Which factor increases the likelihood of a mid-air collision when flying visually?

When flying visually, the factor that significantly increases the likelihood of a mid-air collision is when another aircraft is on a constant relative bearing to you. This situation indicates that the other aircraft is maintaining its position relative to your flight path, which can create a deceptive sense of the aircraft's distance and speed. Consequently, if pilots are not able to recognize the implications of a constant bearing, they may misjudge the other aircraft's trajectory, leading to misunderstandings about potential collision paths.

Having an aircraft maintain a constant relative bearing can lead to situations where pilots fail to take appropriate evasive action, believing they are safe when they may not be. This phenomenon is often referred to as the "highway in the sky" effect, where two aircraft may be moving parallel to each other, which can disguise the risk of a collision if not monitored carefully.

In contrast, bright strobe lights on another aircraft can enhance visibility and awareness, peripheral vision movement can attract attention, and utilizing effective visual scanning techniques generally helps prevent collisions. These factors do not inherently contribute to an increased risk but rather can aid in situational awareness and collision avoidance.