Airworthiness directives › 2021-14-20
AD 2021-14-20 Airworthiness Directives; The Boeing Company Airplanes
Models named: 737. Read the applicability below — it usually turns on serial or part numbers too.
Applicability*9
This AD applies to all The Boeing Company Model 737 airplanes, certificated in any category.
Compliance
Comply with this AD within the compliance times specified, unless already done.
Required actions
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.
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.
Affected ADs
None.
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The directive text above is reproduced from the Federal Register, a work of the United States government and in the public domain. The separation into applicability, compliance and required actions is TrackAD's.*1