Air Traffic Control Separation Minima: Part 2 – Transition to a Trajectory-based System

Abstract

Current strategic plans for Air Traffic Management (ATM) envisage a transition from radar control to a trajectory-based system. Part 1 sketched the historical origins of separation minima and then analysed the safety thinking behind current minima and the issues involved in risk modelling. Part 2 examines the future situation. This focuses on the intermediate steps to the final system – upgraded capabilities in a mixed-equipage system. Future traffic mixes two categories of traffic: V aircraft, i.e. vectored traditional ATC-handled, and 4D aircraft, i.e. flying on 4D trajectories. Conflict probe and other decision support tools will need to be in place, inter alia to prevent controller workload from increasing. Conceptually, future risks in the transition period will be the sum of three types of aircraft encounter risk: V/V, 4D/4D and 4D/V. These pose different kinds of problem for ATC, appropriate conflict alerting systems and risk assessment. The numbers of 4D/V encounters increase rapidly with growth in the proportion of 4D aircraft. With reduced minima, airborne collision avoidance systems would be unlikely to resolve higher relative velocity encounters were the ATC system to fail. It would be a difficult decision to reduce markedly ATC separation minima for any category of aircraft encounters during the transition period.

Relative Position Vectors

“…Third, the MCD is not optimized for present separation rules but instead is the start of a new way of representing the risk of collision (Brooker, 2011a(Brooker, , 2011bParasuraman, Masalonis, & Hancock, 2000). For the kind of dynamic risk-based conflict management discussed in the GATMOC (ICAO, 2005), appropriate separation depends on many situational factors.…”

A 4D ATM Trajectory Concept Integrating GNSS and FMS?

“…The value of S might well be not much less than present minima, because it would be equivalent to the time for pilots to receive and react acceptably to “last ditch collision avoidance”, e.g., TCAS RAs (e.g. see Brooker, 2011).…”

4D-Trajectory Air Traffic Management: ‘Are There ‘Killer Apps?’ – Part 1

“…First, ironically, most past ATM Killer Apps have in fact been safety improvements (Mozdzanowska and Hansman, 2008). TBO would certainly try to reduce risks further, but it is not obvious that there would be a guaranteed step improvement in safety (Brooker, 2011)). This actually demonstrates that safety is very much an 'ATM success story'; the large cumulative investments and process changes over past decades have been very worthwhile.…”