PURPOSE - This specification defines the minimum requirements for the design@ construction@ and performance of continuous flow oxygen masks for passengers in civil aircraft. DESCRIPTION - The mask shall be an oronasal type utilizing a continuous supply of oxygen and comprising a facepiece with valves as required@ a mask suspension device@ a reservoir bag (when used) and a length of tubing for connection to the oxygen supply source. The assembly shall be capable of being stowed suitably to meet the requirements of its intended use. PRESENTATION - When presented@ its immediate application shall be as obvious as possible. The mask shall be capable of quick and easy application. It shall be usable without special orientation. CODING OF PERFORMANCE CLASSIFICATION - A performance classification number shall be assigned to each class of masks. This number shall correspond to the number assigned to the minimum performance curve on the NAS Standard Drawing and shall appear in the part call-out as the first dash number following the NAS Standard Part number. Where the performance of a mask differs appreciably from any of the minimum performance curves existing on the NAS Standard Drawing@ the proven performance curve for this mask may be added to the appropriate NAS Standard Drawing. This mask would then be assigned a performance classification number corresponding to this new performance curve on the NAS Standard Drawing. INTERCHANGEABILITY OF MASK ASSEMBLIES - Same Coding - Masks with the same coding shall be interchangeable. Different Performance Classification Number (remainder of coding the same) - All masks with performance classification numbers which require oxygen flow rates less than the flow rates supplied to the mask from the airplane system at all certificated cabin altitudes are interchangeable on that airplane.