2011-19904. Airworthiness Directives; The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 Series 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 certain Model 737-100 and -200 series airplanes. The existing AD currently requires various inspections for cracks in the outboard chord of the frame at body station (BS) 727 and in the outboard chord of stringer (S) 18A, and repair or replacement of cracked parts. Since we issued that AD, there have been several reports of fatigue cracking in the frame outboard chord at BS 727 and in the radius of the auxiliary chord on airplanes that were not affected by the existing AD. This proposed AD would add airplanes to the applicability statement in the existing AD and add inspections for cracks in the BS 727 frame outboard chords and the radius of the auxiliary chord, for certain airplanes. This proposed AD would also remove the inspections of the outboard chord of S-18A required by the existing AD. We are proposing this AD to detect and correct fatigue cracking of the outboard and auxiliary chords, which could result in reduced structural integrity of the outboard chord and consequent rapid decompression of the airplane.

DATES:

We must receive comments on this proposed AD by September 19, 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: [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 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]; e-mail [e-mail]; 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]; e-mail [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-2011-0722; Directorate Identifier 2010-NM-262-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 June 5, 1995, we issued AD 95-12-17, amendment 39-9268 (60 FR 36981, July 19, 1995), for certain Model 737-100 and -200 series airplanes. That AD requires various inspections for cracks in the outboard chord of the frame at body station (BS) 727 and in the outboard chord of stringer (S) 18A, and repair or replacement of cracked parts. That AD resulted from reports of fatigue cracks in those outboard chords. We issued that AD to prevent such fatigue cracking, which could result in reduced structural integrity of the outboard chords, and subsequent rapid decompression of the airplane.

Actions Since Existing AD Was Issued

Since we issued AD 95-12-17, we have received several reports of fatigue cracking in the frame outboard chord at BS 727 and in the radius of the auxiliary chord. The cracking in the chords occurred on airplanes that had accumulated between 20,000 and 52,000 total flight cycles, and between 27,000 and 74,000 total flight hours. The cracking in the auxiliary chord occurred on airplanes that had accumulated between 46,000 and 85,000 total flight cycles, and between 41,000 and 64,000 total flight hours. This cracking is caused by fatigue. The airplanes that are affected by AD 95-12-17 were produced with outboard chords at BS 727 made of 7075-T6 aluminum; subsequent airplanes were produced with outboard chords made of 7075-T73 aluminum.

In addition, we have determined that the inspections of the outboard chord of S-18A required by the existing AD are no longer necessary. The new inspections (described below) will decrease the probability of cracks in the frame at BS 727 where S-18A is attached.

Relevant Service Information

We reviewed Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006. The existing AD refers to Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; and Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; for accomplishing the required actions. Revision 1 of this service bulletin was issued to include airplanes having 7075-T73 frame outboard chords. Revision 2 of this service bulletin expands the effectivity in Revision 1 of this service bulletin, and adds inspections for cracks of the 7075-T73 frame outboard chord and in the radius of the auxiliary chord, and repair or replacement if necessary.

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 certain requirements of AD 95-12-17. This proposed AD would add airplanes to the applicability statement in the existing AD. This proposed AD would also remove the inspections of the outboard chord of S-18A required by the existing AD, and add inspections for cracks in the BS 727 frame outboard chords and the radius of the auxiliary chord, for certain airplanes. This proposed AD would require accomplishing the actions specified in the service information described previously, except as discussed under “Difference Between the Proposed AD and the Service Information.”

Change to Existing AD

Since AD 95-12-17 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 95-12-17	Corresponding requirement in this proposed AD
paragraph (a)	paragraph (g)
paragraph (b)	paragraph (h)
paragraph (c)	paragraph (i)
paragraph (d)	paragraph (j)
paragraph (e)	removed
paragraph (f)	paragraph (k)
paragraph (g)	paragraph (l)

Difference Between the Proposed AD and the Service Information

Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006, specifies contacting the manufacturer for instructions on how to repair a certain condition, but this AD requires repairing that condition 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 Organization Designation Authorization whom we have authorized to make those findings.

Costs of Compliance

We estimate that this proposed AD affects 574 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	Number of U.S. airplanes
Various inspections (retained actions from existing AD)	4 work-hours × $85 per hour = $340 per inspection cycle	$0	$340 per inspection cycle	$100,640 per inspection cycle	296
Ultrasonic inspection (new proposed action)	13 work-hours × $85 per hour = $1,105 per inspection cycle	0	1,105 per inspection cycle	634,270 per inspection cycle	574
Detailed and HFEC inspections (new proposed actions)	13 work-hours × $85 per hour = $1,105 per inspection cycle	0	1,105 per inspection cycle	634,270 per inspection cycle	574

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

On-Condition Costs

Action	Labor cost	Parts cost	Cost per product
Optional modification (retained action from existing AD)	50 work-hours × $85 per hour = $4,250	$3,680	$7,930
Repair of cracking of the outboard chord frame	514 work-hours × $85 per hour = $42,690	13,586	57,276
Time-limited repair cracking of the outboard chord frame	63 work-hours × $85 per hour = $5,355	2,732	8,087
Repair of cracking of the outboard chord	49 work-hours × $85 per hour = $4,165	4,255	8,420

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) 95-12-17, Amendment 39-9268 (60 FR 36981, July 19, 1995), and adding the following new AD:

The Boeing Company: Docket No. FAA-2011-0722; Directorate Identifier 2010-NM-262-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by September 19, 2011.

Affected ADs

(b) This AD supersedes AD 95-12-17, Amendment 39-9268.

Applicability

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

Subject

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

Unsafe Condition

(e) This AD was prompted by several reports of fatigue cracking in the frame outboard chord at body station (BS) 727, and cracks in the radius of the auxiliary chord on airplanes that were not affected by the existing AD. We are issuing this AD to detect and correct fatigue cracking of the outboard and auxiliary chords, which could result in reduced structural integrity of the outboard chord and consequent rapid decompression of the airplane.

Compliance

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

Restatement of Certain Requirements of AD 95-12-17 With Revised Service Information: Repetitive Inspections and Repair or Replacement

(g) For Model 737-100 and -200 series airplanes on which the BS 727 frame upper outboard chord has been replaced in accordance with Boeing Service Bulletin 737-53-1088: Prior to the accumulation of 30,000 total flight cycles since replacement of the upper outboard chord, or within 4,500 flight cycles after August 18, 1995 (the effective date of AD 95-12-17), whichever occurs later, perform close visual, pulse echo shear wave (PESW), and high frequency eddy current (HFEC) inspections to detect cracks in the outboard chord of the frame at BS 727, in accordance with Part I of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; or Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006; as applicable. As of the effective date of this AD use only Revision 2 of this service bulletin.

(h) For Model 737-100 and -200 series airplanes on which the BS 727 frame upper outboard chord has been replaced in accordance with Boeing Service Bulletin 737-53-1088: Repeat the inspections required by paragraph (g) of this AD at the time specified in paragraphs (h)(1), (h)(2), (h)(3), and (h)(4) of this AD, as applicable, until the optional terminating action described in paragraph (l) of this AD is accomplished.

(1) If, at the time of the most recent inspection required by paragraph (g) or (h) of this AD, the airplane has accumulated 27,000 or more total flight cycles, but fewer than 50,000 total flight cycles since the replacement of the outboard chord: Perform the next inspection within 15,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 15,000 flight cycles until the airplane has accumulated 50,000 or more total flight cycles since the replacement of the outboard chord. Do the inspections required by paragraph (h)(2) of this AD at the time specified.

(2) If, at the time of the most recent inspection required by paragraph (g) or (h) of this AD, the airplane has accumulated 50,000 or more total flight cycles, but fewer than 60,000 total flight cycles, since the replacement of the outboard chord: Perform the next inspection within 7,500 flight cycles. Repeat the inspection thereafter at intervals not to exceed 7,500 flight cycles until the airplane has accumulated 60,000 or more total flight cycles since the replacement of the outboard chord. Do the inspections required by paragraph (h)(3) of this AD at the time specified.

(3) If, at the time of the most recent inspection required by paragraph (g) or (h) of this AD, the airplane has accumulated 60,000 or more total flight cycles, but fewer than 70,000 total flight cycles, since the replacement of the outboard chord: Perform the next inspection within 5,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 5,000 flight cycles until the airplane has accumulated 70,000 or more total flight cycles since the replacement of the outboard chord. Do the inspections required by paragraph (h)(4) of this AD at the time specified.

(4) If, at the time of the most recent inspection required by paragraph (g) or (h) of this AD, the airplane has accumulated 70,000 or more total flight cycles since replacement of the outboard chord: Perform the next inspection within 3,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles.

(i) For Model 737-100 and -200 series airplanes on which the BS 727 frame outboard chord has not been replaced, or on which only the lower outboard chord has been replaced in accordance with Boeing Service Bulletin 737-53-1088: Perform close visual, PESW, and HFEC inspections to detect cracks in the outboard chord of the frame at BS 727, in accordance with Part I of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; or Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006; as applicable. As of the effective date of this AD, use only Revision 2 of this service bulletin. Perform these inspections initially at the time specified in paragraph (i)(1), (i)(2), (i)(3), or (i)(4), as applicable. Repeat these inspections thereafter at the intervals specified in paragraph (j) of this AD.

(1) For airplanes that have accumulated 27,000 or more total flight cycles, but fewer than 50,000 total flight cycles, as of August 18, 1995: Inspect prior within 4,500 flight cycles after August 18, 1995.

(2) For airplanes that have accumulated 50,000 or more total flight cycles, but fewer than 60,000 total flight cycles, as of August 18, 1995: Inspect prior to the accumulation of 2,500 flight cycles after August 18, 1995.

(3) For airplanes that have accumulated 60,000 or more total flight cycles, but fewer than 70,000 total flight cycles as of August 18, 1995: Inspect prior to the accumulation of 1,500 flight cycles after August 18, 1995.

(4) For airplanes that have accumulated 70,000 or more total flight cycles as of August 18, 1995: Inspect prior to the accumulation of 500 flight cycles or within 90 days after August 18, 1995, whichever occurs first.

(j) Repeat the inspections required by paragraph (i) of this AD at the time specified in paragraphs (j)(1), (j)(2), (j)(3), and (j)(4) of this AD, as applicable, until the optional terminating action described in paragraph (l) of this AD is accomplished:

(1) If, at the time of the most recent inspection required by paragraph (i) or (j) of this AD, the airplane has accumulated 27,000 or more total flight cycles, but fewer than 50,000 total flight cycles: Perform the next inspection within 15,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 15,000 flight cycles until the airplane has accumulated 50,000 or more total flight cycles. Do the inspections required by paragraph (j)(2) of this AD at the time specified.

(2) If, at the time of the most recent inspection required by paragraph (i) or (j) of this AD, the airplane had accumulated 50,000 or more total flight cycles, but fewer than 60,000 total flight cycles: Perform the next inspection within 7,500 flight cycles. Repeat the inspection thereafter at intervals not to exceed 7,500 flight cycles until the airplane has accumulated 60,000 or more total flight cycles. Do the inspections required by paragraph (j)(3) of this AD at the time specified.

(3) If, at the time of the most recent inspection required by paragraph (i) or (j) of this AD, the airplane had accumulated 60,000 or more total flight cycles, but fewer than 70,000 total flight cycles: Perform the next inspection within 5,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 5,000 flight cycles until the airplane has accumulated 70,000 or more total flight cycles. Do the inspections required by paragraph (j)(4) of this AD at the time specified.

(4) If, at the time of the most recent inspection required by paragraph (i) or (j) of this AD, the airplane had accumulated 70,000 or more total flight cycles: Perform the next inspection within 3,000 flight cycles. Repeat the inspection thereafter at intervals not to exceed 3,000 flight cycles.

(k) If any crack is found in the outboard chord of the frame at BS 727 during any inspection required by paragraphs (g) through (j) of this AD, accomplish paragraph (k)(1) or (k)(2) of this AD, as applicable, in accordance with Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; or Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006; as applicable. As of the effective date of this AD, use only Revision 2 of this service bulletin.

(1) For any crack that extends from the forward edge of the chord or from the forward fastener hole, but that does not extend past the second fastener hole, accomplish either paragraph (l)(1)(i) or (l)(1)(ii) of this AD. Thereafter, perform initial and repetitive inspections in accordance with paragraphs (g) and (h) of this AD.

(i) Prior to further flight, install the time limited repair. Within 4,500 flight cycles or within 18 months after accomplishing the time-limited repair, whichever occurs first, replace the outboard chord. Or

(ii) Prior to further flight, replace the outboard chord.

Note 1:

Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; and Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006; refer to Boeing Service Bulletin 737-53-1088 as an additional source of guidance for procedures to replace the chord.

(2) For any crack that extends from the forward edge of the chord, or from the forward fastener hole, and that extends past the second fastener hole, prior to further flight, replace the outboard chord in accordance with Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; or Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006; as applicable. As of the effective date of this AD, use only Revision 2 of this service bulletin. Thereafter, perform initial and repetitive inspections in accordance with paragraphs (g) and (h) of this AD.

New Requirements of This AD: Repetitive Inspections/Repair or Replace if Necessary

(l) For airplanes identified in table 5 of paragraph 1.E., “Compliance” of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006: Before the accumulation of 27,000 total flight cycles, or within 5,000 flight cycles after the effective date of this AD, whichever occurs later, do internal detailed and HFEC inspections to detect cracks in the auxiliary chord radius of the frame at BS 727, in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006. Repeat the inspections thereafter at intervals not to exceed 15,000 flight cycles until the optional terminating action described in paragraph (r) of this AD is accomplished. If any crack is found, before further flight, repair in accordance with the requirements in paragraph (p) of this AD.

(m) For airplanes identified in table 2 of paragraph 1.E., “Compliance” of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006: Do the applicable inspections required by paragraph (m)(1) or (m)(2) of this AD at the time specified, in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006. Except as required by paragraph (p) of this AD, if any crack is found during any inspection required by paragraph (m)(1) or (m)(2) of this AD, before further flight, repair in accordance with Part 3 or Part 4 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006, as applicable. Repeat the inspections until the optional terminating action described in paragraph (r) of this AD is accomplished.

(1) For airplanes on which the inspections specified in Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; have not been performed as of the effective date of this AD: Do the inspections required by paragraphs (m)(1)(i) and (m)(1)(ii) of this AD at the time specified.

(i) Before the accumulation of 27,000 total flight cycles, or within 5,000 flight cycles after the effective date of this AD, whichever occurs later: Do ultrasonic and surface HFEC inspections to detect cracks in the forward flange of the outboard chord of the frame at BS 727. Repeat the inspections thereafter at intervals not to exceed 5,000 flight cycles.

(ii) Before the accumulation of 27,000 total flight cycles, or within 10,000 flight cycles after the effective date of this AD, whichever occurs later: Do an open hole eddy current inspection to detect cracks in the forward flange of the outboard chord of the frame at BS 727. Repeat the inspection thereafter at intervals not to exceed 15,000 flight cycles.

(2) For airplanes on which the inspections specified in Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; have been performed as of the effective date of this AD: Repeat the applicable inspection specified in paragraphs (m)(1)(i) and (m)(1)(ii) of this AD thereafter at intervals not to exceed 5,000 flight cycles for the ultrasonic and surface HFEC inspections, and at intervals not to exceed 15,000 flight cycles for the open hole eddy current inspection.

(n) For airplanes identified in table 3 of paragraph 1.E., “Compliance” of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006: Do the applicable inspections required by paragraph (n)(1) or (n)(2) of this AD at the time specified, in accordance with Part 1 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006. Except as required by paragraph (p) of this AD, if any crack is found during any inspection required by paragraphs (n)(1) or (n)(2) of this AD, before further flight, repair in accordance with Part 3 or Part 4 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006, as applicable. Repeat the inspections until the optional terminating action described in paragraph (r) of this AD is accomplished.

(1) For airplanes on which the inspections specified in Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; have not been done as of the effective date of this AD: Do the inspections required by paragraphs (n)(1)(i) and (n)(1)(ii) of this AD at the time specified.

(i) Before the accumulation of 27,000 total flight cycles, or within 5,000 flight cycles after the effective date of this AD, whichever occurs later: Do ultrasonic, low frequency eddy current, and edge HFEC inspections to detect cracks in the forward flange of the outboard chord of the frame at BS 727. Repeat the inspections thereafter at intervals not to exceed 5,000 flight cycles.

(ii) Before the accumulation of 27,000 total flight cycles, or within 10,000 flight cycles after the effective date of this AD, whichever occurs later: Do an open hole eddy current inspection to detect cracks in the forward flange of the outboard chord of the frame at BS 727. Repeat the inspections thereafter at intervals not to exceed 15,000 flight cycles.

(2) For airplanes on which the inspections specified in Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; have been done as of the effective date of this AD: Repeat the applicable inspection specified in paragraphs (n)(1)(i) and (n)(1)(ii) of this AD thereafter at intervals not to exceed 5,000 flight cycles for the ultrasonic, low frequency eddy current, and edge HFEC inspections, and at intervals not to exceed 15,000 flight cycles for the open hole eddy current inspection.

Note 2:

The detailed and eddy current inspections of the outboard chord of S-18A specified in Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006, are not required by this AD.

(o) For airplanes identified in table 4 of paragraph 1.E., “Compliance” of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006: Before the accumulation of 50,000 or more total flight cycles, but fewer than or equal to 60,000 total flight cycles, after accomplishing the modification of the outboard chord of the frame at BS 727 at S-18A: Do a one-time follow-on open hole eddy current inspection to detect cracks in the modified chord in accordance with Part 8 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006.

(p) If any crack is found during any inspection required by paragraphs (l) through (o) of this AD, and the repairs specified in Part 3 and Part 4 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006, can not be installed using the procedures identified in this service bulletin: Before further flight, repair using a method approved in accordance with the procedures specified in paragraph (s) of this AD.

(q) For any airplane on which a time-limited repair is installed on the outboard chord of the frame at body station BS 727 in accordance with Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995: Within 4,500 flight cycles after installation of the repair, or within 6 months after the effective date of this AD, whichever occurs later, replace the repair in accordance with Part 9 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006.

Optional Terminating Action

(r) Accomplishment of the applicable action specified in paragraph (r)(1) or (r)(2) of this AD, in accordance with Part 2 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995; or Part 6 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006; constitutes terminating action for the inspections required by this AD.

(1) Installation of the preventative modification.

(2) Replacement of the cracked chord and installation of the preventative modification.

Alternative Methods of Compliance (AMOCs)

(s)(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: [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 for AD 95-12-17 are approved as AMOCs for the corresponding provisions of this AD.

(5) For airplanes identified in tables 2, 3, and 5 of paragraph 1.E., “Compliance” of Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006: The Manager, Seattle ACO, approves the inspection methods, thresholds, and repetitive intervals therein as an AMOC for the inspections of Structurally Significant Items (SSIs) F-29A and F-29B required by paragraphs (g) and (h) of AD 2008-08-23, Amendment 39-15477 (Boeing 737-100/200/200C Supplemental Structural Inspection Document (SSID) D6-37089, Revision E, dated May 1, 2007), and paragraphs (g) and (h) of AD 2008-09-13, Amendment 39-15494 (Boeing 737-400/500/600 SSID D6-82669, dated May 1, 2007). This approval applies only to SSIs F-29A and F-29B of the applicable SSID and only for the portions of the BS 727 outer chord that have been inspected or that have been repaired or modified in accordance with Boeing Alert Service Bulletin 737-53A1166, Revision 2, dated May 25, 2006. All provisions of ADs 2008-08-23 and 2008-09-13 that are not specifically referenced in this paragraph remain fully applicable and must be done. If operators request this AMOC, they must revise their FAA-approved maintenance or inspection program to incorporate the alternative inspections in this paragraph.

Related Information

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

(u) For service information identified in this 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]; e-mail [e-mail]; 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 July 26, 2011.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.