Definition 1 of 2
Definition
An onboard airborne collision avoidance system that monitors the airspace around an aircraft by interrogating the transponders of nearby aircraft. It evaluates their range, bearing, and altitude, and warns the flight crew of potential conflicts. When a collision threat is detected, the system issues a Traffic Advisory (TA) to alert the crew, and if the threat increases, a Resolution Advisory (RA) directing a vertical maneuver -- climb or descend -- to maintain safe separation.
Plain English
An onboard system that watches for nearby aircraft using their transponder signals and warns the pilots if another aircraft is getting too close, telling them whether to climb or descend to avoid it.
Context Anchor
You may encounter this term in aircraft equipment lists, cockpit alert procedures, instrument training, airline operations, and discussions of midair collision prevention.
Derivation
“Traffic” originally referred to movement or activity, and in aviation it means other aircraft operating nearby. “Collision” comes from a Latin idea meaning “to strike together.” The name describes the system’s purpose: alert the crew to nearby aircraft traffic and help avoid aircraft striking each other.
Why Pilots Care
Provides the last independent layer of protection against mid-air collisions when air traffic control separation has been lost.
Analogy
It is somewhat like a car’s blind-spot warning system, but for aircraft in the air. It does not replace the pilot; it gives timely warning when another aircraft may be too close.
Intuition Check
“Traffic” here does not mean road traffic or general airport busyness; it means other aircraft near your flight path. The system also does not fly the airplane by itself; it warns the crew and, in some versions, gives climb or descent guidance for the pilot to follow.
Example Sentence 1
The crew followed the Traffic Alert and Collision Avoidance System's resolution advisory and climbed to avoid the converging traffic.
Example Sentence 2
A resolution advisory from the Traffic Alert And Collision Avoidance System directed an immediate climb to avoid the conflicting traffic.