EASA AD US-2021-14-20: Superseded by FAA AD 2022-24-09

What to do

Operators of all Boeing 737 models must perform repetitive functional tests of the cabin altitude pressure switches starting from July 20, 2021. Any failed switches must be replaced with serviceable units and test results reported to Boeing as specified. Operators should follow the approved maintenance procedures and comply with all reporting requirements by September 3, 2021.

Summary

FAA Airworthiness Directive 2021-14-20 is a final rule affecting all Boeing Model 737 airplanes. It addresses latent failures of the cabin altitude pressure switches, which are critical for warning flightcrew of cabin depressurization. The directive mandates repetitive functional tests and replacement of faulty switches to ensure continued safety.

What changed

This new airworthiness directive introduces mandatory repetitive functional testing of the cabin altitude pressure switches on Boeing 737 aircraft. It requires on-condition actions including replacement of failed switches and reporting test results to Boeing. The directive also clarifies acceptable maintenance procedures and expands applicability to include older 737 models such as the -100, -200, and -200C series.

Why it matters

This directive is important because latent failures of cabin altitude pressure switches can prevent timely warnings of cabin depressurization, risking flightcrew incapacitation due to hypoxia. Operators and maintenance teams must ensure compliance to prevent potential loss of airplane control. The directive's reporting requirements will help Boeing and the FAA better understand the failure causes and develop future corrective actions.

What to do

Summary

What changed

Why it matters

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