E7-18554. 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 doing repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips; doing applicable corrective and related investigative actions, if necessary; and measuring the fastener spacing and the edge margin; as applicable. As a temporary alternative to doing the actions described previously, this proposed AD would require repetitive external general visual inspections of the skin and lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and applicable corrective actions if necessary. This proposed AD results from a report of several cracked stringer tie clips. We are proposing this AD to prevent multiple cracked stringer tie clips and damaged skin and frames, which could lead to the skin and frame structure developing cracks and consequent decompression of the airplane.

DATES:

We must receive comments on this proposed AD by November 5, 2007.

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: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Fax: [phone].
• Hand Delivery: Room W12-140 on the ground floor of the West Building, 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

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

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 submit any relevant written data, views, or arguments regarding this proposed AD. Send your comments to an address listed in the ADDRESSES section. Include the docket number “FAA-2007-29255; Directorate Identifier 2007-NM-085-AD” at the beginning 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 received 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 web site, 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.

Examining the Docket

You may examine the AD docket on the Internet at http://dms.dot.gov, or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Operations office (telephone [phone]) is located on the ground level of the West Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the Docket Management System receives them.

Discussion

We have received a report of 15 cracked stringer tie clips in the crown skin area between station (STA) 500B and STA 907 between stringer (S) 10L and S-10R, on a Boeing Model 737 airplane. The airplane had accumulated total 31,415 flight cycles. This airplane had three adjacent cracked clips at two consecutive body station frames (six clips total). The six stringer tie clips were cracked along the joint common to the stringer. The six total stringer tie clips were the same formed bonded stringer tie clips that were installed as terminating action in accordance with Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990.

Stringer tie clip cracking along the joint common to the stringer occurs primarily as a result of cyclic loading associated with cabin pressure and flight loads. If three adjacent stringer tie clips on one frame crack, it could result in an inability of the fuselage frame structure to support operating loads. This could result in local skin buckling and deformation of the skin and frame. Multiple cracked stringer tie clips and damaged skin and frames, if not corrected, could lead to the skin and frame structure developing cracks, which could result in decompression of the airplane.

Other Relevant Rulemaking

We previously issued AD 93-08-04, amendment 39-8551 (58 FR 25546, April 27, 1993), for certain Boeing Model 737-100, -200, and -200C series airplanes. That AD requires structural inspections of older airplanes and is part of the Aging Airplane Service Bulletin Structural Modification and Inspection Program. Boeing Service Bulletin 737-53-1085, Revision 1, is one of several service bulletins required by that AD.

This proposed AD would affect the requirements of AD 93-08-04 pertaining to Boeing Service Bulletin 737-53-1085, Revision 1.

We previously issued AD 2002-07-08, amendment 39-12702 (67 FR 17917, April 12, 2002), applicable to certain Boeing Model 737-200, -200C, -300, -400, and -500 series airplanes. That AD requires repetitive inspections to find cracking of the lower skin at the lower row of fasteners in the lap joints of the fuselage, and repair of cracking found. That AD also requires modification of the fuselage lap joints at certain locations, which constitutes terminating action for certain repetitive inspections.

This proposed AD would not affect the current requirements of AD 2002-07-08.

Relevant Service Information

We have reviewed Boeing Special Attention Service Bulletin 737-53-1268, dated August 25, 2006. This service bulletin supersedes Boeing Service Bulletin 737-53-1085, Revision 1.

The service bulletin describes one required inspection and one temporary alternative inspection. Inspection A, the one required inspection, involves the following:

• Doing repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips. The inspection area is from STA 559 to STA 887, STA 360 to STA 540, and STA 907. The inspections from STA 559 to STA 887 are identical to those specified in Boeing Service Bulletin 737-53-1085, Revision 1. If the terminating action was done in accordance with Boeing Service Bulletin 737-53-1085, the inspections need to be restarted in accordance with Boeing Special Attention Service Bulletin 737-53-1268.
• Doing applicable corrective and related investigative actions, if necessary. The corrective actions include replacing any cracked stringer tie clip with a new clip, contacting Boeing for repair instructions, and repairing any damaged lap joints; as applicable. The related investigative actions include doing an internal detailed inspection to detect damaged or deformed skin and frame and to detect damaged lap joints, and doing internal eddy current inspections to detect cracked lap joints; as applicable.
• Measuring the fastener spacing and the edge margin; as applicable.

The initial compliance time for Inspection A is before the accumulation of 25,000 or 35,000 total flight cycles (as applicable), or within 2 or 3 years (as applicable) after the date of the service bulletin, whichever occurs later. The repeat interval for Inspection A is 15,000 or 20,000 flight cycles (as applicable).

Inspection B, which is a temporary alternative to doing Inspection A, involves the following:

• Doing repetitive external general visual inspections of the skin and lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and
• Doing applicable corrective actions if necessary. The corrective actions include contacting Boeing for repair instructions, and repairing any cracked or damaged lap joint and skin.

For Inspection B, the threshold for the initial compliance times ranges between 37,500 and 47,500 total flight cycles, and the grace period for the initial compliance times is 25,000 flight cycles or 6 or 12 months, depending on the number of flight cycles on the airplane. Inspection B must be done before exceeding an inspection period ranging from 5,000 to 50,000 total flight cycles. The repeat interval for Inspection B is 2,500 flight cycles.

The service bulletin also describes procedures for an optional eddy current inspection to detect damaged stringer tie clips and replacement of any cracked clip with a new clip. The optional inspection can be done in addition to and at the same time as Inspection A described previously. The optional inspection will detect damaged stringer clips earlier than the detailed inspection, which may prevent future costly repairs.

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

The service bulletin refers to Boeing Service Bulletin 737-53A1177, Revision 6, dated May 31, 2001, as an additional source of service information for doing an internal eddy current inspection of the lap joint for certain airplane configurations.

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 “Differences Between the Proposed AD and Service Information.”

Differences Between the Proposed AD and Service Information

The service information 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 2,685 airplanes of the affected design in the worldwide fleet. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

Estimated Costs

Action	Work hours 1	Average labor rate per hour	Cost per airplane 1	Number of U.S.-registered airplanes	Fleet cost 1
Inspection A	Between 40 and 103	$80	Between $3,200 and $8,240, per inspection cycle	787	Between $2,518,400 and $6,484,880, per inspection cycle.
Inspection B (temporary alternative to Inspection A)	Between 2 and 109	80	Between $160 and $8,720	787	Between $125,920 and $6,862,640, per inspection cycle.
1 Depending on the airplane configuration.

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-2007-29255; Directorate Identifier 2007-NM-085-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by November 5, 2007.

Affected ADs

(b) AD 93-08-04, amendment 39-8551.

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 Service Bulletin 737-53-1268, dated August 25, 2006.

Unsafe Condition

(d) This AD results from a report of several cracked stringer tie clips. We are issuing this AD to prevent multiple cracked stringer tie clips and damaged skin and frames, which could lead to the skin and frame structure developing cracks and consequent 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.

Service Bulletin References

(f) The term “the service bulletin,” as used in this AD, means the Accomplishment Instructions of Boeing Service Bulletin 737-53-1268, dated August 25, 2006.

Inspection A: Required Internal Inspections, Applicable Corrective and Related Investigative Actions, and Measurement

(g) Do repetitive internal eddy current and detailed inspections to detect cracked stringer tie clips; do applicable corrective and related investigative actions, if necessary; and measure the fastener spacing and the edge margin; as applicable. Do all applicable actions at the applicable compliance times and repeat intervals identified in tables 2 through 8 inclusive of paragraph 1.E., “Compliance,” of the service bulletin; except as provided by paragraphs (i), (j), and (k) of this AD. Do all applicable actions in accordance with the Accomplishment Instructions of the service bulletin, except as provided by paragraph (m) of this AD.

Note 1:

The service bulletin refers to Boeing Service Bulletin 737-53A1177, Revision 6, dated May 31, 2001, as an additional source of service information for doing an internal eddy current inspection of the lap joint for certain airplane configurations.

Inspection B: Temporary Alternative External Inspections and Corrective Actions

(h) As a temporary alternative to doing the actions required by paragraph (g) of this AD, do repetitive external general visual inspections of the skin and lap joints for cracks and evidence of overload resulting from cracked stringer tie clips, and applicable corrective actions if necessary. Do all applicable actions at the applicable compliance times and repeat intervals identified in tables 9 through 12 inclusive of paragraph 1.E., “Compliance,” of the service bulletin, but not to exceed the flight cycles in the “Inspection Period Allowed” column of the tables; except as provided by paragraphs (i) and (l) of this AD. Do all applicable actions in accordance with the Accomplishment Instructions of the service bulletin, except as provided by paragraph (m) of this AD.

Note 2:

The eddy current inspection along the stringer tie clip radius to detect damage and replacement, as applicable, specified in paragraph 3.B.5. of the Accomplishment Instructions of the service bulletin are not required by this AD. The actions are optional and can be done in addition to and at the same time as the actions required by paragraph (g) of this AD.

Exceptions to Service Information

(i) Where the service bulletin specifies a compliance time after the date of the service bulletin, this AD requires compliance within the specified compliance time after the effective date of this AD.

(j) For Model 737-100, -200, and -200C series airplanes, on which Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990, has not been done in accordance with AD 93-08-04: As of the effective date of this AD, do the applicable inspections from STA 559 to STA 887 in accordance with paragraph (g) of this AD, at the applicable compliance times specified in paragraph (b) of AD 93-08-04.

(k) In the first row of tables 5 and 6 of paragraph 1.E., “Compliance,” of the service bulletin, where the service bulletin specifies a compliance time of before 25,000 total airplane flight cycles, this AD requires a compliance time of before the accumulation of 25,000 total flight cycles, or within 2 years after the effective date of this AD, whichever occurs later.

(l) Where the service bulletin specifies no starting point (e.g., “after the date on the service bulletin”) for a grace period, this AD requires compliance within the specified grace period after the effective date of this AD.

(m) Where the service bulletin specifies to contact Boeing for appropriate action: Before further flight, repair the discrepancy using a method approved in accordance with the procedures specified in paragraph (o) of this AD.

Certain Actions End Certain Requirements of AD 93-08-04

(n) Accomplishment of the internal eddy current and detailed inspections for STA 559 to STA 887 in accordance with paragraph (g) of this AD constitutes compliance with the inspections required by paragraph (a) of AD 93-08-04, as it pertains to Boeing Service Bulletin 737-53-1085, Revision 1, dated May 10, 1990. Accomplishment of the internal eddy current and detailed inspections does not terminate the remaining requirements of AD 93-08-04, as it applies to other service bulletins. Operators are required to continue to inspect and/or modify per the other service bulletins listed in that AD.

Alternative Methods of Compliance (AMOCs)

(o)(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 September 12, 2007.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.