If a converging airplane appears to show no relative motion and is becoming larger, what does that indicate?

When a converging airplane appears to show no relative motion and is becoming larger, this indicates that the airplane is on a collision course with your airplane. The absence of relative motion suggests that both aircraft are on similar flight paths, and as the other airplane's size increases in your perspective, it means that you are not separated horizontally. This scenario typically means that both aircraft are heading towards the same point in space, which can lead to a potential conflict in their paths if no evasive actions are taken.

In contrast, if the other options were to occur, the visual cues would differ. For example, if the airplane were gaining altitude, you would likely observe a decrease in perceived size or a change in relative position. Similarly, if the airplane were flying parallel to your path, there would be some lateral motion observed relative to your aircraft. Lastly, if the other airplane was maneuvering for a turn, you would likely notice some discernible motion or change in its trajectory as it navigates its course. Thus, the visual characteristics of a converging airplane that shows no relative motion while getting larger unmistakably point to a collision course.