Narrative:

Aircraft 1 IFR san-lgb. Aircraft 2 IFR unk-sdm. During light to moderate routine traffic (7 aircraft on 2 frequencys UHF/VHF) aircraft 1 departed san climbing to unreadable altitude (pilot's VHF transmission covered by other UHF transmission). I advised aircraft 1 radar contact and instructed climb and maintain 8000' to coincide with requested altitude on flight progress strip believing mistakenly aircraft was M class turboprop. Pilot read back climb and maintain 8000'. After observing data block and checking flight progress I realized my error and re-issued climb and maintain 4000' to coincide with type aircraft and initial route of flight. At this time I was distracted by other radio calls and failed to notice aircraft 1 did not read back the amended altitude. Aircraft I was climbing through 2100' at the time of amended instruction. Approximately 2 mins later I was preoccupied with another aircraft climbing slowly into ZLA airspace on an amended flight plan and failed to notice aircraft 1 climb through 4000'. Shortly thereafter I was alerted to a potential near midair collision by the C/a system with aircraft 2 level at 5000' sebnd, approximately 3 mi and 12 O'clock with aircraft 1 nwbnd now at 4800'. Aircraft 1 was issued a traffic alert and immediate descent to 4000'. The controller working aircraft 2 turned the aircraft east to 100 degrees. Ca system showed aircraft passed west/in 1 1/2 mi. Could have been avoided by controller (me) catching lack of pilot readback on amended altitude, controller catching incorrect filed altitude on strip, pilot hearing amended altitude, pilot filing correct altitude or corrected altitude being relayed. Preoccupation with other duties possibly causing tunnel vision caused missed altitude readback for myself. Not hearing aircraft 1's initial altitude climbing to may have contributed.

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Original NASA ASRS Text

Title: SMT ALLOWED TO CLIMB THROUGH ALT OF OPPOSITE DIRECTION TRAFFIC. LESS THAN STANDARD SEPARATION.

Narrative: ACFT 1 IFR SAN-LGB. ACFT 2 IFR UNK-SDM. DURING LIGHT TO MODERATE ROUTINE TFC (7 ACFT ON 2 FREQS UHF/VHF) ACFT 1 DEPARTED SAN CLBING TO UNREADABLE ALT (PLT'S VHF XMISSION COVERED BY OTHER UHF XMISSION). I ADVISED ACFT 1 RADAR CONTACT AND INSTRUCTED CLB AND MAINTAIN 8000' TO COINCIDE WITH REQUESTED ALT ON FLT PROGRESS STRIP BELIEVING MISTAKENLY ACFT WAS M CLASS TURBOPROP. PLT READ BACK CLB AND MAINTAIN 8000'. AFTER OBSERVING DATA BLOCK AND CHKING FLT PROGRESS I REALIZED MY ERROR AND RE-ISSUED CLB AND MAINTAIN 4000' TO COINCIDE WITH TYPE ACFT AND INITIAL ROUTE OF FLT. AT THIS TIME I WAS DISTRACTED BY OTHER RADIO CALLS AND FAILED TO NOTICE ACFT 1 DID NOT READ BACK THE AMENDED ALT. ACFT I WAS CLBING THROUGH 2100' AT THE TIME OF AMENDED INSTRUCTION. APPROX 2 MINS LATER I WAS PREOCCUPIED WITH ANOTHER ACFT CLBING SLOWLY INTO ZLA AIRSPACE ON AN AMENDED FLT PLAN AND FAILED TO NOTICE ACFT 1 CLB THROUGH 4000'. SHORTLY THEREAFTER I WAS ALERTED TO A POTENTIAL NMAC BY THE C/A SYS WITH ACFT 2 LEVEL AT 5000' SEBND, APPROX 3 MI AND 12 O'CLOCK WITH ACFT 1 NWBND NOW AT 4800'. ACFT 1 WAS ISSUED A TFC ALERT AND IMMEDIATE DSCNT TO 4000'. THE CTLR WORKING ACFT 2 TURNED THE ACFT E TO 100 DEGS. CA SYS SHOWED ACFT PASSED W/IN 1 1/2 MI. COULD HAVE BEEN AVOIDED BY CTLR (ME) CATCHING LACK OF PLT READBACK ON AMENDED ALT, CTLR CATCHING INCORRECT FILED ALT ON STRIP, PLT HEARING AMENDED ALT, PLT FILING CORRECT ALT OR CORRECTED ALT BEING RELAYED. PREOCCUPATION WITH OTHER DUTIES POSSIBLY CAUSING TUNNEL VISION CAUSED MISSED ALT READBACK FOR MYSELF. NOT HEARING ACFT 1'S INITIAL ALT CLBING TO MAY HAVE CONTRIBUTED.

Data retrieved from NASA's ASRS site as of August 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.