ADS-C Climb and Descend Procedure (CDP) – Collision Risk Model (CRM) Review and Comparison

The Federal Aviation Administration (FAA) reviewed the Automatic Dependence Surveillance - Contract (ADS-C) Climb and Descend Procedure (CDP) usage data at the Oakland Air Route Traffic Control Center (ARTCC) from April 2022 to September 2022. Analysis by the International Civil Aviation Authority (ICAO) Separation And Airspace Safety Panel (SASP) Working Group (documented in ICAO publication SASP-WG/37-IP/10) showed that only 1/3 of the attempted CDP clearances were issued successfully; and the most common reason for preventing the issuance of a CDP clearance was that the aircraft pair does not meet the criteria of the initial longitudinal separation minimum for the CDP faster trailing aircraft. The FAA has been investigating the application of CDP (PANS-ATM 5.4.2) to identify areas of improvement to increase usage of the procedure within the US-delegated oceanic airspace and investigate the possibility of increasing the CDP successful clearance rate by varying one or more constraints. This paper first reviews the detailed CDP clearance probing procedure and the requirements it must follow; it then introduces the collision risk model (CRM) related with CDP; compares two previous models and their assumptions. Finally, it recommends some improvements for further development of the CRM and shows some results of CDP risk probability with modified input parameters. Results show the potential to reduce the CDP longitudinal separation minima, to increase the speed difference for the fast-trailing CDP, and increase the time allowed for the CDP aircraft to complete the climb/descent maneuver through the blocking aircraft's altitude from the first ADS-C demand report request. Recommendations for future work include exploring a more accurate distribution of initial longitudinal separation and time when the aircraft reaches the flight level of blocking aircraft.