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###### Department of Transportation

###### Federal Aviation Administration

          - 14 CFR Part 39
          - [Docket No. 98-NM-283-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 747-100 series airplanes, that currently requires repetitive inspections to detect cracking of the outer chord of the body station (BS) 1480 upper and lower bulkhead and longeron splice fitting; repair, if necessary; and modification of the skin splice plate, the outer chord splice fitting, and the stringer interface of the lower bulkhead, if necessary. This action would revise the applicability of the existing AD to add additional airplanes, require accomplishment of previously optional inspections and clarify those inspections, extend certain compliance times, and require additional work in certain areas. This proposal is prompted by reports that fatigue cracking has been found in the outer chord of the BS 1480 bulkhead at the overwing longeron splice on airplanes not subject to the existing AD. The actions specified in this proposed AD are intended to detect and correct fatigue cracking of the outer chord of the BS 1480 upper and lower bulkhead and longeron splice fitting, which could result in reduced structural integrity of the fuselage and the inability to carry limit load.

# DATES:

Comments must be received by December 26, 2000.

# ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 98-NM-283-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. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 98-NM-283-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text. 

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:

Rick Kawaguchi, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-1153; 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 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 98-NM-283-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. 98-NM-283-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

## Discussion

On September 15, 1998, the FAA issued AD 98-20-25, amendment 39-10791 (63 FR 50508, September 22, 1998), applicable to certain Boeing Model 747-100 series airplanes, to require repetitive inspections to detect cracking of the outer chord of the body station (BS) 1480 upper and lower bulkhead and longeron splice fitting, and repair, if necessary. Alternatively, that action requires other repetitive inspections to detect cracking of the BS 1480 upper and lower bulkhead, bulkhead outer chord, web, skin, splice components, and lower bulkhead/stringer interface; and modification of the skin splice plate, the outer chord splice fitting, and the stringer interface of the lower bulkhead, if necessary. That action was prompted by a report indicating that fatigue cracking was found in the outer chord of the BS 1480 bulkhead at the overwing longeron splice, and that the longeron splice fitting was completely severed. The requirements of that AD are intended to detect and correct such fatigue cracking, which could result in reduced structural integrity of the fuselage and the inability to carry limit load.

## Actions Since Issuance of Previous Rule

                    Since the issuance of AD 98-20-25, the FAA has determined that the detailed visual inspections described in paragraph (a)(1) of that AD as one alternative for compliance with that AD may not be adequate to ensure that any fatigue cracking will be detected in a timely manner. Therefore, this action proposes to require detailed visual, ultrasonic, and open-hole high                           ( print page 67312)                        frequency eddy current (HFEC) inspections which were referenced in paragraph (a)(2) of AD 98-20-25 as another alternative for compliance with that AD.                

Paragraph (a)(2) of AD 98-20-25 specifies repetitive inspections of both the upper and lower bulkhead, bulkhead outer chord, web, skin, splice components, and lower bulkhead/stringer interface. The initial inspection is required prior to the accumulation of 10,000 total flight cycles, or within 45 days after October 7, 1998 (the effective date of AD 98-20-25), whichever occurs later. Since the issuance of AD 98-20-25, the FAA has determined that it is appropriate to extend the inspection threshold for the inspection of the bulkhead outer chord, skin, and lower bulkhead/stringer interface. The FAA finds that a repetitive inspection threshold of 20,000 total flight cycles for inspection of the lower bulkhead/stringer interface is adequate to ensure the continued safety of the affected airplanes.

## Explanation of New Relevant Service Information

Since the issuance of AD 98-20-25, the FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000. (AD 98-20-25 references the original issue of that service bulletin, dated July 31, 1997, as an appropriate source of service information.) Like the original issue of the service bulletin, Revision 1 describes procedures for repetitive inspections to detect cracking of the BS 1480 upper and lower bulkhead, bulkhead outer chord, web, skin, splice components, and lower bulkhead/stringer interface; repair, if necessary; and, as part of a certain inspection plan, procedures for modification of the skin splice plate, outer chord splice fitting, and the stringer interface of the lower bulkhead. Revision 1 of the service bulletin expands the effectivity listing specified in the original issue of the service bulletin to include Model 747-400 series airplanes up to line number 1254, includes new instructions for inspection and modification at stringer S-34 in the lower bulkhead/stringer interface area, revises inspection procedures for airplanes with a reinforcement strap installed on the bulkhead outer chord, and references new repair instructions.

## Explanation of Applicability

In the preamble to AD 98-20-25, the FAA specified that the actions required by that AD were considered “interim action” and that the FAA was considering further rulemaking action to supersede that AD to require inspections and modification of the upper and lower bulkhead and overwing longeron at BS 1480 for all Boeing Model 747-100, -200, and -300 series airplanes. The FAA has determined that further rulemaking is indeed necessary; this proposed AD follows from that determination.

In addition, as specified previously, Revision 1 of the service bulletin adds Boeing Model 747-400 series airplanes up to line number 1254 to the effectivity listing. The area of the outer chord of the BS 1480 upper bulkhead on Model 747-400 series airplanes up to and including line number 1096 is essentially the same as that on other Boeing Model 747 series airplanes. Therefore, this proposed AD would require the same inspections of the upper bulkhead for Boeing Model 747-400 series airplanes up to and including line number 1096 as it would require for other Boeing Model 747 series airplanes. Improvements were made during production on the upper bulkhead area on Model 747-400 series airplanes having line numbers 1097 through 1254 inclusive; however, the lower bulkhead area on those airplanes is also essentially the same as on other Model 747 series airplanes. Therefore, this proposed AD also would require the same inspections of the lower bulkhead for Boeing Model 747-400 series airplanes up to and including line number 1254 as it would require for other Boeing Model 747 series airplanes. Improvements were made during production on the lower bulkhead area on Model 747-400 series airplanes having line number 1255 and above, so those airplanes are not subject to this proposed AD.

## 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 98-20-25 to continue to require repetitive inspections to detect cracking of the outer chord of the BS 1480 upper and lower bulkhead and longeron splice fitting; repair, if necessary; and modification of the skin splice plate, the outer chord splice fitting, and the stringer interface of the lower bulkhead, if necessary. This proposed AD would require accomplishment of the actions specified in Revision 1 of the service bulletin described previously, except as discussed below.

## Differences Between Service Bulletin and Proposed AD 

Operators should note that, although the service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, this proposed AD would require the repair of those conditions to be accomplished in accordance with a method approved by the FAA, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings.

## Explanation of Changes Made to AD 98-20-25

Paragraph (a)(2) of this AD is essentially a restatement of paragraph (a)(2) of AD 98-20-25; however, the FAA has revised paragraph (a)(2) of this proposed AD to more accurately state the inspections included in that paragraph. The inspections specified in paragraph (a)(2) of this proposed AD are the same as those specified in paragraph (d) of this proposed AD. Thus, an operator who has inspected an airplane in accordance with paragraph (a)(2) of this AD is not required to inspect in accordance with paragraphs (c) and (d) of this AD.

In addition, the FAA has added a note to the proposed rule to clarify the definition of a detailed visual inspection.

## Cost Impact

There are approximately 1,128 airplanes of the affected design in the worldwide fleet. The FAA estimates that 259 airplanes of U.S. registry would be affected by this proposed AD.

AD 98-20-25 applies to airplanes listed in Groups 1 through 3 of the service bulletin. The detailed visual inspection that is currently offered as one alternative for compliance with AD 98-20-25 takes approximately 16 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required actions on U.S. operators is estimated to be $960 per airplane, per inspection cycle.

                    For airplanes listed in Groups 1 through 3 in the service bulletin (34 U.S.-registered airplanes), the proposed detailed visual, ultrasonic, and open hole HFEC inspections of the upper bulkhead area (which AD 98-20-25 references as an alternative inspection program) would take approximately 32 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost                           ( print page 67313)                        impact of these proposed inspections on U.S. operators is estimated to be $65,280, or $1,920 per airplane, per inspection cycle.                

For airplanes listed in Groups 4 through 22 in the service bulletin (191 U.S.-registered airplanes), the proposed detailed visual, ultrasonic, and open hole HFEC inspections of the upper bulkhead area would take approximately 22 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these inspections on U.S. operators is estimated to be $252,120, or $1,320 per airplane, per inspection cycle.

For all airplanes listed in the applicability of this proposed AD (259 U.S.-registered airplanes), the proposed detailed visual, ultrasonic, and open hole HFEC inspections of the lower bulkhead/stringer interface area would take approximately 30 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these proposed inspections on U.S. operators is estimated to be $466,200, or $1,800 per airplane, per inspection cycle.

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. 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 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 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 39-10791 (63 FR 50508, September 22, 1998), and by adding a new airworthiness directive (AD), to read as follows:

**Boeing:**                                Docket 98-NM-283-AD. Supersedes AD 98-20-25, Amendment 39-10791.                            

*Applicability:*                                Model 747 series airplanes, line numbers (L/N) 1 through 1254 inclusive, 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 (j)(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 fatigue cracking in the outer chord of the body station (BS) 1480 bulkhead at the overwing longeron splice, which could result in reduced structural integrity of the fuselage and the inability to carry limit load, accomplish the following:

## Restatement of Requirements of AD 98-20-25:

## Repetitive Inspections and Repair

(a) For Model 747-100 series airplanes, ­L/N 1 through 87 inclusive: Prior to the accumulation of 10,000 total flight cycles, or within 45 days after October 7, 1998 (the effective date of AD 98-20-25, amendment 39-10791), whichever occurs later, accomplish either paragraph (a)(1) or (a)(2) of this AD.

(1) Perform a detailed visual inspection to detect cracking of the longeron splice fitting at BS 1480, the forward side of the outer chord of the BS 1480 bulkhead at the longeron splice fitting attachment bolts, and the aft side of the outer chord of the BS 1480 bulkhead within two inches above the outer chord splice fitting, on both the left and right sides of the airplane.

# Note 2:

Figure 5 of Boeing Alert Service Bulletin 747-53A2390, dated July 31, 1997, provides an exploded view of the structural components of the splice area for the purpose of parts identification. (However, paragraph (a)(1) of this AD does not require the inspection described in Figure 5.)

# Note 3:

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.”

(i) If any cracking is detected, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative (DER) who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the approval letter must specifically reference this AD.

(ii) Repeat the detailed visual inspection thereafter at intervals not to exceed 250 flight cycles, until the initial inspection required by paragraph (a)(2) or (d) of this AD is accomplished.

(2) Perform detailed visual, ultrasonic, and open hole high frequency eddy current (HFEC) inspections to detect cracking of the upper and lower bulkhead, bulkhead outer chord, web, skin, splice components, and lower bulkhead/stringer interface, in accordance with Figures 5 and 8 of Boeing Alert Service Bulletin 747-53A2390, dated July 31, 1997. Additionally, for airplanes on which the inspection in “Plan B” of the service bulletin is accomplished, modify the skin splice plate, the outer chord splice fitting, and the stringer interface of the lower bulkhead, in accordance with the Accomplishment Instructions of the service bulletin. Accomplishment of these actions constitutes terminating action for the repetitive inspection requirements of paragraph (a)(1) of this AD.

(i) If any cracking is detected, prior to further flight, repair in accordance with the service bulletin, except as provided by paragraph (b) of this AD.

                                (ii) Repeat the inspections thereafter in accordance with the flight safety inspection                                       ( print page 67314)                                    program specified in Figures 1 and 3 of the service bulletin.                            

(b) Where the service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, repair in accordance with a method approved by the Manager, Seattle ACO; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company DER who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the approval letter must specifically reference this AD.

## New Requirements of This AD

## Groups 1 Through 3: Splice Area Work (Compliance Times)

# Note 4:

Airplanes inspected in accordance with paragraph (a)(2) of this AD are not required to be inspected in accordance with paragraphs (c) and (d) of this AD.

(c) For airplanes listed in Groups 1 through 3 in Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000; on which the requirements of paragraph (a)(2) of this AD have NOT been accomplished prior to the effective date of this AD: Accomplish paragraph (d) of this AD at the applicable time specified in paragraph (c)(1), (c)(2), or (c)(3) of this AD.

(1) For airplanes on which the inspection specified in Boeing Service Bulletin 747-53-2333 has not been accomplished: Inspect prior to the accumulation of 10,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later.

(2) For airplanes on which the inspection specified in Boeing Service Bulletin 747-53-2333 has been accomplished, but the full modification specified in that service bulletin has not been accomplished: Inspect at the later of the times specified in paragraphs (c)(2)(i) and (c)(2)(ii) of this AD.

(i) Prior to the accumulation of 10,000 total flight cycles, or within 2,000 flight cycles after accomplishment of the last inspection in accordance with Boeing Service Bulletin 747-53-2333, whichever occurs first.

(ii) Within 1,000 flight cycles after the effective date of this AD.

(3) For airplanes on which the full modification specified in Boeing Service Bulletin 747-53-2333 has been accomplished: Inspect at the later of the times specified in paragraphs (c)(3)(i) and (c)(3)(ii) of this AD.

(i) Prior to the accumulation of 16,000 total flight cycles, or within 6,000 flight cycles after accomplishment of the full modification in accordance with Boeing Service Bulletin 747-53-2333, whichever occurs first.

(ii) Within 1,000 flight cycles after the effective date of this AD.

## Groups 1 Through 3: Splice Area Work (Inspections)

(d) For airplanes listed in Groups 1 through 3 in Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000; on which the requirements of paragraph (a)(2) of this AD have NOT been accomplished prior to the effective date of this AD: At the applicable time specified in paragraph (c) of this AD, accomplish paragraph (d)(1) or (d)(2) of this AD. Accomplishment of the requirements of this paragraph constitutes terminating action for the repetitive inspection requirements specified in paragraph (a)(1) of this AD, or, for the upper bulkhead splice area ONLY, for the inspection requirements specified in paragraph (a)(2) of this AD.

(1) Plan “A”: Perform detailed visual, ultrasonic, and HFEC inspections to detect cracking of the splice area, in accordance with Plan “A” and Figure 5, as defined in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000. Repeat the inspections thereafter in accordance with the flight safety inspection program as specified under Plan “A” and Figure 1 of the service bulletin.

(2) Plan “B”: Modify the skin splice plate and outer chord splice fitting in accordance with Plan “B,” as defined in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000. Perform HFEC inspections and modification, then accomplish repeat open hole HFEC inspections, in accordance with the flight safety inspection program, as specified under Plan “B” and Figure 1 of the service bulletin. Accomplishment of the modification and inspections in accordance with this paragraph terminates the repetitive inspection requirements in paragraph (d)(1) of this AD.

## Groups 4 Through 22: Splice Area Work (Compliance Time and Inspections)

(e) For airplanes listed in Groups 4 though 22 in Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000: Prior to the accumulation of 16,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later, perform detailed visual and ultrasonic inspections to detect cracking of the bulkhead forward flange in accordance with Figure 7 of the service bulletin, and accomplish the requirements of either paragraph (e)(1) or (e)(2) of this AD.

(1) Plan “A”: Perform open hole HFEC inspections to detect cracking of the splice area, in accordance with Plan “A” and Figures 6 and 7, as defined in the Accomplishment Instructions of the service bulletin. Repeat the inspections thereafter in accordance with the flight safety inspection program as specified under Plan “A” and in Figure 2 of the service bulletin.

(2) Plan “B”: Perform open hole HFEC inspections and modification of the upper bulkhead, bulkhead outer chord, web, skin, and splice components; in accordance with Plan “B,” as defined in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000. Thereafter, repeat the open hole HFEC inspections in accordance with the flight safety inspection program as specified under Plan “B” and Figure 2 of the service bulletin. Accomplishment of the modification and inspections in accordance with this paragraph terminates the repetitive inspection requirements specified in paragraph (e)(1) of this AD.

## All Airplanes: Lower Bulkhead/Stringer Interface Work (Compliance Times)

(f) For all airplanes (L/N 1 through 1254 inclusive): At the applicable time specified in paragraph (f)(1) or (f)(2) of this AD, accomplish paragraph (g) of this AD.

(1) For airplanes on which an inspection of the lower bulkhead has NOT been accomplished prior to the effective date of this AD in accordance with paragraph (a)(2) of this AD: Inspect prior to the accumulation of 20,000 total flight cycles, or within 1,000 flight cycles after the effective date of this AD, whichever occurs later.

(2) For airplanes on which an inspection of the lower bulkhead HAS been accomplished prior to the effective date of this AD in accordance with paragraph (a)(2) of this AD: Inspect prior to the accumulation of 20,000 total flight cycles, or at the time of the next scheduled inspection of the lower bulkhead in accordance with paragraph (a)(2) of this AD, whichever occurs later.

## All Airplanes: Lower Bulkhead/Stringer Interface Work (Inspections)

(g) For all airplanes (L/N 1 through 1254 inclusive): At the applicable time specified in paragraph (f) of this AD, accomplish paragraph (g)(1) or (g)(2) of this AD. For airplanes having L/N 1 through 87 inclusive, accomplishment of the requirements of this paragraph constitutes terminating action for the inspection requirements specified in paragraph (a)(2) of this AD for the lower bulkhead/stringer interface area ONLY.

(1) Plan “A”: Perform detailed visual and either ultrasonic or open hole HFEC inspections, as applicable, to detect cracking of the lower bulkhead/stringer interface area, in accordance with Plan “A” and Figure 8, as defined in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000. Repeat the inspections thereafter in accordance with the flight safety program as specified under Plan “A” and Figure 3 or Figure 8 of the service bulletin.

                                (2) Plan “B”: Except as provided by paragraph (h) of this AD, perform open hole HFEC inspections and modification of the lower bulkhead/stringer interface area, in accordance with Plan “B” and Figure 19, as defined in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000. Thereafter, repeat the detailed visual and either ultrasonic or open hole HFEC inspections, as applicable, in accordance with the flight safety inspection program as specified under Plan “B” and Figures 3 and 8 of the service bulletin. Accomplishment of the modification and inspections in accordance with this paragraph terminates the repetitive inspection requirements specified in paragraph (g)(1) of this AD.                                      ( print page 67315)    

## Airplanes Modified With Original Service Bulletin: Post-Modification Work

(h) For any airplane (L/N 1 through 1254 inclusive) on which the modification specified in paragraph (g)(2) was accomplished prior to the effective date of this AD in accordance with the original issue of Boeing Alert Service Bulletin 747-53A2390, dated July 31, 1997: Prior to the accumulation of 20,000 total flight cycles, or within 2,000 flight cycles after the effective date of this AD, whichever occurs later, accomplish post-modification work in accordance with Figure 26 of Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000.

## Repair

(i) Except as provided by paragraph (b) of this AD, if any cracking is detected during any inspection required by this AD, prior to further flight, repair in accordance with Boeing Alert Service Bulletin 747-53A2390, Revision 1; including Appendices A, B, C, and D; dated July 6, 2000.

## Alternative Methods of Compliance

(j)(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 ACO. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.

(2) Alternative methods of compliance, approved previously in accordance with AD 98-20-25, amendment 39-10791, are approved as alternative methods of compliance with paragraph (a) of this AD.

# 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

(k) Special flight permits may be issued in accordance with §§ 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 November 2, 2000,

Donald L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

[FR Doc. 00-28723 Filed 11-8-00; 8:45 am]

BILLING CODE 4910-13-P