AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Supplemental notice of proposed rulemaking (SNPRM); reopening of comment period.

SUMMARY:

The FAA is revising an earlier proposal for certain The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes. This action revises the notice of proposed rulemaking (NPRM) by revising certain inspections to provide the correct thickness callouts for the fuselage skin and bear strap. The FAA is proposing this airworthiness directive (AD) to address the unsafe condition on these products. Since these actions would impose an additional burden over that in the NPRM, the FAA is reopening the comment period to allow the public the chance to comment on these changes.

DATES:

The comment period for the NPRM published in the Federal Register on October 1, 2019 (84 FR 52047), is reopened.

The FAA must receive comments on this SNPRM by June 15, 2020.

ADDRESSES:

You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:

• Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the instructions for submitting comments.
• Fax: 202-493-2251.
• 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: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this SNPRM, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; phone: 562-797-1717; internet: https://www.myboeingfleet.com. You may view this service information at the FAA, Airworthiness Products Section, Operational Safety Branch, 2200 South 216th St., Des Moines, WA. For information on the availability of this material at the FAA, call 206-231-3195. It is also available on the internet at https://www.regulations.gov by searching for and locating Docket No. FAA-2019-0705.

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. FAA-2019-0705; 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 SNPRM, the regulatory evaluation, any comments received, and other information. The street address for Docket Operations is listed above. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Michael Bumbaugh, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3522; email: michael.bumbaugh@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 the ADDRESSES section. Include “Docket No. FAA-2019-0705; Product Identifier 2019-NM-098-AD” at the beginning of your comments. The FAA specifically invites comments on the overall regulatory, economic, environmental, and energy aspects of this SNPRM. The FAA will consider all comments received by the closing date and may amend this SNPRM because of those comments.

The FAA will post all comments, without change, to https://www.regulations.gov, including any personal information you provide. The FAA will also post a report summarizing each substantive verbal contact received about this SNPRM.

Discussion

The FAA issued an NPRM to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes. The NPRM published in the Federal Register on October 1, 2019 (84 FR 52047). The NPRM was prompted by reports of cracks in the bear strap between certain stations, sometimes common to fasteners in the gap cover and emanating from rough sanding marks found on the surface of the bear strap. The NPRM proposed to require inspections of the fuselage skin and bear strap at the forward galley door between certain stations for cracks, and applicable on-condition actions.

Actions Since the NPRM Was Issued

Since the FAA issued the NPRM, the FAA has determined that, for certain inspections specified in the proposed AD, certain thickness callouts for the fuselage skin and bear strap were incorrect. Therefore, the FAA has determined the correct thickness callouts must be included in those inspections.

Comments

The FAA gave the public the opportunity to comment on the NPRM. The following presents the comments received on the NPRM and the FAA's response to each comment.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that accomplishing Supplemental Type Certificate (STC) ST00830SE does not affect the actions specified in the proposed AD.

The FAA concurs with the commenter. The FAA has redesignated paragraph (c) of the proposed AD as paragraph (c)(1) of this AD and added paragraph (c)(2) to this AD to state that installation of STC ST00830SE does not affect the ability to accomplish the actions required by this AD. Therefore, for airplanes on which STC ST00830SE is installed, a “change in product” alternative method of compliance (AMOC) approval request is not necessary to comply with the requirements of 14 CFR 39.17.

Request To Include Updated Service Information

Boeing requested that the FAA revise the NPRM to include a later revision of the service information. Boeing pointed out that the skin and bear strap thicknesses referenced in Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9, 2019, were incorrectly specified as 0.0710 inches and 0.10 inches respectively, which affects the proper calibration of the inspection probe. Boeing stated that the correct skin and bear strap thicknesses should be 0.100 inches and 0.090 inches respectively. Boeing also mentioned that a new revision to the service information that corrects the skin and bear strap thicknesses was being coordinated with the FAA.

The FAA agrees for the reasons provided. Therefore, the FAA has included Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, as the appropriate source of service information for doing the actions specified in this SNPRM. Additionally, the FAA has also included paragraph (i) of this SNPRM to allow credit for actions accomplished before the effective date of this AD, using Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9, 2019, provided that for airplanes on which Option 2, Condition 4, has been done (no external repair and have done the external low frequency eddy current (LFEC) inspection of the forward galley door bear strap and external high frequency eddy current (HFEC) inspection of the fuselage skin for any crack), operators also do the external LFEC inspection of the forward galley door bear strap and external HFEC inspection of the fuselage skin for any crack identified in accordance with Figure 4 of the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, and do all applicable on-condition actions.

Request for Credit for Actions Accomplished Prior to the Effective Date

Alaska Airlines (AAL), United Airlines (UAL), and Delta Air Lines (DAL) requested that the FAA provide credit for accomplishing the actions specified in paragraph (g) of the proposed AD prior to the effective date of this AD in accordance with Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9, 2019 (which was referred to as the appropriate source of information for doing the actions required by paragraph (g) of the proposed AD).

The FAA acknowledges the commenter's requests and agrees to clarify. As previously stated, the FAA has included Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, as the appropriate source of service information for doing the actions specified in this SNPRM. The FAA has also included paragraph (i) of this SNPRM to allow credit for actions accomplished before the effective date of this SNPRM, using Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9, 2019, provided, for certain airplanes, that certain actions are done.

Request To Exclude a Certain Inspection of Certain Repaired Areas

DAL requested that the proposed AD be revised to exclude an internal surface HFEC inspection in areas that were repaired if the repair met certain conditions. DAL noted that the design approval holder has specifically recommended that the surface HFEC inspection not be required if certain repairs have been accomplished, however, those repairs must have been installed after the original issue date of Boeing Alert Requirements Bulletin 737-53A1383 RB and must have been approved by The Boeing Company Organization Designation Authorization (ODA) via FAA Form 8100-9. DAL asked that such repairs be approved as AMOCs, regardless of when the repair was installed.

The FAA agrees to clarify. Paragraph (h)(1) of this AD allows using the notes and flag notes in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, as written. This means that, for actions done “after the original issue date of Boeing Alert Requirements Bulletin 737-53A1383 RB” operators are not required to do the internal surface HFEC in areas where the repair covers the affected inspection zone, provided the repair meets the conditions specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020. Operators do not need to obtain an AMOC to use this provision, provided the repair meets the conditions specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.

However, the FAA notes that this provision does not extend to repairs that were done before the original issue date of Boeing Alert Requirements Bulletin 737-53A1383 RB. Under the provisions of paragraph (i) of this AD, the FAA will consider requests for approval of repairs in this area that affect compliance with this AD and were done before the original issue date of Boeing Alert Requirements Bulletin 737-53A1383 RB if sufficient data are submitted to substantiate that the repair would provide an acceptable level of safety. The FAA has not changed this SNPRM regarding this issue.

Request for AMOC for Repairs Accomplished Before Service Information Publication

Southwest Airlines (SWA) requested that the FAA include previously accomplished repairs for the crack condition identified in Boeing Alert Requirements Bulletin 737-53A1383 RB as an approved AMOC, including repairs accomplished before the original issue date of Boeing Alert Requirements Bulletin 737-53A1383 RB. SWA mentioned that its fleet has repaired many crack conditions common to the inspection area specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, and that most of those repairs were accomplished before Boeing Alert Requirements Bulletin 737-53A1383 RB, was released. SWA also pointed out that those repairs were approved via FAA Form 8100-9.

The FAA disagrees with the commenter's request. Note (b) to Tables 1 and 2 in Boeing Alert Requirements Bulletin 737-53A1383 RB is intended to address repairs that were designed as corrective actions to the unsafe condition addressed in the service information and this AD, are approved by The Boeing Company ODA, and include a follow-on inspection program. For this reason, the FAA allows FAA Form 8100-9 for approved repairs that meet all criteria specified in note (b) to Tables 1 and 2 in Boeing Alert Requirements Bulletin 737-53A1383 RB to be exempted from the inspections in those repaired areas, but does not allow just any FAA-approved repair to be exempted from these required inspections. However, under the provisions of paragraph (i) of this AD, the FAA will consider requests for approval of certain repairs in this area that affect compliance with this AD if sufficient data are submitted to substantiate that the repair would provide an acceptable level of safety. The FAA has not changed this SNPRM regarding this issue.

Request To Clarify Acceptable Previous Repairs

Qantas Airways LTD (Qantas) requested that the FAA clarify whether certain blend repairs would require approval of a new FAA Form 8100-9, to reauthorize the existing repairs. Qantas pointed out that the criteria for the general visual inspection is “any repair.” Qantas also mentioned that a blend repair to a small depth may not be detectable with a general visual inspection (as specified in Boeing Alert Requirements Bulletin 737-53A1383 RB) because the area is shot or flap peened after blending.

The FAA agrees to clarify. Boeing Alert Requirements Bulletin 737-53A1383 RB specifies certain repairs that do not require additional contact with The Boeing Company ODA or the FAA. Those certain repairs are specified in note (a) to Table 1 and notes (a) and (b) to Table 2 of Boeing Alert Requirements Bulletin 737-53A1383 RB as: Fuselage skin blend out within the 737-600 structural repair manual (SRM) 53-00-01, 737-700 SRM 53-00-01, 737-700CONV SRM 53-00-01, 737-700IGW (BBJ) SRM 53-00-01, 737-800 SRM 53-00-01, 737-800BCF SRM 53-00-01, or 737-900 SRM 53-00-01 allowable damage. Any existing repair that is not specified in that section would require additional contact with The Boeing Company ODA or the FAA. The FAA has not changed this SNPRM regarding this issue.

Request To Clarify Exception to the Service Information

Qantas requested that the FAA clarify the intent of the exception to the service information specified in paragraph (h)(2) of the proposed AD. Qantas mentioned its perception that when Boeing Alert Requirements Bulletin 737-53A1383 RB, specifies that “It is not required to contact Boeing,” that the NPRM then requires the operator to contact The Boeing Company ODA.

The FAA agrees to clarify. Boeing Alert Requirements Bulletin 737-53A1383 RB specifies certain conditions, where contact with Boeing is unnecessary. Whereas, the exception specified in paragraph (h)(2) of this SNPRM, states that if Boeing Alert Requirements Bulletin 737-53A1383 RB, specifies to contact Boeing for repair instructions or for alternative inspections, this SNPRM requires doing the repair, or doing the alternative inspections and applicable on-condition actions using a method approved as an AMOC. The exception in paragraph (h)(2) of this AD, therefore, does not affect the statements in Boeing Alert Requirements Bulletin 737-53A1383 RB, that specify “It is not required to contact Boeing.” The FAA has not changed this SNPRM regarding this issue.

Request To Allow Alternate Inspection Procedure

Structural Monitoring Systems PLC (SMS) requested that the FAA allow the use of SMS comparative vacuum monitoring (CVM) structural monitoring sensors (and a CVM nondestructive testing procedure (NDT)) as an alternative to the HFEC inspections of the bear strap. SMS also requested that for the CVM NDT procedure, the FAA set a repetitive inspection frequency to 18,000 flight cycles to reduce the level of repair burden on the operator when a crack is discovered. SMS also requested that the CVM structural monitoring sensors be used to periodically monitor any crack propagation, using damage tolerant assessment data to determine the point of reaching the residual strength capability limit, noting that this is a similar practice to that used on engines. SMS stated that the structural monitoring sensors are less intrusive, require less time to access, and take less time to inspect, while providing an equal level of safety to the proposed HFEC inspection method. SMS further specified that a CVM NDT inspection method can be applied three times (or more) more frequently than the proposed HFEC inspection, while still being less time consuming, because there is no further disassembly/assembly after initial sensor installation. SMS then mentioned that it (SMS) would perform any specific evaluation or testing required by the FAA to demonstrate standard 90 percent probability of detection with 95 percent confidence for the application. SMS mentioned a recent FAA statement acknowledging “that an aircraft structure which is subject to damage tolerance assessment can be considered safe while continuing to operate with an existing [undetected] crack.” SMS specified the belief that the direct quote expresses a philosophy that is supportive of using the CVM structural monitoring sensors, and would allow operators to operate the aircraft until such time as the residual strength capability is reached, using an appropriate inspection interval.

The FAA disagrees with the request to mandate CVM structural monitoring sensors, a repetitive CVM NDT procedure with an 18,000 flight cycle compliance time, and periodic monitoring of crack propagation. SMS did not provide sufficient substantiation to show the effectivity of CVM technology for this application. Therefore, the FAA cannot specify or allow that technology and inspection method as an alternative to those specified in this SNPRM. The FAA has not changed this SNPRM regarding this issue. Once the final rule is published, any person may request approval of an alternative method of compliance (AMOC) under the provisions of paragraph (j) of this AD.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020. This service information describes procedures for inspecting for cracks of the fuselage skin and bear strap at the forward galley door between certain stations, through the use of two alternative inspection methods: (1) Internal and external general visual inspections and internal surface HFEC inspections, and (2) external general visual and external eddy current inspections, and applicable on-condition actions. On-condition actions include inspections for cracks, HFEC inspections for cracks, LFEC inspections for cracks, and repair, depending on the inspection method selected. 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.

FAA's Determination

The FAA is proposing this AD because the FAA 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. Certain revisions to the service information described above expand the scope of the NPRM. As a result, the FAA has determined that it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this SNPRM.

Proposed Requirements of This SNPRM

This SNPRM would require accomplishing the actions specified in the service information described previously. This proposed AD would also allow credit for airplanes that have done Option 2, Condition 4, as specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9, 2019, provided that those airplanes do additional inspections. For information on the procedures and compliance times, see this service information at https://www.regulations.gov by searching for and locating Docket No. FAA-2019-0705.

Costs of Compliance

The FAA estimates that this proposed AD affects 752 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:

The FAA has received no definitive data that would enable the agency to provide cost estimates 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.

The FAA is 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

The FAA 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 this proposed regulation:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Will not affect intrastate aviation in Alaska, and

(3) 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.

2. The FAA amends § 39.13 by adding the following new airworthiness directive (AD):

The Boeing Company: Docket No. FAA-2019-0705; Product Identifier 2019-NM-098-AD.

(a) Comments Due Date

The FAA must receive comments by June 15, 2020.

(b) Affected ADs

None.

(c) Applicability

(1) This AD applies to The Boeing Company Model 737-600, -700, -700C, -800, and -900 series airplanes, certificated in any category, as identified in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.

(2) Installation of Supplemental Type Certificate (STC) ST00830SE does not affect the ability to accomplish the actions required by this AD. Therefore, for airplanes on which STC ST00830SE is installed, a “change in product” alternative method of compliance (AMOC) approval request is not necessary to comply with the requirements of 14 CFR 39.17.

(d) Subject

Air Transport Association (ATA) of America Code 53, Fuselage.

(e) Unsafe Condition

This AD was prompted by reports of cracks in the bear strap from station (STA) 290 to STA 296, and between S-8R and S-9R, sometimes common to fasteners in the gap cover and emanating from rough sanding marks found on the surface of the bear strap. The FAA is issuing this AD to address cracking of the bear strap, which could result in severing of the bear strap, possibly leading to uncontrolled decompression of the airplane and loss of structural integrity of the airplane.

(f) Compliance

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

(g) Required Actions

Except as specified by paragraph (h) of this AD: At the applicable times specified in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, do all applicable actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.

Note 1 to paragraph (g):

Guidance for accomplishing the actions required by this AD can be found in Boeing Alert Service Bulletin 737-53A1383, Revision 1, dated February 19, 2020, which is referred to in Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.

(h) Exceptions to Service Information Specifications

(1) Where Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, uses the phrase “the original issue date of Requirements Bulletin 737-53A1383 RB,” this AD requires using “the effective date of this AD,” except where Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, uses the phrase “the original issue date of Requirements Bulletin 737-53A1383 RB” in a note or flag note.

(2) Where Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, specifies contacting Boeing for repair instructions or for alternative inspections: This AD requires doing the repair, or doing the alternative inspections and applicable on-condition actions, using a method approved in accordance with the procedures specified in paragraph (j) of this AD.

(i) Credit for Previous Actions

This paragraph provides credit for the actions specified in paragraph (g) of this AD, if those actions were performed before the effective date of this AD, using Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9, 2019, except for airplanes on which Option 2, Condition 4 has been done. For airplanes on which Option 2, Condition 4, has been done, credit is given provided operators do the external low frequency eddy current (LFEC) inspection of the forward galley door bear strap and external high frequency eddy current (HFEC) inspection of the fuselage skin for any crack in accordance with Figure 4 of the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020. The compliance time for accomplishing these actions is at the later of the time specified in paragraphs (i)(1) and (2) of this AD. Do all applicable on-condition actions identified in, and in accordance with, the Accomplishment Instructions of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020, at the applicable times specified in the “Compliance” paragraph of Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.

(1) Before 15,000 total flight cycles.

(2) Within 6,000 flight cycles after the effective date of this AD.

(j) Alternative Methods of Compliance (AMOCs)

(1) The Manager, Seattle ACO Branch, 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 certification office, send it to the attention of the person identified in paragraph (k)(1) of this AD. Information may be emailed to: 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.

(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, modification, or alteration required by this AD if it is approved by The Boeing Company Organization Designation Authorization (ODA) that has been authorized by the Manager, Seattle ACO Branch, FAA to make those findings. To be approved, the repair method, modification deviation, or alteration deviation must meet the certification basis of the airplane, and the approval must specifically refer to this AD.

(k) Related Information

(1) For more information about this AD, contact Michael Bumbaugh, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3522; email: michael.bumbaugh@faa.gov.

(2) For service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; phone: 562-797-1717; internet: https://www.myboeingfleet.com. You may view this referenced service information at the FAA, Airworthiness Products Section, Operational Safety Branch, 2200 South 216th St., Des Moines, WA. For information on the availability of this material at the FAA, call 206-231-3195.