In this paper the influence of radiative heat transfer on convective flows in aircraft cabins is considered. The results show that in thermally driven flows radiation heat transfer have an essential impact on the flow and must be considered for accurate flow predictions. A parallel Discrete Transfer Radiation Method (DTRM) for the simulation of the surface to surface radiation heat transfer is coupled with the DLR THETA code. Besides the standard boundary condition for wall heat radiation, a special treatment for transparent boundaries is implemented. It offers the possibility to specify the radiation heat flux and the direction of incidence of the sun through the cabin window. The energy is then distributed in the cabin by the DTRM. The DLR THETA code is an unstructured incompressible Navier-Stokes-Solver developed by the German Aerospace Center (DLR). It supports convective heat transport, very large grids, highly complex geometries and massive parallel computations.