Abstract: More than 14 dB(A) in the highest cabin noise levels of the propeller-driven Y12 aircraft were reduced from the untreated condition. Thus, its interior higher noise environment is improved preliminarily and successfully. This paper deals with the noise control measures applied to the Y12 aircraft. It mainly includes the application of honeycomb sandwich stiffened panels, dynamic absorbers, damping treatments, window acoustic design and replacement of the windows and doors closure devices.The results of cabin noise levels in flight measurements are given for both acoustic pre- and aft-treated No. 4 Y12 aircraft. The analysis of the flight results shows that the noise control measures are effective. The added weight of the noise control package is about 0.8 percent of the total gross takeoff weight of the aircraft.

Key words: propeller-driven aircraft, cabin noise reduction, noise transmission loss, noise absorption, vibration reduction