E7-22104. Airworthiness Directives; Boeing Model 737-100, -200, -200C, -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, -200C, -300, -400, and -500 series airplanes. This proposed AD would require various repetitive inspections for cracking of the upper frame to side frame splice of the fuselage, and other specified and corrective actions if necessary. This proposed AD also provides for an optional preventive modification, which would terminate the repetitive inspections. This proposed AD results from a report that the upper frame of the fuselage was severed between stringers S-13L and S-14L at station 747, and the adjacent frame at station 767 had a 1.3-inch-long crack at the same stringer location. We are proposing this AD to detect and correct fatigue cracking of the upper frame to side frame splice of the fuselage, which could result in reduced structural integrity of the frame and adjacent lap joint. This reduced structural integrity can increase loading in the fuselage skin, which will accelerate skin crack growth and result in decompression of the airplane.

DATES:

We must receive comments on this proposed AD by December 28, 2007.

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:

Wayne Lockett, 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-2007-0184; Directorate Identifier 2007-NM-140-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 a report indicating that the upper frame of the fuselage was severed between stringers S-13L and S-14L at station 747 on one airplane that had completed 41,000 total flight cycles, and that the adjacent frame at station 767 had a 1.3-inch-long crack at the same stringer location. This incident occurred on a Model 737-300 airplane. All cracks in the upper frame originated from the upper end fastener hole of the frame splice common to the fail safe chord. This condition, if not corrected, could result in reduced structural integrity of the frame and adjacent lap joint. This reduced structural integrity can increase loading in the fuselage skin, which will accelerate skin crack growth and result in decompression of the airplane.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-53A1261, including Appendices A through X inclusive, dated January 19, 2006. The service bulletin describes the following procedures for various repetitive inspections for cracking of the upper frame to side frame splice of the fuselage, and other specified and corrective actions if necessary. The inspections and other specified and corrective actions are described below:

• Configuration 1 airplanes on which the preventive modification specified in Boeing Service Bulletin 737-53-1125 has been done: Perform repetitive medium frequency eddy current (MFEC) inspections for cracking of the upper frame, repair of any crack before further flight, an optional preventive modification, which would eliminate the need for the repetitive inspections. The preventive modification also involves a high frequency eddy current (HFEC) inspection for cracking of the fastener holes in the upper frame and side frame, repair of any crack before further flight, and if no crack is found, fabricating and installing a modification angle as defined in the applicable Appendix.
• Configuration 2 airplanes on which the frame repair specified in Boeing Service Bulletin 737-53-1125 has been done: Perform a detailed inspection of the frame repair to make sure it follows the repair given in the applicable Boeing Model 737 Structural Repair Manual (SRM). If the repair is not as given in the SRM, perform any applicable corrective actions. Then perform an HFEC inspection for cracking of the upper frame. If any crack is found, repair before further flight. If no crack is found, repeat the HFEC inspection or contact Boeing for applicable terminating action, which would eliminate the need for the repetitive inspections.
• Configuration 3 airplanes on which the actions specified in Boeing Service Bulletin 737-53-1125 have not been done: Perform an MFEC inspection for cracking of the upper frame. The MFEC inspection is not necessary if the preventive modification is being accomplished. If any crack is found, repair before further flight. If no crack is found, repeat the MFEC inspection or do the preventive modification, which would eliminate the need for the repetitive inspections. When doing the preventive modification, perform an HFEC inspection for cracking of the fastener holes in the upper frame and side frame. If any crack is found, repair before further flight. If no crack is found, fabricate and install a modification angle as defined in the applicable Appendix.

The service bulletin specifies a compliance time for the initial inspection ranging between 30,000 total flight cycles and 50,000 total flight cycles, with a grace period of 5,000 flight cycles after the release date of the service bulletin, whichever occurs later, depending on airplane configuration.

The corrective actions include repair of any cracks found and ensuring that the frame maintains its structural integrity. If, during the accomplishment of the corrective actions, the structure that has been damaged is not covered in the structural repair manual, the service bulletin specifies contacting Boeing for repair. The service bulletin also describes procedures for a preventive modification of the frame splice joints which would eliminate the need for the repetitive inspections. In addition, the service bulletin recommends contacting Boeing for certain repair instructions and terminating action for certain airplanes.

Accomplishing the actions specified in the service information is intended to adequately address the unsafe condition.

Other Related Service Information

Boeing Alert Service Bulletin 737-53A1261 refers to Boeing Message M-7200-02-01294, dated August 20, 2002, as an additional source of service information for accomplishing certain repairs and optional terminating action of the preventive modification.

Boeing Service Bulletin 737-53-1125, dated November 22, 1989, Revision 1, dated September 20, 1990, and Revision 2, dated November 21, 1991, provided a preventive modification to reduce the stress level at the first fastener location in the frame splice common to the fail safe chord. The preventive modification increased the fatigue life of the splice area. However, the service bulletin did not include adequate inspections for cracks prior to accomplishing the preventive modification; therefore, the inspections specified in Boeing Alert Service Bulletin 737-53A1261 (described above) are recommended on airplanes on which that preventive modification has been accomplished in accordance with Boeing Service Bulletin 737-53-1125.

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 Alert Service Bulletin.”

Difference Between Proposed AD and Alert 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 1509 airplanes of the affected design in the worldwide fleet. This proposed AD would affect about 524 airplanes of U.S. registry. The proposed inspections would take between 18 and 38 work hours per airplane, depending on airplane configuration, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the inspections proposed by this AD for U.S. operators is between $754,560 and $1,592,960, or $1,440 and $3,040 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.

§ 39.13

[Amended]

2. The Federal Aviation Administration (FAA) amends § 39.13 by adding the following new airworthiness directive (AD):

Boeing: Docket No. FAA-2007-0184; Directorate Identifier 2007-NM-140-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by December 28, 2007.

Affected ADs

(b) None.

Applicability

(c) This AD applies to Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, certificated in any category; as identified in Boeing Alert Service Bulletin 737-53A1261, dated January 19, 2006.

Unsafe Condition

(d) This AD results from a report that the upper frame of the fuselage was severed between stringers S-13L and S-14L at station 747, and the adjacent frame at station 767 had a 1.3-inch-long crack at the same stringer location. We are issuing this AD to detect and correct fatigue cracking of the upper frame to side frame splice of the fuselage, which could result in reduced structural integrity of the frame and adjacent lap joint. This reduced structural integrity can increase loading in the fuselage skin, which will accelerate skin crack growth and result in 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.

Repetitive Inspections/Corrective Actions

(f) At the applicable compliance time listed in paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1261, including Appendices A through X inclusive, dated January 19, 2006: Do the applicable inspections for cracking of the upper frame to side frame splice of the fuselage by doing all of the actions, as specified in the Accomplishment Instructions of the service bulletin; except as provided by paragraphs (g) and (h) of this AD. Do all applicable specified and corrective actions before further flight in accordance with the service bulletin. Repeat the applicable inspections thereafter at intervals not to exceed 6,000 flight cycles until the terminating action in paragraph (i) of this AD has been accomplished.

(g) If any crack is found during any inspection required by this AD, and the service bulletin specifies to contact Boeing for appropriate action: Before further flight, repair the crack in accordance with the procedures specified in paragraph (j) of this AD.

(h) If, during the accomplishment of the corrective actions required by paragraph (f) of this AD, the structure that has been damaged is not covered in the structural repair manual, before further flight, repair in accordance with the procedures specified in paragraph (j) of this AD.

Optional Terminating Action

(i) Accomplishing the actions specified in paragraph (i)(1) (i)(2) or (i)(3) of this AD, as applicable, terminates the repetitive inspections required by paragraph (f) of this AD for the repaired or modified frames only.

(1) Accomplishment of the repair specified in Part 3 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1261, including Appendices A through X inclusive, dated January 19, 2006, or the preventive modification specified in Part 4 of the Accomplishment Instructions of the service bulletin.

(2) Accomplishment of the repair or the preventive modification specified in Boeing Message M-7200-02-01294, dated August 20, 2002.

(3) Accomplishment of the repair or the preventive modification in accordance with a method approved by the Manager, Seattle ACO.

Alternative Methods of Compliance (AMOCs)

(j)(1) The Manager, Seattle ACO, 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 5, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.