Definition
A proposed third-generation airborne collision avoidance system intended to issue both vertical and horizontal resolution advisories to pilots when another transponder-equipped aircraft poses a collision threat. TCAS III was envisioned as an enhancement over TCAS II, which provides only vertical resolution advisories (climb or descend). Development was not completed and TCAS III was never certified or fielded operationally.
Plain English
A planned upgrade to the standard onboard system that warns pilots about nearby aircraft and tells them how to avoid a collision. Unlike the current system, which only tells pilots to climb or descend, TCAS III was supposed to also tell them to turn left or right. It was never finished or put into service.
Context Anchor
Seen in discussions of airborne traffic-warning equipment and collision-avoidance system levels.
Derivation
TCAS stands for Traffic Alert and Collision Avoidance System. The Roman numeral III marks it as the third planned generation, following TCAS I (traffic advisories only) and TCAS II (traffic advisories plus vertical resolution advisories).
Why Pilots Care
Provides pilots with clear guidance to avoid other aircraft when visual separation is lost.
Intuition Check
Do not read “III” as simply meaning “newer TCAS II.” In this term, it points to the intended added ability to give turn guidance, not just altitude-change guidance.
Example Sentence 1
The textbook explained that TCAS III was intended to add horizontal escape maneuvers, but the program was discontinued before certification.
Example Sentence 2
During the approach briefing the instructor explained how TCAS III improves on earlier versions by adding lateral avoidance options.