Since I work on the same terminal radar type as the one located at O'Hare (ASR-9), I find it hard to believe that this is anything more than operator error.
The controllers at the Tracon are working with "clean" scopes when viewing ASR-9 video meaning
no grass level(noise). The ridiculous amount of processing within the ASR-9 filters out all non-moving returns period unless operators have chosen to deviate from the standard settings at their PPI. This processing time is significant enough to lag the digitized video being displayed to operators by roughly a full sweep of the antenna. Controllers don't see actual radar returns in real-time...its synthetic and delayed before it hits their displays.
The
next generation of terminal radars are now being installed which replaces older systems including the ASR-9 at O'Hare. With even better target processing in the latest versions of radar, O'Hare's
ghost targets should disappear.
[This message has been edited by monopulse (edited 26 May 2000).]