What does a solid diamond symbol on TCAS indicate?

• A. Proximate Traffic
• B. Unknown Traffic
• C. Non-threatening Traffic
• D. Advisory Traffic

Answer: (A)

In TCAS displays, the symbol style around another aircraft communicates how close and potentially threatening it is. A solid diamond around the intruder indicates proximate traffic—aircraft that TCAS has determined is close enough to pose a potential conflict if you stay on your current path. This status signals a need for heightened awareness and prepares you for possible resolution advisories if the situation worsens.

This isn’t unknown traffic, which means the system can’t reliably determine the intruder’s threat level; it isn’t non-threatening traffic, which would imply no immediate concern; and it isn’t advisory traffic, which relates to Traffic Advisories that alert you to nearby traffic without implying an active threat. The solid diamond specifically conveys that the traffic is in the proximate category, requiring attention.