Narrative:

Air carrier X was given a descent clearance to 8000 ft to get below traffic Y at 9000 ft. Training was in progress. When it was observed that air carrier X would not get below the traffic, it was brought to the attention of the trainee. The trainee, not knowing what to do, switched the aircraft to the next sector (me). The trainer called on the landline to give me instructions to stop air carrier X at 10000 ft. I observed air carrier X already descending through 9800 ft. If I gave a clearance back to 10000 ft the aircraft would probably go down to at least 9400 ft before it started to climb again. I issued about a 30-40 degree turn to avoid the traffic. Supplemental information from acn 249543: during training of a developmental controller landing in adjacent approach airspace was given a descent clearance. In an effort to allow the developmental to realize potential conflict with another aircraft, the clearance was allowed. Handoff was effected via ARTS. Believing the developmental now realized the potential conflict and was about to issue a turn or altitude revision, I took no immediate action. The developmental, however, initiated a frequency change. I intervened prior to completion of transmission, instructing aircraft to remain this frequency and to maintain a revised altitude. Aircraft had already changed frequency to adjacent approach. Immediate action was taken to separate aircraft. Had the pilot not changed frequency the error would not have occurred inasmuch as I would have had ample time to avoid the imminent conflict.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.