Aviation Tech
TCAS & ACARS: How Airborne Collision Avoidance & Data Link Messaging Work
A detailed breakdown of TCAS II Resolution Advisories (RA), ACARS VHF/Satellite datalink text messaging, and automated flight ops telemetry.
9 min read Published
1. Traffic Collision Avoidance System (TCAS II)
TCAS II operates independently of ground air traffic control. By interrogating Mode S transponders of nearby aircraft, TCAS creates a 3D protective airspace bubble around the plane.
- Traffic Advisory (TA): Issued ~45 seconds before potential conflict ("TRAFFIC, TRAFFIC").
- Resolution Advisory (RA): Issued ~30 seconds before conflict, giving mandatory vertical guidance to pilots ("CLIMB, CLIMB" or "DESCEND, DESCEND").
2. ACARS Datalink Messaging
ACARS (Aircraft Communications Addressing and Reporting System) is an automated digital datalink system over VHF radio and Inmarsat/Iridium satellites. ACARS transmits OOOI events (Out of gate, Off ground, On ground, In gate), engine health diagnostics, and pilot text messages directly to airline operations centers.
See the codes and radio callsigns of major carriers like Emirates, Delta Air Lines and Lufthansa.