2011-22370. Airworthiness Directives; The Boeing Company Model 737-200, -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 737-300, -400, and -500 series airplanes. The existing AD currently requires repetitive external non-destructive inspections to detect cracks in the fuselage skin along the chem-mill step at stringers S-1 and S-2 right, between station (STA) 827 and STA 847, and repair if necessary. Since we issued that AD, we have received reports of additional crack findings of the fuselage crown skin at the chem-milled steps. This proposed AD would add inspections for cracking in additional fuselage crown skin locations, and repair if necessary. This proposed AD would also reduce the inspection thresholds for certain airplanes, extend certain repetitive inspection intervals, and add airplanes to the applicability of the existing AD. We are proposing this AD to detect and correct fatigue cracking of the fuselage skin panels at the chem-milled steps, which could result in sudden fracture and failure of the fuselage skin panels, and consequent rapid decompression of the airplane.

DATES:

We must receive comments on this proposed AD by October 17, 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:

Wayne Lockett, 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-2011-0914; Directorate Identifier 2010-NM-166-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 December 21, 2009, we issued AD 2010-01-09, Amendment 39-16167 (75 FR 1527, January 12, 2010), for certain Model 737-300, −400, and −500 series airplanes. That AD requires repetitive external non-destructive inspections to detect cracks in the fuselage skin along the chem-mill step at stringers S-1 and S-2 right, between STA 827 and STA 847, and repair if necessary. That AD resulted from a report of a hole in the fuselage skin common to stringers S-1 and S-2 left, between STA 827 and STA 847, on an airplane that diverted to an alternate airport due to cabin depressurization and subsequent deployment of the oxygen masks. We issued that AD to detect and correct fatigue cracking of the fuselage skin panels at the chem-milled steps, which could result in sudden fracture and failure of the fuselage skin panels, and consequent rapid decompression of the airplane.

Actions Since Existing AD Was Issued

Since we issued AD 2010-01-09, we have received reports of new findings of cracking in the fuselage crown skin at the horizontal chem-milled steps at locations between body stations 259.5 and 1016 and between stringers S-10L and S-10R. The cause of the cracking is under investigation.

Relevant Service Information

We reviewed Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011. Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009, was referred to for accomplishing the actions in the existing AD. We also reviewed Boeing Alert Service Bulletin 737-53A1301, Revision 1, dated June 7, 2010. Revision 1 of this service bulletin adds inspections for cracking in additional fuselage crown skin locations, and repair if necessary; it reduces the inspection threshold for certain airplanes; extends certain repetitive inspection intervals; and adds airplanes to the effectivity (Model 737-200 and −200C series airplanes, and Model 737-300, −400, and −500 series without ELT antenna provisions). The new inspection types specified in Revision 1 of this service bulletin are detailed inspections, and optional external nondestructive: ultrasonic phased array inspections. Revision 1 of this service bulletin also recommends contacting Boeing for inspection instructions for Group 26 airplanes. Revision 2 of this service bulletin specifies that no more work is necessary on airplanes changed as specified in Revision 1 of this service bulletin. Revision 2 of this service bulletin only includes minor editorial changes.

Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011; and Boeing Alert Service Bulletin 737-53A1301, Revision 1, dated June 7, 2010; specify that the compliance times for the initial inspections for Groups 2, 8, and 10 airplanes at the ELT antenna provision at stringers S-1 and S-2R between BS 827 and BS 847, are at the latest of the following: Prior to the accumulation of 35,000 total flight cycles, or, depending on inspection locations, within 1,800 flight cycles after the issue date of the original issue or Revision 1 of this service bulletin, or within 1,800 flight cycles after the most recent inspection done in accordance with Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009. For Groups 1 through 12 airplanes, at the new inspection locations, the compliance times are prior to the accumulation of 35,000 total flight cycles, or within 1,800 flight cycles after the issue date of Revision 1 of this service bulletin. For groups 1 through 12, the repetitive inspection interval is 1,800 flight cycles (for Option 1 inspections) and 2,400 flight cycles (for Option 2 inspections). For airplanes on which the inspection procedure is changed from Option 2 to Option 1, the first Option 1 inspection must be done within 2,400 flight cycles after doing the Option 2 inspection. For airplanes on which the inspection procedure is changed from Option 1 to Option 2, the first two Option 2 inspections must be done within 1,800 flight cycles.

Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011; specifies that the compliance times for the initial inspections for Groups 13 through 18 and 21 through 25 airplanes at the ELT antenna provision at stringers S-1 and S-2R, between BS 827 and BS 847, are as follows:

• For airplanes on which the inspections specified in Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009; or Revision 1, dated June 7, 2010; have been done: At the latest of the following, prior to the accumulation of 33,000 total flight cycles, or within 500 flight cycles after the most recent inspection done in accordance with Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009; or Revision 1, dated June 7, 2010.
• For airplanes on which the inspections specified in Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009; or Revision 1, dated June 7, 2010; have not been done: Prior to the accumulation of 33,000 total flight cycles, or within 500 flight cycles after the issue date of Revision 2 of this service bulletin, whichever occurs later.

For Groups 13 through 25, Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011; specifies that the compliance times for the initial inspections for Groups 13 through 25 airplanes at the new inspection locations are as follows: Prior to the accumulation of 33,000 total flight cycles, or within 500 flight cycles after the issue date of Revision 1 of Boeing Alert Service Bulletin 737-53A1301, whichever occurs later.

For Groups 13 through 25, Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011; specifies that the repetitive inspection interval is 500 flight cycles (for Option 1) and 1,000 flight cycles (for Option 2). For airplanes on which the inspection procedure is changed from Option 2 to Option 1, the first Option 1 inspection must be done within 1,000 flight cycles after doing the Option 2 inspection. For airplanes on which the inspection procedure is changed from Option 1 to Option 2, the first two Option 2 inspections must be done within 500 flight cycles.

For Group 26 airplanes, Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, specifies contacting Boeing to obtain engineering and accomplishment instructions for certain inspections.

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 the requirements of AD 2010-01-09, and would add inspections for cracking in additional fuselage crown skin locations, and repair if necessary. This proposed AD would also reduce the inspection thresholds for certain airplanes, extend certain repetitive inspection intervals, and add airplanes to the applicability of AD 2010-01-09. This proposed AD would require accomplishing the actions specified in the service information described previously.

Interim Action

We consider this proposed AD interim action. If final action is later identified, we might consider further rulemaking then.

Costs of Compliance

We estimate that this proposed AD affects 654 airplanes of U.S. registry.

We estimate the following costs to comply with this proposed AD:

Estimated Costs

Action	Work hours	Average labor rate per hour	Cost per product	Number of U.S.-registered airplanes	Fleet cost
Inspection in AD 2010-01-09	2	$85	$170 per inspection cycle	135	$22,950 per inspection cycle.
New inspection in this proposed AD	Between 2 and 30	85	Between $170 and $2,550 per inspection cycle	654	Between $111,180 and $1,667,700 per inspection cycle.

We have received no definitive data that would enable us to provide a cost estimate for the on-condition actions 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) 2010-01-09, Amendment 39-16167 (75 FR 1527, January 12, 2010), and adding the following new AD:

The Boeing Company: Docket No. FAA-2011-0914; Directorate Identifier 2010-NM-166-AD.

Comments Due Date

(a) The FAA must receive comments on this AD action by October 17, 2011.

Affected ADs

(b) This AD supersedes AD 2010-01-09, Amendment 39-16167.

Applicability

(c) This AD applies to all The Boeing Company Model 737-200, −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 reports of additional crack findings of the fuselage crown skin at the chem-milled steps. We are issuing this AD to detect and correct fatigue cracking of the fuselage skin panels at the chem-milled steps, which could result in sudden fracture and failure of the fuselage skin panels, and consequent rapid decompression of the airplane.

Compliance

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

Restatement of Requirements of AD 2010-01-09, Amendment 39-16167

Initial and Repetitive Inspections

(g) For airplanes identified in Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009: Before the accumulation of 35,000 total flight cycles, or within 500 flight cycles after February 16, 2010 (the effective date of AD 2010-01-09), whichever occurs later, except as provided by paragraph (i) of this AD, do an external non-destructive inspection (NDI) to detect cracks in the fuselage skin along the chem-mill steps at stringers S-1 and S-2 right, between station (STA) 827 and STA 847, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009; or Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011. If no cracking is found, repeat the inspection thereafter at intervals not to exceed 500 flight cycles; except as provided by paragraphs (i) and (n) of this AD. Accomplishing the inspections required by paragraph (j) of this AD terminates the inspections required by this paragraph.

Repair

(h) If any crack is found during any inspection required by paragraph (g) of this AD, and Boeing Alert Service Bulletin 737-53A1301, dated September 3, 2009; or Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011; specifies to contact Boeing for repair instructions: Before further flight, repair the crack using a method approved in accordance with the procedures specified in paragraph (q) of this AD.

Optional Terminating Action for Repetitive Inspections in Paragraph (g) of This AD

(i) Installing an external repair doubler along the chem-milled steps at stringers S-1 and S-2 right, between STA 827 and STA 847, constitutes terminating action for the repetitive inspections required by paragraph (g) of this AD for the repaired area only, provided all of the conditions specified in paragraphs (i)(1), (i)(2), and (i)(3) of this AD are met.

(1) The repair is installed after September 3, 2009;

(2) The repair was approved by the FAA or by a Boeing Company Authorized Representative or the Boeing Commercial Airplanes Organization Designation Authorization (ODA) that has been authorized by the Manager, Seattle Aircraft Certification Office (ACO) to make such findings; and

(3) The repair extends a minimum of three rows of fasteners on each side of the chem-mill line in the circumferential direction.

New Inspections Including Additional Locations and Reduced Inspection Intervals

Groups 1 Through 25: Initial and Repetitive Inspections

(j) For Groups 1 through 25 airplanes identified in Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011: Except as provided by paragraph (k) of this AD, at the applicable time specified in paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, do the applicable inspections required by paragraphs (j)(1) and (j)(2) of this AD, in accordance with paragraphs 3.B.1 through 3.B.25 of the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011. If no cracking is found, repeat the applicable inspections thereafter at the applicable intervals specified in paragraph 1.E., “Compliance,” of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011; except as provided by paragraphs (m) and (n) of this AD. Doing the inspections required by this paragraph terminates the inspections required by paragraph (g) of this AD.

(1) For Groups 2, 8, 10, 13 through 18, and 21 through 25 airplanes: Do a detailed inspection and an external non-destructive inspection (NDI) (medium frequency eddy current inspection, magneto optical imaging inspection, c-scan inspection, or ultrasonic phased array inspection) for cracking in the fuselage skin at the chem-mill steps at S-1 and S-2R between STA 827 and STA 847, as identified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011.

(2) For Groups 1 through 25 airplanes: Do a detailed inspection and an external NDI (medium frequency eddy current inspection; magneto optical imaging inspection, c-scan inspection, or ultrasonic phased array inspection) for cracking in the fuselage skin at the chem-mill steps at the specified locations other than at S-1 and S-2R between STA 827 and STA 847, as identified in the Accomplishment Instructions of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011.

Note 1:

Option 1 of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, specifies a detailed inspection, and one additional inspection (external NDI, medium frequency eddy current inspection, magneto optical imaging inspection, or c-scan inspection). Option 2 specifies a detailed inspection and an external ultrasonic phased array inspection. These options have different compliance times after the initial inspection.

(k) Where Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, specifies a compliance time after “the date of Revision 1,” or “the date of Revision 2” of that service bulletin, this AD requires compliance within the specified time after the effective date of this AD.

Repair

(l) If any crack is found during any inspection required by paragraph (j) of this AD: Before further flight, repair the crack using a method approved in accordance with the procedures specified in paragraph (q) of this AD. Doing the repair ends the repetitive inspections required by paragraph (j) for the repaired area only.

Optional Terminating Action for Repetitive Inspections

(m) Installing an external repair doubler along the chem-milled steps at any location identified in Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, constitutes terminating action for the repetitive inspections required by paragraph (j) of this AD for the repaired area only, provided all of the conditions specified in paragraphs (m)(1), (m)(2), and (m)(3) of this AD are met.

(1) The repair is installed after the applicable date specified in paragraph (m)(1)(i) and (m)(1)(ii) of this AD.

(i) For repairs at S-1 and S-2R between STA 827 and STA 847: Installed after September 3, 2009.

(ii) For repairs at locations other than at S-1 and S-2R between STA 827 and STA 847: Installed after June 7, 2010.

(2) The repair was approved by the FAA or by a Boeing Company Authorized Representative or the Boeing Commercial Airplanes Organization Designation Authorization (ODA) that has been authorized by the Manager, Seattle Aircraft Certification Office (ACO) to make such findings; and

(3) The repair extends a minimum of three rows of fasteners on each side of the chem-mill line in the circumferential direction.

(n) Accomplishing a modification of the chem-milled steps at any location identified in Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, using a method approved in accordance with the procedures specified in paragraph (q)(1) of this AD, terminates the repetitive inspections required by paragraphs (g) and (j) of this AD for the modified area only.

Group 26 Airplanes

(o) For Group 26 airplanes identified in Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011: Within 1,800 flight cycles after the effective date of this AD, accomplish applicable inspections and corrective action, as identified in the service bulletin, using a method approved in accordance with the procedures specified in paragraph (q)(1) of this AD.

Credit for Actions Accomplished in Accordance With Previous Service Information

(p) Actions done before the effective date of this AD in accordance with Boeing Alert Service Bulletin 737-53A1301, Revision 1, dated June 7, 2010, are acceptable for compliance with the corresponding requirements of this AD.

Alternative Methods of Compliance (AMOCs)

(q)(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 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 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.

Related Information

(r) 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; phone: [phone]; fax: [phone]; e-mail: [e-mail].

(s) 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 August 25, 2011.

Ali Bahrami,

Manager Transport Airplane Directorate, Aircraft Certification Service.