Airworthiness Directives; Various Boeing and McDonnell Douglas Transport Category Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to various Boeing and McDonnell Douglas transport category airplanes. This AD 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. This action is necessary to prevent incapacitation of the flightcrew due to lack of oxygen, which could result in loss of control of the airplane. This action is intended to address the identified unsafe condition.