This paper describes a noise reduction program for the Convair-Liner 340, a 44 passenger, 2 engine commercial passenger airplane. A systematic approach to the problem is outlined, involving: (1) the determination of the existing noise situation within the passenger cabin, including quantitative information on the identification of contributing sources; (2) the development of design criteria for aircraft passenger cabins, and (3) the specification of the amount of noise reduction required as a function of frequency and of position within the aircraft to achieve criterion levels. An exhaust muffler of special design, double windows, damping materials for the fuselage skin, and additional acoustical blankets as interior treatment, constituted the principal noise control measures specified. The distribution of these measures was based on the noise reduction required at the various positions within the cabin. Measured sound pressure levels are presented showing the effectiveness of the noise reduction measures. The results of this program are combined with results of earlier aircraft quieting studies [H. W. Rudmose and L. L. Beranek, J. Aeronaut. Sci. 14, 79–96 (February, 1947)] to produce modified design charts and procedures for the calculation of cabin noise levels.