Airworthiness Directives; The Boeing Company Airplanes

We are superseding Airworthiness Directive (AD) 2012-19-11 for certain The Boeing Company Model 737 airplanes. AD 2012-19-11 required incorporating design changes to improve the reliability of the cabin altitude warning system by installing a redundant cabin altitude pressure switch, replacing the aural warning module (AWM) with a new or reworked AWM, and changing certain wire bundles or connecting certain previously capped and stowed wires as necessary. For certain airplanes, AD 2012-19-11 also required prior or concurrent incorporation of related design changes by modifying the instrument panels, installing light assemblies, modifying the wire bundles, and installing a new circuit breaker, as necessary. This AD was prompted by the report of a flightcrew not receiving an aural warning during a lack-of-cabin pressurization event. We are issuing this AD to prevent the loss of cabin altitude warning, which could delay flightcrew recognition of a lack of cabin pressurization, and could result in incapacitation of the flightcrew due to hypoxia (a lack of oxygen in the body), and consequent loss of control of the airplane.