This study focuses on development of mathematical model of Infrared Signature from the first principles using MATLAB environment. The model is used for IR Signature studies and further adopted for aircraft susceptibility analysis with its computed Infrared Signature level (IRSL). The model is validated with the existing literature data of the IRSL from the engine parts of an Aircraft and thus finding the lock-on range from an Air to air missile. This paper reviews the steps to find the lock-on range, with particular focus on IR signature prediction for aerial platforms. In this investigation, the lock-on envelope is estimated in 1.9-2.9μm, 3-5μm and 8-12μm bands, considering various sources of IR signature from aircraft engine surfaces for aerial platforms. The developed model is important for further susceptibity studies of aerial platforms for survivability improvements related studies for any new design configurations and are an important factor of stealth technology.