2012-15601. Airworthiness Directives; The Boeing Company Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to supersede an existing airworthiness directive (AD) that applies to all The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The existing AD currently requires repetitive inspections to detect cracking in the web of the aft pressure bulkhead at body station 1016 at the aft fastener row attachment to the “Y” chord, and corrective actions if necessary. That AD was prompted by several reports of fatigue cracking at that location, which could result in rapid decompression of the fuselage. Since we issued that AD, we have received additional reports of cracks found in the aft pressure bulkhead. This proposed AD would add various inspections for discrepancies at the aft pressure bulkhead, and related investigative and corrective actions if necessary. We are proposing this AD to detect and correct such fatigue cracking, which could result in rapid decompression of the fuselage.

DATES:

We must receive comments on this proposed AD by August 13, 2012.

ADDRESSES:

You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, 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: Deliver to Mail address above 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, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone [phone], extension 1; fax [phone]; Internet https://www.myboeingfleet.com. You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. For information on the availability of this material at the FAA, call 425-227-1221.

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 (phone: [phone]) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Alan Pohl, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington 98057-3356; phone: [phone]; fax: [phone]; email: [e-mail].

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-2012-0645; Directorate Identifier 2011-NM-052-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

On April 9, 1999, we issued AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999), for all The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. That AD requires repetitive inspections of the web of the aft pressure bulkhead at body station 1016 at the aft fastener row attachment to the “Y” chord; and corrective actions, if necessary. That AD resulted from reports of fatigue cracking found at that location on The Boeing Company Model 737 series airplanes. We issued that AD to detect and correct such fatigue cracking, which could result in rapid decompression of the fuselage.

Actions Since Existing AD Was Issued

Since we issued AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999), we have received reports that cracks have been found in four general areas of the aft pressure bulkhead: In the web at the web-to-“Y” chord interface, in the web at the outer circumferential tear strap, in the web near the dome cap, and in the “Z” stiffeners near the dome cap. Cracks have been reported in these new areas on airplanes that have accumulated between 21,246 and 68,000 total flight cycles, and between 17,500 and 61,000 total flight hours.

Relevant Service Information

We reviewed Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011. The service information describes procedures and compliance times for various inspections for discrepancies (including cracking, misdrilled fastener holes, elongated fastener holes, corrosion, oil-cans, and existing repairs) at the aft pressure bulkhead, and related investigative and corrective actions if necessary, as follows:

• Repetitive detailed and low frequency eddy current (LFEC) inspections of the aft side of the upper bulkhead web, or detailed and high frequency eddy current (HFEC) inspections from the forward side of the bulkhead, to detect cracks, incorrectly drilled fastener holes, or elongated fastener holes; and related investigative actions, including HFEC and detailed inspections to detect additional cracks, incorrectly drilled fastener holes, or elongated fastener holes on the section of the web of the forward side of the bulkhead.
• Repetitive detailed, surface HFEC, and subsurface LFEC inspections to detect cracks, incorrectly drilled fastener holes, or elongated fastener holes of the lower bulkhead web from the forward or aft side of the bulkhead.
• A one-time LFEC inspection to detect cracks on the aft side of the bulkhead of the web located under the outer circumferential tear strap, or a one-time HFEC inspection to detect cracks from the forward side of the bulkhead of the web located under the outer circumferential tear strap.
• A detailed inspection from the aft side of the bulkhead for oil-canning, and related investigative actions. The related investigative actions include detailed and HFEC inspections for cracks, and a measurement of the depth and width of the oil-can. For airplanes on which oil-cans are found within limits, the service information specifies an option of doing repetitive detailed and HFEC inspections for cracks of the oil-canning and eventual repair. Doing the repair terminates the repetitive inspections.
• Repetitive eddy current inspections to detect cracks of the dome cap at the center of the bulkhead.
• Repetitive HFEC inspections to detect cracks of the “Z” stiffener flanges at the dome cap in the center of the bulkhead.
• A detailed inspection of the bulkhead web and of the stiffeners for existing repairs; and, depending on the findings, repetitive HFEC or LFEC inspections of the web for cracking; replacement of existing repairs with new repairs, and damage tolerance inspections.
• The corrective actions include repairing discrepancies (including cracking, misdrilled fastener holes, elongated fastener holes, corrosion, oil-cans, and existing repairs), or for certain discrepancies, contacting Boeing for repair instructions.
• The initial compliance times vary depending on inspection type and area. The earliest initial inspection is within 375 flight cycles after the effective date of this AD. The latest initial inspection is within 6,000 flight cycles or 24 months after the effective date of this AD, whichever occurs first.

The compliance times for the option, for airplanes on which oil-cans are found within limits, of doing repetitive detailed and HFEC inspections for cracks of the oil-canning and eventual repair are as follows: The initial inspections are done before further flight. The repetitive interval is 1,200 flight cycles. The repair must be done within 12,000 flight cycles after the oil-can was found.

The repetitive inspections range from intervals not to exceed 6,000 flight cycles to intervals not to exceed 12,000 flight cycles, depending on the inspection type and area.

FAA's Determination

We are proposing this AD because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.

Proposed AD Requirements

This proposed AD would retain all requirements of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999). This proposed AD would also require accomplishing the actions specified in the service information described previously, except as discussed under “Differences Between the Proposed AD and the Service Information.”

Changes to Existing AD

This proposed AD would retain all requirements of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999). Since AD 99-08-23 was issued, the AD format has been revised, and certain paragraphs have been rearranged. As a result, the corresponding paragraph identifiers have changed in this proposed AD, as listed in the following table:

Revised Paragraph Identifiers

Requirement in AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)	Corresponding requirement in this proposed AD
paragraph (a)	paragraph (g)
paragraph (b)	paragraph (h)
paragraph (c)	paragraph (i)
paragraph (d)	paragraph (j)

Boeing Commercial Airplanes has received an Organization Designation Authorization (ODA). We have revised this proposed AD to delegate the authority to approve an alternative method of compliance for any repair required by this proposed AD to the Boeing Commercial Airplanes ODA rather than a Designated Engineering Representative (DER).

We have revised the date of the document specified in paragraph (j)(1) of this proposed AD (which is a restatement of paragraph (d)(1) of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)), to November 5, 1995, as specified in the “Incorporation of Reference” paragraph of AD 99-08-23 (paragraph (g) of AD 99-08-23).

Differences Between the Proposed AD and the Service Information

Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, 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:

• In accordance with a method that we approve; or
• Using data that meet the certification basis of the airplane, and that have been approved by the Boeing Commercial Airplanes Organization Designation Authorization (ODA) whom we have authorized to make those findings.

Costs of Compliance

We estimate that this proposed AD affects 566 airplanes of U.S. registry. We estimate the following costs to comply with this proposed AD:

Estimated Costs

Action	Labor cost	Parts cost	Cost per product	Cost on U.S. operators
LFEC [retained actions from AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)]	8 work-hours × $85 per hour = $680	$0	$680	$384,880.
Detailed visual inspection [retained actions from AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)]	2 work-hours × $85 per hour = $170	0	$170	$96,220.
Detailed, HFEC, and LFEC inspections of the web at the “Y” chord of the bulkhead, the web located under the outer circumferential tear strap, the “Z” stiffeners at the dome cap, and existing repairs [new proposed action]	Up to 60 work-hours × $85 per hour = $5,100 per inspection cycle	0	$5,100 per inspection cycle	$2,886,600 per inspection cycle.

We estimate the following costs to do any necessary on-condition inspections that would be required based on the results of the proposed initial inspection. We have no way of determining the number of aircraft that might need these inspections:

On-Condition Costs

Action	Labor cost	Parts cost	Cost per product
Detailed and HFEC inspections for oil-canning	1 work-hour × $85 per hour = $85	$0	$85
LFEC or HFEC inspections for cracking	2 work-hours × $85 per hour = $170	0	170

We have received no definitive data that would enable us to provide cost estimates for the crack repairs specified in this proposed AD.

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),

(3) Will not affect intrastate aviation in Alaska, and

(4) 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.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Incorporation by reference
• 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 removing airworthiness directive (AD) 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999), and adding the following new AD:

The Boeing Company: Docket No. FAA-2012-0645; Directorate Identifier 2011-NM-052-AD.

(a) Comments Due Date

The FAA must receive comments on this AD action by August 13, 2012.

(b) Affected ADs

This AD supersedes AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999).

(c) Applicability

This AD applies to all The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes; certificated in any category.

(d) Subject

Joint Aircraft System Component (JASC)/Air Transport Association (ATA) of America Code 53, Fuselage.

(e) Unsafe Condition

This AD was prompted by several reports of fatigue cracks in the aft pressure bulkhead. We are issuing this AD to detect and correct such fatigue cracking, which could result in rapid decompression of the fuselage.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Retained Initial Inspection

This paragraph restates the initial inspection required by paragraph (a) of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999). Perform either inspection specified by paragraph (g)(1) or (g)(2) of this AD at the time specified in paragraph (h) of this AD.

(1) Perform a low frequency eddy current (LFEC) inspection from the aft side of the aft pressure bulkhead to detect discrepancies (including cracking, misdrilled fastener holes, and corrosion) of the web of the upper section of the aft pressure bulkhead at body station 1016 at the aft fastener row attachment to the “Y” chord, from stringer 15 left to stringer 15 right, in accordance with Boeing 737 Nondestructive Test Manual D6-37239, Part 6, Section 53-10-54, dated December 5, 1998.

(2) Perform a detailed visual inspection of the aft fastener row attachment to the “Y” chord from the forward side of the aft pressure bulkhead to detect discrepancies (including cracking, misdrilled fastener holes, and corrosion) of the entire web of the aft pressure bulkhead at body station 1016.

(h) Retained Compliance Times

This paragraph restates the compliance times specified in paragraph (b) of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999). Perform the inspection required by paragraph (g) of this AD at the time specified in paragraph (h)(1), (h)(2), or (h)(3) of this AD, as applicable.

(1) For airplanes that have accumulated 40,000 or more total flight cycles as of May 10, 1999 (the effective date of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)): Inspect within 375 flight cycles or 60 days after May 10, 1999, whichever occurs later.

(2) For airplanes that have accumulated 25,000 or more total flight cycles and fewer than 40,000 total flight cycles as of May 10, 1999 (the effective date of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)): Inspect within 750 flight cycles or 90 days after May 10, 1999, whichever occurs later.

(3) For airplanes that have accumulated fewer than 25,000 total flight cycles as of May 10, 1999 (the effective date of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999)): Inspect prior to the accumulation of 25,750 total flight cycles.

(i) Retained Repetitive Inspections

This paragraph restates the repetitive inspections required by paragraph (c) of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999). Within 1,200 flight cycles after performing the initial inspection required by paragraph (g) of this AD, and thereafter at intervals not to exceed 1,200 flight cycles: Perform either inspection specified by paragraph (g)(1) or (g)(2) of this AD.

(j) Retained Corrective Actions

This paragraph restates the corrective actions required by paragraph (d) of AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999). If any discrepancy is detected during any inspection required by paragraph (g), (h), or (i) of this AD: Prior to further flight, accomplish the actions specified by paragraphs (j)(1) and (j)(3) of this AD, and paragraph (j)(2) of this AD, if applicable.

(1) Perform a high frequency eddy current inspection from the forward side of the bulkhead to detect cracking of the web at the “Y” chord attachment, around the entire periphery of the “Y” chord, in accordance with Boeing 737 Nondestructive Test Manual D6-37239, Part 6, Section 51-00-00, Figure 23, dated November 5, 1995.

(2) If the most recent inspection performed in accordance with paragraph (g) of this AD was not a detailed visual inspection: Accomplish the actions specified by paragraph (g)(2) of this AD. If the inspection was a detailed visual inspection, it is not necessary to repeat that inspection prior to further flight.

(3) Repair any discrepancy such as cracking or corrosion or misdrilled fastener holes using a method approved in accordance with the procedures specified in paragraph (u) of this AD.

(k) New Requirements: Inspections of the Web at the “Y” Chord Upper Bulkhead From S-15L to S-15R

At the later of the times specified in paragraphs (k)(1) and (k)(2) of this AD: Do detailed and LFEC inspections of the aft side of the bulkhead web, or do detailed and HFEC inspections from the forward side of the bulkhead, and do all applicable related investigative and corrective actions; in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraphs (r)(1) and (r)(3) of this AD. Inspect for cracks, incorrectly drilled fastener holes, and elongated fastener holes. Do all applicable related investigative and corrective actions before further flight. Repeat the inspections at the applicable times specified in table 1 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(1) Prior to the accumulation of 25,000 total flight cycles.

(2) Except as required by paragraphs (r)(2) and (r)(4) of this AD, at the later of the times specified in the “Compliance Time” column in table 1 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(l) New Requirements: Inspections of the Web at the “Y” Chord in the Lower Bulkhead From S-15L to S-15R

Except as required by paragraphs (r)(2) and (r)(5) of this AD, at the applicable time specified in table 2 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Do detailed and eddy current inspections of the web from the forward or aft side of the bulkhead for cracks, incorrectly drilled fasteners, and elongated fasteners, in accordance with Part III of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraphs (r)(1) and (r)(3) of this AD. If any crack, incorrectly drilled fastener, elongated fastener, or corrosion is found, before further flight, repair the web using a method approved in accordance with the procedures specified in paragraph (u) of this AD. Repeat the inspections at the applicable times specified in table 2 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(m) New Requirements: One-Time Inspection Under the Tear Strap

Except as required by paragraphs (r)(2) and (r)(5) of this AD, at the applicable time specified in table 3 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Do a one-time LFEC inspection for cracks on the aft side of the bulkhead of the web located under the outer circumferential tear strap, or do a one-time HFEC inspection for cracks from the forward side of the bulkhead of the web located under the outer circumferential tear strap, in accordance with Part II of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraph (r)(1) of this AD. If any cracking is found, before further flight, repair the bulkhead using a method approved in accordance with the procedures specified in paragraph (u) of this AD.

(n) New Requirements: Inspection for Oil-Canning

Except as required by paragraph (r)(2) of this AD, at the applicable time specified in table 4 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Do a detailed inspection from the aft side of the bulkhead for oil-canning and do all applicable related investigative and corrective actions, in accordance with Part II of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraph (r)(1) of this AD. Do all related investigative and corrective actions before further flight. Thereafter, repeat the inspection at the applicable times specified in table 4 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011. For oil-cans found within the limits specified in Part II of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: In lieu of installing the repair before further flight, at the applicable times specified in table 4 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, do initial and repetitive detailed and HFEC inspections for cracks of the oil-canning and install the repair, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011. If any crack is found, before further flight, repair the cracking using a method approved in accordance with the procedures specified in paragraph (u) of this AD. Installing the repair terminates the repetitive inspections for cracks.

(o) New Requirements: Inspection of the Dome Cap at the Center of the Bulkhead

Except as required by paragraphs (r)(2) and (r)(5) of this AD, at the applicable time specified in table 5 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Do an eddy current inspection to detect any cracking of the dome cap at the center of the bulkhead, and do all applicable corrective actions, in accordance with Part IV of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011. Do all corrective actions before further flight. Repeat the inspection at the times specified in table 5 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(p) New Requirements: Inspection of the Forward Flange of the “Z” Stiffeners at the Dome Cap

Except as required by paragraphs (r)(2) and (r)(5) of this AD, at the applicable time specified in table 6 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Do an HFEC inspection to detect any cracking of the “Z” stiffener flanges at the dome cap in the center of the bulkhead, in accordance with Part V of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraph (r)(1) of this AD. If any crack is found, before further flight, repair the flanges using a method approved in accordance with the procedures specified in paragraph (u) of this AD. Repeat the inspection at the applicable times specified in table 6 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(q) New Requirement: Inspection for Existing Repairs on the Bulkhead

Except as required by paragraph (r)(2) of this AD, at the applicable time specified in table 7 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Do a detailed inspection of the bulkhead web and stiffeners for existing repairs, in accordance with Part VI of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraph (r)(1) of this AD.

(1) If any repair identified in the “Condition” column of table 8 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, is found and the “Reference” column refers to Appendix A, B, C, or D of that service bulletin: At the applicable times specified in table 8 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraph (r)(2) of this AD, do a HFEC inspection or a LFEC inspection of the web for cracking, in accordance with Appendix A, B, C, or D, as applicable, of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011. If any cracking is found, before further flight, repair using a method approved in accordance with the procedures specified in paragraph (u) of this AD. Repeat the inspections, thereafter, at the applicable intervals specified in table 8 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(2) If any repair identified in the “Condition” column of table 8 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, is found and the “Reference” column refers to Appendix E of that service bulletin: At the applicable times specified in table 8 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, except as required by paragraph (r)(2) of this AD, remove the repair and replace with a new repair, in accordance with Appendix E of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011.

(3) If any non-SRM (structural repair manual) repair is found and the repair does not have FAA-approved damage tolerance inspections, except as required by paragraph (r)(2) of this AD, at the applicable time specified in table 7 of Paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011: Contact the Boeing Commercial Airplanes Organization Designation Authorization (ODA) that has been authorized by the Manager, Seattle ACO, for damage tolerance inspections. Do those damage tolerance inspections at the times given using a method approved in accordance with the procedures specified in paragraph (u) of this AD.

(r) Exceptions to the Service Bulletin

(1) Where Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, specifies to contact Boeing for repair instructions: Before further flight, repair using a method approved in accordance with the procedures specified in paragraph (u) of this AD.

(2) Where Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, specifies a compliance time “after the date of Revision 1 to this service bulletin,” “from the date of Revision 3 of this service bulletin,” “after the date of Revision 3 to this service bulletin,” or “of the effective date of AD 99-08-23,” this AD requires compliance within the specified compliance time after the effective date of this AD.

(3) Access and restoration procedures specified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, are not required by this AD. Operators may do those procedures following their maintenance practices.

(4) Where table 1 of paragraph 1.E., “Compliance” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, specifies a compliance time relative to actions done “in accordance with paragraph (a)(2) of AD 99-08-23,” this AD requires compliance within the specified compliance time relative to actions specified in paragraph (g)(2) of this AD.

(5) Where the Condition columns in tables 2, 3, 5, and 6 of paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1214, Revision 4, dated December 16, 2011, refer to total flight cycles, this AD applies to the airplanes with the specified total flight cycles as of the effective date of this AD.

(s) Terminating Action

Accomplishment of the requirements of paragraphs (k) through (q) of this AD terminates the requirements of paragraphs (g) through (j) of this AD.

(t) Credit for Previous Actions

This paragraph provides credit for the actions required by paragraphs (k) through (s) of this AD, if the actions were performed before the effective date of this AD using the service bulletins specified in paragraphs (t)(1) through (t)(4) of this AD.

(1) Boeing Alert Service Bulletin 737-53A1214, dated June 17, 1999.

(2) Boeing Alert Service Bulletin 737-53A1214, Revision 1, dated June 22, 2000.

(3) Boeing Alert Service Bulletin 737-53A1214, Revision 2, dated May 24, 2001.

(4) Boeing Alert Service Bulletin 737-53A1214, Revision 3, dated January 19, 2011.

(u) Alternative Methods of Compliance (AMOCs)

(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. In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the ACO, send it to the attention of the person identified in the Related Information section of this AD. Information may be emailed to: [e-mail].

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local flight standards district office/certificate holding district office.

(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 the Boeing Commercial Airplanes Organization Designation Authorization (ODA) that 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.

(4) AMOCs approved previously in accordance with AD 99-08-23, Amendment 39-11132 (64 FR 19879, April 23, 1999), are approved as AMOCs for the corresponding provisions of this AD.

(v) Related Information

(1) For more information about this AD, contact Alan Pohl, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington 98057-3356; phone: [phone]; fax: [phone]; email: [e-mail].

(2) For service information identified in this proposed AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone [phone], extension 1; fax [phone]; Internet https://www.myboeingfleet.com. You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. For information on the availability of this material at the FAA, call 425-227-1221.

Issued in Renton, Washington, on June 18, 2012.

John P. Piccola,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.