What are ACAS II range limitations?
The required nominal tracking range of the ACAS II is 14 NM. However, when operating in high density, the interference limiting feature may reduce system range to 4.5 NM which is the range adequate to provide protection for a 500 kts encounter. Some ACAS implementation allow for the use of the Mode S extended squitter, the normal surveillance range may be increased beyond the nominal 14 NM. However, this information is not used for collision avoidance purposes. The equipment is not intended to interrogate a target unless the altitude information indicates that it is within 10,000 ft of own altitude. ACAS II will neither display nor give alerts against intruders with a vertical speed in excess of 10,000 ft/min.
