  This paper presents a novel collision avoidance strategy for unmanned
aircraft detect and avoid that requires only information about the relative
bearing angle between an aircraft and hazard. It is shown that this
bearing-only strategy can be conceived as the solution to a novel differential
game formulation of collision avoidance, and has several intuitive properties
including maximising the instantaneous range acceleration in situations where
the hazard is stationary or has a finite turn rate. The performance of the
bearing-only strategy is illustrated in simulations based on test cases drawn
from draft minimum operating performance standards for unmanned aircraft detect
and avoid systems.
