The present study attempts a numerical investigation of the complex flowfield that occurs when an underexpanded jet collides against a solid surface. Numerous examples of this problem can be found in the aerospace industry (e.g., rocket test stands, multistage separation). A simplified geometry, already employed in previous experimental inquiries, was chosen as a test case: an underexpanded, axisymmetric, air jet impinging on a flat plate at varied angles. The three-dimensional Navier-Stokes equations were solved by means of a second-order-accurate Roe-type algorithm with a generalized grid formulation. The computational domain includes the convergent-divergent nozzle and the external field. The numerical results show various jet-shock and shock-shock interactions and compare very well with experimental data, including shadowgraph pictures and both location and values of the peak pressures on the inclined plate. This investigation focused on performing a thorough comparison between experiments and simulations, thereby establishing some level of confidence in the accuracy and reliability of the numerical tool developed, CHEM. CHEM can accommodate more complicated and realistic geometries and physical conditions than those encountered in this study: with further refinement and validation it can be used for rocket plume and plume/solid surface interaction simulations, both on the ground and in flight.