Source: https://www.federalregister.gov/documents/2008/06/11/E8-12761/airworthiness-directives-boeing-model-737-600--700--700c--800-and--900-series-airplanes
Timestamp: 2018-02-25 16:13:55
Document Index: 503584173

Matched Legal Cases: ['art 39', 'art 6', 'art 6', 'art 6', 'art 6', 'art 6']

This AD is effective July 16, 2008.
73 FR 32991
32991-32993 (3 pages)
Docket No. FAA-2007-29333
Directorate Identifier 2007-NM-141-AD
Amendment 39-15547
AD 2008-12-04
E8-12761
Request To Provide Exception for Previously Installed Repairs
Request To Allow Optional Eddy Current Inspection Method
Request To Improve Detail in Service Bulletin
Request To Extend Repetitive Interval To Match C-Check Interval
Inspections and Replacement, As Applicable
Terminating Action for Certain Repetitive Inspections
Exceptions to the Service Bulletin Procedures for Previously Installed Repairs
https://www.federalregister.gov/d/E8-12761 https://www.federalregister.gov/d/E8-12761
Start Preamble Start Printed Page 32991
We are adopting a new airworthiness directive (AD) for certain Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. This AD requires various repetitive inspections to detect cracks along the chemically milled steps of the fuselage skin or missing or loose fasteners in the area of the preventative modification or repairs, replacement of the time-limited repair with the permanent repair if applicable, and applicable corrective actions if necessary, which would end certain repetitive inspections. This AD results from a fatigue test that revealed numerous cracks in the upper skin panel at the chemically milled step above the lap joint. We are issuing this AD to detect and correct such fatigue-related cracks, which could result in the crack tips continuing to turn and grow to the point where the skin bay flaps open, causing decompression of the airplane.
We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to certain Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. That NPRM was published in the Federal Register on September 28, 2007 (72 FR 55118) (An extension of the comment period for that NPRM was published in the Federal Register on November 14, 2007 (72 FR 64009)). That NPRM proposed to require various repetitive inspections to detect cracks along the chemically milled steps of the fuselage skin or missing or loose fasteners in the area of the preventative modification or repairs, replacement of the time-limited repair with the permanent repair if applicable, and applicable corrective actions if necessary, which would end certain repetitive inspections.
Southwest Airlines notes that the proposed AD does not state how to do the inspection in an area that has a previously installed repair. Southwest Airlines states that AD 2004-18-06, amendment 39-13784 (69 FR 54206, September 8, 2004), which addresses chemically milled steps of the fuselage skin for Boeing Model 737-200, -200C, -300, -400, and -500 series airplanes, contains an exception that addresses the issue of a previously installed repair. Southwest Airlines asks that we include a similar exception in this AD.
We agree that the NPRM needs to be clarified regarding procedures for previously installed repairs, and have added new paragraphs (j) and (k) to this AD to explain the exceptions. We note that the exception to the procedures required by paragraph (g) of this AD is similar to the exception in AD 2004-18-06, except that for this AD, post-preventive modifications and repair supplemental inspections are required for repairs installed in accordance with Boeing Special Attention Service Bulletin 737-53-1232, dated April 2, 2007 (cited as the appropriate source of service information for accomplishing the actions in the NPRM). We have also re-identified subsequent paragraphs accordingly.
Continental Airlines (Continental) requests that we allow the use of the eddy current inspection procedures given in the Boeing 737 Non-Destructive Test (NDT) Manual, Part 6, Subjects 53-30-25 (c-scan eddy current inspection), as an alternative to Subjects 53-30-19 and 53-30-23 listed in Boeing Special Attention Service Bulletin 737-53-1232, dated April 2, 2007. Continental notes that the eddy current procedure in Subject 53-30-25 was approved as an alternative method of compliance (AMOC) for AD 2005-13-27, amendment 39-14164 (70 FR 36821, June 27, 2005), which mandates a similar fuselage skin inspection for Boeing Model 737-300, -400, and -500 series airplanes.
We agree that the NDT method Continental specifies provides an acceptable means to find cracking in the internal surface of the fuselage skin at the edge of a sub-surface doubler. Therefore, we have revised this AD to include a new paragraph (l)(4) to the AMOC paragraph (paragraph (j) of the NPRM). Paragraph (l)(4) states that Boeing Model 737 NDT Manual, Part 6, Subject 53-30-25, is an AMOC for Subjects 53-30-19 and 53-30-23.
Boeing requests that we clarify the wording in paragraph (g) of the NPRM to indicate which corrective actions are required and when. Boeing specifically states that the word “applicable” is missing from paragraph (g) of the NPRM, and requests that the paragraph state “accomplishing all of the applicable actions specified in the Accomplishment Instructions of the service bulletin.” Boeing explains that, without the word “applicable,” the AD would require accomplishment of all actions within the Accomplishment Instructions, even those that do not apply under certain conditions.
We agree to clarify paragraph (g) for the stated reasons. We have revised paragraph (g) of this AD to include the word “applicable” in the requested place. Start Printed Page 32992
The Air Transport Association (ATA) on behalf of its member Delta Airlines, requests that we encourage Boeing to improve the level of detail in Boeing Special Attention Service Bulletin 737-53-1232, dated April 2, 2007, specifically Part V of the Accomplishment Instructions, “Preventative Modification.” The commenters explain that the current data and figures for the modification are vague and could lead to considerable variation among operators in interpretation and installation. The commenters also state that, as a minimum, Boeing should issue a set of engineering drawings for typical modification parts for each affected group of airplanes, and incorporate them into a revision of the service bulletin.
We disagree that the level of detail in Part V of the service bulletin is insufficient. As shown in Part V and its associated figures, modification doublers and fillers are to be centered in the skin pocket with their width determined by the existing fastener spacing common to the lap splice. Adding engineering drawings to the information already in the service bulletin could result in confusion due to variations in fastener spacing common to the lap joints. We have not changed the AD in this regard.
The ATA, on behalf of its member Alaska Airlines, requests that we extend the repetitive inspection intervals proposed in the NPRM and express them in terms of C-check intervals. The commenters explain that the current repetitive inspection intervals are not sufficient to bridge successive C-checks, and will thus make it necessary to have a frequent and possibly repetitive inspection in the line environment. The commenters further state that the preventive modification proposed in the NPRM would lengthen the repetitive inspection interval from 1,500 flight cycles to either 4,000 or 6,000 flight cycles. In the commenters' opinion, this action does not justify the cost or manpower for doing the preventive modification.
We do not agree with the commenter's request to extend the repetitive intervals. We have determined that the proposed compliance time represents the maximum interval of time allowable for the affected airplanes to continue to safely operate before the modification is done. We determined the inspection intervals in this AD using damage tolerance methods to ensure that damage can be detected before it becomes critical on the structure. Also, compliance intervals cannot be based on nonspecific intervals such as a C-check. Since maintenance schedules vary among operators, there would be no assurance that corrective action would be done within the timeframe for safe operation of the airplane. Further, in developing appropriate compliance times for this AD, we considered the urgency associated with the subject unsafe condition, and the practical aspect of accomplishing the required actions within a period of time that corresponds to the normal scheduled maintenance for most affected operators. The repetitive intervals following preventative modification were part of these considerations. We have not changed the AD in this regard.
There are about 871 airplanes of the affected design in the worldwide fleet. This AD affects about 378 airplanes of U.S. registry. The inspections take between 11 and 25 work hours per airplane depending on the airplane configuration, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the AD for U.S. operators is between $332,640 and $756,000, or between $880 and $2,000 per airplane, per inspection cycle.
2008-12-04 Boeing: Amendment 39-15547. Docket No. FAA-2007-29333; Directorate Identifier 2007-NM-141-AD.
(a) This airworthiness directive (AD) is effective July 16, 2008.
(c) This AD applies to Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes, certificated in any category; as identified in Boeing Special Attention Service Bulletin 737-53-1232, dated April 2, 2007. Start Printed Page 32993
(d) This AD results from a fatigue test that revealed numerous cracks in the upper skin panel at the chemically milled step above the lap joint. We are issuing this AD to detect and correct such fatigue-related cracks, which could result in the crack tips continuing to turn and grow to the point where the skin bay flaps open, causing decompression of the airplane.
(f) The term “service bulletin,” as used in this AD, means Boeing Special Attention Service Bulletin 737-53-1232, dated April 2, 2007.
(g) At the applicable compliance times listed in Tables 1, 2, and 3 of paragraph 1.E., “Compliance,” of the service bulletin, or within the time specified in paragraph (g)(1) or (g)(2) of this AD, as applicable, whichever occurs later, and thereafter at the applicable repeat intervals listed in Tables 1, 2, and 3: Do the applicable inspections and replacement by accomplishing all the applicable actions specified in the Accomplishment Instructions of the service bulletin.
(1) For airplanes specified in Tables 1 and 2 of paragraph 1.E., “Compliance,” of the service bulletin: Do the applicable initial inspection required by paragraph (g) of this AD within 36 months after the effective date of this AD.
(2) For airplanes specified in Table 3 of paragraph 1.E., “Compliance,” of the service bulletin: Do the applicable initial inspection and replacement required by paragraph (g) of this AD within 24 months after the effective date of this AD.
(h) If any crack or loose or missing fastener is found during any applicable inspection required by paragraph (g) of this AD, before further flight, do the applicable corrective action in accordance with the service bulletin; except, where the service bulletin specifies to contact Boeing for appropriate action, before further flight, repair the crack using a method approved in accordance with the procedures specified in paragraph (l) of this AD.
(i) For airplanes on which the preventative modification specified in the service bulletin has not been installed: Accomplishing the preventative modification, time-limited repair, or permanent repair in accordance with the service bulletin ends the applicable repetitive external detailed inspections required by paragraph (g) of this AD.
(j) For any airplane subject to the requirements of paragraph (g) of this AD: Inspections done at the compliance times specified in Table 1 of paragraph 1.E., “Compliance,” of the service bulletin 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 chemically milled step. Post-repair supplemental inspections are to be done at the times specified in Table 2 of paragraph 1.E., “Compliance,” of the service bulletin.
(k) For any airplane that has an external doubler covering the chemically milled step, but the doubler does not span the step by a minimum of 3 rows of fasteners above and below the chemically milled step: Instead of requesting approval for an alternative method of compliance (AMOC) in accordance with the procedures specified in paragraph (l) of this AD, one method of compliance with the inspection requirement of paragraph (g) of this AD is to inspect all chemically milled steps covered by the repair using non-destructive test (NDT) methods in accordance with the Boeing 737 NDT Manual, Part 6, Subject 53-30-20. These repairs are to be considered time-limited and are subject to the post-repair supplemental inspections and replacement at the times specified in Table 3 of paragraph 1.E., “Compliance,” of the service bulletin.
(4) Use of Boeing Model 737 NDT Manual, Part 6, Subject 53-30-25, is an AMOC for Boeing Model 737 NDT Manual, Part 6, Subjects 53-30-19 and 53-30-23, as specified in the service bulletin.
(m) You must use Boeing Special Attention Service Bulletin 737-53-1232, dated April 2, 2007, to do the actions required by this AD, unless the AD specifies otherwise.
[FR Doc. E8-12761 Filed 6-10-08; 8:45 am]