Definition
In TCAS terminology, an aircraft that is within 6 nautical miles horizontally and 1,200 feet vertically of your aircraft, but does not yet meet the criteria to be classified as a traffic advisory or resolution advisory threat. It is shown on the TCAS display as a solid white or cyan diamond.
Plain English
A nearby aircraft that TCAS is tracking and showing on your display because it is close enough to be worth knowing about, but it is not currently a threat that needs action.
Context Anchor
Seen on traffic displays when using a Traffic Alert and Collision Avoidance System during instrument flight.
Derivation
Proximate comes from the Latin proximus, meaning 'nearest' or 'closest.' In TCAS, it refers to traffic that is close to you in distance and altitude, but not close enough to trigger an alert.
Why Pilots Care
Maintains awareness of surrounding traffic so pilots can visually acquire and avoid other aircraft before a conflict develops.
Intuition Check
Proximate does not mean any aircraft you happen to see nearby. In this context, it means aircraft within defined horizontal and vertical limits that has not reached alert status.
Example Sentence 1
The crew noted two proximate aircraft on the TCAS display, both about 4 miles away and 800 feet below their cruise altitude.
Example Sentence 2
The pilot scanned the proximate aircraft symbols before accepting a descent clearance.