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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. 99-NM-78-AD] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Notice of proposed rulemaking (NPRM). 

# 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                           ( print 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                           ( print 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                           ( print 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. 

§ 39.13 

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                                       ( print 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                                       ( print 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