Airworthiness Directives; Boeing Model 737 Airplanes

The FAA is adopting a new airworthiness directive (AD) for all Boeing Model 737 airplanes. This AD requires revising the airplane flight manual to advise the flightcrew of improved procedures for pre- flight setup of the cabin pressurization system, as well as improved procedures for interpreting and responding to the cabin altitude/ configuration warning horn. This AD results from reports that airplanes have failed to pressurize, and that the flightcrews failed to react properly to the cabin altitude warning horn. We are issuing this AD to prevent failure of the airplane to pressurize and subsequent failure of the flightcrew to recognize and react to a valid cabin altitude warning horn, which could result in incapacitation of the flightcrew due to hypoxia (lack of oxygen in body) and consequent loss of airplane control.