Airworthiness Directive · Amendment 39-16876 · Fuselage
The Boeing Company Model 737-200, -200C, -300, -400, and -500 Series Airplanes
This AD applies to all The Boeing Company Model 737-200, -200C, -300, -400, and -500 series airplanes, certificated in any category.
We are superseding an existing airworthiness directive (AD) for certain Model 737-300, -400, and -500 series airplanes. That 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. This new AD adds inspections for cracking in additional fuselage crown skin locations, and repair if necessary. This new AD also reduces the inspection thresholds for certain airplanes, extends certain repetitive inspection intervals, and adds airplanes to the applicability of the existing AD. 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.
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.
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.
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), FAA, 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.
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 stringers 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 of Boeing Alert Service Bulletin 737-53A1301, Revision 2, dated April 25, 2011, specifies a detailed inspection and an external ultrasonic phased array inspection. These options have different compliance times after the initial inspection.
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.
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.
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.
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.
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.
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.
