[Federal Register Volume 61, Number 94 (Tuesday, May 14, 1996)]
[Rules and Regulations]
[Pages 24206-24208]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-11824]



Federal Aviation Administration

14 CFR Part 39

[Docket No. 95-NM-117-AD; Amendment 39-9613; AD 96-10-08]
RIN 2120-AA64

Airworthiness Directives; Boeing Model 737-300, -400, and -500 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.


SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737-300, -400, and -500 series 
airplanes, that requires inspection to detect damage of a wire bundle 
and clamp that are located in the electronic/electrical (E/E) equipment 
bay, and repair of the damaged wire bundle. That action also requires 
replacement of the existing steel clamp with a nylon clamp, and 
rearrangement of the clamp installation. This amendment is prompted by 
a report of fire in the E/E equipment bay due to electrical arcing 
caused by chafing of a wire bundle. The actions specified by this AD 
are intended to prevent chafing of a wire bundle that could cause short 
circuiting of the wire bundle, and could result in smoke and fire in 
the E/E equipment bay.

DATES: Effective June 13, 1996.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of June 13, 1996.
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 95-NM-117-AD, 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 Oshiro, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (206) 227-2793; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-300, -
400, and -500 series airplanes was published in the Federal Register on 
October 13, 1995 (60 FR 53307). That action proposed to require a 
visual inspection to detect damage of the wire bundle and clamp in the 
electronic/electrical (E/E) equipment bay, and repair, if necessary. 
Additionally, that action proposed to require replacement of the rubber 
cushioned steel clamp with a nylon clamp, and the installation of 
additional clamps to prevent contact between wire bundle W2132 (or 
W0132) and power feeder wire bundle W0142.
    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 Proposal

    One commenter supports the proposed rule.

Request to Withdraw the Rule: Basis May be an Isolated Incident

    One commenter requests that the FAA first review the findings on 
airplanes inspected thus far and, if no incorrect routing exists on 
other airplanes, the proposed rule should be withdrawn. This commenter 
states that the Supplementary Information section of the preamble to 
the proposal only states that an unsafe condition is ``likely to 
exist'' on other airplanes, and asks that further explanation be given 
as to why the FAA believes other airplanes may be affected. This 
commenter has received no reports of similar conditions on other 
    The FAA agrees that fleetwide corrective actions should not be 
mandated in response to incidents determined to be truly ``isolated.'' 
In this case, however, AD action is warranted since the FAA has 
confirmed that the incident described in the notice was the result of a 
manufacturing error, and that this error was repeated on numerous 
airplanes. As part of its investigation, the FAA conducted inspections 
of 10 airplanes in the manufacturer's production facility. These 
inspections revealed that incorrect wire bundle clamps were installed 
in each of these airplanes. Furthermore, a review of manufacturing 
records indicates that this condition exists in approximately 620 
previously delivered airplanes. In light of this evidence, the FAA has 
determined that the condition addressed by this AD is not the result of 
a single isolated incident, as the commenter suggests.

Request to Withdraw the Rule: No Essential Flight Circuits are Involved 

    One commenter requests that the AD be withdrawn because of the fact 
that no essential flight circuits were affected as a result of the 
damage to the wiring. The wire bundle involved in the damage is not 
associated with flight-critical systems.
    The FAA agrees that loss of the systems associated with the damaged 
wire bundle would not significantly affect safe flight and landing of 
the airplane. The FAA's primary concern, however, is not the loss of 
system function, but the possibility of chafing of a wire bundle that 
could cause short circuiting of the wire bundles. Such short circuiting 
of the wire bundles could result in an undetected in-flight fire, since 
Electrical Equipment (E/E) bays of Model 737 airplanes are not equipped 
with fire detection systems.

Request to Withdraw the Proposal: No ``Formal'' Service Document Exists

    One commenter contends that the FAA should not issue an AD that 
cites an ``informal'' service letter (Boeing Service Letter 737-SL-24-
106, dated March 10, 1995) as the appropriate

[[Page 24207]]

source of instructions for accomplishing the proposed actions. The 
commenter maintains that a ``formal'' service bulletin should be issued 
if the manufacturer finds the chafing problem to be more than an 
isolated incident.
    The FAA does not concur with the commenter. The fact that the 
manufacturer chose to publish the service information in a form other 
than a ``formal'' service bulletin, is not a justifiable reason to 
withdraw the proposed AD. It is appropriate for the FAA to reference in 
AD's any document that is available to affected operators and contains 
procedural instructions necessary for conducting required actions. 
Further, the decision to mandate corrective actions via the AD process 
is based on the FAA's assessment of the potential hazardous condition, 
not the assessment by the manufacturer.

Request to Withdraw the Rule: Service Information Incomplete

    Two commenters state that the service letter, cited in the proposed 
rule as the appropriate service information, contains an incomplete 
list of parts. The commenters assert that the service letter only 
indicates a ``family'' of hardware, and leaves the determination of the 
appropriate clamp diameters and screw lengths up to the operators. The 
commenters request that an AD not be issued unless the manufacturer 
finds it advisable to publish a formal service bulletin containing a 
complete and accurate list of parts.
    The FAA acknowledges the commenters' observation that the service 
letter contains an incomplete list of parts; however, that list is not 
incomplete to the extent that the AD should be withdrawn. The FAA finds 
that clarification of these parts is necessary so that operators will 
have no difficulty performing the requirements of this AD. In those 
situations where part numbers are incomplete, the undefined parameters 
are limited to non-critical part dimensions or, in the case of the 
NAS42DD-6 spacer, a dimension and finish. The function of the subject 
parts is to establish a reasonable amount of separation from 
surrounding structure by providing positive mechanical support for the 
wire bundles. In these applications, a high degree of precision in the 
unspecified dimensions is not essential. It also is reasonable to 
assume that the modification will be accomplished by trained personnel, 
whose discretion in the selection of part sizes is appropriate. Such 
discretion will give operators the flexibility needed to deal with 
slight manufacturing variations in the wire bundle installation of the 
affected area. The FAA agrees that some guidance may prove useful to 
operators unfamiliar with the parts identified in the service letter; 
therefore, the FAA has revised paragraph (a) of the final rule to 
include descriptions for the installation of the screw size, spacer 
clearance, and specific finish requirements for the spacers.

Request to Extend Compliance Time

    Two commenters request that the compliance time of the proposed 
rule be increased from the proposed 12 months to 18 months. The 
commenters state that extending the compliance period will allow 
operators to accomplish the inspection during a scheduled ``C'' check, 
when airplanes are brought to the main maintenance base for an extended 
hold. Adoption of a 12-month compliance time would require affected 
operators to special schedule airplanes so that the requirements of the 
rule can be accomplished; this would entail additional expenses over 
what the FAA estimated in its cost impact information.
    The FAA concurs that the compliance time can be extended somewhat. 
The FAA's intent was that the inspections be conducted during a 
regularly scheduled maintenance visit for the majority of the affected 
fleet. The FAA now recognizes that 15 months corresponds more closely 
to the interval representative of the majority of affected operators' 
normal maintenance schedules. Extending the compliance time by three 
additional months will not adversely affect safety, and will allow the 
modification to be performed at a base during regularly scheduled 
maintenance. Paragraph (a) of the final rule has been revised to 
reflect a compliance time of 15 months.

Request to Revise Cost Impact Information

    One commenter requests that the FAA's cost impact estimation be 
revised to specify that two work hours are required to accomplish the 
proposed modification, instead of one work hour. The commenter explains 
that the access to the work area is from under the cabin floor, and the 
personnel performing the modification are in an awkward position and 
are unable to fully view the work area. Because of these factors, the 
modification would take a longer time that the FAA's estimated one work 
    The FAA does not concur. The cost impact information, below, 
describes only the ``direct'' costs of the specific actions required by 
this AD. The FAA's estimate of 1 work hours necessary to accomplish the 
required actions is based on the best data available to date, and 
represents the time necessary to perform only the actions actually 
required by this AD. The FAA recognizes, that in accomplishing the 
requirements of any AD, operators may incur ``incidental'' costs in 
addition to the ``direct'' costs. The cost analysis in AD rulemaking 
actions, however, typically does not include incidental costs, such as 
the time required to gain access and close up, planning time, or time 
necessitated by other administrative actions. Because incidental costs 
may vary significantly from operator to operator, they are almost 
impossible to calculate.


    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.

Cost Impact

    There are approximately 620 Model 737-300, -400, and -500 series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 195 airplanes of U.S. registry will be affected by this 
AD, that it will take approximately 1 work hour per airplane to 
accomplish the required actions, and that the average labor rate is $60 
per work hour. Required parts will cost approximately $25 per airplane. 
Based on these figures, the cost impact of the AD on U.S. operators is 
estimated to be $16,575, or $85 per airplane.
    The cost impact figure discussed above is 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.

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.
    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

[[Page 24208]]

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:


    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:

96-10-08  Boeing: Amendment 39-9613. Docket 95-NM-117-AD.

    Applicability: Model 737-300, -400, and -500 series airplanes, 
as listed in Boeing Service Letter 737-SL-24-106, dated March 10, 
1995; certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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 
    To prevent short circuiting of a wire bundle located in the 
electrical/electronics (E/E) equipment bay, which could result in 
smoke and fire, accomplish the following:
    (a) Within 15 months after the effective date of this AD, 
accomplish the requirements of paragraphs (a)(1), (a)(2), and 
(a)(3), of this AD in accordance with Boeing Service Letter 737-SL-
24-106, dated March 10, 1995.

    Note 2: Screws having part number (P/N) NAS1801-3-( ) and 
spacers having P/N NAS42DD-6-( ), used to install the clamps as 
specified by this service letter, should be selected to provide a 
minimum of 0.25 inch clearance between wire bundles and surrounding 
structure and objects. Additionally, the spacers should have a part 
number having a chemical film finish code of ``FC'' or a gray 
anodize finish code of ``N.''

    (1) Perform a visual inspection to detect damage of the wire 
bundle and clamps in the E/E compartment. If any damage is detected, 
prior to further flight, repair in accordance with the service 
    (2) Reclamp wire bundle W2132 (or W0132) by removing the steel 
cushioned clamp and installing a nylon clamp on the aft side of the 
existing nut and bolt hole at body station (BS) 360, water line (WL) 
203, left buttock line (LBL) 57, in accordance with the service 
    (3) Install additional clamps to wire bundles W2132 (or W0132) 
and power feeder wire bundle WO142, in accordance with the service 
    (b) Within 10 days after detecting any damage to the wire bundle 
or clamp as a result of the inspection required by paragraph (a) of 
this AD, submit a report of the damage findings to the FAA, 
Transport Airplane Directorate, Seattle Manufacturing Inspection 
District Office (MIDO), Attention: George Carter, 1601 Lind Avenue 
SW., Renton, Washington 98055-4056; telephone (206) 237-6229; fax 
(206) 965-0264. Information collection requirements contained in 
this regulation have been approved by the Office of Management and 
Budget (OMB) under the provisions of the Paperwork Reduction Act of 
1980 (44 U.S.C. 3501 et seq.) and have been assigned OMB Control 
Number 2120-0056.
    (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 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (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) The actions shall be done in accordance with Boeing Service 
Letter 737-SL-24-106, dated March 10, 1995, including Attachments I 
and II. 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.
    (f) This amendment becomes effective on June 13, 1996.

    Issued in Renton, Washington, on May 6, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
[FR Doc. 96-11824 Filed 5-13-96; 8:45 am]