This paper addresses the problem of collision avoidance for fixed-wing unmanned aerial vehicles. The angular velocity of the aircraft is adjusted in order to avert a possible collision with cooperative or uncooperative obstacles. The novelty of this work is that the control law uses only the line-of-sight angle as feedback, which can be obtained from an inertial measurement unit and a gimbaled camera mounted onboard the vehicle. This work aims at providing a solution to the collision avoidance problem for small low-cost unmanned aerial platforms, which are not equipped with sensors capable of measuring data such as position and velocity of the obstacle. This problem of practical relevance is faced from a theoretical standpoint. A Lyapunov based analysis is outlined, which provides safety guarantees under a given set of assumptions that the obstacle must satisfy. Simulation results are presented to validate the theoretical findings.