This paper presents the development process of an airborne multi-sensor system for autonomous detection and tracking of flying obstacles. The hardware/software prototype integrating Detect, Sense, and Avoid capability, has been designed and realized by the Italian Aerospace Research Center and the Department of Aerospace Engineering of the University of Naples “Federico II”. First of all, system architecture is described. The sensing subsystem is comprised of a Ka-band airborne pulsed radar, a visible panchromatic high-resolution camera, a visible color high-resolution camera, two thermal infrared cameras, and a processing unit for sensor data fusion. Estimated performance of radar/electro-optical sensor fusion is reported. Then the ground ...