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###### Department of Transportation

###### Federal Aviation Administration

          - 14 CFR Part 39
          - [Docket No. FAA-2008-0669; Directorate Identifier 2007-NM-350-AD]
          - RIN 2120-AA64

# AGENCY:

Federal Aviation Administration (FAA), DOT.

# ACTION:

Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.

# SUMMARY:

We are revising an earlier proposed airworthiness directive (AD) for certain Boeing Model 737-600, -700, and -800 series airplanes. The original NPRM would have required an inspection of the free flange of the lower stringers of the wing center section for drill starts, and applicable related investigative and corrective actions. The original NPRM resulted from drill starts being found on the free flange of the lower stringers of the wing center section during a quality assurance inspection at the final assembly plant. This action revises the original NPRM by expanding the inspection area to include the free flange, the vertical web, and the fillet radius between the vertical web and the free flange. We are proposing this supplemental NPRM to prevent cracks from propagating from drill starts in the free flange, vertical web, and radius between the free flange and vertical web of the lower stringers of the wing center section lower stringers, which could cause a loss of structural integrity of the wing center section and may result in a fuel leak.

# DATES:

We must receive comments on this supplemental NPRM by March 31, 2009.

# ADDRESSES:

You may send comments by any of the following methods:
      -  Federal eRulemaking Portal:                          Go to                          http://www.regulations.gov.                          Follow the instructions for submitting comments.                    
      -  Fax:                          202-493-2251.                    
      -  Mail:                          U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.                    
      -  Hand Delivery:                          U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.                               ( print page 9777)      

                        For service information identified in this proposed AD, contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207; telephone 206-544-9990; fax 206-766-5682; e-mail                         *DDCS@boeing.com;*                         Internet                         *https://www.myboeingfleet.com.*                         You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington. For information on the availability of this material at the FAA, call 425-227-1221 or 425-227-1152.                    

## Examining the AD Docket

                    You may examine the AD docket on the Internet at                     *http://www.regulations.gov*; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (telephone 800-647-5527) is in the                     **ADDRESSES**                     section. Comments will be available in the AD docket shortly after receipt.                

# FOR FURTHER INFORMATION CONTACT:

Nancy Marsh, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 917-6440; fax (425) 917-6590.

# SUPPLEMENTARY INFORMATION:

## Comments Invited

                    We invite you to send any written relevant data, views, or arguments about this proposed AD. Send your comments to an address listed under the                     **ADDRESSES**                     section. Include “Docket No. FAA-2008-0669; Directorate Identifier 2007-NM-350-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.                

                    We will post all comments we receive, without change, to                     *http://www.regulations.gov,*                     including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.                

## Discussion

                    We issued a notice of proposed rulemaking (NPRM) (the “original NPRM”) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to certain Boeing Model 737-600, -700, and -800 series airplanes. That original NPRM was published in the                     **Federal Register**                     on June 24, 2008 (73 FR 35593). That original NPRM proposed to require inspecting the free flange of the lower stringers of the wing center section for drill starts, and applicable related investigative and corrective actions.                

## Comments

We gave the public the opportunity to participate in developing this AD. We considered the comment received.

## Request To Clarify Inspection Requirements

Boeing notes that the original NPRM would have required an inspection of the free flange of the stringer, whereas paragraph 3.B.2. of the Accomplishment Instructions in Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007, calls for inspection as given in Figure 1 of the service bulletin. Figure 1 specifies that the free flange, vertical web, and radius between the free flange and vertical web must be inspected. (The original NPRM referred to this service bulletin as the appropriate source of service information for the proposed actions.) The commenter requests that we clarify whether the inspection area is to include the free flange, vertical web, and the fillet radius.

We agree that the original NPRM is unclear whether the inspection area includes all three parts of the stringer. The service bulletin does not consistently include all three parts of the stringer. The “Background” section, the “Action” section, Paragraph 1.C., “Reason,” Paragraph 1.D., “Description,” and Paragraph 3.B., “Work Instructions,” refer only to the free flange for the inspection. Only a note in Figure 1, Sheet 4, contains any reference to all three areas of inspection—free flange, vertical web, and the fillet radius. We have determined that all three areas must be inspected to adequately address the identified unsafe condition. We have revised paragraph (g) of the supplemental NRPM to explicitly state these three areas of inspection. We have also revised the description of the area in the summary and paragraph (e) of the supplemental NPRM.

## Actions Since the Original NPRM Was Issued

We have added a new paragraph (d) to this proposed AD to specify the Air Transport Association (ATA) of America code identifying the subject, and re-identified the subsequent paragraphs accordingly.  

## FAA's Determination and Proposed Requirements of the Supplemental NPRM

We are proposing this supplemental NPRM because we evaluated all pertinent information and determined an unsafe condition exists and is likely to exist or develop on other products of the same type design. The change described above expands the scope of the original NPRM. As a result, we have determined that it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this supplemental NPRM.

## Costs of Compliance

We estimate that this proposed AD would affect 17 airplanes of U.S. registry. We also estimate that it would take 7 work-hours per product to comply with this proposed AD. The average labor rate is $80 per work-hour. Based on these figures, we estimate the cost of this proposed AD to the U.S. operators to be $9,520, or $560 per product.

## Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. “Subtitle VII: Aviation Programs,” describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in “Subtitle VII, Part A, Subpart III, Section 44701: General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

## Regulatory Findings

We 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 this proposed regulation:                          ( print page 9778)    

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.

You can find our regulatory evaluation and the estimated costs of compliance in the AD Docket.

# List of Subjects in 14 CFR Part 39

      - Air transportation
      - Aircraft
      - Aviation safety
      - Incorporation by reference
      - 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 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. The FAA amends § 39.13 by adding the following new AD:

**Boeing:**                                 Docket No. FAA-2008-0669; Directorate Identifier 2007-NM-350-AD.                            

## Comments Due Date

(a) We must receive comments by March 31, 2009.

## Affected ADs

(b) None.

## Applicability

(c) This AD applies to Boeing Model 737-600, -700, and -800 series airplanes, certificated in any category, as identified in Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007.

## Subject

(d) Air Transport Association (ATA) of America Code 57: Wings.

## Unsafe Condition

(e) This AD results from drill starts being found on the free flange of the lower stringers of the wing center section during a quality assurance inspection at the final assembly plant. We are issuing this AD to prevent cracks from propagating from drill starts in the free flange, vertical web, and radius between the free flange and vertical web of the lower stringers of the wing center section lower stringers, which could cause a loss of structural integrity of the wing center section and may result in a fuel leak.

## Compliance

(f) Comply with this AD within the compliance times specified, unless already done.

## Inspection and Related Investigative and Corrective Actions

(g) Before the accumulation of 18,000 total flight cycles, or within 90 days after the effective date of this AD, whichever occurs later, do a detailed inspection of the free flange, vertical web, and radius between the free flange and vertical web of the lower stringers of the wing center section for any drill start, and do all applicable related investigative and corrective actions, by accomplishing all the applicable actions specified in paragraphs 3.B.2 and 3.B.4 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007; except as provided in paragraph (h) of this AD. The applicable related investigative and corrective actions must be done before further flight.

(h) If any crack is found during any inspection required by paragraph (g) of this AD, and Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007, specifies to contact Boeing for appropriate action: Before further flight, repair the crack using a method approved in accordance with the procedures specified in paragraph (i) of 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 using the procedures found in 14 CFR 39.19. Send information to ATTN: Nancy Marsh, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 917-6440; fax (425) 917-6590.

(2) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your principal maintenance inspector (PMI) or principal avionics inspector (PAI), as appropriate, or lacking a principal inspector, your local Flight Standards District Office. The AMOC approval letter must specifically reference this AD.

(3) An AMOC that provides an acceptable level of safety may be used for any repair required by this AD, if it is approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization who has been authorized by the Manager, Seattle ACO, to make those findings. For a repair method to be approved, the repair must meet the certification basis of the airplane, and the approval must specifically refer to this AD.

Issued in Renton, Washington, on February 20, 2009.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

 [FR Doc. E9-4732 Filed 3-5-09; 8:45 am]

BILLING CODE 4910-13-P