E8-14185. Airworthiness Directives; Boeing Model 737-600, -700, and -800 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to adopt a new airworthiness directive (AD) for certain Boeing Model 737-600, -700, and -800 series airplanes. This proposed AD would require inspecting the free flange of the lower stringers of the wing center section for drill starts, and applicable related investigative and corrective actions. This proposed 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 proposing this AD to prevent cracks from propagating from drill starts in the free flange of the lower stringers of the wing center section, 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 proposed AD by August 8, 2008.

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: [phone].
• 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.

For service information identified in this AD, contact Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

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 [phone]) 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 [phone]; fax [phone].

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 received reports of drill starts being found on the free flange of the lower stringers of the wing center during a quality assurance inspection at the final assembly plant. The drill starts were caused by a manufacturing error during wing assembly. Cracks could propagate from drill starts in the free flange of the lower stringers of the wing center section. This condition, if not corrected, could result in loss of structural integrity of the wing center section and may result in a fuel leak.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007. The service bulletin describes procedures for doing a detailed inspection of the free flange of the upper and lower stringers of the wing center section for drill starts, and applicable related investigative and corrective actions. The related investigative actions include doing high frequency eddy current (HFEC) open hole inspections for any cracks. The corrective actions include doing the zero-timing procedure at each drill start, oversizing the hole, installing new fasteners if the hole is within the service bulletin tolerance limits, and contacting Boeing for certain repair conditions, as applicable.

Accomplishing certain actions specified in the service bulletin is intended to adequately address the identified unsafe condition.

Requirements of This Proposed AD

We are proposing this AD because we evaluated all relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of this same type design. This proposed AD would require accomplishing the actions specified in the service information described previously, except as discussed under “Differences Between the Proposed AD and Service Bulletin.”

Differences Between the Proposed AD and Service Bulletin

Although Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007, specifies a detailed inspection and applicable related investigative and corrective actions of the free flange of the upper and lower stringers of the wing center section, this proposed AD would require those actions for only the lower stringers of the wing center section. The lower stringers are the tension surface of the wing box, and therefore are subject to cracking. We do not consider cracking of the upper surface a safety issue.

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

• Using a method that we approve; or
• Using data that meet the certification basis of the airplane, and that have been approved by an Authorized Representative for the Boeing Commercial Airplanes Delegation Option Authorization Organization whom we have authorized to make those findings.

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:

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
• 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

[Amended]

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 August 8, 2008.

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.

Unsafe Condition

(d) This proposed AD results from drill starts being found on the free flange of the lower stringers of the wing center during a quality assurance inspection at the final assembly plant. We are proposing this AD to prevent cracks from propagating from drill starts in the free flange 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

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

Inspection and Related Investigative and Corrective Actions

(f) 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 of the lower stringers of the wing center section for any drill start, and do any 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 the Boeing Alert Service Bulletin 737-57A1294, dated April 23, 2007; except as provided in paragraph (g) of this AD. The applicable related investigative and corrective actions must be done before further flight.

(g) If any crack is found during any inspection required by paragraph (f) 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 (h) of this AD.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, ATTN: Nancy Marsh, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone [phone], fax [phone] has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.

(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 appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO.

(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.

Issued in Renton, Washington, on June 12, 2008.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.