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Federal Register / Vol. 86, No. 136 / Tuesday, July 20, 2021 / Rules and Regulations List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows:
PART 39AIRWORTHINESS
DIRECTIVES
1. The authority citation for part 39
continues to read as follows:

Authority: 49 U.S.C. 106g, 40113, 44701.
39.13

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

20211420 The Boeing Company:
Amendment 3921647; Docket No.
FAA20210561; Project Identifier AD
202100623T.
a Effective Date This airworthiness directive AD is effective July 20, 2021.
b Affected ADs None.
c Applicability This AD applies to all The Boeing Company Model 737 airplanes, certificated in any category.
d Subject Air Transport Association ATA of America Code 21, Air conditioning.
e Unsafe Condition This AD was prompted by reports of latent failures of the cabin altitude pressure switches. The FAA is issuing this AD to address the unexpectedly high rate of latent failure of both pressure switches on the same airplane which could result in the cabin altitude warning system not activating if the cabin altitude exceeds 10,000 feet, resulting in hypoxia of the flightcrew, and loss of control of the airplane.

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f Compliance Comply with this AD within the compliance times specified, unless already done.
g Repetitive Functional Tests Except as specified in paragraph j of this AD: At the latest of the times specified in paragraphs g1 through 3 of this AD, perform the initial functional test of the cabin altitude pressure switches, and before further flight, do all applicable on-condition actions, in accordance with the Functional Test Requirements section of Boeing Multi Operator Message MOMMOM210292
01B, dated June 23, 2021. Repeat the functional test thereafter at intervals not to exceed 2,000 flight hours and do all applicable on condition actions before further flight.

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1 Within 2,000 flight hours since the last functional test of the cabin altitude pressure switches.
2 Prior to the accumulation of 2,000 total flight hours on the airplane.
3 Within 90 days after the effective date of this AD.
Note 1 to paragraph g: Additional guidance for performing the functional test required by paragraph g of this AD can be found in 737200 Airplane Maintenance Manual AMM 213311/501, 737CL AMM
TASK CARD 310260101, 737CL AMM
TASK CARD 310100101, 737NG AMM
TASK CARD 310200001, and 737MAX
AMM TASK CARD 310200001, and other approved maintenance procedures.
h Reporting for Switch Failure If any switch fails the initial functional test required by paragraph g of this AD: At the applicable time specified in paragraph h1
or 2 of this AD, report the results of that functional test, in accordance with Boeing Multi Operator Message MOMMOM21
029201B, dated June 23, 2021.
1 If the functional test was done on or after the effective date of this AD: Submit the report within 10 days after the functional test.
2 If the functional test was done before the effective date of this AD: Submit the report within 10 days after the effective date of this AD.
i Repetitive Reporting of Tested Fleet Within 40 days, but no earlier than 30
days, after the effective date of this AD: Send a report to Boeing listing the total number of airplanes, including tail numbers, in the operators fleet that have been tested since the effective date of this AD, in accordance with Boeing Multi Operator Message MOM
MOM21029201B, dated June 23, 2021.
Thereafter, send a report for the number of airplanes tested, at intervals of 30 days for a total period of 12 months. A report is not required for any 30-day interval in which no airplanes were tested.
j Exceptions to Service Information Specifications 1 Where Boeing Multi Operator Message MOMMOM21029201B, dated June 23, 2021, refers to certain task cards for the functional test, that service information is not required by this AD, and any approved maintenance procedures are acceptable for the functional test.
2 Where Boeing Multi Operator Message MOMMOM21029201B, dated June 23, 2021, specifies replacing failed switches with new or serviceable switches, this AD
requires replacement with serviceable switches, which include any switches that are eligible for installation.
3 Where Boeing Multi Operator Message MOMMOM21029201B, dated June 23, 2021, specifies the on-condition additional step of increasing the altitude to 20,000 feet if the cabin altitude warning does not activate by 11,000 feet, this AD requires that additional step only during the initial functional test.

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k 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 Related Information.
Information may be emailed to 9-ANMSeattle-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 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.
l Related Information For more information about this AD, contact Nicole Tsang, Aerospace Engineer, Cabin Safety and Environmental Systems Section, FAA, Seattle ACO Branch, 2200
South 216th St., Des Moines, WA 98198;
phone and fax: 2062313959; email:
Nicole.S.Tsang@faa.gov.
m 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. 552a 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 Multi Operator Message MOM
MOM21029201B, dated June 23, 2021.
ii Reserved 3 For service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services C&DS, 2600 Westminster Blvd., MC 110SK57, Seal Beach, CA 907405600;
telephone 5627971717; internet https
www.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 2062313195.
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, email fedreg.legal@nara.gov, or go to: https
www.archives.gov/federal-register/cfr/ibrlocations.html.

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