04-26031. Airworthiness Directives; Boeing Model 737-600, -700, -700C, -800 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 737-600, -700, -700C, and -800 series airplanes. This proposed AD would require inspecting/measuring the length of the attachment fasteners between the nacelle support fittings and the lower wing skin panels, and related investigative/corrective actions if necessary. This proposed AD is prompted by a report from the manufacturer that in production, during the installation of certain attachment fasteners for the nacelle support fittings, only one washer was installed instead of two. We are proposing this AD to prevent inadequate fastener clamp-up, which could result in cracking of the fastener holes, cracking along the lower wing skin panels, fuel leaking from the wing fuel tanks onto the engines, and possible fire.

DATES:

We must receive comments on this proposed AD by January 10, 2005.

ADDRESSES:

Use one of the following addresses to submit comments on this proposed AD.

• DOT Docket Web site: Go to http://dms.dot.gov and follow the instructions for sending your comments electronically.
• Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
• Mail: Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW., Nassif Building, Room PL-401, Washington, DC 20590.
• By fax: [phone].
• Hand Delivery: Room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

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

You can examine the contents of this AD docket on the Internet at http://dms.dot.gov,, or at the Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW., room PL-401, on the plaza level of the Nassif Building, Washington, DC.

FOR FURTHER INFORMATION CONTACT:

Robert Hardwick, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Docket Management System (DMS)

The FAA has implemented new procedures for maintaining AD dockets electronically. As of May 17, 2004, new AD actions are posted on DMS and assigned a docket number. We track each action and assign a corresponding directorate identifier. The DMS AD docket number is in the form “Docket No. FAA-2004-99999.” The Transport Airplane Directorate identifier is in the form “Directorate Identifier 2004-NM-999-AD.” Each DMS AD docket also lists the directorate identifier (“Old Docket Number”) as a cross-reference for searching purposes.

Comments Invited

We invite you to submit any written relevant data, views, or arguments regarding this proposed AD. Send your comments to an address listed under ADDRESSES. Include “Docket No. FAA-2004-19682; Directorate Identifier 2004-NM-88-AD” in the subject line of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments submitted by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://dms.dot.gov,, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of that website, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov.

We are reviewing the writing style we currently use in regulatory documents. We are interested in your comments on whether the style of this document is clear, and your suggestions to improve the clarity of our communications that affect you. You can get more information about plain language at http://www.faa.gov/​language and http://www.plainlanguage.gov.

Examining the Docket

You may examine the AD docket in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone [phone]) is located on the plaza level of the Nassif Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the DMS receives them.

Discussion

We have received a report indicating that, during the production of certain Boeing Model 737-600, -700, -700C, and -800 series airplanes, it was discovered that certain attachment fasteners that attach the nacelle support fittings to the lower wing skin panels were improperly installed. The affected fasteners were installed during production with only one washer instead of two, which could cause the nut to tighten against the thread runout on the fastener shank rather than clamping the joint. This condition can be identified by checking the thread protrusion between the top of the nut and the end of the fastener to determine if the thread protrusion is outside of the limits specified by the manufacturer. Discrepant thread protrusion could indicate inadequate clamp-up between the nacelle support fittings and the lower wing skin panels. Adequate clamp-up compresses the components together, which assists in preventing cracking. Inadequate clamp-up, if not corrected, could result in cracking of the fastener holes, cracking along the lower wing skin panels, fuel leaking from the wing fuel tanks onto the engines, and possible fire.

Relevant Service Information

We have reviewed Boeing Service Bulletin 737-57-1275, dated September 4, 2003. The service bulletin describes procedures for inspecting/measuring the thread protrusion of certain attachment fasteners between the lower wing skin panels and the nacelle support fittings, marking fasteners with measurements outside of the specified thread protrusion limits, and related investigative and corrective actions. For fasteners with measurements outside of the specified limits, the related investigative actions include reaming the affected fastener holes and doing a high frequency eddy current inspection of the complete fastener hole stack-up for cracking. If no cracking is found, the corrective actions include reaming the holes to the next nominal diameter and installing new fasteners. If cracking is found, the service bulletin specifies contacting Boeing for repair information. For repaired areas, the service bulletin also specifies doing fuel leak inspections. Accomplishing the actions specified in the service bulletin will 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 inspecting/measuring the length of the attachment fasteners between the nacelle support fittings and the lower wing skin panels, and related investigative/corrective actions if necessary. The proposed AD would require you to use the service information described previously to perform these actions, except as discussed under “Differences Between the Proposed AD and Service Information.”

Differences Between the Proposed AD and Service Information

The service bulletin states that the inspection/measurement should be done within 30,000 flight cycles or 30,000 flight hours from airplane delivery, whichever is first. For airplanes not modified by Supplemental Type Certificate (STC) ST00830SE, this proposed AD specifies doing the inspection/measurement prior to the accumulation of 30,000 total flight cycles or 30,000 total flight hours, whichever is first. For airplanes modified by that STC, the proposed AD specifies doing the inspection/measurement prior to the accumulation of 25,000 total flight cycles or 25,000 total flight hours, whichever is first. The STC is an airplane modification that installs winglets. We have determined that airplanes with winglets have increased wing loads, which could result in cracking at a lower threshold than airplanes without winglets.

The service bulletin also 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:

• Using a method that we approve; or
• Using data that meet the type certification basis of the airplane, and that have been approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings.

Costs of Compliance

This proposed AD would affect about 751 airplanes worldwide. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

Estimated Costs

Action	Work hours	Average labor rate per hour	Parts	Cost per airplane	Number of U.S.-registered airplanes	Fleet cost
Inspection/Measurement	12	$65	Nominal	$780	302	$235,560

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 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 airworthiness directive (AD):

-

Boeing: Docket No. FAA-2004-19682; Directorate Identifier 2004-NM-88-AD.

Comments Due Date

(a) The Federal Aviation Administration (FAA) must receive comments on this AD action by January 10, 2005.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-600, -700, -700C, and -800 series airplanes; line numbers 1 through 761 inclusive, except for line numbers 596, 683, 742, 749, 750, 751, 754, 755, 759, and 760; certificated in any category;

Unsafe Condition

(d) This AD was prompted by a report from the manufacturer that in production, during installation of certain attachment fasteners for the nacelle support fittings, only one washer was installed instead of two. We are issuing this AD to prevent inadequate fastener clamp-up, which could result in cracking of the fastener holes, cracking along the lower wing skin panels, fuel leaking from the wing fuel tanks onto the engines, and possible fire.

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.

Inspection/Measurement and Related Investigative and Corrective Actions

(f) At the applicable time specified in paragraph (f)(1) or (f)(2) of this AD: Inspect/measure the length of certain attachment fasteners between the lower wing skin panels and the nacelle support fittings. Do the inspection/measurement, and all applicable related investigative and corrective actions, in accordance with the Accomplishment Instructions of Boeing Service Bulletin 737-57-1275, dated September 4, 2003, except as provided by paragraph (g) of this AD.

(1) For airplanes modified by Supplemental Type Certificate (STC) ST00830SE as of the effective date of this AD: Prior to the accumulation of 25,000 total flight hours or 25,000 total flight cycles, whichever is first.

(2) For airplanes not modified by STC ST00830SE as of the effective date of this AD: Prior to the accumulation of 30,000 total flight hours or 30,000 total flight cycles, whichever is first.

(g) If accomplishing a corrective action as required by paragraph (f) of this AD, and the service bulletin specifies to contact Boeing for repair information: Before further flight, do the 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, the approval must specifically reference this AD.

Alternative Methods of Compliance (AMOCs)

(h)(1) The Manager, Seattle ACO, FAA, has the authority to approve AMOCs for this AD, if requested using 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 such findings. For a repair method to be approved, the approval must specifically refer to this AD.

Issued in Renton, Washington, on November 10, 2004.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.