ACR X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM ACFT Y. SYS ERROR.

Narrative

ACR X WAS GIVEN A DSCNT CLRNC TO 8000 FT TO GET BELOW TFC Y AT 9000 FT. TRAINING WAS IN PROGRESS. WHEN IT WAS OBSERVED THAT ACR X WOULD NOT GET BELOW THE TFC; IT WAS BROUGHT TO THE ATTN OF THE TRAINEE. THE TRAINEE; NOT KNOWING WHAT TO DO; SWITCHED THE ACFT TO THE NEXT SECTOR (ME). THE TRAINER CALLED ON THE LANDLINE TO GIVE ME INSTRUCTIONS TO STOP ACR X AT 10000 FT. I OBSERVED ACR X ALREADY DSNDING THROUGH 9800 FT. IF I GAVE A CLRNC BACK TO 10000 FT THE ACFT WOULD PROBABLY GO DOWN TO AT LEAST 9400 FT BEFORE IT STARTED TO CLB AGAIN. I ISSUED ABOUT A 30-40 DEG TURN TO AVOID THE TFC. SUPPLEMENTAL INFORMATION FROM ACN 249543: DURING TRAINING OF A DEVELOPMENTAL CTLR LNDG IN ADJACENT APCH AIRSPACE WAS GIVEN A DSCNT CLRNC. IN AN EFFORT TO ALLOW THE DEVELOPMENTAL TO REALIZE POTENTIAL CONFLICT WITH ANOTHER ACFT; THE CLRNC WAS ALLOWED. HDOF WAS EFFECTED VIA ARTS. BELIEVING THE DEVELOPMENTAL NOW REALIZED THE POTENTIAL CONFLICT AND WAS ABOUT TO ISSUE A TURN OR ALT REVISION; I TOOK NO IMMEDIATE ACTION. THE DEVELOPMENTAL; HOWEVER; INITIATED A FREQ CHANGE. I INTERVENED PRIOR TO COMPLETION OF XMISSION; INSTRUCTING ACFT TO REMAIN THIS FREQ AND TO MAINTAIN A REVISED ALT. ACFT HAD ALREADY CHANGED FREQ TO ADJACENT APCH. IMMEDIATE ACTION WAS TAKEN TO SEPARATE ACFT. HAD THE PLT NOT CHANGED FREQ THE ERROR WOULD NOT HAVE OCCURRED INASMUCH AS I WOULD HAVE HAD AMPLE TIME TO AVOID THE IMMINENT CONFLICT.