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Proposed Rule

Airworthiness Directives; The Boeing Company 737-200, -200C, -300, -400, and -500 Series Airplanes

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Start Preamble

AGENCY:

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

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain Boeing Model 737-200, -200C, -300, -400, and -500 series airplanes. The existing AD currently requires repetitive inspections to find fatigue cracking of certain upper and lower skin panels of the fuselage, and follow-on and corrective actions if necessary. The existing AD also includes a terminating action for the repetitive inspections of certain modified or repaired areas only. This proposed AD would add new inspections for cracking of the fuselage skin along certain chem-milled lines, and corrective actions if necessary. This proposed AD would also reduce certain thresholds and intervals required by the existing AD. This proposed AD results from reports of new findings of vertical cracks in the fuselage skin along the chem-milled steps adjacent to the butt joints. We are proposing this AD to detect and correct fatigue cracking of the skin panels, which could result in sudden fracture and failure of the skin panels of the fuselage, and consequent rapid decompression of the airplane.

DATES:

We must receive comments on this proposed AD by April 22, 2011.

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 proposed AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone 206-544-5000, extension 1; fax 206-766-5680; e-mail me.boecom@boeing.com; 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 (telephone 800-647-5527) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

Start Further Info

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 (425) 917-6447; fax (425) 917-6590; e-mail: wayne.lockett@faa.gov.

End Further Info End Preamble Start Supplemental Information

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-2011-0155; Directorate Identifier 2009-NM-141-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 August 26, 2004, we issued AD 2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004), for certain Model 737-200, -200C, -300, -400, and -500 series airplanes. That AD requires repetitive inspections to find fatigue cracking of certain upper and lower skin panels of the fuselage, and follow-on and corrective actions if necessary. That AD also includes a terminating action for the repetitive inspections of certain modified or repaired areas only. That AD resulted from reports indicating new findings of cracks were found along the edges of the chem-milled pockets in the upper skin at certain stringers. We issued that AD to find and fix fatigue cracking of the skin panels, which could result in sudden fracture and failure of the skin panels of the fuselage, and consequent rapid decompression of the airplane.

Actions Since Existing AD Was Issued

Since we issued AD 2004-18-06, we have received reports of new findings of vertical cracks in the fuselage skin along the chem-milled steps adjacent to the butt joints and at certain body stations on airplanes with between 45,100 flight cycles (65,200 flight hours) and 67,400 flight cycles (70,800 flight hours).

A decompression event connected to chem-milled steps occurred in July 2009 (after issuance of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009) and resulted in re-evaluation of the inspection thresholds and repetitive intervals. The new data and analysis require the repetitive intervals be reduced from those currently specified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. These new repetitive intervals are defined in the differences section of the NPRM.

Explanation of Relevant Service Information

We have reviewed Boeing Alert Service Bulletin 737-53A1210, Revision 2, dated March 3, 2009; and Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001, was referred to as the appropriate source of service information for accomplishing the actions in the existing AD.

Boeing Alert Service Bulletin 737-53A1210, Revision 2, describes procedures for, among other things, Start Printed Page 12620repetitive external detailed and eddy current inspections for cracking of the fuselage skin along certain chem-milled lines, and corrective actions if necessary. The corrective actions include doing a time-limited repair or a permanent repair, as applicable. After installation of a time-limited repair, an external detailed inspection is done of the repaired area for cracks and loose or missing fasteners. For airplanes on which cracks are found, this service bulletin recommends contacting Boeing for repair instructions and repairing; and, for airplanes on which loose or damaged fasteners are found this service bulletin specifies replacing any damaged or loose fasteners. This service bulletin adds an optional preventive modification for Groups 3, 5, 6, and 8 at body station (BS) 500D through BS 520 on Model 737-300 airplanes, and BS 482B through BS 520, stringer 12, on Model 737-500 airplanes. This service bulletin also reduces the effectivity specified in Revision 1, and contains editorial changes.

Boeing Alert Service Bulletin 737-53A1210, Revision 3, clarifies certain work instructions. This service bulletin also specifies that more work is necessary for airplanes on which the actions in Boeing Alert Service Bulletin 737-53A1210, dated December 14, 2000; or Revision 1, dated October 25, 2001; were done. In addition, Revision 3 of this service bulletin adds the airplanes that were incorrectly removed from the effectivity in Revision 2 of this service bulletin, which were not identified until after Revision 2 of this service bulletin was issued. Therefore, the effectivity in Revision 3 of this service bulletin is the same as the effectivity in Revision 1 of this service bulletin.

Boeing Alert Service Bulletin 737-53A1210, Revision 3, specifies that the repetitive inspection interval is 4,500 flight cycles.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to develop on other airplanes of the same type design. For this reason, we are proposing this AD, which would supersede AD 2004-18-06 and would retain certain requirements of the existing AD. 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 Service Information.” This proposed AD also reduces the compliance time of 40,000 total flight cycles for doing certain actions in AD 2004-18-06; this proposed AD specifies a compliance time of 35,000 total flight cycles in paragraph (s) of this AD.

Differences Between the Proposed AD and Service Information

Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, specifies to contact the manufacturer for disposition of certain repair 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) that we have authorized to make those findings.

Boeing Alert Service Bulletin 737-53A1210, Revision 2, dated March 3, 2009, specifies that no airplanes were added or removed from the effectivity; however, the manufacturer has informed us that there were airplanes incorrectly removed in the “Identification by Customer, Customer Code, Group and Variable Number” section in Paragraph 1.A.1 of Revision 2 of this service bulletin. In light of the fact that Revision 3 of this service bulletin includes those airplanes in its effectivity, and includes all the actions specified in Revision 2 of this service bulletin, this proposed AD would require that the new actions be done in accordance with Revision 3 of this service bulletin.

Paragraph 1.E of Boeing Alert Service Bulletin 737-53A1210, Revision 3, specifies a repetitive inspection interval of 4,500 flight cycles; that interval is expected to be reduced when this service bulletin is revised. The manufacturer has informed us that it has re-evaluated the inspection interval because it would not address the identified unsafe condition soon enough to ensure an acceptable level of safety for the affected fleet. In light of this fact, we find that a repetitive inspection interval of 1,800 flight cycles, for the actions specified in Tables 1 through 5, represents an appropriate interval of time for affected airplanes to continue to operate without compromising safety.

Part 8 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, specifies a post-repair inspection of the skin chem-milled crack repair at stringer 12; that inspection is not required by this proposed AD. The damage tolerance inspections specified in Table 7 of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, may be used in support of compliance with section 121.1109(c)(2) or 129.109(c)(2) of the Federal Aviation Regulations (14 CFR 121.1109(c)(2) or 14 CFR 129.109(c)(2)).

Explanation of Change to This Proposed AD

Boeing Commercial Airplanes has received an Organization Delegation Authority (ODA), which replaces their previous designation as a Designated Engineering Representative (DER). We have revised paragraphs (j) and (l)(2) of this proposed AD to delegate the authority to approve an alternative method of compliance for any repair required by this AD to the Boeing Commercial Airplanes ODA.

Change to Existing AD

This proposed AD would retain certain requirements of AD 2004-18-06. Since AD 2004-18-06 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 2004-18-06Corresponding requirement in this proposed AD
paragraph (a)paragraph (g)
paragraph (b)paragraph (h)
paragraph (c)paragraph (i)
paragraph (d)paragraph (j)
paragraph (e)paragraph (k)
paragraph (f)paragraph (l)
paragraph (g)paragraph (m)
paragraph (h)paragraph (n)
paragraph (i)paragraph (o)

We have revised paragraph (m) of this proposed AD to specify that doing paragraph (b) or (c), as applicable, of AD 2003-14-06, Amendment 39-13225, after the effective date of this proposed AD does not terminate any of the actions required by paragraph (g) of this proposed AD. Recent reports of cracking have shown that a detailed inspection alone is not sufficient to find cracks in the fuselage skin. The cracking begins on the internal surface of the skin and grows outward, not becoming visible on the external surface until the crack is at least three inches in length. Actions accomplished before the effective date of this AD in accordance with AD 2003-14-06, which terminate certain requirements of paragraph (g) of this proposed AD, are reinstated with the new requirements specified in paragraph (p) of this proposed AD.Start Printed Page 12621

Costs of Compliance

There are about 903 airplanes of U.S. registry affected by AD 2004-18-06.

The inspections of the crown area that are required by AD 2004-18-06 take about 94 work hours per airplane to accomplish, at an average labor rate of $85 per work hour. Based on these figures, the estimated cost of the currently required inspections is $7,990 per airplane, per inspection cycle.

The inspections of the lower lobe area that are required by AD 2004-18-06 take about 96 work hours per airplane to accomplish, at an average labor rate of $85 per work hour. Based on these figures, the estimated cost of the currently required inspections is $8,160 per airplane, per inspection cycle.

Should an operator elect to install the preventive modification specified in AD 2004-18-06 it will take about 108 work hours per airplane to accomplish, at an average labor rate of $85 per work hour. Based on these figures, the estimated cost of the modification is $9,180 per airplane.

The new proposed inspections would affect about 701 airplanes of U.S. registry.

The new proposed inspections would take about 27 work hours per airplane, at an average labor rate of $85 per work hour. Based on these figures, the estimated cost of the new actions specified in this proposed AD for U.S. operators is $1,608,795, or $2,295 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),

(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.

Start List of Subjects

List of Subjects in 14 CFR Part 39

End List of Subjects

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

Start Part

PART 39—AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Start Authority

Authority: 49 U.S.C. 106(g), 40113, 44701.

End Authority
[Amended]

2. The FAA amends § 39.13 by removing amendment 39-13784 (69 FR 54206, September 8, 2004) and adding the following new AD:

The Boeing Company: Docket No. FAA-2011-0155; Directorate Identifier 2009-NM-141-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by April 22, 2011.

Affected ADs

(b) This AD supersedes AD 2004-18-06, Amendment 39-13784. AD 2002-07-08, Amendment 39-12702; and AD 2003-14-06, Amendment 39-13225; affect this AD.

Applicability

(c) This AD applies to The Boeing Company Model 737-200, -200C, -300, -400, and -500 series airplanes, certificated in any category, as listed in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

Subject

(d) Air Transport Association (ATA) of America Code 53: Fuselage.

Unsafe Condition

(e) This AD results from new findings of vertical cracks along chem-milled steps adjacent to the butt joints. The Federal Aviation Administration is issuing this AD to detect and correct fatigue cracking of the skin panels, which could result in sudden fracture and failure of the skin panels of the fuselage, and consequent rapid decompression of the airplane.

Compliance

(f) You are responsible for having the actions required by this AD performed within the compliance times specified, unless the actions have already been done.

Restatement of Certain Requirements of AD 2004-18-06, Amendment 39-13784

External Detailed and Eddy Current Inspections

(g) For Groups 1 through 5 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001: Before the accumulation of 35,000 total flight cycles, or within 4,500 flight cycles after October 13, 2004 (the effective date of AD 2004-18-06), whichever is later, do external detailed and eddy current inspections of the crown area and other known areas of fuselage skin cracking, per Part 1 and Figure 1 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. As of the effective date of this AD, use only Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Repeat the external detailed and eddy current inspections at intervals not to exceed 4,500 flight cycles until paragraph (i), (j)(1)(ii), (k), (l), or (m) of this AD has been done, as applicable. Although paragraph 1.D. of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001, references a reporting requirement, such reporting is not required by this AD. Accomplishing the actions required by paragraph (p) or (q) of this AD ends the repetitive requirements in this paragraph.

Note 1:

For the purposes of this AD, a detailed inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”

(h) For all airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001, do an external detailed inspection of the lower lobe area and section 41 of the fuselage for cracking, per Part 2 and Figure 2 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in accordance with Part 4 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, Start Printed Page 12622dated July 16, 2009. As of the effective date of this AD, use only Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. At the earlier of the times specified in paragraphs (h)(1) and (h)(2) of this AD, do the inspection specified in this paragraph and repeat the inspection thereafter at intervals not to exceed 4,500 flight cycles until paragraph (j)(2) or (k) of this AD has been done, as applicable. Accomplishing the actions required by paragraph (s) of this AD ends the requirements in this paragraph.

(1) Within 9,000 flight cycles after doing the most recent internal detailed inspection.

(2) Within 4,500 flight cycles after October 13, 2004, or before the accumulation of 40,000 total flight cycles, whichever occurs later.

Preventive Modification

(i) For Groups 3 and 5 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001: If no cracking is found during any inspection required by paragraph (g) of this AD, doing the preventive modification of the chem-milled pockets in the upper skin as specified in Part 5 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or as specified in Part 7 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as required by paragraph (x) of this AD; ends the repetitive external detailed and eddy current inspections required by paragraph (g) of this AD for the modified area only. As of the effective date of this AD, use only Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

Corrective Actions

(j) If any cracking is found during any inspection required by paragraph (g), (h), (p), (q), or (s) of this AD, before further flight, do the actions specified in paragraphs (j)(1) and (j)(2) of this AD, as applicable, in accordance with the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or Revision 3, dated July 16, 2009. As of the effective date of this AD, use only Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Where Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or Revision 3, dated July 16, 2009; specify to contact Boeing for repair instructions, before further flight, repair per a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA; or per data meeting the type certification basis of the airplane if it is approved by the Boeing Commercial Airplanes Organization Designation Authorization (ODA) or any other person 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.

(1) Except as provided by paragraph (k) of this AD, for cracking of the crown area, do the repair specified in either paragraph (j)(1)(i) or (j)(1)(ii) of this AD.

(i) Do a time-limited repair per Part 4 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in accordance with Part 6 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as required by paragraph (x) of this AD, then do the actions required by paragraph (l) of this AD at the times specified in that paragraph.

(ii) Do a permanent repair per Part 3 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in accordance with Part 5 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Installation of a permanent repair ends the repetitive inspections required by paragraph (g) of this AD for the repaired area only. Installation of the lap joint repair specified in paragraph (g) of AD 2002-07-08, Amendment 39-12702, is considered acceptable for compliance with the corresponding permanent repair specified in this paragraph for the repaired areas only.

(2) Except as provided by paragraph (k) of this AD, for cracking of the lower lobe area and Section 41, repair per Part 2 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in accordance with paragraph (j)(2)(i) or (j)(2)(ii) of this AD. Accomplishment of this repair ends the repetitive inspections required by paragraph (h) of this AD for the repaired area only. As of the effective date of this, do the repair specified in paragraph (j)(2)(i) or (j)(2)(ii) of this AD.

(i) Do a time-limited repair in accordance with Part 6 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as required by paragraph (x) of this AD, then do the actions required by paragraph (l) of this AD at the times specified in that paragraph.

(ii) Do a permanent repair in accordance with Part 5 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

Optional Repair Method

(k) For cracking in any area specified in paragraphs (j)(1) and (j)(2) of this AD within the limitations of the applicable structural repair manual (SRM) specified in table 1 of this AD, repair any cracks per the applicable SRM specified in table 1 of this AD. Accomplishment of the applicable repair terminates the repetitive inspections required by paragraphs (g) and (h) of this AD for the repaired area only.

Table 1—SRM References

ModelSubject/figureRevisionDateSRM
737-100, -200 series airplanes53-30-3, Figure 48102September 10, 2010Boeing 737-100/-200 SRM, D6-15565.
737-300 series airplanes53-00-01, Figure 22992November 10, 2010Boeing 737-300 SRM D6-37635.
737-400 series airplanes53-00-01, Figure 23175November 10, 2010Boeing 737-400 SRM, D6-38246.
737-500 series airplanes53-00-01, Figure 22970November 10, 2010Boeing 737-500 SRM, D6-38441.

Follow-on and Corrective Actions

(l) If a time-limited repair is done, as specified in paragraph (j)(1)(i) or (j)(2)(i) of this AD: Do the actions specified in paragraphs (l)(1), (l)(2), and (l)(3) of this AD, at the times specified in paragraphs (l)(1), (l)(2), and (l)(3) of this AD, per the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

(1) Within 3,000 flight cycles after doing the repair: Do the actions specified in paragraph (l)(1)(i) or (l)(1)(ii) of this AD. Then repeat the applicable inspection specified in paragraph (l)(1)(i) or (l)(1)(ii) of this AD at intervals not to exceed 3,000 flight cycles until permanent rivets are installed in the repaired area, which ends the repetitive inspections for this paragraph. As of the effective date of this AD, do only the inspections specified in paragraph (l)(1)(ii) of this AD.

(i) For repairs done before the effective date of this AD: Do a detailed inspection of the repaired area for loose fasteners per Part 4 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001, or do the actions specified in paragraph (l)(1)(ii) of this AD. If any loose fastener is found, before further flight, replace with a new fastener per Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001.

(ii) For repairs done after the effective date of this AD: Do a detailed inspection of the repaired area for loose, damaged, and missing fasteners in accordance with Part 6 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. If any loose, missing, or damaged fastener is found, before further flight, replace with a new fastener in accordance with Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

(2) At the applicable time specified in paragraph (l)(2)(i) and (l)(2)(ii) of this AD: Do inspections of the repaired area for cracking per Part 4 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in Start Printed Page 12623accordance with Part 6 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. If any cracking is found, before further flight, repair per a method approved by the Manager, Seattle ACO, or per data meeting the type certification basis of the airplane if it is approved by the Boeing Commercial Airplanes ODA or any other person 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.

(i) For repairs done before the effective date of this AD: Within 4,000 flight cycles after doing the repair, do the inspections.

(ii) For repairs done on or after the effective date of this AD: Within 3,000 flight cycles after doing the repair, do the inspections.

(3) At the earlier of the times specified in paragraphs (l)(3)(i) and (l)(3)(ii) of this AD: Make the repair permanent per Part 4 and Figure 20 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001, or do the permanent repair in accordance with Part 5 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, which ends the repetitive inspections for the repaired area only. As of the effective date of this AD, make the repair permanent in accordance with Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

(i) Within 10,000 flight cycles after doing the repair in accordance with Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001.

(ii) At the later of the times specified in paragraphs (l)(3)(ii)(A) and (l)(3)(ii)(B) of this AD.

(A) Within 6,000 flight cycles after doing the repair.

(B) Within 1,000 flight cycles after the effective date of this AD.

Optional Terminating Action for Repetitive Eddy Current Inspections if Done Before the Effective Date of This AD

(m) Accomplishment of paragraph (b) or (c), as applicable, of AD 2003-14-06, Amendment 39-13225, before the effective date of this AD ends the repetitive eddy current inspections required by paragraph (g) of this AD for that skin panel only; however, the repetitive external detailed inspections required by paragraph (g) of this AD are still required for all areas. As of the effective date of this AD, accomplishing paragraph (b) or (c), as applicable, of AD 2003-14-06, Amendment 39-13225, does not end the repetitive eddy current inspections required by paragraph (g) of this AD.

Credit for Actions Done per Previous Service Bulletin

(n) Inspections, repairs, and preventive modifications done before October 13, 2004, in accordance with Boeing Alert Service Bulletin 737-53A1210, dated December 14, 2000, are acceptable for compliance with the corresponding actions required by paragraphs (g), (h), (i), (j), (k), and (l) of this AD.

Exception to Service Bulletin Procedures

(o) For airplanes subject to the requirements of paragraphs (g), (h), (p), and (q) of this AD: Inspections are not required in areas that are spanned by an FAA-approved repair that has a minimum of 3 rows of fasteners above and below the chem-milled step. If an external doubler covers the chem-milled step, but does not span it by a minimum of 3 rows of fasteners above and below, in lieu of requesting approval for an alternative method of compliance (AMOC), one option to comply with the inspection requirement of paragraphs (g) and (h) of this AD is to inspect all chem-milled steps covered by the repair using internal nondestructive test (NDT) methods in accordance with Part 6 of the Boeing 737 Non-Destructive Test NDT Manual. As of the effective date of this AD, inspect in accordance with Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.

New Requirements of This AD

Repetitive Inspections and Corrective Actions if Necessary

(p) For Groups 1 through 5 and 9 through 21 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, on which the inspections required by paragraph (g) of this AD have been done before the effective date of this AD: At the applicable time specified in paragraph (p)(1) or (p)(2) of this AD, do external detailed and eddy current inspections of the crown area and other known areas of fuselage skin cracking in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009; except as provided by paragraph (o) of this AD. Repeat the external detailed and eddy current inspections thereafter at intervals not to exceed 1,800 flight cycles. Accomplishing the inspections required by this paragraph ends the repetitive inspections required by paragraph (g) of this AD. Before further flight, do all applicable corrective actions as specified in paragraph (j) of this AD.

(1) For airplanes on which any action specified in paragraph (i), (j)(1)(ii), (k), (l), or (m) of this AD has been done: Within 1,800 flight cycles after the effective date of this AD.

(2) For airplanes on which actions specified in paragraphs (i), (j)(1)(ii), (k), (l), and (m) of this AD have not been done: Within 4,500 flight cycles after doing the most recent inspection required by paragraph (g) of this AD, or within 1,800 flight cycles after the effective date of this AD, whichever is later.

(q) For Groups 1 through 5 and 9 through 21 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009; on which the inspections required by paragraph (g) of this AD have not been done before the effective date of this AD: Before the accumulation of 35,000 total flight cycles, or within 1,800 flight cycles after the effective date of this AD, whichever is later, do external detailed and eddy current inspections of the crown area and other known areas of fuselage skin cracking in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Repeat the external detailed and eddy current inspections thereafter at intervals not to exceed 1,800 flight cycles. Before further flight, do all applicable corrective actions as specified in paragraph (j) of this AD.

(r) For Group 1 through 5 and 9 through 21 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009: At the later of the times specified in paragraphs (r)(1) and (r)(2) of this AD, do external detailed and eddy current inspections for vertical cracks in the fuselage skin along the chem-milled steps of the butt joints, in accordance with Part 3 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Repeat the inspections thereafter at intervals not to exceed 1,800 flight cycles or 1,800 flight hours, whichever occurs first. If any cracking is found, before further flight, repair in accordance with Part 5 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Doing the repair terminates the repetitive inspections specified in this paragraph for the repaired area only.

(1) Before the accumulation of 55,000 total flight cycles or 55,000 total flight hours, whichever occurs first.

(2) Within 1,800 flight cycles or 1,800 flight hours after the effective date of this AD, whichever occurs first.

(s) For Groups 1 through 21 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009: Before the accumulation of 35,000 total flight cycles or within 4,500 flight cycles after the effective date of this AD, whichever is later, do external detailed and eddy current inspections for horizontal cracks along the chem-milled lines of the fuselage skin of the lower lobe area and section 41, in accordance with Part 4 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009; except as required by paragraph (u) of this AD. Repeat the inspections thereafter at intervals not to exceed 4,500 flight cycles. Accomplishing the inspections required by this paragraph ends the repetitive inspections required by paragraph (h) of this AD. Before further flight, do all applicable corrective actions as specified in paragraph (j) of this AD.

(t) For Groups 4, 11, and 16 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009: Before the accumulation of 25,000 total flight cycles or within 4,500 flight cycles after the effective date of this AD, whichever is later, do external detailed and eddy current inspections for horizontal cracks along the chem-milled lines of the fuselage skin of the fuselage window belt area in accordance with Part 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Repeat the inspections thereafter at intervals not to exceed 4,500 flight cycles. If any cracking is found, before further flight, repair using a Start Printed Page 12624method approved in accordance with paragraph (y) of this AD.

(u) For Groups 3, 5, 9, 10, 12, 14, 15, 17, 18, 19, 20, and 21 airplanes identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009: Do the actions specified in paragraph (u)(1) or (u)(2) of this AD, as applicable.

(1) For airplanes on which the inspections required by paragraph (g) of this AD have been done before the effective date of this AD: Within 4,500 flight cycles after doing the most recent inspection required by paragraph (g) of this AD, do external detailed and eddy current inspections for horizontal cracks along the chem-milled lines of the fuselage skin of the fuselage window belt area in accordance with Part 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Repeat the inspections thereafter at intervals not to exceed 4,500 flight cycles. If any cracking is found, before further flight, repair in accordance with Part 8 of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as required by paragraph (x) of this AD.

(2) For airplanes on which the inspections required by paragraph (g) of this AD have not been done before the effective date of this AD: Before the accumulation of 25,000 total flight cycles or within 4,500 flight cycles after the effective date of this AD, whichever is later, do external detailed and eddy current inspections for horizontal cracks along the chem-milled lines of the fuselage skin of the fuselage window belt area in accordance with Part 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. Repeat the inspections thereafter at intervals not to exceed 4,500 flight cycles. If any cracking is found, before further flight, repair in accordance with Part 8 of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as required by paragraph (x) of this AD.

Repair and Preventive Modification

(v) For airplanes on which cracking is found during any inspection required by paragraph (p), (q), (r), or (s) of this AD, as applicable, doing the repair of the chem-milled area in the skin, as specified in Part 5 or Part 6 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, ends the repetitive external detailed and eddy current inspections required by paragraph (p), (q), (r), or (s) of this AD, as applicable, for the repaired area only.

Note 2:

Part 8 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, specifies a post-repair inspection of the skin chem-milled crack repair at stringer 12; that inspection is not required by this AD. The damage tolerance inspections specified in Table 7 of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, may be used in support of compliance with section 121.1109(c)(2) or 129.109(c)(2) of the Code of Federal Regulations (14 CFR 121.1109(c)(2) or 14 CFR 129.109(c)(2)).

(w) For airplanes on which no cracking is found during any inspection required by paragraph (p) or (q) of this AD, as applicable, doing the preventive modification of the chem-milled areas in the skin at stringer S-12, as specified in Part 7 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as required by paragraph (x) of this AD, ends the repetitive external detailed and eddy current inspections required by paragraph (p) or (q) of this AD, as applicable, for the modified area only.

Exception to Boeing Alert Service Bulletin 737-53A1210, Revision 3

(x) Where Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, specifies to contact Boeing for repair instructions, before further flight, repair using a method approved in accordance with paragraph (y) of this AD.

Alternative Methods of Compliance (AMOCs)

(y)(1) The Manager, Seattle Aircraft Certification Office (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 e-mailed to: 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.

(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 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 2004-18-06, Amendment 39-13784, are approved as AMOCs for the corresponding provisions of this AD.

Related Information

(z) For more information about this AD, contact Wayne Lockett, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 917-6447; fax (425) 917-6590; e-mail: wayne.lockett@faa.gov.

Start Signature

Issued in Renton, Washington on February 22, 2011.

Kalene C. Yanamura,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

End Signature End Part End Supplemental Information

[FR Doc. 2011-5159 Filed 3-7-11; 8:45 am]

BILLING CODE 4910-13-P