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###### Department of Transportation

###### Federal Aviation Administration 

          - 14 CFR Part 39 
          - [Docket No. 2002-NM-289-AD] 
          - RIN 2120-AA64 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Notice of proposed rulemaking (NPRM). 

# SUMMARY:

                        This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 737-100, -200, and -200C series airplanes. This proposal would require repetitive inspections to detect discrepancies of certain fuselage skin panels located just aft of the wheel well, and repair if necessary. The actions specified by the proposed AD are intended to detect and correct                               ( print page 898)                            fatigue cracking of the skin panels, which could cause rapid decompression of the airplane. This action is intended to address the identified unsafe condition.                     

# DATES:

Comments must be received by February 23, 2004. 

# ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2002-NM-289-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 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:

Suzanne Lucier, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 917-6438; fax (425) 917-6590. 

# 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 2002-NM-289-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. 2002-NM-289-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. 

## Discussion 

The FAA has received reports of fatigue cracking of the skins and doublers located aft of the wing, between body station (BS) 727 and BS 1016, and between body stringers 14 and 25, on numerous Boeing Model 737-100, -200, and -200C series airplanes. On some airplanes, reinforcing angles had been installed on the skin doublers; however, cracking was detected on both modified and unmodified airplanes. The cracking has been attributed to fatigue from a combination of shear stresses due to repeated wrinkling of the skin, and the skin chem-milled pockets configuration. Such fatigue cracking, if not corrected, could cause rapid decompression of the airplane. 

## Related Rulemaking 

AD 90-06-02, amendment 39-6489 (55 FR 8372, March 7, 1990), requires numerous modifications to aging Model 737 series airplanes. That AD requires, among other things, accomplishment of the preventive modification specified in Boeing Service Bulletin 737-53-1065, Revision 1, dated October 12, 1989, of certain fuselage skin panels in the subject area. 

Since AD 90-06-02 was issued, the FAA has received reports indicating that several airplanes developed fatigue cracking in the fuselage skin panels even after the skin panels had been modified or repaired in accordance with that AD. While the cause of this post-modification or post-repair skin cracking has not yet been determined, it is evident that the previous modifications or repairs may not have adequately addressed the original fatigue cracking problem. 

## Explanation of Relevant Service Information 

The FAA has reviewed and approved Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001, including Evaluation Form. This service bulletin describes procedures for various actions on 42 different groups of airplanes, based on airplane configuration differences. The service bulletin includes procedures in different areas of the airplane for: 
    - A subsurface eddy current or magnetic optical imaging inspection on the exterior skin to detect skin cracking or other damage in zones 1 and 3;
    - An internal HFEC inspection, if cracking is detected during the eddy current or magnetic optical imaging inspection, to detect cracking along the edge of the tearstrap and disbonding of the bonded doubler;
    - A blind fastener repair, which would extend the interval for the next HFEC inspection;
    - A general visual inspection of the exterior side of the skin in Zone 2;
    - Repair of cracking;
    - Removal of wrinkles from the skin to allow the repair to be done;
    - Reinspecting unrepaired areas at regular intervals; and
    - Installation of reinforcing angles, which would extend the interval for the next inspection.

Accomplishment of the actions specified in the 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 require repetitive inspections to detect discrepancies of certain fuselage skin panels located just aft of the wheel well, and repair if necessary. The purpose of these inspections is to detect fatigue cracking of the skin panels, which could cause rapid decompression of the airplane. The proposed inspections are to be accomplished in accordance with the service bulletin, except as discussed below. 

## Differences Between the Service Bulletin and the Proposed AD 

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. 

                    Although the service bulletin recommends that operators report certain crack findings, this AD would not require such a report.                           ( print page 899)    

## Interim Action 

This is considered to be interim action. The manufacturer has advised that it is developing an improved preventive modification intended to address the identified unsafe condition for unmodified skin areas. After this modification is developed, approved, and available, the FAA may consider additional rulemaking. 

## Cost Impact 

There are approximately 1,000 airplanes of the affected design in the worldwide fleet. The FAA estimates that 390 airplanes of U.S. registry would be affected by this proposed AD. 

It would take approximately 47 to 88 work hours per airplane (depending on configuration) to accomplish the proposed inspections, at an average labor rate of $65 per work hour. Based on these figures, the cost impact of the inspections proposed by this AD is estimated to be $3,055 to $5,720 per airplane, per inspection cycle. 

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this proposed 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 substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. 

                    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 adding the following new airworthiness directive: 

**Boeing:**                                 Docket 2002-NM-289-AD.                            

*Applicability:*                                 All Model 737-100, -200, and -200C series airplanes; certificated in any category.                             

*Compliance:*                                 Required as indicated, unless accomplished previously.                             

To detect and correct fatigue cracking of the skin panels, which could cause rapid decompression of the airplane, accomplish the following: 

## Repetitive Inspections: Unmodified Skin Areas 

(a) For fuselage skin panel areas that have not been modified with stiffening angles: Before the airplane accumulates 16,000 total flight cycles, or within 4,500 flight cycles after the effective date of this AD, whichever occurs later, inspect the unmodified fuselage side skins just aft of the main wheelwell, and perform all follow-on actions, in accordance with Part I of the Accomplishment Instructions of Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001. If no cracking, loose fasteners, disbonding, or damage is found: Repeat the inspection at the time specified in paragraph 1.E., of the service bulletin, as applicable, except as provided by paragraph (d) of this AD. 

## Repetitive Inspections: Modified Skin Areas 

(b) For fuselage skin panel areas that have been modified with stiffening angles in accordance with Boeing Service Bulletin 737-53-1065, dated April 19, 2001: Within 16,000 flight cycles after the modification, or within 4,500 flight cycles after the effective date of this AD, whichever occurs later, inspect the modified areas as specified in accordance with Part I of Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001. Repeat the inspection at the time specified in paragraph 1.E., of the service bulletin, as applicable, except as provided by paragraph (d) of this AD. If any cracks, loose fasteners, disbonding, or damage is found: Repair before further flight in accordance with the requirements of paragraph (d) of this AD. 

## Terminating Action for Inspections of Modified Skin Areas 

(c) For fuselage skin panel areas that have been modified with stiffening angles in accordance with Boeing Service Bulletin 737-53-1065, dated April 19, 2001: At the later of the times specified by paragraphs (c)(1) and (c)(2) of this AD: Perform a subsurface eddy current or magneto optical imaging inspection to detect subsurface skin cracks along the edge of the bonded doubler, in accordance with Figure 10 of Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001. If any cracks are found, repair before further flight in accordance with paragraph (d) of this AD. Accomplishment of this inspection and all applicable corrective actions terminates the repetitive inspections required by paragraph (b) of this AD for the modified areas. 

(1) Inspect within 24,500, but not fewer than 20,000, flight cycles after the modification of the skin. 

(2) Inspect within 4,500 flight cycles after the effective date of this AD. 

## Repair: Modified and Unmodified Skin Areas 

(d) If any cracking is detected during any inspection required by this AD: Do the actions specified by paragraph (d)(1) or (d)(2) of this AD before further flight. Do the actions in accordance with Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001, except as required by paragraph (e) of this AD. 

(1) Do a time-limited repair (including a detailed inspection of the skin in the area of the repair to detect corrosion and doubler disbonding) in accordance with Part III of the Accomplishment Instructions of the service bulletin. 

(i) After the time-limited repair has been accomplished: At intervals not to exceed 3,000 flight cycles, perform an external general visual inspection of the repair to detect loose or missing fasteners, in accordance with Part III of the Accomplishment Instructions of the service bulletin, until the actions specified in paragraph (d)(1)(v) of this AD have been accomplished. 

(ii) After the time-limited repair has been accomplished: At intervals not to exceed 4,500 flight cycles, perform an internal inspection of the repair to detect cracking or doubler disbonding using general visual and high-frequency eddy current methods, in accordance with Figure 11 of the service bulletin, until the actions specified in paragraph (d)(1)(v) of this AD have been accomplished. 

(iii) If any cracking is found during any inspection required by paragraph (d)(1) of this AD: Repair before further flight in accordance with paragraph (e) of this AD. 

                                (iv) If any disbonding is found during any inspection required by paragraph (d)(1) of this AD: Repair before further flight in                                       ( print page 900)                                    accordance with Part II of the service bulletin.                             

(v) Within 10,000 flight cycles after accomplishment of the time-limited repair: Make the repair permanent in accordance with Part III of the Accomplishment Instructions of the service bulletin. Permanent repair of an area terminates the repetitive inspections specified in this AD for that repaired area only. 

(2) Do a permanent repair (including an inspection using external subsurface eddy current or magneto optical imaging methods to detect cracks at the chem-milled step in each adjacent bay of the fuselage skin, a detailed inspection of the skin in the area of the repair for corrosion and doubler disbonding, and applicable corrective action) of the cracked area, in accordance with Part II of the Accomplishment Instructions of the service bulletin. Permanent repair of an area terminates the repetitive inspections specified in this AD for that repaired area only. 

## Exceptions to Service Bulletin Procedures 

(e) During any inspection required by this AD, if any discrepancy (including cracking) is detected for which the service bulletin specifies to contact Boeing for appropriation action: Before further flight, 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 Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved, as required by this paragraph, the approval letter must specifically refer to this AD. 

(f) Although Boeing Service Bulletin 737-53-1065, Revision 2, dated April 19, 2001, recommends that cracks found in Zone 2 be reported to Boeing, this AD does not require such a report. 

## Alternative Methods of Compliance 

(g)(1) In accordance with 14 CFR 39.19, the Manager, Seattle ACO, FAA, is authorized to approve alternative methods of compliance (AMOCs) for this AD. 

(2) An AMOC that provides an acceptable level of safety may be used for any repair required by this AD, if it is approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. 

Issued in Renton, Washington, on December 30, 2003. 

Michael J. Kaszycki, 

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. 

[FR Doc. 04-272 Filed 1-6-04; 8:45 am] 

BILLING CODE 4910-13-P