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Federal Register / Vol. 86, No. 87 / Friday, May 7, 2021 / Proposed Rules
https www.regulations.gov by searching for and locating Docket No.
FAA20210332.
Examining the AD Docket You may examine the AD docket on the internet at https
www.regulations.gov by searching for and locating Docket No. FAA2021
0332; or in person at Docket Operations between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
The AD docket contains this NPRM, any comments received, and other information. The street address for Docket Operations is listed above.
FOR FURTHER INFORMATION CONTACT: Greg Rutar, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200
South 216th St., Des Moines, WA 98198;
phone and fax: 2062313529; email:
Greg.Rutar@faa.gov.
SUPPLEMENTARY INFORMATION:
Comments Invited The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments to an address listed under ADDRESSES. Include Docket No.
FAA20210332; Project Identifier AD
202001414T at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA will consider all comments received by the closing date and may amend the proposal because of those comments.
Except for Confidential Business Information CBI as described in the following paragraph, and other information as described in 14 CFR
11.35, the FAA will post all comments received, without change, to https
www.regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this proposed AD.
Confidential Business Information CBI is commercial or financial information that is both customarily and actually treated as private by its owner.
Under the Freedom of Information Act FOIA 5 U.S.C. 552, CBI is exempt from public disclosure. If your comments responsive to this NPRM
contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI

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as PROPIN. The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI
should be sent to Greg Rutar, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 2062313529; email: Greg.Rutar@
faa.gov. Any commentary that the FAA
receives which is not specifically designated as CBI will be placed in the public docket for this rulemaking.
Background The FAA has received reports that shimming requirements were not met during the assembly of certain areas of the front spar pickle fork and front spar outer chord structural joints, which can result in reduced fatigue thresholds of the affected structural joints. The existing inspection program does not adequately detect this fatigue cracking.
The affected locations are common to the front spar pickle fork, between stringer S22 and stringer S25, and the front spar body chord, between stringer S25 and buttock line BL 0, on the left and right sides. Not meeting the shimming requirements during assembly of the station STA 873 front spar pickle fork and front spar body chord structure joints results in excessive pull-up forces, fastener shanking, excessive burr heights in metallic members, and metallic chips foreign object debris in fastened interfaces, which all degrade fatigue performance of any affected structural joints.
Undetected fatigue cracking could weaken primary structure so it cannot sustain limit load, which could result in reduced structural integrity of the airplane.
Related Service Information Under 1
CFR Part 51
The FAA reviewed Boeing Alert Requirements Bulletin B78781205
SB53007500 RB, Issue 001, dated September 8, 2020. The service information describes procedures for repetitive high frequency eddy current HFEC inspections for cracking around all the fasteners common to the front spar pickle fork outer chord surface between stringer S22 and stringer S24
at STA 873 on the left and right sides, and along the entire forward edge of the front spar pickle fork outer chord covered by the body chord splice angle between stringer S24 and stringer S25
at STA 873 on the left and right sides, and repair of any cracking found. The service information also describes procedures for repetitive ultrasonic UT

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inspections for cracking of the front spar pickle fork outer chord along the upper, lower and aft edges of the end fittings at stringer S23 at STA 873, on the left and right sides, and repair of any cracking found.
The FAA also reviewed Boeing Alert Requirements Bulletin B78781205
SB53007600 RB, Issue 001, dated September 8, 2020. The service information describes procedures for repetitive HFEC inspections for cracking along the entire forward edge of the front spar body chord in the area covered by the body chord splice angle at stringer S25 on the left and right sides, and the splice fitting at BL 0, STA 873, and repair of any cracking found. The service information also describes procedures for repetitive detailed inspections of the front spar body chord horizontal flange surface between stringer S26 to stringer S40
at STA 873 on the left and right sides and repair of any cracking found. The service information also describes procedures for repetitive UT inspections for cracking of the of the front spar body chord horizontal flange along the upper and lower edges of the end fittings at stringer S27, at STA 873 on the left and right sides, and repair of any cracking found.
This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in the ADDRESSES section.
FAAs Determination The FAA is proposing this AD
because the agency 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 require accomplishment of the actions identified in Boeing Alert Requirements Bulletins B78781205SB53007500 RB
and B78781205SB53007600 RB, both Issue 001, both dated September 8, 2020, described previously, except for any differences identified as exceptions in the regulatory text of this proposed AD.
For information on the procedures and compliance times, see this service information at https
www.regulations.gov by searching for and locating Docket No. FAA2021
0332.
Explanation of Requirements Bulletin The FAA worked in conjunction with industry, under the Airworthiness
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