applicability: Model 737-600, -700, and -800 series airplanes, 
equipped with power distribution panels (PDP) 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, dated April 29, 1999; 
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 (e)(1) 
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 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 PDPs P91 and P92. (Refer to the Boeing 737-600, -700, -800, 
-900 Airplane Maintenance Manual (AMM), Section 24-21-71, Page 402, 
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, Page 403, Figure 
401 (Sheet 2), for the location of the access holes on the PDPs.) 
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, Page 405, 
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, 
Page 405, 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.

    Note 2: For the purposes of this AD, a general visual inspection 
is defined as: ``A visual examination of an interior or exterior 
area, installation, or assembly to detect obvious damage, failure, 
or irregularity. This level of inspection is made under normally 
available lighting conditions such as daylight, hangar lighting, 
flashlight, or drop-light, and may require removal or opening of

[[Page 55075]]

access panels or doors. Stands, ladders, or platforms may be 
required to gain proximity to the area being checked.''

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, 
until paragraph (d) of this AD is accomplished.

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 assemblies with new assemblies having the same part 
numbers as the removed assemblies, in accordance with the procedures 
specified in Boeing 737-600, -700, -800, -900 AMM, Chapter 24-21-22. 
Repeat the replacement thereafter within 1,000 flight hours after 
every eighth torque check required by paragraph (b) of this AD, in 
accordance with the procedures specified in the AMM, until paragraph 
(d) of this AD is accomplished.

Optional Terminating Action

    (d) Replacement of existing PDP rigid bus assemblies with new, 
improved PDP rigid bus assemblies having part number 1032181-2 or 
1032185-2, as applicable, according to Boeing Service Bulletin 737-
24-1128, dated April 29, 1999, constitutes terminating action for 
the requirements of this AD.

Alternative Methods of Compliance

    (e)(1) 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. 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.
    (2) Alternative methods of compliance, approved previously in 
accordance with AD 99-08-03, amendment 39-11107, are approved as 
alternative methods of compliance for the corresponding requirements 
of this AD.

    Note 3: 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

    (f) 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.

Incorporation by Reference

    (g) The actions required by paragraph (b) of this AD shall be 
done in accordance with Boeing Maintenance Tip 737 MT 24-003, dated 
May 14, 1998. The optional terminating action, if accomplished, 
shall be done in accordance with Boeing Service Bulletin 737-24-
1128, dated April 29, 1999. This incorporation by reference was 
approved by the Director of the Federal Register in accordance with 
5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from 
Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 
98124-2207. Copies may be inspected at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the 
Office of the Federal Register, 800 North Capitol Street, NW., suite 
700, Washington, DC.

Effective Date

    (h) This amendment becomes effective on December 6, 2001.

    Issued in Renton, Washington, on October 23, 2001.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-27187 Filed 10-31-01; 8:45 am]
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