Most literature on system identification and aircraft flight dynamics is written specifically for full sized aircraft and many assumptions of the dynamics are made and used in aerodynamic identification. As the size of the aircraft is reduced to the size of a small fixed wing UAV some of these assumptions are no longer valid as a result of increased coupling between the dynamic modes of the vehicle and non-linearities in the dynamics increase. In this paper, a linearized time invariant model is determined for a fixed wing twin engined UAV using the standard Output Error Method. Although the identified system captures an approximation of the aircraft motion, it does not accurately capture the full flight dynamics of the aircraft which suggests that more advanced methods are needed to fully capture the dynamics of the system or different data preparation techniques are required.