Summary
We propose to adopt a new airworthiness directive (AD) for certain Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. This proposed AD would require installing two warning level indicator lights on the P2-2 center instrument panel in the flight compartment for certain airplanes. For a certain other airplane, this proposed AD would require activating the cabin altitude warning and takeoff configuration warning lights. For all airplanes, this proposed AD also would require revising the airplane flight manual to remove certain requirements included by previous AD actions, to require new pressure altitude limitations for certain airplanes, and to advise the flightcrew of the following changes: revised emergency procedures to use when a cabin altitude warning or rapid depressurization occurs, and revised cabin pressurization procedures for normal operations. This proposed AD results from a design change in the cabin altitude warning system that would address the identified unsafe condition. We are proposing this AD to prevent 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 control of the airplane.