Airworthiness Directives; Various Boeing and McDonnell Douglas Transport Category Airplanes

This amendment revises an existing airworthiness directive (AD), applicable to various Boeing and McDonnell Douglas transport category airplanes, that currently requires revising the Airplane Flight Manual (AFM) to advise the flightcrew to don oxygen masks as a first and immediate step when the cabin altitude warning horn sounds. The actions specified by that AD are intended to prevent incapacitation of the flightcrew due to lack of oxygen, which could result in loss of control of the airplane. This amendment removes certain requirements for certain airplanes and revises the direction to the flightcrew to don oxygen masks as a first and immediate step when the cabin altitude warning occurs, rather than "when the cabin altitude warning horn sounds." This action is intended to address the identified unsafe condition.