ACR X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR. CTLR TRAINING IN PROGRESS.

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I ALLOWED MY RADAR DEVELOPMENTAL TO WORK THE SECTOR; EVEN THOUGH IT HAD BECOME TOO BUSY AND COMPLEX FOR HER ABILITIES. I SHOULD HAVE BEEN MORE ACTIVE AS THE INSTRUCTOR. ACR X AND ACR Y; BOTH NON RADAR; FL190 AND FL180 RESPECTIVELY; SAME RTE. DEVELOPMENTAL ALLOWED ACR Y DATA BLOCK TO REMAIN STATIONARY; COAST TRACK. SHE RADAR IDENTED ACR X AND DSNDED THE ACFT THROUGH ACR Y. THE PLT OF ACR Y RPTED THE INCIDENT ON FREQ; AND MAY OR MAY NOT RPT THIS AS A NEAR MIDAIR. ACR Y WAS ON AN INCORRECT BEACON CODE; BUT SINCE THE ACFT WAS NON RADAR; WE HAD NO WAY OF KNOWING THIS. THE DATA BLOCK DID NOT FOLLOW THE FLT PLAN; THUS THE DATA BLOCK WAS NOT IN THE SAME POS AS THE ACFT. WHEN ACR X CAME INTO RADAR COVERAGE; THE DEVELOPMENTAL DID NOT SEE A TARGET OR DATA BLOCK ON ACR Y IN THAT AREA; SO SHE DSNDED ACR X. POOR RADAR COVERAGE; WRONG BEACON CODE; AND DEVELOPMENTAL'S INABILITY TO KEEP UP; ALL WERE CONTRIBUTORY FACTORS. I WATCHED THE DEVELOPMENTAL PUT HERSELF INTO A VERY DIFFICULT SIT; WHEN I SHOULD NOT HAVE LET THAT HAPPEN. MY DESIRE FOR HER TO LEARN FROM HER OWN MISTAKES RESULTED IN THE SECTOR BECOMING UNSAFE.