This disclosure is directed to systems and methods for aircraft collision avoidance with speed-based collision alert time thresholds. In one example, a system is configured to determine predicted trajectories for an own aircraft and a target aircraft. The system is further configured to determine whether a violation of protected airspace is predicted between the own aircraft and the target aircraft. The system is further configured to determine whether a predicted time to closest approach between the own aircraft and the target aircraft is less than an alert threshold time based on a speed of the own aircraft. The system is further configured to generate an alert output, in response to determining that a violation of protected airspace is predicted and that the predicted time to closest approach between the own aircraft and the target aircraft is less than the alert threshold time based on the speed of the own aircraft.