Source: https://www.federalregister.gov/documents/2003/06/18/03-15327/airworthiness-directives-boeing-model-737-200--200c--300--400-and--500-series-airplanes
Timestamp: 2018-02-22 13:08:44
Document Index: 153774290

Matched Legal Cases: ['art 4', 'art 5', 'art 1', 'art 2', 'art 5', 'art 4', 'art 3', 'art 2', 'art 4', 'art 4', 'art 4']

36515-36518 (4 pages)
Differences Between Proposed AD and Service Bulletin 737-53A1210, Revision 1
https://www.federalregister.gov/d/03-15327 https://www.federalregister.gov/d/03-15327
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-200, -200C, -300, -400, and -500 series airplanes. This proposal would require repetitive inspections to find fatigue cracking of certain upper and lower skin panels of the fuselage, and follow-on and corrective actions, if necessary. This proposal also includes terminating action for the repetitive inspections of Start Printed Page 36516certain modified or repaired areas only. This action is necessary 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. This action is intended to address the identified unsafe condition.
Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2001-NM-246-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2001-NM-246-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.
Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2001-NM-246-AD.” The postcard will be date stamped and returned to the commenter.
Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2001-NM-246-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.
The FAA has received reports indicating that cracks were found along the edges of the chem-milled pockets in the upper skin at stringer S-12, and above the S-4, S-10, and S-14 lap joints, on several Boeing Model 737 series airplanes. The cracks were up to 6 inches long and multiple adjacent bays were found to be cracked along the same stringers on three of the airplanes. The airplanes had accumulated between 34,574 and 56,949 total flight cycles. Additionally, skin cracks up to 4 inches long located below the S-14 lap joint along the bonded skin doublers were reported on 25 other airplanes which had accumulated between 22,786 and 80,113 total flight cycles.
Analysis by the manufacturer revealed that these cracks are caused by fatigue due to high bending stresses at the edge of chem-milled pockets or bonded skin doublers. Such fatigue cracking could result in sudden fracture and failure of the skin panels of the fuselage, and consequent rapid decompression of the airplane.
This proposed AD is related to AD 2002-07-08, amendment 39-12702 (67 FR 17917, April 12, 2002). That AD references Boeing Service Bulletin 737-53A1177, Revision 6, dated May 31, 2001, as the appropriate source of service information for accomplishment of the specified actions. (The AD also referenced, for accomplishment of certain actions, Boeing Alert Service Bulletin 737-53A1177, Revision 1, dated September 19, 1996; Revision 2, dated July 24, 1997; Revision 3, dated September 18, 1997; Revision 4, dated September 2, 1999; and Revision 5, dated February 15, 2001.) That AD is applicable to certain Boeing Model 737 series airplanes and requires repetitive inspections to find cracking of the lower skin at the lower row of fasteners in the lap joints of the fuselage, and repair of any cracking found. That AD also requires modification of the fuselage lap joints at certain locations, which constitutes terminating action for repetitive inspections of the modified areas. Additionally, that AD requires replacement of a preventive modification with an improved modification.
We have reviewed and approved Boeing Alert Service Bulletin 737-53A1210, Revision 1, including Appendix A and Evaluation Form, dated October 25, 2001. The service bulletin describes procedures for repetitive external detailed and eddy current inspections to find fatigue cracking of the upper and lower skin panels of the fuselage (crown area and lower lobe area) at stringer S-12, and above the S-4, S-10, and S-14 lap joints, and repair of any cracking with either a permanent or time-limited repair.
For airplanes on which a time-limited repair is done, Part 4 of the service bulletin describes procedures for a subsequent permanent repair within 10,000 flight cycles after installation of the time-limited repair. Doing a permanent repair eliminates the need for the repetitive inspections for the repaired area only.
For Group 3, 5, 6, and 8 airplanes only, on which no cracking is found, Part 5 of the service bulletin provides procedures for a preventive modification of the chem-milled pockets in the upper skins at stringer S-12, between body station (BS) 500D and BS 520, which would end the repetitive inspections for the modified area only. Start Printed Page 36517
The service bulletin also describes procedures for repetitive follow-on visual inspections for cracking of the lower lobe skins from S-15L to S-15R between stations 360 and 1016 and in section 41; replacement of any loose fasteners with new fasteners; an internal eddy current inspection of the skin, tear straps, and lap joint in each adjacent bay for cracking; and repair of any cracking found.
Accomplishment of the actions specified in Service Bulletin 737-53A1210, Revision 1, is intended to adequately address the identified unsafe condition.
The service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, but this proposed AD would require the repair of those conditions to be done per a method approved by the FAA, or per data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings.
The service bulletin recommends that, after installation of a time-limited repair, an internal eddy current inspection should be done at the first “C-check” or within 4,000 flight cycles, whichever is last. Because “C-check” schedules vary among operators, such a nonspecific interval would provide no assurance that operators would do the inspection within the prescribed schedule. This proposed AD would require that the inspection be done within 4,000 flight cycles after the repair installation. We find that a 4,000-flight-cycle interval is appropriate for affected airplanes to continue to operate without compromising safety.
Although the service bulletin recommends that operators report inspection results to the manufacturer, this proposed AD does not contain such a reporting requirement.
This is considered to be interim action for Group 7 airplanes. Although the service bulletin described previously does not include the inspection of the crown area (upper lobe) for Group 7 airplanes, as specified in paragraph (a) of this proposed AD, the manufacturer has advised that it currently is developing a new service bulletin to address those airplanes. Once the FAA has reviewed and approved the service bulletin, we may consider additional rulemaking to mandate those inspections.
There are approximately 2,200 airplanes of the affected design in the worldwide fleet. The FAA estimates that 903 airplanes of U.S. registry would be affected by this proposed AD.
It would take approximately 94 work hours per airplane to accomplish the proposed inspections of the crown area, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these proposed inspections on U.S. operators is estimated to be $5,092,920, or $5,640 per airplane, per inspection cycle.
It would take approximately 96 work hours per airplane to accomplish the proposed inspections of the lower lobe area, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these proposed inspections on U.S. operators is estimated to be $5,201,280, or $5,760 per airplane, per inspection cycle.
Should an operator elect to install the preventive modification, it would take approximately 108 work hours to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the preventive modification is estimated to be $6,480 per airplane.
Boeing: Docket 2001-NM-246-AD.
Compliance: Required as indicated, unless accomplished previously. Start Printed Page 36518
(a) For Groups 1 through 6 and Group 8 airplanes: 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 of the crown area skin panels of the fuselage for cracking, per Part 1 and Figure 1 of the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, including Appendix A and excluding Evaluation Form, dated October 25, 2001. Repeat the inspections at least every 4,500 flight cycles until paragraph (c) or (d)(1)(ii) of this AD has been done, as applicable. Although paragraph 1.D. of the service bulletin references a reporting requirement, such reporting is not required by this AD.
(b) For all airplanes: Before the accumulation of 40,000 total flight cycles, or within 4,500 flight cycles after the effective date of this AD, whichever is later, 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, including Appendix A and excluding Evaluation Form, dated October 25, 2001. Repeat the inspection at least every 9,000 flight cycles until paragraph (d)(2) of this AD has been done, as applicable.
(c) For Groups 3, 5, 6, and 8 airplanes: If no cracking is found during any inspection required by paragraph (a) 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, including Appendix A and excluding Evaluation Form, dated October 25, 2001, ends the repetitive inspections for the modified area only.
(d) If any cracking is found during any inspection required by paragraph (a) or (b) of this AD, before further flight, do the actions specified in paragraphs (d)(1) and (d)(2) of this AD, as applicable, per the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, including Appendix A and excluding Evaluation Form, dated October 25, 2001. Where the service bulletin specifies 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 approved by a Boeing Company Designated Engineering Representative (DER) who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the approval letter must specifically reference this AD.
(1) For cracking of the crown area, do the repair specified in either paragraph (d)(1)(i) or (d)(1)(ii) of this AD. 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 action specified in this paragraph for the lap joint areas only.
(i) Do a time-limited repair per Part 4 of the Work Instructions of the service bulletin, then do the actions required by paragraph (e) of this AD at the times specified in that paragraph.
(ii) Do a permanent repair per Part 3 of the Work Instructions of the service bulletin. Installation of a permanent repair ends the repetitive inspections required by paragraph (a) of this AD for the repaired area only.
(2) For cracking of the lower lobe area and Section 41, repair per Part 2 of the Work Instructions of the service bulletin. Accomplishment of this repair ends the repetitive inspections required by paragraph (b) of this AD for the repaired area only.
(e) If a time-limited repair is done, as specified in paragraph (d)(1)(i) of this AD: Do the actions specified in paragraphs (e)(1), (e)(2), and (e)(3) of this AD, at the times specified, per the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 1, including Appendix A and excluding Evaluation Form, dated October 25, 2001.
(1) Within 3,000 flight cycles after doing the repair: Do a general visual inspection of the repaired area for loose fasteners per Part 4 of the Work Instructions of the service bulletin. If any loose fastener is found, before further flight, replace with a new fastener per the service bulletin. Then repeat the inspection at least every 3,000 flight cycles until permanent rivets are installed in the repaired area, which ends the repetitive inspections for this paragraph.
(2) Within 4,000 flight cycles after doing the repair: Do an internal eddy current inspection of the skin, tear straps, and lap joint in each adjacent bay of the repaired area for cracking, per Part 4 of the Work Instructions of the service bulletin. 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 approved by a Boeing Company DER who has been authorized by the FAA to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the approval letter must specifically reference this AD.
(3) Within 10,000 flight cycles after doing the repair: Make the repair permanent per Part 4 and Figure 20 of the Work Instructions of the service bulletin, which ends the repetitive inspections for the repaired area only.
(f) Inspections, repairs, and preventive modifications done before the effective date of this AD per Boeing Alert Service Bulletin 737-53A1210, dated December 14, 2000, are acceptable for compliance with the corresponding actions required by this AD.
[FR Doc. 03-15327 Filed 6-17-03; 8:45 am]