How can a pilot determine if another aircraft is on a collision course?

Determining whether another aircraft is on a collision course involves understanding the dynamics of their movements in three-dimensional space and how those movements are perceived visually. When there is no apparent relative motion between two aircraft, it indicates that they are on a collision course. This means that, from the pilot's perspective, the other aircraft appears to maintain a constant position relative to them, suggesting that the two aircraft are moving towards the same point in space.

In practical terms, pilots can use visual cues and instruments to assess their own aircraft's trajectory in relation to that of others. If two aircraft are on a direct intercepting path, the distance between them does not seem to change, which is a critical warning sign of a potential mid-air conflict. The lack of apparent movement provides a clear indication to key in on, prompting the pilot to take evasive action if necessary.

The other choices describe scenarios that do not reliably indicate a collision course. For example, seeing the nose of each aircraft pointed at the same point in space could suggest they are converging, but it lacks the precision of measuring relative motion. Similarly, if the other aircraft appears larger and closer, this could simply be a factor of distance rather than a direct indicator of a collision. Likewise, while altitude