The service bulletin recommends compliance times at the following approximate intervals, depending on the lap splice location: TableService Bulletin Recommended Compliance Times Action Recommended compliance time Initial inspection.................. Ranging from 28,000 to 75,000 total flight cycles. Initial supplemental inspection..... 56,000 flight cycles after repair incorporation. Repetitive supplemental inspections. Ranging from 5,000 to 7,500 flight cycles.

Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other airplanes of this same type design. Therefore, we are proposing this AD, which would require you to use the service information described previously to perform the required actions, except as discussed under ``Difference Between the Proposed AD and Service Bulletin.''

Difference Between the Proposed AD and Service Bulletin

The service bulletin specifies that you may contact the manufacturer for instructions on how to repair certain conditions, but this proposed AD would require you to repair those conditions in one of the following ways:

Costs of Compliance

This proposed AD would affect about 4 airplanes worldwide and 2 airplanes of U.S. registry. The following table provides the estimated costs to comply with this proposed AD.
The average labor rate is $65 per work hour. The cost impact of the proposed AD on U.S. operators is estimated to be $83,855.
TableCost Impact For airplanes listed in the referenced service Per airplane bulletin as group Work hours Parts cost cost 1............................................. Inspection: 2................... None $130 Modification: 38................ $105 2,575 2............................................. Inspection: 2................... None 130 Modification: 30................ 104 2,054 3............................................. Inspection: 2................... None 130 Modification: 42................ 106 2,836 4............................................. Repair: 920..................... 16,200 76,000 Regulatory Findings

We have determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD 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.

For the reasons discussed above, I certify that the 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. 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.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD. See the ADDRESSES section for a location to examine the regulatory evaluation.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety. The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows: PART 39AIRWORTHINESS 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. The FAA amends Sec. 39.13 by adding the following new airworthiness directive (AD):
Boeing: Docket No. FAA200418996; Directorate Identifier 2004NM 40AD.
Comments Due Date
(a) The Federal Aviation Administration (FAA) must receive comments on this AD action by October 18, 2004.
Affected ADs
(b) None.
Applicability
(c) This AD applies to Boeing Model 737700 and 800 series airplanes, certificated in any category; having variable and serial numbers listed in Table 1 of this AD.
Table 1.Applicable Variable and Serial Numbers
Variable No. Serial No. Group YA004................................... 27837 1 YA005................................... 27836 2 YA201................................... 28004 4 YC003................................... 27977 3 Unsafe Condition
(d) This AD was prompted by a report indicating that localized pitting in the lower skin panels was found during production on a limited number of airplanes. We are issuing this AD to detect and correct premature fatigue cracking at certain lap splice locations and consequent rapid decompression of the airplane.
Compliance
(e) You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.
Initial Inspection and/or Repair
(f) At the applicable times specified in Table 1 of paragraph 1.E., ``Compliance'' of Boeing Service Bulletin 737531256, dated September 18, 2003, do the applicable actions specified in Table 2 of this AD in accordance with the Accomplishment Instructions of the service bulletin.
Table 2.Initial Inspection and/or Repair
For airplanes identified in
the service bulletin as Requirements
(1) Groups 1, 2, and 3....... Do an external ultrasonic inspection for pitting and cracks of the lower skin panel at the lap joint.
(2) Groups 1 and 2........... Trim the inner skin and install two exterior doublers (including related investigative actions).
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(3) Group 3.................. Install three exterior doublers. (4) Group 4.................. Replace the fuselage skin assembly with a new assembly.
Repetitive Inspections
(g) For Groups 1, 2, and 3 airplanes identified in Boeing Service Bulletin 737531256, dated September 18, 2003: At the applicable times specified in Table 2 of paragraph 1.E.,
``Compliance'' of the service bulletin, do the repetitive
supplemental inspections of the lower skins and external doublers for discrepancies in accordance with the Accomplishment Instructions of the service bulletin.
Corrective Action
(h) If any discrepancy is found during any action required by this AD, before further flight, repair per a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or per 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, the approval must specifically reference this AD.
Alternative Methods of Compliance (AMOCs)
(i)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.
(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 DER who has been authorized by the Manager, Seattle ACO, to make those findings. For a repair method to be approved, the approval must specifically refer to this AD.

Issued in Renton, Washington, on August 20, 2004. Kevin M. Mullin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.
[FR Doc. 0420124 Filed 9204; 8:45 am]
BILLING CODE 491013P

FOR FURTHER INFORMATION CONTACT

Sue Lucier, Aerospace Engineer, Airframe Branch, ANM120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 980554056; telephone (425) 9176438; fax (425) 9176590.