E7-22923. Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 737-300, -400, and -500 series airplanes. This proposed AD would require repetitive inspections for cracking of the body buttock line (BBL) 0.07 floor beam between body station (BS) 651 and BS 676 and between BS 698 and BS 717, and related investigative and corrective actions if necessary. This AD also provides an optional terminating action for the repetitive inspections. This proposed AD results from reports of cracking in the BBL 0.07 floor beam. We are proposing this AD to prevent failure of the main deck floor beams at certain body stations due to fatigue cracking, which could result in rapid decompression of the airplane.

DATES:

We must receive comments on this proposed AD by January 10, 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-2007-0226; Directorate Identifier 2007-NM-187-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.

Other Related Rulemaking

On July 12, 2001, we issued AD 2001-14-20, amendment 39-12331 (66 FR 38354, July 24, 2001), applicable to certain Boeing Model 737-100 and -200 series airplanes. AD 2001-14-20 requires repetitive inspections to find fatigue cracking in the main deck floor beams located at certain body stations, and repair if necessary. AD 2001-14-20 also provides for optional terminating action for the repetitive inspections. AD 2001-14-20 addresses fatigue cracking in the main deck floor beams on Model 737-100 and -200 series airplanes, while this proposed AD would address the same unsafe condition on Boeing Model 737-300, -400, and -500 series airplanes.

Discussion

Since we issued AD 2001-14-20, several operators have reported cracking in the body buttock line (BBL) 0.07 floor beam on Model 737-300, -400, and -500 series airplanes. The cracks were similar to those found on the Model 737-100 and -200 series airplanes, which are addressed by AD 2001-14-20. Investigation revealed that the cracks were caused by fatigue resulting from pressurization flexure. Failure of the main deck floor beam at certain body stations due to fatigue cracking could result in rapid decompression of the airplane.

Relevant Service Information

We have reviewed Boeing Service Bulletin 737-57-1210, Revision 2, dated June 13, 2007. For Model 737-300, -400, and -500 series airplanes, the service bulletin describes procedures for accomplishing repetitive detailed inspections for cracking of the BBL 0.07 floor beam between body station (BS) 651 and BS 676 and between BS 698 and BS 717, and doing related investigative and corrective actions if necessary. The related investigative action includes doing a high frequency eddy current (HFEC) inspection of the fastener holes for cracking (1) prior to modifying the floor beam, or (2) if any cracking is found in the web (between BS 651 and BS 676 and between BS 698 and BS 717) or in the upper chord (between BS 651 and BS 676) during the detailed inspection. The corrective actions include the following:

• Repairing any cracking in accordance with the service bulletin, if cracking is found in the web (between BS 651 and BS 676 and between BS 698 and BS 717) or in the upper chord (between BS 651 and BS 676) during the detailed inspection but no cracking is found during the HFEC inspection. Accomplishing the repair would eliminate the need for the repetitive inspections for the area in which the repair is installed.
• Contacting Boeing for repair instructions, (1) if cracking is found in the web (between BS 651 and BS 676 and between BS 698 and BS 717) or in the upper chord (between BS 651 and BS 676) during the HFEC inspections, (2) if cracking is found in the chords or stiffeners (between BS 698 and BS 717) or outside the typical crack locations (between BS 651 and BS 676 and between BS 698 and BS 717) during the detailed inspection, or (3) if cracking is found during the HFEC prior to modifying the floor beam.

The service bulletin also provides procedures for modifying the floor beam, if no cracking is found during the detailed and HFEC inspections. Accomplishing the modification (optional terminating action) would eliminate the need for the repetitive inspections for the area in which the modification is installed.

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. For this reason, we are proposing this AD, which would require accomplishing the actions specified in the service information described previously, except as discussed under “Difference Between the Proposed AD and Service Bulletin.”

Difference Between the Proposed AD and Service Bulletin

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

There are about 1,961 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 599 airplanes of U.S. registry. The proposed inspections would take about 4 work hours per airplane, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the proposed AD for U.S. operators is $191,680, or $320 per airplane, per inspection cycle.

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 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 and placed it in the AD docket. 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 Federal Aviation Administration (FAA) amends § 39.13 by adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-0226; Directorate Identifier 2007-NM-187-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by January 10, 2008.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-300, -400, and -500 series airplanes, certificated in any category; as identified in Boeing Service Bulletin 737-57-1210, excluding Appendix A, Revision 2, dated June 13, 2007.

Unsafe Condition

(d) This AD results from reports of cracking in the body buttock line (BBL) 0.07 floor beam. We are issuing this AD to prevent failure of the main deck floor beams at certain body stations due to fatigue cracking, which could result in 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.

Inspections and Related Investigative/Corrective Actions

(f) Before the accumulation of 20,000 total flight hours, or within 7,000 flight cycles after the effective date of this AD, whichever occurs later: Do the detailed inspections for cracking of the BBL 0.07 floor beam between body station (BS) 651 and BS 676 and between BS 698 and BS 717, and do all the applicable related investigative and corrective actions before further flight, by accomplishing all of the applicable actions specified in paragraphs B.2. and B.4. of the Accomplishment Instructions of Boeing Service Bulletin 737-57-1210, excluding Appendix A, Revision 2, dated June 13, 2007, except as provided by paragraph (g) of this AD. Repeat the inspections thereafter at intervals not to exceed 7,000 flight cycles. Installing a repair in accordance with paragraphs B.2. and B.4. of the Accomplishment Instructions of the service bulletin, or doing the modification in accordance with paragraph (h) of this AD, terminates the repetitive inspections for the applicable area only.

Exception to Corrective Action

(g) If any cracking is found during any inspection required by this AD, and Boeing Service Bulletin 737-57-1210, excluding Appendix A, Revision 2, dated June 13, 2007, specifies to contact Boeing for appropriate action: Before further flight, repair the cracking using a method approved in accordance with the procedures specified in paragraph (i) of this AD.

Optional Terminating Action

(h) If no cracking is found during the detailed inspection and related investigative action required by paragraph (f) of this AD: Accomplishing the modification of the BBL 0.07 floor beam between BS 651 and BS 676 and between BS 698 and BS 717, as applicable, in accordance with paragraphs B.2. and B.4., as applicable, of the Accomplishment Instructions of Boeing Service Bulletin 737-57-1210, excluding Appendix A, Revision 2, dated June 13, 2007, terminates the repetitive inspections for the applicable area only.

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) 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, and the approval must specifically refer to this AD.

Issued in Renton, Washington, on November 13, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.