The design and characterization of flat panel a-Si:H arrays for imaging applications in radiotherapy and diagnostic radiology has already begun. Future improvements in design and performance will be heavily reliant on the results of computer simulations capable of accurately predicting the behavior of the arrays in a variety of operating conditions. These results will allow the design of new arrays to be optimized for the particular application before they are committed to fabrication. This paper outlines the results of an investigation into the effects of varying a number of array parameters and operating conditions using a simulation code which models the operation of a-Si:H devices. The results are compared with actual measurements from arrays fabricated at Xerox PARC.