Airworthiness Directive · Amendment 39-21647 · Air conditioning
The Boeing Company Airplanes
Superseded. A later AD replaced this one: AD 2022-24-09. Comply with the one in force.
This AD applies to all The Boeing Company Model 737 airplanes, certificated in any category.
The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 737 airplanes. This AD was prompted by reports of latent failures of the cabin altitude pressure switches. This AD requires repetitive functional tests of the pressure switches, and on- condition actions, including replacement, if necessary. The FAA is issuing this AD to address the unsafe condition on these products.
Except as specified in paragraph (j) of this AD: At the latest of the times specified in paragraphs (g)(1) 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 MOM-MOM-21-0292-01B, 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.
(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 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 737MAX AMM TASK CARD 31-020-00-01, and other approved maintenance procedures.
If any switch fails the initial functional test required by paragraph (g) of this AD: At the applicable time specified in paragraph (h)(1) or (2) of this AD, report the results of that functional test, in accordance with Boeing Multi Operator Message MOM-MOM-21-0292-01B, 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.
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 operator's fleet that have been tested since the effective date of this AD, in accordance with Boeing Multi Operator Message MOM-MOM-21-0292-01B, 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.
(1) Where Boeing Multi Operator Message MOM-MOM-21-0292-01B, 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 MOM-MOM-21-0292-01B, 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 MOM-MOM-21-0292-01B, 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.
