Currently doing an assignment and it to analyse an accident where older atc systems could have been at fault. In 1995 there was an incident where two aircraft came closer than the then current separation standard due to an air traffic controllers miscalculation. With new tech such as ADS-B, are there ways the controller can be alerted of possible loss of separations with the aircraft they are handling?

  • $\begingroup$ It would help to know what research you have already done. Most ATC systems have a number of safety nets, none of which are based purely on ADS-B (since radar is much more accurate). $\endgroup$ Sep 13, 2019 at 6:19
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    $\begingroup$ @J.Hougaard Radar is rarely more accurate than ADS-B. The accuracy of ADS-B is in the order of 10 meters, the position noise is far less than with radar. The problem is that there are quite a few rogue ADS-B installations flying around. Until they are sorted out, the integrity of ADS-B position data is not sufficient to support most safety cases. $\endgroup$
    – DeltaLima
    Sep 13, 2019 at 10:37

2 Answers 2


Most air traffic control systems nowaday have various safety net functions built into them. Short Term Conflict Alerting is one of these functions.

Short Term Conflict Alerting (STCA) works on the basis of extrapolating the current position using velocity and turn rate to predict imminent separation violations. If such a imminent separation violation is detected, the system will alert the air traffic controller.

The next level of conflict alering is Medium Term Conflict Detection (MTCD); this is not considered a safety net, but a tool that assists the Controller in detecting conflicts early on (up to 20 minutes in advance). Instead of relying on simple position extrapolation, MTCD uses more advance trajectory predictions that combine knowledge of the current aircraft position and velocity with information from aircraft performance models, flight plan, weather and given ATC instructions. MTCD development started 20 years ago, and the tool is now being implemented in various ATC systems.

  • $\begingroup$ Very interesting @DeltaLima and thanks for your response. I am sure this does help alleviate the controllers workload and keep them on their toes. here is the link for the accident report if anyone is interested. atsb.gov.au/publications/investigation_reports/1995/aair/… $\endgroup$
    – Pitttypit
    Sep 14, 2019 at 13:31
  • $\begingroup$ DeltaLima, you probably worked some of the same projects that I did! (I was ZDV's DY) $\endgroup$
    – atc_ceedee
    Jul 8, 2021 at 13:58

In the US, ARTCCs have had conflict detection built into the radar data processing system since the vacuum tube era. It's a bit primitive, being based on current track and speed data (doesn't work well if the aircraft is turning), and it does not make use of route or course information.

We also have a system (URET) that uses actual route information, upper wind data, and aircraft performance characteristics (according to aircraft type) to alert controllers of possible conflictions. The system does not use real-time radar data, however, which can throw off its accuracy. It sits next to the radar position, so it's not "on the scope". It's still a great tool, although, I must admit, I prefer flight progress strips (I'm old).

The best technology I've seen is the User Preferred Routing (UPR) tool (also known as Direct-to), which was developed at the NASA Ames Research Laboratory, initially tested at Denver ARTCC, and later deployed on a test basis at Fort Worth ARTCC.

This tool uses real-time tracking data, upper wind data, aircraft characteristics, holding pattern tracking, and offers on-the-scope functionality for plotting reroutes.

Its deployment status, however is in limbo, and it was removed from field use several years ago.


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