2023-06364. Airworthiness Directives; The Boeing Company Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final rule; request for comments.

SUMMARY:

The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 737-8, -8200, and -9 airplanes. This AD was prompted by a report indicating that certain engine anti-ice (EAI) exhaust duct fasteners were inadequately torqued. This AD requires an inspection or records review to determine the serial number of each engine inlet; and if any affected engine inlet is found, an inspection of the EAI exhaust duct fasteners to determine the gap spacing and if all fasteners are installed, applicable related investigative and corrective actions, and part marking. This AD also limits the installation of affected parts. The FAA is issuing this AD to address the unsafe condition on these products.

DATES:

This AD is effective April 11, 2023.

The Director of the Federal Register approved the incorporation by reference of a certain publication listed in this AD as of April 11, 2023.

The FAA must receive comments on this AD by May 11, 2023.

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 regulations.gov. Follow the instructions for submitting comments.

• Fax: [phone].

• 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: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

AD Docket: You may examine the AD docket at regulations.gov by searching for and locating Docket No. FAA-2023-0440; 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 final rule, any comments received, and other information. The street address for Docket Operations is listed above.

Material Incorporated by Reference:

• For service information identified in this final rule, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone [phone]; website 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. It is also available at regulations.gov under Docket No. FAA-2023-0440.

FOR FURTHER INFORMATION CONTACT:

Samuel Dorsey, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail].

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written data, views, or arguments about this final rule. Send your comments to an address listed under ADDRESSES . Include Docket No. FAA-2023-0440 and Project Identifier AD-2023-00245-T at the beginning of your comments. The most helpful comments reference a specific portion of the final rule, 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 this final rule 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 regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this final rule.

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 AD 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 AD, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI 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 AD. Submissions containing CBI should be sent to Samuel Dorsey, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail]. Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

The FAA has received a report indicating that during a pre-flight check, the flightcrew discovered a bolt protruding through a drain hole at the bottom of the engine inlet near the EAI exhaust vent. Boeing determined that some of the fasteners for EAI exhaust ducts were installed at the factory with inadequate torque due to the use of a prohibited yoke-style torque wrench adapter at a significant angle. When used at a sufficiently large angle, which is expected due to the restricted access in the area of the EAI exhaust duct, this adapter will produce a significant under-torque of the installed fasteners. Inadequately-torqued fasteners may loosen over time due to engine vibration, eventually causing the fastener to drop into the inlet inner barrel.

The EAI system injects high-temperature bleed air from the engine into the interior of the inlet lip to prevent the formation of icing on the exterior of the inlet lip. This EAI exhaust air then exits the rear of the inlet lip through the EAI exhaust duct, which passes through the inlet inner barrel prior to exhausting air overboard. The composite construction of the inlet inner barrel structure is susceptible to heat damage at the temperatures of the EAI exhaust air should a leak occur.

These inadequately torqued (loose or missing) fasteners for the EAI exhaust duct could allow EAI exhaust air to escape from the EAI exhaust duct via two scenarios. In the first scenario, the loose or missing fasteners allow the EAI exhaust duct to vibrate excessively, which, when combined with the redistribution of structural loads onto the other fasteners, may lead to fatigue cracking of the EAI exhaust duct. This fatigue cracking would ultimately progress to a rupture of the EAI exhaust duct. In the second scenario, the loose or missing fasteners may allow EAI exhaust air to escape from a limited location. This escaping air may impinge directly on the inner barrel structure, depending on which specific fasteners are loose or missing. In both scenarios, EAI exhaust air enters the inlet inner barrel causing heat damage, which will compromise the structural integrity of the inlet, eventually leading to inlet failure and separation under normal flight loads.

Failure and separation of the inlet will lead to failure of the corresponding engine due to airflow disruption and ingestion of debris, and likely to failure and separation of the associated fan cowl. Damage to the engine and engine nacelle could result in a loss of engine thrust, increased nacelle drag, and disruption of airflow over the wing, which may excessively reduce the controllability and climb performance of the airplane; and damage from debris departing the engine and nacelle, which could impact the fuselage and empennage, could result in personal injury to passengers and loss of control of the airplane.

The FAA is issuing this AD to address the unsafe condition on these products.

FAA's Determination

The FAA is issuing this AD because the agency has determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023. (Attachments I and II of this document are dated March 2, 2023.) The service information specifies procedures for an inspection to determine the serial number of each engine inlet, and if any affected engine inlet is found, an inspection of the EAI exhaust duct fasteners to determine the gap spacing and if all fasteners are installed, applicable related investigative and corrective actions, and part-marking the engine inlet. Related investigative actions include an inspection of the fasteners for proper torque, general visual and high frequency eddy current inspections of the EAI exhaust duct flange and fastener holes for cracking, and visual inspections of the inner barrel for thermal exposure ( i.e., heat damage). Corrective actions include re-torque of fasteners, repairing or replacing EAI exhaust ducts, repairing thermal exposure, and replacing the engine inlet. 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.

AD Requirements

This AD requires accomplishing the actions identified as “(RC)” (required for compliance) in the Work Instructions of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, described previously, except as discussed under “Differences Between this AD and the Service Information,” and except for any differences identified as exceptions in the regulatory text of this AD.

For information on the procedures and compliance times, see this service information at regulations.gov under Docket No. FAA-2023-0440.

Differences Between This AD and the Service Information

Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, specifies that the actions must be done on all airplanes. However, airplanes produced after a certain production line number were verified to have properly torqued EAI exhaust duct fasteners. Therefore, paragraph (g) of this AD only applies to airplanes with an original airworthiness certificate or original export certificate of airworthiness issued on or before the effective date of the AD. The parts installation limitation specified in paragraph (i) of this AD applies to all airplanes.

Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, includes an inspection to verify the serial number of the inlet. This AD also allows a review of airplane maintenance records in lieu of the inspection to verify the serial number of the inlet if the serial number of the inlet can be conclusively determined from that review.

Interim Action

The FAA considers this AD to be an interim action. The FAA is investigating if design changes may be needed to prevent a future common-cause failure of the EAI exhaust duct. If final action is later identified, the FAA might consider further rulemaking then.

Justification for Immediate Adoption and Determination of the Effective Date

Section 553(b)(3)(B) of the Administrative Procedure Act (APA) (5 U.S.C. 551 et seq.) authorizes agencies to dispense with notice and comment procedures for rules when the agency, for “good cause,” finds that those procedures are “impracticable, unnecessary, or contrary to the public interest.” Under this section, an agency, upon finding good cause, may issue a final rule without providing notice and seeking comment prior to issuance. Further, section 553(d) of the APA authorizes agencies to make rules effective in less than thirty days, upon a finding of good cause.

An unsafe condition exists that requires the immediate adoption of this AD without providing an opportunity for public comments prior to adoption. The FAA has found that the risk to the flying public justifies forgoing notice and comment prior to adoption of this rule because loose or missing fasteners for the EAI exhaust duct might allow EAI exhaust air to enter the inlet interior causing heat damage, which could compromise the structural integrity of the inlet, eventually leading to inlet failure and separation under normal flight loads. Failure and separation of the inlet will lead to failure of the corresponding engine due to airflow disruption and ingestion of debris and likely failure and separation of the associated fan cowl. Damage to the engine and engine nacelle could result in a loss of engine thrust, increased nacelle drag, and disruption of airflow over the wing which may excessively reduce the controllability and climb performance of the airplane; and damage from debris departing the engine and nacelle, which could impact the fuselage and empennage, could result in personal injury to passengers and loss of control of the airplane. Accordingly, notice and opportunity for prior public comment are impracticable and contrary to the public interest pursuant to 5 U.S.C. 553(b)(3)(B).

In addition, the FAA finds that good cause exists pursuant to 5 U.S.C. 553(d) for making this amendment effective in less than 30 days, for the same reasons the FAA found good cause to forgo notice and comment.

Regulatory Flexibility Act

The requirements of the Regulatory Flexibility Act (RFA) do not apply when an agency finds good cause pursuant to 5 U.S.C. 553 to adopt a rule without prior notice and comment. Because the FAA has determined that it has good cause to adopt this rule without notice and comment, RFA analysis is not required.

Costs of Compliance

The FAA estimates that this AD affects 330 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD:

Estimated Costs

Action	Labor cost	Parts cost	Cost per product	Cost on U.S. operators
Inspection or records review to determine serial number of engine inlet	1 work-hour × $85 per hour = $85	$0	$85	$28,050
Inspection of fastener gaps and to determine if all fasteners are installed, and engine inlet part-marking	2 work-hour × $85 per hour = $170 per inlet (2 inlets per airplane)	0	340	112,200

The FAA estimates the following costs to do any necessary on-condition actions that would be required based on the results of the inspection to of fastener gaps and to determine if all fasteners are installed. The FAA has no way of determining the number of aircraft that might need these actions:

On-Condition Costs *

Action	Labor cost	Parts cost	Cost per product
Inspection of the fasteners for proper torque	1 work-hour × $85 per hour = $85 per inlet	$0	$85 per inlet.
EAI exhaust duct inspection	1 work-hour × $85 per hour = $85 per inlet	0	85 per inlet.
EAI exhaust duct replacement	1 work-hour × $85 per hour = $85 per inlet	10,000 per inlet	10,085 per inlet.
Inner barrel thermal exposure inspection	1 work-hour × $85 per hour = $85 per inlet	0	85 per inlet.
Inlet replacement	12 work-hours × $85 per hour = $1,020 per inlet	1,741,000 per inlet	1,742,020 per inlet.
Re-torquing	1 work-hour × $85 per hour = $85 per inlet	0	85 per inlet.
* For repair of the EAI exhaust duct and repairing thermal exposure, the FAA has no definitive data on which to base the cost estimate for those actions.

The FAA has included all known costs in its cost estimate. According to the manufacturer, however, some or all of the costs of this AD may be covered under warranty, thereby reducing the cost impact on affected operators.

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

This AD will not have federalism implications under Executive Order 13132. This AD will 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 that this AD:

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

(2) Will not affect intrastate aviation in Alaska.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Incorporation by reference
• Safety

The Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 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.

§ 39.13

[Amended]

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

2023-06-10 The Boeing Company: Amendment 39-22396; Docket No. FAA-2023-0440; Project Identifier AD-2023-00245-T.

(a) Effective Date

This airworthiness directive (AD) is effective April 11, 2023.

(b) Affected ADs

None.

(c) Applicability

This AD applies to all The Boeing Company Model 737-8, -8200, and -9 airplanes, certificated in any category.

(d) Subject

Air Transport Association (ATA) of America Code 30, Ice and Rain Protection; 71, Powerplant.

(e) Unsafe Condition

This AD was prompted by a report indicating that certain engine anti-ice (EAI) exhaust duct fasteners were inadequately torqued during installation at the factory. The FAA is issuing this AD to address loose or missing fasteners for the EAI exhaust duct that may allow EAI exhaust air to enter the inlet inner barrel causing heat damage that will compromise the structural integrity of the inlet, eventually leading to inlet failure and separation under normal flight loads. The unsafe condition, if not addressed, will lead to failure of the corresponding engine due to airflow disruption and ingestion of debris and likely failure and separation of the associated fan cowl. Damage to the engine and engine nacelle could result in a loss of engine thrust, increased nacelle drag, and disruption of airflow over the wing, which may excessively reduce the controllability and climb performance of the airplane; and damage from debris departing the engine and nacelle, which could impact the fuselage and empennage, could result in personal injury to passengers and loss of control of the airplane.

(f) Compliance

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

(g) Required Actions

For airplanes with an original airworthiness certificate or original export certificate of airworthiness issued on or before the effective date of the AD: Except as specified by paragraph (h) of this AD, at the applicable times specified in the “Suggested Operator Action” section of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, do all applicable actions identified as “RC” (required for compliance) in, and in accordance with, the Work Instructions of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023. Perform all applicable related investigative and corrective actions before further flight.

(h) Exceptions to Service Information Specifications

(1) Where the “Suggested Operator Action” section of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, specifies doing “the following actions within the given time from the publication of this service letter,” this AD requires accomplishing the actions within the specified compliance times after “the effective date of this AD.”

(2) Where the “Suggested Operator Action” section of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, specifies “corrective actions,” for this AD, those actions include “corrective and related investigative actions.”

(3) A review of airplane maintenance records is acceptable in lieu of the inspection to verify the serial number of the inlet specified in step A.1. of the Work Instructions of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, if the serial number of the inlet can be conclusively determined from that review.

(4) Where Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, specifies contacting Boeing for repair or further instructions: This AD requires doing the repair and applicable instructions before further flight using a method approved in accordance with the procedures specified in paragraph (l) of this AD.

(5) Where the Work Instructions of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, refers to the structural repair manual, replace the text “737-8/8200/9 Structural Repair Manual (SRM) 51-40-04, Revision 18/9/15,” with “737-8 Structural Repair Manual (SRM) 51-40-04, Revision 18 or 19; 737-8200 SRM 51-40-04, Revision 9 or 10; or 737-9 SRM 51-40-04, Revision 15 or 16.”

(i) Parts Installation Limitation

As of the effective date of this AD, no person may install an engine inlet assembly with a serial number listed in Attachment I of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023, on any airplane unless all applicable actions required by paragraph (g) of this AD have been done for that inlet.

(j) 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 Service Letter 737-SL-71-081, dated February 20, 2023, provided the conditions specified in paragraphs (j)(1) and (2) of this AD are met.

(1) An inspection or records review has been done to verify the inlet serial number is not included in the additional serial numbers identified in Attachment I of Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023; and the serial number of the inlet can be conclusively determined from that inspection or review.

(2) Where the Work Instructions of Boeing Service Letter 737-SL-71-081, dated February 20, 2023, refer to the structural repair manual (SRM) to apply torque, the applicable SRM identified in paragraph (j)(2)(i), (ii), or (iii) of this AD was used to apply the torque.

(i) Boeing 737-8 SRM 51-40-04, Revision 18, dated November 10, 2022; or Revision 19, dated March 10, 2023.

(ii) Boeing 737-8200 SRM 51-40-04, Revision 9, dated November 10, 2022; or Revision 10, dated March 10, 2023.

(iii) Boeing 737-9 SRM 51-40-04, Revision 15, dated November 10, 2022; or Revision 16, dated March 10, 2023.

(k) Special Flight Permit

(1) Special flight permits, as described in 14 CFR 21.197 and 21.199, may be issued to move the airplane to a maintenance facility prior to performing the required inspections.

(2) If, during the inspections required by paragraph (g) of this AD, only one engine is found with an inlet having any crack or thermal damage: Special flight permits, as described in 14 CFR 21.197 and 21.199, may be issued to operate the airplane to a location where the requirements of this AD can be accomplished provided the conditions specified in paragraph (k)(2)(i) and (ii) of this AD, as applicable, are met.

(i) The EAI is deactivated on the affected engine in accordance with the operator's existing Minimum Equipment List.

(ii) For any inlet with any thermal exposure ( i.e., heat damage) on the inner barrel, The Boeing Company Organization Designation Authorization (ODA) is contacted to obtain concurrence for issuance of a special flight permit and The Boeing Company ODA concurs. Operators must comply with any flight limitations provided by The Boeing Company ODA. The concurrence with any limitations must specifically refer to this AD.

(3) If, during the inspections required by paragraph (g) of this AD, both engines are found with inlets having any crack or thermal exposure: Special flight permits, as described in 14 CFR 21.197 and 21.199, are not allowed.

(l) 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 responsible Flight Standards 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 (m) of this AD. Information may be emailed to: [e-mail].

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the responsible Flight Standards 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 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.

(4) Except as required by paragraph (h) of this AD: For service information that contains steps that are labeled as Required for Compliance (RC), the provisions of paragraphs (l)(4)(i) and (ii) of this AD apply.

(i) The steps labeled as RC, including substeps under an RC step and any figures identified in an RC step, must be done to comply with the AD. If a step or substep is labeled “RC Exempt,” then the RC requirement is removed from that step or substep. An AMOC is required for any deviations to RC steps, including substeps and identified figures.

(ii) Steps not labeled as RC may be deviated from using accepted methods in accordance with the operator's maintenance or inspection program without obtaining approval of an AMOC, provided the RC steps, including substeps and identified figures, can still be done as specified, and the airplane can be put back in an airworthy condition.

(m) Related Information

For more information about this AD, contact Samuel Dorsey, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone: [phone]; email: [e-mail].

(n) Material Incorporated by Reference

(1) The Director of the Federal Register approved the incorporation by reference (IBR) of the service information listed in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use this service information as applicable to do the actions required by this AD, unless the AD specifies otherwise.

(i) Boeing Service Letter 737-SL-71-081-A, Revision A, dated March 3, 2023.

Note 1 to paragraph (n)(2)(i): Attachments I and II of this document are dated March 2, 2023.

(ii) [Reserved]

(3) 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; telephone [phone]; website myboeingfleet.com.

(4) 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.

(5) You may view this service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, [e-mail], or go to: www.archives.gov/​federal-register/​cfr/​ibr-locations.html.

Issued on March 17, 2023.

Christina Underwood,

Acting Director, Compliance & Airworthiness Division, Aircraft Certification Service.