Airworthiness Directive · Amendment 39-22249 · Air conditioning
The Boeing Company Airplanes
This AD applies to all The Boeing Company Model 737-100, -200, -200C, -300, -400, -500, -600, -700, -700C, -800, -900, and -900ER series airplanes, and Model 737-8, 737-9, and 737-8200 airplanes, certificated in any category.
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.
(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 inch (0.673 cm) X 7/16-20-UNJF-3A and less than or equal to 0.438 inch (1.113 cm) X 7/16-20-UNJF-3A for the flareless end; or
(ii) Less than or equal to 0.5 inch (1.27 cm) total with greater than or equal to 0.265 inch (0.673 cm) X 7/16-20-UNJF-3A thread for AN4 flared end.
Note 1 to paragraph (g): Additional guidance for performing the functional test required by paragraph (g) of this AD can be found in Boeing 737-200 Aircraft Maintenance Manual (AMM) 21-33-11/501, Boeing 737-300/400/500/600/700/800/900/7/8/8200/9 AMM 21-33-00/501, 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 cabin altitude warning switch fails any functional test as required 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 inoperative are included in the operator's existing FAA-approved MEL.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
