From the standpoint of marketing as well as safety, control of aircraft interior noise is of considerable interest to the manufacturers of business aircraft. The interior acoustics engineer in the industry, having no fund of accumulated experience or research to draw from in the industry itself, has to piece together a working design procedure from a knowledge of boundary-layer theory, jet noise, random vibrations, and architectural acoustics to meet an acceptable cabin noise criterion for the small aircraft. In this paper, methods are outlined to calculate the cabin noise levels due to the three main noise sources-the boundary-layer pressure fluctuations, jet exhaust, and internal equipment. Formulas for quick estimation of overall noise levels due to these sources as well as methods to obtain octave band levels are given. The paper also discusses manufacture or service-related noises and methods for identifying their sources.