On-site inspections (OSI) will be an important process to deter and help verify compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). An important tool in narrowing the possible locations to collect evidence of a nuclear test during an on-site inspection may be over-flights of the general area using aerial gamma spectroscopy which can measure the energy and intensity of gamma radiation and help identify areas that may warrant further investigation of areas of high concentrations of radioactivity. This paper will investigate the capabilities of gamma ray detectors that are typically used in aerial searches. Modeling and simulation results of the detector response for radionuclide species for an OSI will be presented for a variety of assumed releases, depositions on the ground, and times after a suspected Treaty violation for typical over flight heights and speeds. This data will provide information on the possible applicability for airborne spectroscopy and the challenges and limitations of this tool for OSI. Of particular interest will be analysis of the data for gross count, regions of interest, and isotope identification types of algorithms and the characteristics of each.