DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2022-0588; Project Identifier AD-2022-00114-T;
Amendment 39-22249; AD 2022-24-09]
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2021-14-
20, which applied to all The Boeing Company Model 737 airplanes. AD
2021-14-20 required repetitive functional tests of the cabin altitude
pressure switches, and on-condition actions, including replacement, if
necessary. AD 2021-14-20 also required reporting test results. This AD
was prompted by data collected from the reports required by AD 2021-14-
20, which 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 AD retains the repetitive
functional tests and on-condition actions, and specifies certain
adapter requirements for the functional tests. The FAA is issuing this
AD to address the unsafe condition on these products.
DATES: This AD is effective January 26, 2023.
AD Docket: You may examine the AD docket at regulations.gov under
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 final rule, any comments received, and other
information. The address for Docket Operations is U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
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: 206-231-
3959; email: Nicole.S.Tsang@faa.gov.
The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 to supersede AD 2021-14-20, Amendment 39-21647 (86 FR
38214, July 20, 2021) (AD 2021-14-20). AD 2021-14-20 applied to all The
Boeing Company Model 737 airplanes. The NPRM published in the Federal
Register on July 7, 2022 (87 FR 40460). The NPRM was prompted by
reports of latent failures of the cabin altitude pressure switches, and
the determination that using certain adapters while performing a
functional test may lead to false failures of the cabin altitude
pressure switches. In the NPRM, the FAA proposed to retain the
repetitive functional tests and on-condition actions, and specify
certain adapter requirements for the functional tests. 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.
Discussion of Final Airworthiness Directive
The FAA received a comment from the Air Line Pilots Association
(ALPA), who supported the NPRM without change.
The FAA received additional comments from four commenters,
including United Airlines, Delta Air Lines, American Airlines, and
Boeing. The following presents the comments received on the NPRM and
the FAA's response to each comment.
Request To Revise Note 1 to Paragraph (g)
Delta Air Lines (DAL) asked that the FAA revise note 1 to paragraph
(g) of the proposed AD to call out equivalent applicable Boeing 737
Aircraft Maintenance Manual (AMM) procedures, in addition to calling
out the procedures in the 737 Task Card. DAL stated that the 737 Task
Cards called out in Note 1 to paragraph (g) of the proposed AD are not
easily accessible to the maintenance personnel performing the tasks on
the aircraft. DAL added that the AMM procedure is more commonly used
and easily accessed by the Aircraft Maintenance Technician, so the
addition of the reference to the AMM procedure avoids potential
confusion when the maintenance task is being performed.
The FAA agrees with the commenter's request for the reasons
provided. The FAA has revised Note 1 to paragraph (g) of this AD to
include the equivalent applicable Boeing 737 Aircraft Maintenance Manual
procedures referenced in Delta's comment.
Request To Correct Typographical Error
DAL noted that Boeing 737-600/700/800/900 Aircraft Maintenance
Manual (AMM) is identified in note 1 to paragraph (g) of the proposed
AD as ``Airplane Maintenance Manual'' instead of ``Aircraft Maintenance
The FAA has corrected the reference accordingly.
Request To Return to MRB Interval
United Airlines (UAL) asked that the interval established in the
Maintenance Review Board (MRB) be eventually re-established. UAL stated
that tooling was determined to be a significant contributor to
inconsistencies in the testing of the cabin altitude test switch. UAL
added that AD 2021-14-20 would be superseded by the proposed AD to
require improved AMM content defining appropriate tooling. In light of
these published AMM improvements, UAL recommended a return to the
interval established in the MRB.
The FAA does not agree with the commenter's request. Boeing
provided the fleet data collected from AD 2021-14-20 and the trend data
after operators incorporated the improved AMM content. The FAA
evaluated this data and determined through risk analysis that the
interval established in the MRB was unacceptable. Therefore, the FAA
has not changed this AD in this regard.
Request To Remove Hose Length Requirement
American Airlines (AA) stated that the FAA should remove the hose
length requirement of ``25 to 40 ft'' specified in figure 1 to
paragraph (g) of the proposed AD. AA stated that the hose length
requirement is an unnecessary restriction. AA added that a longer or
shorter hose should not significantly affect the application of a
controlled vacuum, and therefore should not affect the accuracy of the
cabin altitude pressure switch functional test.
The FAA does not agree with the commenter's request. There are
instructions to use a Barfield Pitot Hose, or equivalent 25- to 40-foot
hose, to standardize the equipment that operators use while performing
the cabin altitude warning switch functional test and to prevent false
test failures. There is potential concern that a hose longer than 40
feet could have a kink in the hose that may be unnoticed by the
operator, which could result in a false test failure. The FAA has not
changed this AD in this regard.
Request To Use Specific Adapters for Functional Test
Boeing asked that the proposed AD not specify particular adapters
for use during performance of the pressure switch functional test.
Boeing stated that the proposed AD should instead direct operators to
use only those adapters listed in the current Boeing AMM revision or
subsequent revisions. Boeing added that if new or improved adapters
become available and/or the AMM adapter list is modified, an
alternative method of compliance (AMOC) will have to be approved to add
them as approved adapters for the AD, which is not an efficient
The FAA does not agree to require operators to use only those
adapters listed in the existing Boeing AMM revision or subsequent
revisions. Figure 1 to paragraph (g) of this AD shows the same list of
adapters identified in the current Boeing AMM. Approval of an AMOC to
use new or improved adapters would not be necessary if the adapters
meet the specifications in either paragraph (g)(2)(i) or (ii) of this
AD. Therefore, the FAA has not changed this AD in this regard.
The FAA reviewed the relevant data, considered any comments
received, and determined that air safety requires adopting this AD as
proposed. Accordingly, the FAA is issuing this AD to address the unsafe
condition on these products. Except for minor editorial changes, and
any other changes described previously, this AD is adopted as proposed
in the NPRM. None of the changes will increase the economic burden on
Costs of Compliance
The FAA estimates that this AD affects 2,693 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this AD:
||Cost per product
||Cost on U.S. operators
||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
operators that might need to purchase an adapter.
The FAA estimates the following costs to do any necessary on-
condition actions 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:
||1 work-hour x $85 per 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
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
(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
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.
Sec. 39.13 [Amended]
2. The FAA amends Sec. 39.13 by:
a. Removing Airworthiness (AD) 2021-14-20, Amendment 39-21647 (86 FR
38214, July 20, 2021); and
b. Adding the following new AD: