Collision Avoidance for Rotorcraft in Urban Airspace with ACAS Xr

ACAS Xr is an aircraft collision avoidance system now in final development intended for rotorcraft, both traditional helicopters with a pilot on board as well as the emerging vehicles and operational concepts of Urban Air Mobility (UAM) and Advanced Air Mobility (AAM). Recognizing that operations in congested urban airspace are common for helicopters now and likely to increase as UAM/AAM concepts mature, ACAS Xr introduces collision avoidance alerting and guidance designed for this environment. These high-density operations are best exemplified now by operations such as the structured routes in and around New York City, and it is expected that similar patterns of operation will spread as UAM/AAM matures. Flight data from New York City were first analyzed to identify design objectives for ACAS Xr alerting, and the alerting and guidance logic inherited from previous versions of ACAS X was then refined via threat logic scaling and new online costs. The resulting logic was tested in simulation with both historically observed encounters and statistically representative generated encounters. The modified logic reduces the alert rate in observed encounters by more than 50%. The reduced alert rate does decrease the safety margin, but the logic’s safety performance exceeds the ICAO benchmark.