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Lusch’s Midair Collisions Investigations

It was in 1985, after a commuter aircraft narrowly missed having a midair collision with an aircraft that assuredly had to be detected by one of our radar sites, yet was NOT displayed on my “radar scope,” that I began to question why that could be. That is when I learned about “radar sort boxes” and the software process termed “selective rejection.” I learned from firsthand observation that a an overwhelming amount of radar data is NOT utilized in the presentation of aircraft targets for the enroute air traffic controller. That lead to my writing an Unsatisfactory Condition Report in 1988, which I entitled Selective Rejection of Low Altitude Radar Data at Air Route Traffic Control Centers: An Unsatisfactory Compromise (click SelRej.pdf). The 1989 response to my UCR was “...the methods used to filter and display radar data are sound, including the selective rejection process” (click UCRreply.pdf). I disagreed with that conclusion. I went on to author another paper, entitled, Real Targets – Unreal Displays: The inadvertent Suppression of Critical Radar Data (click RTUD.pdf). It was later republished in the Journal of Air Traffic Control (click RTUD_JofATC_JanMar92.pdf). “Selective rejection” exists to this day (see “Deja vu”). I have given new life to a slide show I created back in February 2000. That was based upon the slide show I created for my RTUD presentation at the Sixth International Symposium on Aviation Psychology (click Lusch_RTUD_twice_revived_slide_show.pdf).

The disappearance of American Airlines Flight 77 from the Indy Center radar displays on 9/11 exemplifies the unsatisfactory compromise that I have been addressing. Learn more here.

Why can’t we process all radar data, from all radars, all the time, so as to be certain that we don’t lose an aircraft from our displays? The answer I got in 1992 centered around the fact that the current processing model is based on a uniprocessor, such that “only one function is executed at any one instance.” (click RTUDreply.pdf). Some may think of my concerns as outdated, as En Route Automation Modernization (ERAM) is very nearly online. However, when one looks closely, one finds that the term “radar sort box” has been replaced with the term “selective sort cell” (see the old-to-new terminology change of RSB to SSC on page 8 of this document). Thus, it appears that a considerable amount of radar data will still go unused. When it comes to processing radar data from multiple radars, Williard C. Meilander thinks it is time for a paradigm shift. Learn more here.

Thomas G. Lusch (about) (contact)

July 21, 2010

Note: There is more than one way in which an aircraft’s properly operating transponder, that is detected by secondary radar, can be invisible to an air traffic controller. For example, see what can occur when airspace assigned to one radar facility is not adequately covered by the radar site the facility utilizes (see this example). And there is yet another problem that is the result of an incompatibility between Mode S interrogators and older ATCRBS transponders. Learn of my personal experience here.

P.S. I also have a keen interest in the midair collision that occurred in 1984 near San Luis Obispo, CA.

Learn about my Barefoot For Nourishment initiative here.