what is acas used for
ACAS is being used to describe short-range systems intended to prevent actual metal-on-metal collisions. In contrast, ASAS is being used to describe longer-range systems used to maintain standard en route separation between aircraft (5 nm {9.25 km} horizontal /1000' {305 m} vertical). Obstacle Collision Avoidance System is a ground based system that uses a low powered radar mounted on or near the obstacle. 2  The radar detects aircraft in the proximity of the obstacle and firstly warns aircraft via flashing medium intensity lights and secondly warns aircraft of the obstacle via a VHF broadcast.
The Airborne Collision Avoidance System II (ACAS II) was introduced in order to reduce the risk of mid-air collisions or near mid-air collisions between aircraft.It serves as a last-resort safety net irrespective of any separation standards.he safety benefits delivered by ACAS are usually expressed in terms of the risk ratio (does ACAS make safety better or worse?). For Europe, ACAS is estimated to reduce the risk of mid-air collision by a factor of about 5 (i.e. a risk ratio of 22%).