Airworthiness Directives; Boeing Model 737-100, -200, -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 737-100, -200, -300, -400, and -500 series airplanes. This proposed AD would require repetitive inspections for fatigue cracking in the longitudinal floor beam web, upper chord, and lower chord located at certain body stations, and repair if necessary. This proposed AD results from several reports of cracks in the center wing box longitudinal floor beams, upper chord, and lower chord. We are proposing this AD to detect and correct fatigue cracking of the upper and lower chords and web of the longitudinal floor beams, which could result in rapid loss of cabin pressure.

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: 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.

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 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-2007-0224; Directorate Identifier 2007-NM-188-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 have received several reports of fatigue cracks in the center wing box longitudinal floor beams on certain Boeing Model 737-100, -200, -300, -400, and -500 series airplanes. The cracks were found in the longitudinal floor beam web, upper chord, and lower chord at left buttock line (LBL) 24.8, right buttock line (RBL) 24.8, LBL 45.5 and RBL 45.5, between Station (STA) 656 and STA 727B. The airplanes had accumulated between 17,000 and 70,000 total flight cycles. These fatigue cracks are attributed to cyclic pressurization loads, fuel loads, and passenger loads. Fatigue cracking of the upper and lower chords and web of the longitudinal floor beams, if not corrected, could result in rapid loss of cabin pressure.

Related Rulemaking

On December 30, 1998, we issued AD 98-11-04 R1, amendment 39-10984 (64 FR 987) applicable to Boeing Model 737-100 and -200 series airplanes. That AD requires revising the FAA-approved maintenance program to include inspections that will give no less than the required damage tolerance rating for each structural significant item (SSI) if they are not effective for the SSI, and repair of cracked structure. Certain actions in this proposed AD are considered alternative methods of compliance (AMOCs) for paragraphs (b) and (c) of AD 98-11-04 R1.

Relevant Service Information

We have reviewed Boeing Service Bulletin 737-57-1296, dated June 13, 2007. The service bulletin describes procedures for the following:

• Detailed inspections for any crack in the upper chord of the longitudinal floor beam at LBL 24.8 and RBL 24.8, between STA 656 and STA 685.
• High frequency eddy current inspections for any crack in the lower chord of the longitudinal floor beam at LBL 24.8 and RBL 24.8, between STA 660 and STA 666.
• Detailed inspections for any crack in the longitudinal floor beam web at LBL 24.8, RBL 24.8, LBL 45.5, and RBL 45.5, between STA 705 and STA 715.
• Detailed inspections for any crack in the horizontal flange of the upper chord of the longitudinal floor beam at LBL 24.8, RBL 24.8, LBL 45.5, and RBL 45.5, at STA 727B.

The compliance times specified are as follows:

For Groups 1 and 2 airplanes: Before the accumulation of 20,000 total flight cycles, or within 6,000 flight cycles after the service bulletin date, whichever occurs later. Repeat the inspections thereafter at intervals not to exceed 6,000 flight cycles.

For Group 3 airplanes: Before the accumulation of 20,000 total flight cycles, or within 7,000 flight cycles after the service bulletin date, whichever occurs later. Repeat the inspections thereafter at intervals not to exceed 7,000 flight cycles.

If a crack is found, the service bulletin recommends contacting Boeing before further flight for repair instructions. If no crack is found, the procedures in the service bulletin specify repeating the inspections. 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 Information.”

Difference Between the Proposed AD and Service Information

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 2,852 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 652 airplanes of U.S. registry. The proposed inspection would take approximately 13 work hours per airplane, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the proposed inspection for U.S. operators is $678,080, or $1,040 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.