AD 2001-01-13

[Federal Register Volume 66, Number 16 (Wednesday, January 24, 2001)]
[Rules and Regulations]
[Pages 7568-7574]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 01-1662]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2000-NM-313-AD; Amendment 39-12084; AD 2001-01-13]
RIN 2120-AA64


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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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[[Page 7569]]

SUMMARY: This amendment adopts a new airworthiness directive (AD); 
applicable to all Boeing Model 737-300, -400, and -500 series 
airplanes. This AD requires, among other actions, a one-time detailed 
visual inspection of the fuel quantity indicating system (FQIS) wiring 
and fuel tubing on the inboard side of the right wing rib wing buttock 
line (WBL) 227 and on the aft side of stringer No. 13 to determine if 
clearance exists between the FQIS wire harness and the refuel tube and 
tube coupling, and to detect any loose or broken refuel tube clamp or 
bracket or chafing of the FQIS wire harness; and corrective actions, if 
necessary. This action is necessary to detect and correct chafing and 
to prevent electrical contact between the FQIS wiring and the 
surrounding structure, which, in conjunction with another wiring 
failure outside the fuel tank, could result in fire or explosion of the 
fuel tank. This action is intended to address the identified unsafe 
condition.

DATES: Effective February 28, 2001.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of February 28, 2001.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, PO Box 3707, Seattle, 
Washington 98124-2207. This information may be examined 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.

FOR FURTHER INFORMATION CONTACT: Sherry Vevea, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Seattle Aircraft Certification 
Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone 
(425) 227-1360; fax (425) 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 all Boeing Model 737-300, -400, 
and -500 series airplanes was published in the Federal Register on 
October 3, 2000 (65 FR 58966). That action proposed to require, among 
other actions, a one-time detailed visual inspection of the fuel 
quantity indicating system (FQIS) wiring and fuel tubing on the inboard 
side of the right wing rib wing buttock line (WBL) 227 and on the aft 
side of stringer No. 13 to determine if clearance exists between the 
FQIS wire harness and the refuel tube and tube coupling, and to detect 
any loose or broken refuel tube clamp or bracket or chafing of the FQIS 
wire harness; and corrective actions, if necessary.

Actions Since Issuance of Previous Proposal

    Since the issuance of the notice of proposed rulemaking (NPRM), the 
FAA has reviewed and approved Boeing Alert Service Bulletin 737-
28A1168, Revision 1, dated January 11, 2001. This new revision revises 
the format of Boeing Alert Service Bulletin 737-28A1168, dated 
September 26, 2000; adds certain text, references, drawings, parts and 
materials, and notes; revises a compliance time; makes certain 
technical changes; and adds certain tables and figures. In addition, 
the new revision does not include the procedure for a permanent repair 
(splicing the wires) if any damage to the wire harness is detected. 
Revision 1 of the service bulletin adds no additional work for the 
operators.

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.

Requests To Remove or Change the Compliance Plan Requirement

    The Air Transport Association (ATA) of America and two of its 
members request removing or changing the requirement in paragraph (a) 
of the proposed AD for submitting a compliance plan schedule to the 
FAA. The commenters state that it is unnecessary for operators to 
submit compliance plan schedules because operators already have 
internal planning schedules for accomplishing required actions. 
Therefore, submitting a schedule would not accelerate completion of the 
work required and would not improve operational safety.
    One of the commenters states that the proposed rule should allow 
more flexibility in consideration of unforeseen circumstances. One 
suggestion is for the FAA to omit the requirement [in paragraph (a) of 
the proposed AD] for operators to submit specific dates to the FAA, and 
allow operators to submit a ``date range'' for accomplishing the 
inspection and corrective actions [required by paragraph (b) of the 
proposed AD]. Another suggestion is for operators to submit a ``running 
plan of completion'' (e.g., five airplanes in the first month, another 
five in the second month) until the AD requirements for an operator's 
fleet are met. The commenter states the adoption of either of these 
suggestions would enable the operators to meet the compliance time 
required by the proposed AD, yet still allow operators to include the 
inspection into a flight schedule with minimal impact on operations.
    If the FAA does not accept the preceding recommendations, the 
commenters recommend that the compliance plan requirement include 
enough flexibility so that schedule updates are not required. The 
commenters also recommend that schedules should include enough 
flexibility to allow for unforeseen circumstances for the following 
reasons:
    <bullet> The proposed AD does not specify whether updates to the 
schedule would be required (or allowed). For that reason, it is unclear 
whether it would be necessary to submit a schedule change, or whether 
an alternative method of compliance (AMOC) would be required for such a 
change.
    <bullet> It is impractical to require operators to submit a 
schedule for accomplishing the proposed inspections within a 6-month 
period because a variety of operational factors would require changes 
on a daily basis.
    The commenters add that the principal maintenance inspector (PMI) 
should be allowed to verify an operator's maintenance program and 
confirm the accomplishment of AD requirements. (This is already within 
the scope of the PMI's responsibilities.) Confirmation of the 
accomplishment of the required actions by the PMI would not impose upon 
the operators an inflexible compliance schedule that would require 
frequent adjustments. Flexible schedules would decrease the impact on 
airline operations.
    The FAA does not concur that the requirement for operators to 
submit a compliance plan schedule should be removed or changed. The 
purpose of the plan is to ensure that operators are able to meet the 6-
month compliance time specified in paragraph (b) of the proposed AD for 
accomplishing the inspection and corrective actions. Because of the 
work involved, 6 months is an aggressive compliance time that can be 
met only if operators carefully plan their compliance schedules at the 
outset. However, we consider that a 6-month compliance time for 
accomplishing the inspection and corrective action requirements is 
necessary because of the risks associated with any chafed wiring in 
fuel tanks.
    The proposed AD would require a one-time submittal of a plan that 
identifies each of the operator's affected airplanes, and the dates and 
maintenance events when the required

[[Page 7570]]

actions will be accomplished. It would not require operators to 
strictly adhere to the plan or to submit updates to the FAA. To clarify 
this, we have added NOTE 2 to the final rule, stating that operators 
are not required to submit revisions to the compliance plan required by 
paragraph (a) of this AD. It is expected that the responsible PMI will 
confirm the ongoing accomplishment of the actions required by the AD 
for each operator's affected fleet. We view the compliance plan as the 
starting point for discussions between the PMI's and their operators.
    We acknowledge that, in certain instances, it may be necessary for 
operators to request extensions to the 6-month compliance time 
specified by paragraph (b) of the proposed AD for accomplishing the 
inspection and corrective actions. However, submitting a compliance 
plan within the proposed 15-day compliance time specified by paragraph 
(a) of the proposed AD will help to ensure that operators have 
considered all factors necessary for meeting inspection and corrective 
action requirements at the beginning of the compliance time period. If 
an operator later requests an extension of the compliance time, we will 
consider the submitted compliance plan, and the operator's reasons for 
not meeting it, in determining whether a requested extension to the 
schedule is justified. In the past, some operators were unable to meet 
the requirements of certain AD's within the compliance time due to poor 
planning. As a result, last-minute requests for extensions put 
operators at risk of grounding airplanes, depending upon the FAA 
resources available to process the extensions and FAA willingness to 
grant extensions.
    In light of this information, we consider it necessary for 
operators to engage in compliance planning. In addition, we consider 
that the requirement for operators to submit a compliance plan will 
minimize unscheduled out-of-service time and the grounding of 
airplanes. No change to paragraph (a) of the final rule is necessary in 
this regard.

Request To Clarify Compliance Plan Requirement for Foreign Airlines

    One commenter, the Civil Aviation Authority (CAA) of the United 
Kingdom, requests clarification that the compliance plan requirement in 
the proposed AD does not apply to foreign airlines.
    The FAA concurs that the compliance plan required by paragraph (a) 
of the proposed AD does not apply to non-U.S.-registered airplanes. 
Because only U.S.-registered airplanes are under FAA jurisdiction, we 
cannot require the accomplishment of the proposed action on airplanes 
registered outside the United States. If the CAA elects to adopt the 
requirements of this final rule, the CAA would determine whether a 
compliance plan is needed and how it would be handled. The compliance 
plan requirement in this AD is intended to verify to the FAA that the 
affected U.S.-registered airplanes will be able to meet the 
requirements of the proposed AD within the specified compliance time. 
No change to paragraph (a) of the final rule is necessary in this 
regard.

Requests To Extend the Compliance Time

    The ATA states that several operators have requested that the 
proposed 6-month compliance time for the inspection and corrective 
actions, as required by paragraph (b) of the proposed AD, be extended. 
ATA suggests an extension to 18 months, another commenter suggests 15 
months, and another commenter suggests a minimum of 12 months. In 
general, the commenters consider that the 6-month compliance time is 
too short for the following reasons:
    <bullet> Only two confirmed instances of FQIS wire harness chafing 
have occurred that prompted the release of the proposed NPRM. In one of 
those cases, there was flight deck indication of the chafing, by 
intermittent FQIS errors, that could have been used by the operator to 
locate a potential chafing problem before any secondary failure could 
cause an ignition event.
    <bullet> The proposed 6-month compliance time would require 
approximately 600 to 1,200 inspections to be accomplished on an 
unscheduled basis, potentially requiring special routing to capable 
maintenance stations. Unscheduled fuel tank inspections increase the 
risks to maintenance personnel involved with fuel tank entry, whereas 
routine and planned maintenance inspections provide a more controlled 
and safe environment. Such a compliance time would require additional 
maintenance shifts, and additional elapsed time out-of-service if 
corrective actions are required. In addition, any other maintenance 
that could be accomplished during time out-of-service, aside from the 
requirements of this proposed AD, would be limited.
    <bullet> Although Boeing Alert Service Bulletin 737-28A1168 was 
issued on September 26, 2000, it is not reasonable to consider the time 
between publication of the proposed AD and the effective date of the 
final rule as time fully available to operators for accomplishing the 
required inspection in light of the significant operational and 
economic impact of a 6-month compliance time.
    The commenters state that, based on the above reasons, an extension 
of the compliance time is necessary to allow accomplishment of the 
actions required by the proposed AD during scheduled intermediate 
maintenance visits of the majority of operators when appropriate 
facilities and personnel are available. To mitigate the safety concerns 
relative to extending the compliance time, one operator proposes to 
alert all maintenance personnel of the problem addressed in the 
proposed AD and of the potential safety implications. The commenters 
consider that extending the compliance time would still allow operators 
to maintain a level of safety equivalent to that intended by the 
proposed AD.
    The FAA does not concur that the 6-month compliance time required 
by paragraph (b) of the proposed AD should be extended, except for 
those airplanes that have accomplished the requirements of AD 99-03-04, 
as specified in paragraph (c) of the final rule. We point out that the 
commenters have provided no technical justification regarding how the 
level of safety could be maintained during the extended period. In 
addition, they have not provided specific information or data on the 
risk factors that may exist for maintenance personnel in accomplishing 
the actions required by the proposed AD. In developing an appropriate 
compliance time for the FQIS wire harness inspection and corrective 
actions, the FAA considered not only the degree of urgency associated 
with addressing the subject unsafe condition, but the practical aspect 
of inspecting the FQIS wire harness and addressing any discrepancy 
found within an interval of time that parallels normal scheduled 
maintenance for the majority of affected operators. With regard to the 
degree of urgency associated with this unsafe condition, we evaluated 
the risk associated with chafed wiring in the fuel tank in determining 
that the 6-month compliance time required by paragraph (b) of the 
proposed AD is necessary to ensure the safety of the fleet.
    Following the Trans World Airlines (TWA) Flight 800 accident, the 
National Transportation Safety Board (NTSB) performed FQIS safety 
analysis that revealed several scenarios where a combination of a 
latent failure or aging condition within the fuel tank and a subsequent 
single failure or electrical interference condition outside the tank 
can cause an ignition source to occur inside a fuel tank. Examples of 
these in-

[[Page 7571]]

tank and out-of-tank conditions that can contribute to a multiple-
failure ignition scenario were found in airplane service records and on 
airplanes that were inspected by the FAA and the NTSB. In light of 
these findings, we have determined that these same types of scenarios 
are applicable to Model 737-300 through -500 series airplanes.
    We have received reports indicating that four additional operators 
found damaged FQIS wire harness wiring in the right main fuel tank due 
to chafing against the refuel tube. To date, seven occurrences of FQIS 
wire chafing have been reported to the FAA, with the estimate that only 
a small portion of the affected airplanes have been inspected 
(including those airplanes that were inspected as part of the Fuel 
System Safety Program). In attempting to preclude future fuel tank 
explosions, we find it necessary to address all aspects of viable 
ignition scenarios to ensure that potential failures of the fuel system 
cannot contribute to ignition of the flammable fuel vapors in airplane 
fuel tanks. By requiring an inspection of the FQIS wire harness and 
corrective actions, ``best practices'' are used inside the tank (to 
eliminate the possibility of creating latent ``spark-gap'' locations in 
the event of high voltage on the FQIS wires). This final rule will 
adequately address the identified unsafe condition and meet the 
appropriate fail-safe standards to provide the level of safety (i.e., 
tank ignition events should never occur) intended by the regulations in 
place at the time of the original certification of the design.
    Related to the one commenter's justification for extending the 
compliance time based on alerting its maintenance personnel of the 
unsafe condition, the FAA finds that, while it is always necessary for 
certificate holders to notify maintenance personnel of an unsafe 
condition, such notification does not actually effect compliance with 
AD requirements. Therefore, the FAA deems that justifying an extension 
of the compliance time on this basis is not appropriate.
    In regard to the flight deck indication of the FQIS wire harness 
chafing by intermittent FQIS errors, the manufacturer stated that 
erroneous fuel quantity readings ``might'' be evident in the flight 
deck. A short of the FQIS wire is likely to be detectable when it 
becomes a hard failure, which occurs if the bare wire remains in 
contact with structure, or if the FQIS circuit forms a hard connection 
to another circuit due to a failure condition outside the fuel tank. 
However, an intermittent connection to another circuit may not be 
evident to flight or maintenance crews, but could still create a risk 
of an in-tank arc. In the minutes immediately preceding the in-flight 
breakup of the TWA Flight 800 airplane, the cockpit voice recorder 
indicated that the crew noticed a fuel flow indicator that was 
providing erratic indications. Such indications could have been due to 
a failure occurring in a wire bundle. The NTSB investigation determined 
that the fuel flow indicator wiring was routed in the same wire bundle 
as FQIS wiring on the TWA Flight 800 airplane. Because a chafed or bare 
FQIS wire normally operates at five volts depending upon the attitude 
of the airplane, the amount of fuel in the tank, and the conditions of 
flight, it is possible that such conditions might not cause a short 
that is detectable in the flight deck. The other reported chafing event 
discussed in the proposed AD was found during an operator's heavy 
maintenance check, which was not associated with trouble-shooting an 
FQIS indication problem.
    After careful consideration of all of the preceding information, we 
have determined that 6 months represents an appropriate interval of 
time for accomplishing the proposed inspections of the FQIS wire 
harness and corrective actions to ensure that an acceptable level of 
safety is maintained. However, under the provisions of paragraph (e) of 
the final rule, the FAA may approve requests for adjusting the 
compliance time if data are submitted to confirm that such an 
adjustment would provide an acceptable level of safety. No change was 
made to the compliance time required by paragraph (b) of the final 
rule.

Requests To Clarify the Inspection and Corrective Action Requirements

    1. One commenter requests revising the ``Explanation of Relevant 
Service Information'' section in the proposed AD by adding the 
corrective action ``relocating the lockwire away from the FQIS 
wiring.'' In addition, the words ``or lockwire'' should be added after 
the word ``jumper'' in paragraph (b)(1) of the proposed AD. These 
clarifications are necessary because incorrectly installed lockwires 
could also damage the FQIS wires.
    The FAA concurs that it is necessary to clarify that, if necessary, 
the lockwire should be relocated away from the FQIS wiring. Although 
the ``Explanation of Relevant Information'' section is not included in 
the final rule, we have revised paragraph (b)(1) of the final rule to 
read ``and relocate the bonding jumper or lockwire away from the 
wiring, if necessary.''
    2. That same commenter also requests deleting a corrective action 
that specifies ``splicing the wires'' in the ``Explanation of Relevant 
Service Information'' section of the proposed AD. Related to this, the 
commenter requests that paragraph (b)(3)(iii) of the proposed rule, 
which includes a splicing requirement, be deleted from the proposed AD. 
The commenter requests this change because, since the issuance of the 
proposed AD, the commenter has determined that the procedure for 
splicing the FQIS wires in the right main fuel tank inboard of right 
wing station WBL 227 is not practical. As a result, the Accomplishment 
Instructions of Revision 1 of the service bulletin does not include 
procedures for the splicing repair that were included in the original 
issue of the service bulletin. Instead, Revision 1 specifies repairing 
FQIS wire harness damage to the wire shield of the shielded wire or to 
the conductor of the unshielded wire by replacing the FQIS wire 
harness.
    Although the FAA concurs that the proposed AD should not include a 
splicing requirement, we again point out that the Explanation of 
Relevant Service Information section is not included in the final rule. 
However, we have deleted paragraph (b)(3)(iii) from the final rule to 
remove the splicing requirement. After reviewing the procedure for 
splicing the wires, we have concluded that, because of the difficulties 
associated with installing a splice to the FQIS wire harness in the 
right wing station WBL 227, replacement of the FQIS wire harness is 
more appropriate. However, we have added NOTE 3 to the final rule to 
give operators credit for accomplishing the repair by splicing the 
wires per the procedure included in the original issuance of the 
service bulletin.
    3. Another commenter requests revising paragraph (b) of the 
proposed AD to clarify that the inspection is to determine whether a 
``minimum'' of 3/8-inch clearance exists between the FQIS wire harness 
and the refuel tube and tube coupling. The FAA concurs that such 
clarification is necessary, and has changed paragraph (b) of the final 
rule accordingly.

Requests To Revise the Cost Estimate

    1. The ATA states that several operators request the FAA revise the 
cost estimates in the proposed AD. These commenters recommend that the 
cost estimate take into account fleetwide estimates of elapsed time 
out-of-service, and include costs associated with access and closure 
procedures. The ATA points out that the inspection in the original 
issue of the service bulletin specifies 17.5 work hours, which includes 
the time required to drain, vent, access, enter, and close the fuel

[[Page 7572]]

tank. That estimate is significantly greater than the estimate in the 
proposed AD of 1 work hour. The affected airplanes would be out of 
service from 1 to 4 days, during which other maintenance activities 
would be limited. The commenters suggest that the cost estimate should 
include:
    <bullet> Costs for access and closure procedures because the 
majority of the proposed inspections must be done on an unscheduled 
basis, and many of the scheduled visits would not provide the required 
access.
    <bullet> Costs for elapsed time out-of-service for the entire fleet 
because additional time is required for any discrepancy detected. In 
addition, other maintenance activities are greatly limited because 
electrical power to the airplane is secured during much of the out-of-
service period.
    The FAA does not concur. The cost impact information describes only 
the ``direct'' costs of the specific actions required by this AD. We 
recognize that, in accomplishing the requirements of any AD, operators 
may incur ``incidental'' costs in addition to ``direct'' costs. The 
cost analysis in AD rulemaking actions, however, typically does not 
include incidental costs, such as the time necessary to drain, vent, 
enter, and close a fuel tank. Because incidental costs may vary 
significantly from operator to operator, they are almost impossible to 
calculate.
    Even though, as stated in the proposed rule, we recognize that 
airplanes could be taken out of service for as long as 2 days, we do 
not have enough information to evaluate the number of airplanes that 
may be affected or the additional downtime that may be required. 
Therefore, providing a fleet-wide estimate of the elapsed time out-of-
service would be futile.
    Further, because AD's require specific actions to address specific 
unsafe conditions, they appear to impose costs that would not otherwise 
be borne by operators. However, because of the general obligation of 
operators to maintain and operate aircraft in an airworthy condition, 
this appearance is deceptive. Attributing those costs solely to the 
issuance of this AD is unrealistic because, in the interest of 
maintaining and operating safe aircraft, prudent operators would 
accomplish the required actions even if they were not required to do so 
by the AD. In this case, we have determined that direct and incidental 
costs are still outweighed by the safety benefits of the AD. No change 
was made to the cost estimate in the final rule.
    2. The ATA also recommends that the FAA review the cost allocated 
for replacing a wiring harness. One operator indicates that actual 
costs are 10 per cent greater than the cost cited in the proposal. The 
FAA infers that the commenters are requesting including the cost of the 
FQIS wire harness in the Cost Impact section of the proposed rule.
    The FAA does not concur with the commenters' requests to include 
the cost of an FQIS wiring harness in the Cost Impact section of the 
proposed rule. The Cost Impact section of the proposed AD only includes 
the costs associated with the ``direct'' costs of the specific actions 
required, which include developing a compliance plan and inspecting the 
FQIS wiring harness in the right main fuel tank. The proposed AD does 
not include the cost of ``on-condition'' actions, such as replacing a 
damaged FQIS wiring harness if one is detected during the required 
inspection (``repair, if necessary''). Such on-condition repair actions 
would be required to be accomplished, regardless of AD direction, to 
correct an unsafe condition identified in an airplane and to ensure the 
airworthiness of that airplane, as required by the Federal Aviation 
Regulations. No change was made to the cost estimate in the final rule.

Request To Clarify the Applicability of the Proposed AD

    One commenter requests clarification of whether the requirements of 
the proposed AD includes airplanes that have been modified by 
installing BFGoodrich transient suppression devices and transient 
suppression units. The FAA infers that the commenter is requesting 
issuance of an AMOC for those airplanes that have been modified per AD 
99-03-04, amendment 39-11018 (64 FR 4959, February 2, 1999).
    The FAA partially concurs with the commenter's request. AD 99-03-04 
requires the installation of components to provide shielding and 
separation of the fuel system wiring (that is routed to the fuel tanks) 
from adjacent wiring. That AD also requires the installation of flame 
arrestors and pressure relief valves in the fuel vent system. The 
actions of that AD are intended to prevent possible ignition of fuel 
vapors in the fuel tank and external ignition of fuel vapor exiting the 
fuel vent system, and consequent propagation of a flame front into the 
fuel tanks.
    Although we acknowledge that AD 99-03-04 addresses the potential 
for ignition sources within airplane fuel tanks, both AD 99-03-04 and 
the proposed AD address different aspects of the multiple-failure 
ignition scenarios identified by the NTSB and the FAA in the course of 
accident investigation. The proposed AD addresses the potential for 
chafed FQIS wiring in the fuel tank, and provides a means to avoid 
introducing ignition energy onto the FQIS wires outside of the tank, 
which will ensure that operators maintain the level of safety intended 
by the regulations. Therefore, compliance with the actions of the 
proposed AD would be required, even though an operator has accomplished 
the actions required by AD 99-03-04. However, we have determined that 
extending the compliance time from 6 to 18 months is appropriate for 
all affected airplanes that have been modified per AD 99-03-04, because 
those airplanes incorporate an additional level of circuit protection 
that significantly reduces the likelihood that an exposed conductor 
inside a fuel tank will become an ignition source. We have added a new 
paragraph (c) to the final rule to include this conditional compliance 
time extension for the referenced airplanes.

Request To Ensure Parts Availability

    One commenter, the CAA, requests information regarding the 
availability of parts and support from the manufacturer and applicable 
vendors to support all affected airline operators, including the 
worldwide fleet, in accomplishing the corrective actions required by 
the proposed AD within the compliance time of 6 months. The FAA infers 
the commenter is requesting information regarding the availability of 
FQIS wiring harness parts and the support needed to inspect and correct 
any discrepancies found while accomplishing the actions required by the 
proposed AD.
    The FAA concurs with the commenters'' request for assurance that 
adequate parts and support will be available for all operators in 
meeting the requirements of the proposed AD. In response, the FAA has 
received a statement from the manufacturer that the parts needed to 
replace FQIS wiring harnesses will be readily available to the 
operators, and that such parts are always kept in stock and replenished 
continually. In addition, the service bulletin includes a list of the 
parts and materials needed by the operator to meet the requirements of 
the proposed AD, along with the applicable reference material and 
drawings.

Request for Information of Actions Taken To Eliminate Clamp Failure

    One commenter, the Safety Regulation Group of the CAA, requests 
information on any actions that have been taken to eliminate failure of 
the refuel tube clamp due to a preload on the clamp.

[[Page 7573]]

The proposed rule attributed FQIS wire chafing to ``a refuel tube broke 
due to a preload on the clamp.'' This caused the refuel tube to move 
and subsequently come in contact with the FQIS wire. As paragraph (b) 
of the proposed AD requires only a one-time inspection, failures of the 
clamp may occur after that inspection is accomplished. As a result, 
further chafing of the FQIS wire could occur and go unnoticed.
    The FAA concurs with the commenter's request for more information 
of the actions taken to eliminate failure of the refuel tube clamp. In 
response, we offer the following information:
    <bullet> The manufacturer attributed the broken refuel tube clamp 
to a preload on the clamp. The slotted support bracket, along with the 
clamp, holds the refuel tube to structure and can be installed with a 
preload because of possible shifting of the bracket. The preload on the 
clamp could have occurred during production or during operator 
maintenance of the airplane.
    <bullet> The service bulletin includes procedures for inspecting 
loose or broken refuel tube clamps or slotted support brackets, 
replacing broken refuel tube clamps, replacing or repairing broken 
slotted support brackets, and verifying that there is no preload on the 
refuel tube or clamps. Inspecting the refuel tube clamp and bracket and 
determining that no preloads exist on those components will help 
prevent future failure of the clamp due to the existence of a preload 
on the clamp.
    <bullet> The FAA will initiate discussions with the manufacturer 
regarding any changes that might be required to the maintenance manuals 
to alert maintenance personnel to the potential of a preload on the 
refuel tube clamp.
    No change to the body of the final rule was necessary in this 
regard.

Request To Revise the Reporting Requirement

    One commenter suggests that, instead of requiring operators to 
submit a compliance plan [as specified in paragraph (a) of the proposed 
AD], the FAA should revise the reporting requirement in paragraph (c) 
of the proposed AD [cited as paragraph (d) in the final rule] to 
require operators to report their inspection findings to the FAA (as 
well as to the manufacturer). The commenter considers that such a 
change would enable operators to maintain flexibility in their 
schedules, and keep the FAA informed of the operator's ability to meet 
AD requirements.
    The FAA does not concur that it is necessary to require operators 
to submit inspection findings to the FAA. We point out that the 
manufacturer will send reports of such findings to the FAA, so a 
revision to the reporting requirement in paragraph (d) of the final 
rule is not necessary.

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.

Interim Action

    This is considered to be interim action until final action is 
identified, at which time the FAA may consider further rulemaking.

Cost Impact

    There are approximately 1,974 Model 737-300, -400, and -500 series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 796 airplanes of U.S. registry will be affected by this 
AD.
    It will take approximately 1 work hour per airplane to accomplish 
the required inspection, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of this inspection on U.S. 
operators is estimated to be $47,760, or $60 per airplane.
    It will take approximately 16 work hours per airplane to accomplish 
the required compliance plan, at an average labor rate of $60 per work 
hour. Based on these figures, the cost impact of the compliance plan on 
U.S. operators is estimated to be $764,160, or $960 per airplane.
    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 adding the following new 
airworthiness directive:

2001-01-13  Boeing: Amendment 39-12084. Docket 2000-NM-313-AD.

    Applicability: All Model 737-300, -400, and -500 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 (e) of 
this AD.

[[Page 7574]]

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 detect and correct chafing and to prevent electrical contact 
between the fuel quantity indicating system (FQIS) wiring and the 
surrounding structure, which, in conjunction with another wiring 
failure outside the fuel tank, could result in fire or explosion of 
the fuel tank, accomplish the following:

Compliance Plan

    (a) Within 15 days after the effective date of this AD, submit a 
plan to the FAA that identifies a schedule for compliance with 
paragraph (b) of this AD. This schedule must include, for each of 
the operator's affected airplanes, the dates and maintenance events 
(e.g., letter checks) when the required actions will be 
accomplished. For purposes of this paragraph, ``FAA'' means the 
Principal Maintenance Inspector (PMI) for operators that are 
assigned a PMI, or the cognizant Flight Standards District Office 
for other operators. 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.

    Note 2: Operators are not required to submit revisions to the 
compliance plan required by paragraph (a) of this AD to the FAA.

Inspection and Corrective Actions

    Note 3: Repairs accomplished by splicing the wires in accordance 
with the procedure included in Boeing Alert Service Bulletin 737-
28A1168, dated September 26, 2000, prior to the effective date of 
this AD, are considered acceptable for compliance with the 
requirements of paragraphs (b)(1), (b)(2), and (b)(3) of this AD.

    (b) Except as provided by paragraph (c) of this AD: Within 6 
months after the effective date of this AD, perform a one-time 
detailed visual inspection of the FQIS wiring and fuel tubing on the 
inboard side of the right wing rib wing buttock line (WBL) 227 and 
on the aft side of stringer No. 13 to determine if clearance of 3/8 
inch or greater exists between the FQIS wire harness and the refuel 
tube and tube coupling, and to detect any loose or broken refuel 
tube clamp or bracket, or chafing of the FQIS wire harness, in 
accordance with Boeing Alert Service Bulletin 737-28A1168, Revision 
1, dated January 11, 2001.

    Note 4: For the purposes of this AD, a detailed visual 
inspection is defined as: ``An intensive visual examination of a 
specific structural area, system, installation, or assembly to 
detect damage, failure, or irregularity. Available lighting is 
normally supplemented with a direct source of good lighting at 
intensity deemed appropriate by the inspector. Inspection aids such 
as mirror, magnifying lenses, etc., may be used. Surface cleaning 
and elaborate access procedures may be required.''

    (1) If the clearance between the FQIS wire harness and the 
refuel tube is less than 3/8 inch, prior to further flight, readjust 
the refuel tube, and relocate the bonding jumper or lockwire away 
from the wiring, if necessary, in accordance with the service 
bulletin.
    (2) If any loose or broken refuel tube clamp or bracket is 
found, prior to further flight, replace the broken clamp with a new 
clamp; repair the broken bracket or replace the broken bracket with 
a new bracket; and secure the loose clamp or bracket; as applicable; 
in accordance with the service bulletin.
    (3) If any chafing of the FQIS wiring harness is found, prior to 
further flight, replace the wire harness with a new wire harness or 
accomplish the applicable action(s) specified in paragraph (b)(3)(i) 
or (b)(3)(ii) of this AD, in accordance with the service bulletin.
    (i) For jacket damage only that is less than 1-inch in length 
with no sign of abrasion to the wire insulation: Install a teflon 
sleeve over the wiring. At the next scheduled ``C'' Check, but no 
later than 15 months after the effective of this AD, repair the wire 
harness or replace the wire harness with a new wire harness.
    (ii) For jacket damage or a harness with an exposed shield or 
conductor and the insulation of the other wire is not damaged (there 
can be no broken shield strands if the shield wire is damaged or no 
broken wire strands if the unshielded wire is damaged): Install a 
teflon sleeve over the wiring terminal and along the wire to the 
damaged area.
    (c) For airplanes on which the modification per AD 99-03-04, 
amendment 39-11018, has been accomplished prior to the effective 
date of this AD: Within 18 months after the effective date of this 
AD, perform the actions specified in paragraph (b), and in paragraph 
(b)(1) or (b)(2) of this AD, in accordance with Boeing Alert Service 
Bulletin 737-28A1168, Revision 1, dated January 11, 2001.

Reporting Requirement

    (d) Submit a report of inspection findings to Service Bulletin 
Engineering, Boeing Commercial Airplane Group, P.O. Box 3707, Mail 
Stop 2H-37, Seattle, Washington 98124-2207; at the applicable time 
specified in paragraph (d)(1) or (d)(2) of this AD. The report must 
include all the information specified in the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-28A1168, Revision 
1, dated January 11, 2001. 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.
    (1) For airplanes on which the inspection required by paragraph 
(b) of this AD is accomplished after the effective date of this AD: 
Submit the report within 10 days after performing the inspection.
    (2) For airplanes on which the inspection required by paragraph 
(b) of this AD has been accomplished prior to the effective date of 
this AD: Submit the report within 10 days after the effective date 
of this AD.

Alternative Methods of Compliance

    (e) 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 PMI, who may add comments and then send it to the 
Manager, Seattle ACO.

    Note 5: 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) Except for the requirements of paragraph (a) of this AD, the 
actions shall be done in accordance with Boeing Alert Service 
Bulletin 737-28A1168, Revision 1, dated January 11, 2001. 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. This information may 
be examined at the FAA, Transport Airplane Directorate, 1601 Lind 
Avenue, SW., Renton, Washington. 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 February 28, 2001.

    Issued in Renton, Washington, on January 11, 2001.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-1662 Filed 1-23-01; 8:45 am]
BILLING CODE 4910-13-P