Summary
We are revising an earlier proposed airworthiness directive (AD) for certain The Boeing Company Model 737-600, -700, -700C, -800, - 900, and -900ER series airplanes. That NPRM proposed to require, for certain airplanes, installing two warning level indicator lights on each of the P1-3 and P3-1 instrument panels in the flight compartment. That NPRM also proposed to require revising the airplane flight manual to remove certain requirements of previous AD actions, and to advise the flightcrew of the following changes: revised non-normal procedures to use when a cabin altitude warning or rapid depressurization occurs, and revised cabin pressurization procedures for normal operations. That NPRM was prompted by a design change in the cabin altitude warning system that would address the identified unsafe condition. This action revises that NPRM by adding airplanes to the applicability; adding airplanes to the installation requirement, including, for certain airplanes, replacing the existing P5-16 and P5-10 panels; and, for certain airplanes, replacing the basic P5-16 panel with a high altitude landing P5-16 panel. We are proposing this supplemental NPRM 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 the body), and consequent loss of control of the airplane. Since these actions impose an additional burden over that proposed in the NPRM, we are reopening the comment period to allow the public the chance to comment on these proposed changes.