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PROPOSED AD THE BOEING COMPANY: Docket No. FAA-2022-0588; Project Identifier AD-2022-00114-T.
(a) COMMENTS DUE DATE

    The FAA  must receive  comments on  this airworthiness  directive (AD)
    action by August 22, 2022.

(b) AFFECTED ADS

    This AD replaces AD 2021-14-20,  Amendment 39-21647 (86 FR 38214, July
    20, 2021) (AD 2021-14-20).

(c) APPLICABILITY

    This AD applies to all The Boeing Company  Model 737-100, -200, -200C,
    -300, -400, -500, -600, -700, -700C, -800, -900 and -900ER series air-
    planes and Model 737-8, 737-9, and 737-8200 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 alti-
    tude pressure switches, and the determination that using certain adap-
    ters while performing a functional test may lead to false 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.

(f) COMPLIANCE

    Comply with this AD within the compliance times specified,  unless al-
    ready done.

(g) REPETITIVE FUNCTIONAL TESTS

(1) At the latest of the times  specified  in paragraphs (g)(1)(i) through
    (iii) of  this AD,  perform a  functional test  of the  cabin altitude
    pressure switches  having part  number 214C50-2,  using an  adapter as
    specified in figure 1  to paragraph (g) of  this AD, or an  equivalent
    adapter, and matching  hose to connect  to the cabin  altitude warning
    switch.  Repeat the  functional test  thereafter at  intervals not  to
    exceed 2,000 flight hours. If,  during any functional test, any  cabin
    altitude pressure switch fails to  activate at an altitude of  between
    9,000 and 11,000 feet, replace the switch before further flight.

(i) Within 2,000 flight hours  since the last functional test of the cabin
    altitude pressure switches.

(ii) Prior to the accumulation of 2,000 total flight hours on the airplane

(iii) Within 90 days after the effective date of this AD.

(2) Adapters are considered  to  be  equivalent as long as the mating side
    with the switch meets the specifications in either paragraph (g)(2)(i)
    or (ii) of this AD:

(i) Greater than or equal to 0.265 inches (0.673 cm) X 7/16-20-UNJF-3A and
    less than  or  equal  to 0.438 inches (1.113 cm) X 7/16-20-UNJF-3A for
    the flareless end; or

(ii) Less than or equal to 0.5 inches (1.27 cm) total with greater than or
     equal  to  0.265 inches (0.673 cm) X 7/16-20-UNJF-3A  thread  for AN4
     flared end.

        FIGURE 1 TO PARAGRAPH (G) OF THIS AD  FUNCTIONAL TEST ADAPTERS
    ______________________________________________________________________
    Use one of the following adapters or an equivalent adapter, and match-
    ing hose to connect to the cabin altitude warning switch:

    (1) SAE J514 part number  (P/N) 070220 90 Degree Straight Thread Elbow
        and appropriate sized O-ring (Preferred).

    - Use a Barfield Pitot Hose, or equivalent 25 feet (7.62 m) to 40 feet
      (12.19 m) long hose, with #4 AN fitting to the adapter and quick dis
      -connect (if applicable) to the air data test set.

    - Make sure that the flat side of the adapter  is  connected  with the
      cabin altitude warning switch.

    NOTE: Do not connect the flared side of the adapter with the cabin al-
    titude warning switch. Connecting the flared side of the adapter  with
    the cabin altitude  warning switch may  bottom out the  cabin altitude
    warning switch, resulting in false test results.

    (2) SAE J514 P/N 070320 45 Degree Straight Thread Elbow  and appropri-
        ate sized Oring (Preferred).

    - Use a Barfield Pitot Hose, or equivalent 25 feet (7.62 m) to 40 feet
      (12.19 m) long hose, with #4 AN fitting to the adapter and quick dis
      -connect (if applicable) to the air data test set.

    - Make sure that the flat side  of  the  adapter is connected with the
      cabin altitude warning switch.

    NOTE: Do not connect the flared side of the adapter with the cabin al-
    titude warning switch. Connecting the flared side of the adapter  with
    the cabin altitude  warning switch may  bottom out the  cabin altitude
    warning switch, resulting in false test results.

    (3) SAE J514 P/N 070120 Straight Thread Connector Short  and appropri-
        ate sized Oring (Preferred).

    - Use a Barfield Pitot Hose, or equivalent 25 feet (7.62 m) to 40 feet
      (12.19 m) long hose, with #4 AN fitting to the adapter and quick dis
      -connect (if applicable) to the air data test set.

    - Make sure that the flat side  of  the  adapter is connected with the
      cabin altitude warning switch.

    NOTE: Do not connect the flared side of the adapter with the cabin al-
    titude warning switch. Connecting the flared side of the adapter  with
    the cabin altitude  warning switch may  bottom out the  cabin altitude
    warning switch, resulting in false test results.

    (4) AS21900-4 (or MS21900-4) Flareless Tube to Flared Tube Adapter and
        appropriate sized O-ring (Preferred).

    - Use a Barfield Pitot Hose, or equivalent 25 feet (7.62 m) to 40 feet
      (12.19 m) long hose, with #4 AN fitting to the adapter and quick dis
      -connect (if applicable) to the air data test set.

    - Make sure that the flat side  of  the  adapter is connected with the
      cabin altitude warning switch.

    NOTE: Do not connect the flared side of the adapter with the cabin al-
    titude warning switch. Connecting the flared side of the adapter  with
    the cabin altitude  warning switch may  bottom out the  cabin altitude
    warning switch, resulting in false test results.

    (5) P/N JUD321 Hose Fitting with MS28778-4 O-ring (Eaton Aerospace LLC
        Bethel, CT 02750) (Preferred).

    - Use a Barfield Pitot Hose, or equivalent 25 feet (7.62 m) to 40 feet
      (12.19 m) long hose, with #4 AN fitting to the adapter and quick dis
      -connect (if applicable) to the air data test set.

    (6) AN807-4D (or AS5180D04 or AS5180W04) Tube to Hose Adapter, AN924-4
        nut and appropriate sized O-ring  (on  the  mating  side  with the
        switch) and spacer or washers (Alternate).

    NOTE: This adapter  can be used  if the steps below are carefully fol-
    lowed. This adapter is not preferred because if the AN924-4 nut is not
    connected carefully as recommended below,  this  may  bottom  out  the
    cabin altitude warning switch, resulting in false test results.

    - Use a Barfield Pitot Hose, or equivalent 25 feet (7.62 m) to 40 feet
      (12.19 m) long hose,  with  quick disconnect  (if applicable) to the
      air data test set.

    - Make sure that the thread length, including fitting end after the in
      -stallation of AN924-4 nut  and  appropriate  sized  7/16 spacer  or
      washers, is less than 0.5 inch (1.270 cm)  to  avoid  false test re-
      sults.
    ______________________________________________________________________

Note 1 to paragraph (g): Additional guidance for performing the functional
test required by paragraph (g) of this AD can be found in 737-200 Airplane
Maintenance Manual (AMM)  21-33-11/501,  737CL AMM TASK CARD 31-026-01-01,
737CL AMM TASK CARD 31-010-01-01, 737NG AMM TASK CARD 31-020-00-01 and 737
MAX AMM TASK CARD 31-020-00-01, and other approved maintenance procedures.

(h) MINIMUM EQUIPMENT LIST PROVISIONS

    If any cabin altitude warning switch fails  any functional test as re-
    quired by this AD,  the airplane  may be operated  as specified in the
    operator's existing FAA-approved MEL, provided provisions that specify
    operating the airplane  at  a  flight altitude at or below 10,000 feet
    mean sea level  (MSL)  with the cabin altitude warning system inopera-
    tive are included in the operator's existing FAA-approved MEL.

(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 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.

(2) Before using any approved AMOC,  notify your appropriate principal in-
    spector, or lacking a principal inspector,  the manager of the respon-
    sible 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,  modifica-
    tion 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  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:
    206-231-3959; email: Nicole.S.Tsang@faa.gov.

(2) For service information identified in this AD that is not incorporated
    by reference, contact Boeing Commercial Airplanes, Attention: Contrac-
    tual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal
    Beach, CA  90740-5600;  telephone 562-797-1717;  internet https://www.
    myboeingfleet.com.

Issued on May 16, 2022. Gaetano A Sciortino, Deputy Director for Strategic
Initiatives,  Compliance & Airworthiness Division,  Aircraft Certification
Service.

DATES: The FAA must receive comments  on  this  proposed  AD by August 22,
2022.
PREAMBLE 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2022-0588; Project Identifier AD-2022-00114-T]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: The FAA proposes to supersede Airworthiness Directive (AD)
2021-14-20, which applies to all The Boeing Company Model 737
airplanes. AD 2021-14-20 requires repetitive functional tests of the
cabin altitude pressure switches, and on-condition actions, including
replacement, if necessary. AD 2021-14-20 also requires reporting test
results. Since the FAA issued AD 2021-14-20, data collected from the
reports required by AD 2021-14-20 revealed that the switches were
subject to false test failures due to lack of clear instructions for
setup of the test adapters during the functional tests. This proposed
AD would retain the repetitive functional tests and on-condition
actions, and specify certain adapter requirements for the functional
tests. The FAA is proposing this AD to address the unsafe condition on
these products.

DATES: The FAA must receive comments on this proposed AD by August 22,
2022.

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

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2022-0588; 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: 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: 206-
231-3959; email: Nicole.S.Tsang@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. FAA-2022-0588; Project Identifier
AD-2022-00114-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
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 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
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: 206-231-3959; email:
Nicole.S.Tsang@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 issued AD 2021-14-20, Amendment 39-21647 (86 FR 38214, July
20, 2021) (AD 2021-14-20), for all The Boeing Company Model 737
airplanes. AD 2021-14-20 was prompted by reports of latent failures of
the cabin altitude pressure switches. AD 2021-14-20 requires repetitive
functional tests of the pressure switches, and on-condition actions,
including replacement, if necessary. The agency issued AD 2021-14-20 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.

Actions Since AD 2021-14-20 Was Issued

Since the FAA issued AD 2021-14-20, Boeing, Eaton Aerospace (the
cabin altitude warning switch supplier) and the FAA analyzed data
collected from the reports required by AD 2021-14-20. That data
revealed that the switches were subject to false test failures due to
lack of clear instructions for setup of the test adapters during the
functional tests.

For most of the switches that were tested by the supplier after failing
a functional test, no fault was found in the switches. Instead, it was
determined that if a test adapter not meeting certain criteria (threads
having a full thread depth of no greater than 0.438 inches (1.113 cm)
and an overall length less than 0.500 inches (1.270 cm)) is connected
to the cabin altitude warning switch, false failures may occur during
the functional test. Based on this analysis, Boeing revised its
airplane maintenance manual (AMM) procedures, which provide guidance
for performing the functional test, to specify criteria for the
adapters and matching hoses (those that are 25 feet to 40 feet (7.62 to
12.19 meters) long, with #4 AN fitting to the adapter and quick
disconnect (if applicable) to the air data test set). The matching hose
criteria ensures there is a connection between the pressure switch and
the air data test set. The FAA determined that AD 2021-14-20 should be
superseded to ensure the functional tests are performed using the
correct adapters to avoid false failure results. In addition, the FAA
determined that sufficient data has been received regarding the cause
of the failures of the cabin altitude pressure switches. Therefore, the
reporting required by AD 2021-14-20 is no longer needed. This proposed
AD would therefore retain the repetitive functional tests and on-
condition actions, and specify certain adapter requirements for the
functional tests.

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.

Proposed AD Requirements in This NPRM

This proposed AD would retain certain requirements of AD 2021-14-
20. This proposed AD would continue to require repetitive functional
tests of the pressure switches having part number 214C50-2, and on-
condition actions, including replacement, if necessary. This proposed
AD would require using adapters and matching hoses meeting certain
criteria when performing the functional tests, as specified in figure 1
to paragraph (g) of this AD. This proposed AD would also eliminate the
reporting required by AD 2021-14-20.

Effect of Certain Installation Procedures on Accomplishment of AD
Requirements


The FAA issued AD 2015-21-11, Amendment 39-18304 (80 FR 65927,
October 28, 2015) (AD 2015-21-11) applicable to certain Model 737-100,
-200, -200C, -300, -400, -500, -600, -700, -700C, -800, -900, and -
900ER series airplanes. AD 2015-21-11 requires, among other actions,
the installation of a redundant cabin altitude pressure switch in
accordance with specified Boeing service information. The FAA has since
approved numerous supplemental type certificates (STCs) and other means
for installing the redundant pressure switch. As a result of its
oversight of these newly-installed switches, the FAA has determined
that use of approved maintenance procedures for the cabin altitude
pressure switch functional test other than the task cards specified in
Note 1 to paragraph (g) of this AD, is acceptable for the functional
test, provided the adapter meets the criteria specified in paragraph
(g) of this AD. Therefore, those other procedures do not require
approval of an alternative method of compliance (AMOC).

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 2,693 airplanes of U.S. registry. The FAA estimates the
following costs to comply with this proposed AD:

Estimated Costs

Action
Labor cost
Parts cost
Cost per product
Cost on U.S. operators
Functional test 1 work-hour x $85 per hour = $85 per test * $ $85 per test $228,905 per test

* If the operator needs to buy an adapter, the FAA estimates the adapter
could cost up to $3,644. The FAA has no way of determining the number of
operators that might need to purchase an adapter.

The FAA estimates the following costs to do any necessary on-
condition actions that would be required based on the results of the
functional test. 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
Switch replacement 1 work-hour x $85 per hour = $85
$1,278
$1,363

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 has 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 that the 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.

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.

Sec. 39.13 [Amended]

2. The FAA amends Sec. 39.13 by:

a. Removing Airworthiness Directive (AD) AD 2021-14-20, Amendment 39-
21647 (86 FR 38214, July 20, 2021), and

b. Adding the following new AD: