Airworthiness Directives: The Boeing Company Airplanes

Airworthiness Directives; The Boeing Company Airplanes

Dates

The FAA must receive comments on this proposed AD by January 12, 2023.

Examining the AD Docket

You may examine the AD docket at regulations.gov by searching for and locating Docket No. FAA-2022-1063; 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.

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. FAA-2022-1063; Project Identifier AD-2021-01339-T" 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 this 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 regulations.gov , including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM.

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 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 Chris Baker, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3552; email: [email protected]. Any commentary that the FAA receives that is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

This proposed AD was prompted by the discovery of a safety issue related to the reliability of the oxygen sensor of the airplane's NGS.

The NGS is an onboard inert gas system that reduces the flammability of the airplane's center fuel tank. The NGS uses an air separation module (ASM) to separate oxygen and nitrogen from the air. The ASM uses input from an oxygen sensor. After the ASM separates the oxygen-enriched air from the nitrogen-enriched air, the NGS returns nitrogen-enriched air to the fuel tank, and vents the oxygen-enriched air overboard. These actions reduce the flammability of the fuel tank.

Boeing discovered that the oxygen sensor's reliability can degrade over time. Degraded performance by the sensor could result in the ASM failing to produce nitrogen-enriched air, and the fuel tank becoming more flammable due to excessive oxygen-enriched air. Such additional flammability, if coupled with an ignition source in the fuel tank, could lead to a fuel tank explosion. This proposed AD would require adding an airworthiness limitation to require periodic replacement of the oxygen sensor.

This proposed AD would apply to airplanes with an original airworthiness certificate or original export certificate of airworthiness issued on or before April 1, 2021, as well as airplanes with line numbers 7668, 7678, and 7915. Boeing did not start delivering airplanes with Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness Limitations, D626A011-9-04, dated January 2019, which addresses this issue, until after April 1, 2021, and delivered airplanes with line numbers 7668, 7678, and 7915 with an earlier revision of that document. The applicability in this proposed AD is therefore limited to airplanes that were delivered with a version of Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness Limitations, D626A011-9-04 dated prior to January 2019.

FAA's Determination

The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness Limitations, D626A011-9-04, dated January 2019. This service information describes, among other airworthiness limitations (AWLs), airworthiness limitation instruction (ALI) AWL No. 47-AWL-09, "Nitrogen Generation System-Oxygen Sensor," for replacing oxygen sensors. 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.

Proposed AD Requirements in This NPRM

This proposed AD would require revising the existing maintenance or inspection program, as applicable, to incorporate a new airworthiness limitation.

This proposed AD would require revisions to certain operator maintenance documents to include new actions (replacements). Compliance with these actions is required by 14 CFR 91.403(c). For airplanes that have been previously modified, altered, or repaired in the areas addressed by this proposed AD, the operator may not be able to accomplish the actions described in the revisions. In this situation, to comply with 14 CFR 91.403(c), the operator must request approval for an alternative method of compliance according to paragraph (i) of this proposed AD.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 62 airplanes of U.S. registry. The FAA estimates the following costs to comply with this proposed AD:

The FAA has determined that revising the existing maintenance or inspection program takes an average of 90 work-hours per operator, although the agency recognizes that this number may vary from operator to operator. Since operators incorporate maintenance or inspection program changes for their affected fleet(s), the FAA has determined that a per-operator estimate is more accurate than a per-airplane estimate. Therefore, the FAA estimates the average total cost per operator to be $7,650 (90 work-hours × $85 per work-hour).

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) Would not affect intrastate aviation in Alaska, and

(3) Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

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

The Boeing Company: Docket No. FAA-2022-1063; Project Identifier AD-2021-01339-T.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by January 12, 2023.

(b) Affected ADs

None.

(c) Applicability

This AD applies to The Boeing Company Model 737-8, 737-9, and 737-8200 airplanes, certificated in any category, identified in paragraphs (c)(1) and (2) of this AD.

(1) Airplanes with an original airworthiness certificate or original export certificate of airworthiness issued on or before April 1, 2021.

(2) Airplanes with line numbers 7668, 7678, and 7915.

(d) Subject

Air Transport Association (ATA) of America Code 28, Fuel.

(e) Unsafe Condition

This AD was prompted by significant changes made to an airworthiness limitation (AWL) related to the nitrogen generation system (NGS). The FAA is issuing this AD to prevent increasing the flammability exposure of the center fuel tank, which together with an ignition source in the fuel tank, could lead to a fuel tank explosion and consequent loss of the airplane.

(f) Compliance

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

(g) Maintenance or Inspection Program Revision

Within 60 days after the effective date of this AD, revise the existing maintenance or inspection program, as applicable, to incorporate the information specified in AWL No. 47-AWL-09, "Nitrogen Generation System-Oxygen Sensor," of Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness Limitations, D626A011-9-04, dated January 2019. The initial compliance time for the airworthiness limitation instruction (ALI) task is: Within 18,000 flight hours after the date of issuance of the original airworthiness certificate or the original export certificate of airworthiness, within 18,000 flight hours after the most recent replacement was performed as specified in AWL No. 47-AWL-09, or within 12 months after the effective date of this AD, whichever is latest.

(h) No Alternative Actions or Intervals

After the existing maintenance or inspection program has been revised as required by paragraph (g) of this AD, no alternative actions ( e.g., inspections) or intervals may be used unless the actions and intervals are approved as an alternative method of compliance (AMOC) in accordance with the procedures specified in paragraph (i) of this AD.

(i) 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 (j)(1) of this AD. Information may be emailed to: [email protected].

(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 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.

(j) Related Information

(1) For more information about this AD, contact Chris Baker, Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-3552; email: [email protected].

(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; telephone 562-797-1717; internet 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.