
Dec. 2, 2024
The FAA recently published a revised advisory circular (AC) on airborne collision avoidance systems (ACAS), which provides an acceptable means to address operational use of collision avoidance systems (CAS), including ACAS and traffic alert and collision avoidance systems (TCAS).
Title 14 of the Code of Federal Regulations refers to “CAS” or “TCAS,” while Title 49 of the CFRs and the international community refer to “ACAS.”
Review FAA AC 90-120: Operational Use of Airborne Collision Avoidance Systems
The AC was previously in the 120-series of ACs, applying to air carriers, but now applies more broadly across a wider range of aircraft and operational rules. The revised AC applies to Part 121 and 135 air carriers and entities providing training to those air carriers, Part 91 subpart K fractional ownership operations, operations of large airplanes under Part 125, foreign air carriers operating under Part 129, and Part 142 training centers, as well as large aircraft subject to Part 91 subpart G.
This new AC also clarifies language between the previous AC and related regulations, particularly guidance involving parallel runway operations.
“In summary, this revised AC updates pilot and operator guidance on airborne collision avoidance and broadens the applicability,” said Richard Boll, chair, NBAA Domestic Operations Committee, Airspace and Flight Technologies Subcommittee. “It provides new guidance regarding closely spaced parallel runway operations and safety considerations when switching to TA-only mode.”
It also introduces new ACAS X software, Boll added.
“ACAS X is the next generation of software replacing TCAS. ACAS X is more sophisticated than the TCAS systems we use now,” he said. “The technology and algorithms currently used date back to the 1970s. This new system can evaluate threats and, through a Monte Carlo simulation, process hundreds of scenarios and determine the ‘least cost’ or lowest risk, most efficient option for collision avoidance.”
ACAS X is not mandatory at this time, but products will be coming online over the next few years.
Finally, the AC provides sample ACAS ground and flight training programs and an ACAS resolution advisory reporting form.
NBAA said operators should incorporate applicable AC guidance into their training programs.