[Federal Register Volume 65, Number 83 (Friday, April 28, 2000)]
[Proposed Rules]
[Pages 24889-24894]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-10670]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-78-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to certain Boeing Model 737-
100, -200, -300, -400, and -500 series airplanes. That AD currently 
requires inspection of the fueling float switch wiring in the center 
fuel tank to detect discrepancies, accomplishment of corrective 
actions, and installation of double Teflon sleeving over the wiring of 
the float switch. In lieu of the above mentioned requirements, that AD 
provides for deactivation of the float switch. This proposed action 
would eliminate the option for deactivation of the float switch and 
require, for all affected airplanes, repetitive inspections of the 
float switch wiring to detect discrepancies; replacement of the float 
switch and wiring, if necessary; and replacement of the double Teflon 
sleeving. For certain airplanes, this action also would add a new 
requirement for inspection and installation of partial double Teflon 
sleeving in a certain area. The actions specified by the proposed AD 
are intended to detect and correct chafing of the direct current 
powered float switch wiring insulation in the center fuel tank and the 
resultant arcing from the wiring to the in-tank conduit, which could 
present an ignition source inside the fuel tank and result in a 
consequent fire or explosion.

DATES: Comments must be received by June 12, 2000.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-78-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.
    The service information referenced in the proposed rule 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.

FOR FURTHER INFORMATION CONTACT: Dorr M. Anderson, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2684; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be

[[Page 24890]]

considered before taking action on the proposed rule. The proposals 
contained in this notice may be changed in light of the comments 
received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-78-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 99-NM-78-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On February 23, 1999, the FAA issued AD 99-05-12, amendment 39-
11060 (64 FR 10213, March 3, 1999), applicable to certain Boeing Model 
737-100, -200, -300, -400, and -500 series airplanes. [A correction of 
that AD was published in the Federal Register on March 9, 1999 (64 FR 
11533).] That AD requires removal of the fueling float switch and 
wiring in the center fuel tank and inspection of the float switch 
wiring to detect discrepancies, and either reinstallation of existing 
float switch and wiring, or replacement of the float switch and wiring 
with a new float switch and wiring. That action also requires 
installation of double Teflon sleeving over the wiring of the float 
switch. In lieu of the above mentioned requirements, that AD requires 
deactivation of the float switch, accomplishment of specific fueling 
procedures, and installation of Caution signs. That action was prompted 
by a report indicating that chafing of the direct current (DC) powered 
float switch wiring insulation in the center fuel tank has occurred on 
several airplanes. The requirements of that AD are intended to detect 
and correct such chafing and the resultant arcing from the wiring to 
the in-tank conduit, which could present an ignition source inside the 
fuel tank and consequent fire/explosion.

Actions Since Issuance of Previous Rule

    Since the issuance of that AD, the airplane manufacturer has 
examined fueling float switch wiring removed from the center fuel tank 
of airplanes that have accumulated between 4,000 and 20,000 total 
flight hours. Significant wire chafing was observed on wiring removed 
from airplanes that have accumulated as few as 12,000 total flight 
hours.
    In addition, the FAA finds that the conduit-enclosed float switch 
wiring installation is not a fail-safe design. Therefore, the FAA finds 
that repetitive inspections to detect discrepancies of the fueling 
float switch wiring in the center fuel tank are necessary to ensure 
safe operation.
    Furthermore, when AD 99-05-12 was issued, it contained provisions 
for deactivation of the center tank float switch, and reinstallation of 
any existing float switch wiring having worn insulation. In the 
preamble to that AD, the FAA indicated that the actions required by 
that AD were considered ``interim action'' and that further rulemaking 
action was being considered. Such further rulemaking could include a 
requirement for replacement of the existing float switch and wiring 
with a new float switch and wiring for any airplane on which the float 
switch was deactivated or on which an existing float switch with worn 
insulation was reinstalled. The FAA now has determined that further 
rulemaking action is indeed necessary, and this proposed AD follows 
from that determination.

Other Relevant Rulemaking

    On January 26, 1999, the FAA issued AD 99-03-04, amendment 39-11018 
(64 FR 4959, February 2, 1999), which requires modification of certain 
Model 737 series airplanes to provide shielding and separation of the 
fuel system wiring (that is routed to the fuel tanks) from adjacent 
wiring. That AD is intended to prevent electrical transients induced by 
electromagnetic interference or electrical short circuit conditions 
that could cause arcing of fuel system wiring or fuel quantity 
indication system probes. Such electrical transients would not cause 
ignition of fuel vapors in the fuel tank unless the wiring or probes in 
the tank had a latent short circuit condition between probe terminals, 
between probe to structure, between terminal block to structure, 
between in-tank wires, or between an in-tank wire to structure. This 
proposed rule is intended to address a separate possible source of 
ignition in the fuel tanks: arcing from the float switch wiring to the 
in-tank conduit that burns through the conduit wall into the fuel tank.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-28A1132, Revision 2, dated June 17, 1999. Except as discussed 
below, the procedures described in Revision 2 are essentially similar 
to those described in the original issue and Revision 1 of the alert 
service bulletin, which were referenced as the appropriate sources of 
service information for the actions in AD 99-05-12.
    For airplanes that have accumulated between 10,000 and 30,000 total 
flight hours, Revision 2 of the alert service bulletin describes 
procedures for a detailed visual inspection of the fueling float switch 
wiring in the center fuel tank at the exit of the conduit on the front 
spar; replacement of the float switch and wiring with a new float 
switch and wiring, if necessary; and installation of partial double 
Teflon sleeving over the wiring of the float switch.
    Accomplishment of the actions specified in the alert service 
bulletin is intended to adequately address the identified unsafe 
condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would supersede AD 99-05-12 to continue to require 
inspection of the fueling float switch wiring in the center fuel tank 
to detect discrepancies, accomplishment of corrective actions, and 
installation of double Teflon sleeving over the wiring of the float 
switch. The proposed AD would remove the option for deactivation of the 
float switch, which was provided in AD 99-05-12, and, for airplanes on 
which such deactivation was accomplished previously, would require 
accomplishment of the inspection to detect discrepancies of the fueling 
float switch wiring in the center fuel tank, corrective actions, and 
installation of double Teflon sleeving. For certain airplanes, the 
proposed AD also would add a new requirement for inspection and 
installation of partial double Teflon sleeving over the wiring of the 
fueling float switch in the center fuel tank. The proposed AD also 
would require repetitive inspections of the float switch wiring to 
detect discrepancies; replacement of the float switch and wiring, if 
necessary; and replacement of the double Teflon sleeving. The actions 
would be required

[[Page 24891]]

to be accomplished in accordance with the alert service bulletin 
described previously, except as discussed below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that the alert service bulletin only 
describes a one-time inspection of the float switch wiring and 
installation of double Teflon sleeving for airplanes that were not 
originally manufactured with double Teflon sleeving. However, this 
proposed AD would require repetitive inspections of the fueling float 
switch wiring in the center fuel tank to detect discrepancies; 
replacement of the float switch and wiring, if necessary; and 
replacement of the double Teflon sleeving for all affected Model 737-
100, -200, -300, -400, and -500 series airplanes. As stated previously, 
the conduit-enclosed float switch wiring installation is not a fail-
safe design; therefore, repetitive inspections are necessary to ensure 
safe operation.
    Operators also should note that this proposed AD would be 
applicable to all Model 737-100, -200, -300, -400, and -500 series 
airplanes; on which the center wing tanks are activated; excluding 
those airplanes equipped with center wing tank volumetric topoff 
systems, or alternate current (AC) powered center tank float switches. 
The effectivity listing of Boeing Alert Service Bulletin 737-28A1132, 
Revision 2, dated June 17, 1999, includes Model 737-200, -300, -400, 
and -500 series airplanes having L/N 1 through 3108. The effectivity 
listing of Revision 2 of the alert service bulletin does not include 
airplanes on which Teflon sleeving was installed during production 
(i.e., L/N 3109 and subsequent). However, as explained above, this 
proposed AD would require repetitive inspections of the fueling float 
switch wiring in the center fuel tank to detect discrepancies; 
replacement of the float switch and wiring, if necessary; and 
replacement of the double Teflon sleeving with new sleeving. Therefore, 
airplanes on which Teflon sleeving was installed during production 
would not be exempt from these repetitive actions.
    Operators also should note that, although the alert service 
bulletin allows deactivation of the center tank float switch for up to 
18 months in lieu of installation of partial double Teflon sleeving, 
this proposed AD would only allow deactivation of the fueling float 
switch in the event that exposed copper conductor is detected during 
the inspection specified in paragraph (h) of this AD, and would require 
replacement of the float switch and wiring, and installation of double 
Teflon sleeving, within 90 days after deactivation. This proposed AD 
also would no longer allow deactivation in lieu of the inspection and 
sleeving installation specified in paragraph (b) of this AD. For those 
airplanes on which the float switch was deactivated prior to the 
effective date of this AD in accordance with paragraph (c) of AD 99-05-
12, this proposed AD would require reactivation of the float switch; 
inspections of the fueling float switch wiring in the center fuel tank 
to detect discrepancies; replacement of the float switch and wiring, if 
necessary; and installation of double Teflon sleeving; within 12 months 
after the effective date of this AD.

Explanation of Change Made to Restatement of AD 99-05-12

    Paragraph (a) of this proposed rule, which is restated from AD 99-
05-12, states that the paragraph applies to airplanes having line 
numbers 1 through 3108 inclusive. Paragraph (a) of AD 99-05-12 did not 
specify that the paragraph applied to particular line numbers. The FAA 
has determined that airplanes having line numbers 3109 and subsequent 
have double Teflon sleeving installed over the wiring of the float 
switch during production. Therefore, it is not necessary for operators 
of these airplanes to accomplish paragraph (a). [The appropriate 
inspection procedures for airplanes having line numbers 3109 and 
subsequent are specified in paragraph (k) of this AD.]
    Also, the FAA has clarified the inspection requirement contained in 
AD 99-05-12. Whereas the AD specified a visual inspection, the FAA has 
revised the restatement of requirements in this proposed AD to clarify 
that its intent is to require a detailed visual inspection. 
Additionally, a note has been added to the proposed AD to define that 
inspection.

Cost Impact

    There are approximately 2,870 Model 737-100, -200, -300, -400, and 
-500 series airplanes of the affected design in the worldwide fleet. 
The FAA estimates that 1,121 airplanes of U.S. registry would be 
affected by this proposed AD.
    The removal and inspection of the fueling float switch in the 
center fuel tank and installation of double Teflon sleeving that is 
provided as an option for compliance with AD 99-05-12, and would be 
required as a repetitive inspection in this proposed AD, takes 
approximately 18 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Required parts cost approximately $30 
per airplane. Based on these figures, the cost impact of the removal 
and inspection of the float switch and installation of double Teflon 
sleeving on U.S. operators is estimated to be $1,244,310, or $1,110 per 
airplane, per inspection cycle.
    For operators required to accomplish the inspection of the float 
switch at the exit of the conduit on the front spar and installation of 
partial double Teflon sleeving that are proposed in this AD action, it 
would take approximately 3 work hours per airplane to accomplish, at an 
average labor rate of $60 per work hour. Required parts would cost 
approximately $5 per airplane. Based on these figures, the cost impact 
of the proposed inspection of the float switch at the exit of the 
conduit on the front spar and installation of partial double Teflon 
sleeving of this AD on U.S. operators is estimated to be $185 per 
airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the current or proposed 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have 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 proposal would not have federalism implications 
under Executive Order 13132.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation

[[Page 24892]]

Administration proposes to amend 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 39-11060 (64 FR 
11533, March 9, 1999), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 99-NM-78-AD. Supersedes AD 99-05-12, Amendment 39-
11060.

    Applicability: Model 737-100, -200, -300, -400, and -500 series 
airplanes, on which the center wing tanks are activated; excluding 
those airplanes equipped with center wing tank volumetric topoff 
systems, or alternate current (AC) powered center tank float 
switches; 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 (l)(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 detect and correct chafing of the direct current powered 
float switch wiring insulation in the center fuel tank and the 
resultant arcing from the wiring to the in-tank conduit, which could 
present an ignition source inside the fuel tank and result in a 
consequent fire or explosion, accomplish the following:

Restatement of Requirements of AD 99-05-12

Compliance Time for Initial Inspection

    (a) For airplanes having line numbers (L/N) 1 through 3108 
inclusive: Prior to the accumulation of 30,000 total flight hours, 
or within 30 days after March 18, 1999 (the effective date of AD 99-
05-12), whichever occurs later, accomplish the requirements of 
paragraph (b) or (c) of this AD. For airplanes on which the 
requirements of this paragraph are accomplished after the effective 
date of this AD: Except as provided in paragraph (h)(2)(i) of this 
AD, only the requirements of paragraph (b) of this AD may be 
accomplished.

Initial Inspection: Procedures

    (b) Remove the fueling float switch and wiring from the center 
fuel tank and perform a detailed visual inspection of the float 
switch wiring to detect discrepancies (i.e., evidence of electrical 
arcing, exposure of the copper conductor, presence or scent of fuel 
on the electrical wires, or worn insulation), in accordance with 
Part 1 of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-28A1132, dated December 2, 1998; Revision 1, dated 
January 15, 1999; or Revision 2, dated June 17, 1999. After the 
effective date of this AD, only Revision 2 may be used. Pay 
particular attention to the wire bundle where it passes through the 
wing pylon vapor seals and under the wire bundle clamps.

    Note 2: 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.''

Initial Inspection: Follow-On Actions

    (1) If no discrepancy is detected, prior to further flight, 
accomplish either paragraph (b)(1)(i) or (b)(1)(ii) of this AD.
    (i) Measure the resistance between the wires and the float 
switch housing, in accordance with the alert service bulletin.
    (A) If the resistance is less than 200 megohms, prior to further 
flight, replace the float switch and wiring with a new float switch 
and wiring, and install double Teflon sleeving over the wiring of 
the float switch, in accordance with the alert service bulletin. For 
airplanes on which the actions required by this paragraph were 
accomplished prior to the effective date of this AD in accordance 
with AD 99-05-12, amendment 39-11060: If the replacement float 
switch and wiring are not available, prior to further flight, 
accomplish the requirements specified in paragraphs (c) and (d) of 
this AD.
    (B) If the resistance is greater than or equal to 200 megohms, 
prior to further flight, blow dirt out of the conduit, install 
double Teflon sleeving over the wiring of the float switch, and 
reinstall the existing float switch, in accordance with the alert 
service bulletin.
    (ii) Replace the float switch and wiring with a new float switch 
and wiring, and install double Teflon sleeving over the wiring of 
the float switch, in accordance with the alert service bulletin. For 
airplanes on which the actions required by this paragraph were 
accomplished prior to the effective date of this AD in accordance 
with AD 99-05-12, amendment 39-11060: If the replacement float 
switch and wiring are not available, prior to further flight, 
accomplish the requirements specified in paragraphs (c) and (d) of 
this AD.
    (2) If any worn insulation is detected, and if no copper 
conductor is exposed, and if no evidence of arcing is detected; 
accomplish the requirements specified in either paragraph (b)(1)(i) 
or (b)(1)(ii) of this AD. After the effective date of this AD, only 
the requirements of paragraph (b)(1)(ii) may be accomplished.
    (3) If any electrical arcing or exposed copper conductor is 
detected, prior to further flight, accomplish either paragraph 
(b)(3)(i) or (b)(3)(ii) of this AD.
    (i) Replace any section of the electrical conduit where the 
arcing occurred with a new section, in accordance with the alert 
service bulletin, and accomplish the requirements specified in 
paragraph (b)(1)(ii) of this AD.
    (ii) Perform a detailed visual inspection to detect fuel leaks 
of the electrical conduit, in accordance with the alert service 
bulletin.
    (A) If no fuel leak is detected, prior to further flight, 
accomplish the requirements specified in paragraph (b)(1)(ii) of 
this AD. For airplanes on which the inspection required by paragraph 
(b)(3)(ii) was accomplished PRIOR to the effective date of this AD 
in accordance with AD 99-05-12, amendment 39-11060: Repeat the 
inspection required by paragraph (b)(3)(ii) of this AD thereafter at 
intervals not to exceed 1,500 flight hours, until the replacement 
required by paragraph (b)(3)(ii)(B) or (f) of this AD is 
accomplished. For airplanes on which the inspection required by 
paragraph (b)(3)(ii) is accomplished AFTER the effective date of 
this AD: Within 1,500 flight hours or 6 months after accomplishment 
of the inspection in accordance with paragraph (b)(3)(ii) of this 
AD, whichever occurs first, replace the electrical conduit with new 
conduit in accordance with Boeing Alert Service Bulletin 737-
28A1132, Revision 2. The existing float switch, wiring, and double 
Teflon sleeving may be reinstalled after replacement of the conduit.
    (B) If any fuel leak is detected, prior to further flight, 
replace any section of the electrical conduit where the leak is with 
a new section, in accordance with the alert service bulletin. Prior 
to further flight after accomplishment of the replacement, 
accomplish the requirements specified in paragraph (b)(1)(ii) of 
this AD. Accomplishment of electrical conduit replacement 
constitutes terminating action for the repetitive inspection 
requirements of paragraph (b)(3)(ii)(A) of this AD.
    (4) If any presence or scent of fuel on the electrical wires is 
detected, prior to further flight, locate the source of the leak and 
replace the damaged conduit with a new conduit, in accordance with 
the alert service bulletin; and accomplish the requirements 
specified in either paragraph (b)(1)(i) or (b)(1)(ii) of this AD, 
unless accomplished previously in accordance with paragraph (b)(1), 
(b)(2), or (b)(3) of this AD.

Deactivation of Float Switch

    (c) Accomplish the requirements specified in either paragraph 
(c)(1) or (c)(2) of this AD, in accordance with Part 2 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
28A1132, dated December 2, 1998; Revision 1, dated January 15, 1999; 
or Revision 2, dated June 17, 1999. Except as provided by paragraph 
(h)(2)(i) of this AD, after the effective date of this AD, the 
requirements of this paragraph may no longer be accomplished.
    (1) Deactivate the center tank float switch (i.e., cut the two 
wires for the float switch at the splices on the front spar and cap 
and

[[Page 24893]]

stow the four wire ends), paint a Caution that shows a conservative 
maximum fuel capacity for the center tank on the underside of the 
right-hand wing near the fueling station door, and install an INOP 
placard on the fueling panel.
    (2) Deactivate the center tank float switch (i.e., cut, stow, 
and splice the two wires for the float switch at the splices on the 
front spar), and paint a Caution that shows a conservative maximum 
fuel capacity for the center tank on the underside of the right-hand 
wing near the fueling station door.

Deactivation of Float Switch: Additional Requirements

    (d) For airplanes on which the requirements specified in 
paragraph (c) of this AD have been accomplished: Accomplish the 
requirements specified in paragraphs (d)(1), (d)(2), and (d)(3) of 
this AD. Except as provided by paragraph (h)(2)(i) of this AD, after 
12 months after the effective date of this AD, the requirements of 
this paragraph may no longer be accomplished.
    (1) Operators must ensure that airplane fueling crews are 
properly trained in accordance with the procedures specified in 
Boeing Telex M-7200-98-04486, dated December 1, 1998, or procedures 
approved by the FAA. This one-time training must be accomplished 
prior to utilizing the procedures specified in paragraph (d)(3) of 
this AD.
    (2) Prior to fueling the airplane, perform a check to verify 
that the fueling panel center tank quantity indicator is operative. 
Repeat this check thereafter prior to fueling the airplane. If the 
fueling panel center tank quantity indicator is not operative, prior 
to further flight, replace the fueling panel center tank quantity 
indicator with a serviceable part.
    (3) One of the two manual fueling procedures for the center fuel 
tank must be used for each fueling occurrence, in accordance with 
Boeing Telex M-7200-98-04486, dated December 1, 1998, or a method 
approved by the FAA.

    Note 3: For the purposes of this AD, the term ``the FAA,'' is 
defined in paragraph (d) of this AD as ``the cognizant Principal 
Maintenance Inspector (PMI).''


    Note 4: Where there are differences between Boeing Alert Service 
Bulletin 737-28A1132 and this AD, the AD prevails.

Deactivation of Float Switch: Dispatch

    (e) Dispatch with the center fuel tank float switch deactivated, 
in accordance with Boeing Alert Service Bulletin 737-28A1132, dated 
December 2, 1998; Revision 1, dated January 15, 1999; or Revision 2, 
dated June 17, 1999; is allowed until replacement float switches and 
wiring are available for installation. Where there are differences 
between the Master Minimum Equipment List (MMEL) and the AD, the AD 
prevails. Except as provided by paragraph (h)(2)(i) of this AD, 
after 12 months after the effective date of this AD, the 
requirements of this paragraph may no longer be accomplished.

New Requirements of This AD

Replacement of Conduit

    (f) For airplanes having L/N 1 through 3108 inclusive, on which 
the inspection required by paragraph (b)(3)(ii) of this AD has been 
accomplished prior to the effective date of this AD in accordance 
with AD 99-05-12, amendment 39-11060, and on which replacement of 
the conduit specified in paragraph (b)(3)(ii)(B) has NOT been 
accomplished: Within 1,500 flight hours or 6 months after the 
effective date of this AD, whichever occurs first, replace the 
electrical conduit with new conduit in accordance with Boeing Alert 
Service Bulletin 737-28A1132, Revision 2, dated June 17, 1999. 
Following replacement of the conduit, the existing float switch, 
wiring, and double Teflon sleeving may be reinstalled. Such 
replacement of the conduit constitutes terminating action for the 
repetitive inspection requirements of paragraph (b)(3)(ii)(A) of 
this AD.

Initial Inspection: Airplanes With Deactivated Float Switch

    (g) For airplanes having line numbers 1 through 3108 inclusive 
on which paragraphs (c) and (d) have been accomplished prior to the 
effective date of this AD: Within 12 months after the effective date 
of this AD, reactivate the center tank float switch in accordance 
with Boeing Alert Service Bulletin 737-28A1132, Revision 2, dated 
June 17, 1999; and accomplish the requirements of paragraph (b) of 
this AD. Following accomplishment of paragraph (b) of this AD, 
``Cautions'' painted and placards installed in accordance with 
paragraph (c) of this AD may be removed from the airplane.

Initial Inspection and Follow-On Actions

    (h) For airplanes having line numbers 1 through 3108 inclusive 
on which the actions required by paragraph (b) or (c) of this AD 
have NOT been accomplished prior to the effective date of this AD: 
Prior to the accumulation of 10,000 total flight hours or within 90 
days after the effective date of this AD, whichever occurs later, 
except as provided by paragraph (i) of this AD, perform a detailed 
visual inspection to detect exposure of the copper conductor of the 
float switch wiring at the exit of the conduit on the front spar in 
accordance with Part 3 of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-28A1132, Revision 2, dated June 17, 1999.
    (1) If no exposed copper conductor is detected, prior to further 
flight, install partial double Teflon sleeving over the wiring of 
the float switch in accordance with the alert service bulletin, and, 
prior to the accumulation of 30,000 total flight hours, accomplish 
paragraph (b) of this AD.
    (2) If any exposed copper conductor is detected, accomplish the 
requirements of paragraphs (h)(2)(i), (h)(2)(ii), and (h)(2)(iii) of 
this AD.
    (i) Prior to further flight, accomplish the deactivation 
requirements specified in paragraphs (c) and (d) of this AD. And,
    (ii) Within 90 days after deactivation, remove the float switch 
and wiring and replace with a new float switch and wiring, and 
install double Teflon sleeving over the wiring of the float switch, 
in accordance with Part 1 of the Accomplishment Instructions of the 
alert service bulletin, and reactivate the switch. Accomplishment of 
the requirements of this paragraph constitutes terminating action 
for the inspection required by paragraph (b) of this AD. And,
    (iii) Following accomplishment of paragraph (h)(2)(ii) of this 
AD, ``Cautions'' painted and placards installed in accordance with 
paragraph (c) of this AD may be removed from the airplane.

Exception to Requirements of Paragraph (h)

    (i) Airplanes on which the inspection required by paragraph (b) 
of this AD is accomplished within 90 days after the effective date 
of this AD are not required to be inspected in accordance with 
paragraph (h) of this AD.

Repetitive Inspections: Compliance Times

    (j) For all airplanes: Accomplish the inspection specified in 
paragraph (k) of this AD at the time specified in paragraph (j)(1), 
(j)(2), or (j)(3), as applicable, and repeat the inspection 
thereafter at intervals not to exceed 30,000 flight hours.
    (1) For airplanes having line numbers 1 through 3108 inclusive 
on which a new float switch and wiring was installed in accordance 
with paragraph (b)(1)(ii) or (h)(2)(ii) of this AD, OR on which no 
discrepancy was found during the inspection specified in paragraph 
(b) of this AD and the existing float switch and wiring were 
reinstalled: Inspect within 30,000 flight hours after installation 
of double Teflon sleeving.
    (2) For airplanes having line numbers 1 through 3108 inclusive 
on which worn insulation of the existing float switch wiring was 
found during the inspection specified in paragraph (b) of this AD 
and the existing float switch and wiring were reinstalled: Inspect 
within 15,000 flight hours after installation of the double Teflon 
sleeving.
    (3) For airplanes having line numbers 3109 and subsequent: 
Inspect prior to the accumulation of 30,000 total flight hours.

Repetitive Inspections: Procedures

    (k) Remove the fueling float switch and wiring from the center 
fuel tank and perform a detailed visual inspection of the float 
switch wiring to detect discrepancies (i.e., evidence of electrical 
arcing, exposure of the copper conductor, presence or scent of fuel 
on the electrical wires, or worn insulation), in accordance with 
Part 1 of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-28A1132, Revision 2, dated June 17, 1999. Pay 
particular attention to the wire bundle where it passes through the 
wing pylon vapor seals and under the wire bundle clamps.

Repetitive Inspections: Follow-On Actions

    (1) If no discrepancy is detected, prior to further flight, 
accomplish either paragraph (k)(1)(i) or (k)(1)(ii) of this AD.
    (i) Measure the resistance between the wires and the float 
switch housing, in accordance with the alert service bulletin.
    (A) If the resistance is less than 200 megohms, prior to further 
flight, replace the float switch and wiring with a new float

[[Page 24894]]

switch and wiring, and replace the double Teflon sleeving over the 
wiring of the float switch with new sleeving, in accordance with the 
alert service bulletin.
    (B) If the resistance is greater than or equal to 200 megohms, 
prior to further flight, blow dirt out of the conduit, replace the 
double Teflon sleeving over the wiring of the float switch with new 
sleeving, and reinstall the existing float switch, in accordance 
with the alert service bulletin.
    (ii) Replace the float switch and wiring with a new float switch 
and wiring, and replace the double Teflon sleeving over the wiring 
of the float switch with new sleeving, in accordance with the alert 
service bulletin.
    (2) If any worn insulation is detected, and if no copper 
conductor is exposed, and if no evidence of arcing is detected: 
Prior to further flight, accomplish the requirements specified in 
paragraph (k)(1)(ii) of this AD.
    (3) If any electrical arcing or exposed copper conductor is 
detected, prior to further flight, accomplish either paragraph 
(k)(3)(i) or (k)(3)(ii) of this AD.
    (i) Replace any section of the electrical conduit where the 
arcing occurred with a new section, in accordance with the alert 
service bulletin, and accomplish the requirements specified in 
paragraph (k)(1)(ii) of this AD.
    (ii) Perform a detailed visual inspection to detect fuel leaks 
of the electrical conduit, in accordance with the alert service 
bulletin.
    (A) If no fuel leak is detected, prior to further flight, 
accomplish the requirements specified in paragraph (k)(1)(ii) of 
this AD. Within 1,500 flight hours or 6 months after accomplishment 
of the inspection specified in paragraph (k)(3)(ii), whichever 
occurs first, replace the electrical conduit with new conduit, in 
accordance with Boeing Alert Service Bulletin 737-28A1132, Revision 
2, dated June 17, 1999. The existing float switch, wiring, and 
double Teflon sleeving may be reinstalled after replacement of the 
conduit.
    (B) If any fuel leak is detected, prior to further flight, 
replace any section of the electrical conduit where the leak is with 
a new section, in accordance with the alert service bulletin. Prior 
to further flight after accomplishment of the replacement, 
accomplish the requirements specified in paragraph (k)(1)(ii) of 
this AD.
    (4) If any presence or scent of fuel on the electrical wires is 
detected, prior to further flight, locate the source of the leak and 
replace the damaged conduit with a new conduit, in accordance with 
the alert service bulletin; and accomplish the requirements 
specified in either paragraph (k)(1)(i) or (k)(1)(ii) of this AD, 
unless accomplished previously in accordance with paragraph (k)(1), 
(k)(2), or (k)(3) of this AD.

Alternative Methods of Compliance

    (l)(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, 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 5: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Manager, Seattle ACO.

    (2) Alternative methods of compliance, approved previously in 
accordance with AD 99-05-12, amendment 39-11060, are approved as 
alternative methods of compliance with this AD.

Special Flight Permits

    (m) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on April 24, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-10670 Filed 4-27-00; 8:45 am]
BILLING CODE 4910-13-P