Narrative:

Air carrier X, a northbound medium large transport, was level at 16,000 en route to sea. Widebody transport Y departed pdx at XA37, en route to seattle requesting FL200. At XA40 Y checked on out of 110 for 130 (per LOA). Y was told to 'climb and maintain FL200, resume normal speed leaving FL180'. In addition to X and Y, a commuter and another air carrier were being sequenced in trail to sea. Also another widebody transport and 2 turboprops had departed pdx and sequencing decisions were being made with respect to these aircraft also. At XA41 the controller issued a crossing restriction to a general aviation pilot who read back the wrong clearance. The clearance was reissued and readback was correct. Widebody transport Y was observed out of 142 climbing to 200 less than 5 mi from air carrier X. Y was told 'maintain 150 for traffic'. The pilot did not respond. The clearance was repeated and read back. 48 seconds after the first clearance to maintain 150 was issued the pilot began descent. The closest the 2 aircraft came was 3.3 mi and 600'. The conflict alert and the immediate alert failed to trigger. The r-side controller had been on position for 3 mins. Suggestion: change parameters of conflict alert so that some warning occurs in situations where overtake exists. There are several situations where loss of separation occurs and no conflict alert triggers. Supplemental information from acn 122773: air carrier X was at 16,000'. This aircraft was cleared direct btg, finney 3 arrival to sea. Air carrier Y departed pdx en route to sea. Pdx approach assigned Y a vector to intercept the btg 360R and was cleared finney 3 arrival to sea. I was instructing a student on the radar position.

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Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN TWO ACR ACFT. OPERATIONAL ERROR.

Narrative: ACR X, A NBOUND MLG, WAS LEVEL AT 16,000 ENRTE TO SEA. WDB Y DEPARTED PDX AT XA37, ENRTE TO SEATTLE REQUESTING FL200. AT XA40 Y CHECKED ON OUT OF 110 FOR 130 (PER LOA). Y WAS TOLD TO 'CLIMB AND MAINTAIN FL200, RESUME NORMAL SPEED LEAVING FL180'. IN ADDITION TO X AND Y, A COMMUTER AND ANOTHER ACR WERE BEING SEQUENCED IN TRAIL TO SEA. ALSO ANOTHER WDB AND 2 TURBOPROPS HAD DEPARTED PDX AND SEQUENCING DECISIONS WERE BEING MADE WITH RESPECT TO THESE ACFT ALSO. AT XA41 THE CTLR ISSUED A XING RESTRICTION TO A GENERAL AVIATION PLT WHO READ BACK THE WRONG CLRNC. THE CLRNC WAS REISSUED AND READBACK WAS CORRECT. WDB Y WAS OBSERVED OUT OF 142 CLIMBING TO 200 LESS THAN 5 MI FROM ACR X. Y WAS TOLD 'MAINTAIN 150 FOR TFC'. THE PLT DID NOT RESPOND. THE CLRNC WAS REPEATED AND READ BACK. 48 SECONDS AFTER THE FIRST CLRNC TO MAINTAIN 150 WAS ISSUED THE PLT BEGAN DSCNT. THE CLOSEST THE 2 ACFT CAME WAS 3.3 MI AND 600'. THE CONFLICT ALERT AND THE IMMEDIATE ALERT FAILED TO TRIGGER. THE R-SIDE CTLR HAD BEEN ON POSITION FOR 3 MINS. SUGGESTION: CHANGE PARAMETERS OF CONFLICT ALERT SO THAT SOME WARNING OCCURS IN SITUATIONS WHERE OVERTAKE EXISTS. THERE ARE SEVERAL SITUATIONS WHERE LOSS OF SEPARATION OCCURS AND NO CONFLICT ALERT TRIGGERS. SUPPLEMENTAL INFORMATION FROM ACN 122773: ACR X WAS AT 16,000'. THIS ACFT WAS CLRED DIRECT BTG, FINNEY 3 ARR TO SEA. ACR Y DEPARTED PDX ENRTE TO SEA. PDX APCH ASSIGNED Y A VECTOR TO INTERCEPT THE BTG 360R AND WAS CLRED FINNEY 3 ARR TO SEA. I WAS INSTRUCTING A STUDENT ON THE RADAR POSITION.

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.