The complex behaviour of a fuselage-cavity system in a modern propeller aircraft has been analysed with the finite element method. In the analysis the interaction between the fluid and the structure has been taken into account in a physical coupling formulation. The results obtained show that, at some frequencies, this coupling is very important for the vibro-acoustic system response.The eigenfrequencies and eigenmodes of the fuselage-cavity found in the analysis are compared with experimental modal analysis on a mock-up of the aircraft. The agreement is very good from 10-130 Hz. Especially the modes with strong coupling are well pronounced in the experiments.