In this work, the radar cross section at 10 GHz of a metallic and a radar absorbent-coated S-shaped airway duct has been computed using three different methods: the method of moments, Multi Level Fast Multipole Method and geometrical optics in combination with physical optics. The results show that the method of moment is the most suited method for computing the radar signature of the metallic airway duct if enough internal computer memory is available. For the radar absorbent-coated airway duct, all three methods work well and therefore the most computationally efficient method, geometrical optics in combination with physical optics can be used.