Narrative:

Small transport X at 12,000 en route from sun to bfi on IFR flight plan. Over PDT pilot stated 'had problem with left engine' and requested to land at PDT. I issued an immediate descent clearance to 6000. Then I turned the small transport X to 250 degree to avoid the atx Y that was below him at 11,000 en route, opposite direction, on the same airway. I also turned the atx Y to 070 degree to avoid the small transport X. During descent, only 4.2 mi separation existed when aircraft were less than a thousand feet apart. Small transport X secured left engine, subsequently landed safely at PDT airport without incident. Pilot of small transport X later stated trouble was a blown cylinder head in left engine.

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Original NASA ASRS Text

Title: SMT WAS DESCENDED THROUGH AN ALT OCCUPIED BY ANOTHER ACFT DUE TO AN ENGINE PROBLEM, RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: SMT X AT 12,000 ENRTE FROM SUN TO BFI ON IFR FLT PLAN. OVER PDT PLT STATED 'HAD PROBLEM WITH LEFT ENGINE' AND REQUESTED TO LAND AT PDT. I ISSUED AN IMMEDIATE DSCNT CLRNC TO 6000. THEN I TURNED THE SMT X TO 250 DEG TO AVOID THE ATX Y THAT WAS BELOW HIM AT 11,000 ENRTE, OPPOSITE DIRECTION, ON THE SAME AIRWAY. I ALSO TURNED THE ATX Y TO 070 DEG TO AVOID THE SMT X. DURING DSCNT, ONLY 4.2 MI SEPARATION EXISTED WHEN ACFT WERE LESS THAN A THOUSAND FEET APART. SMT X SECURED LEFT ENGINE, SUBSEQUENTLY LANDED SAFELY AT PDT ARPT WITHOUT INCIDENT. PLT OF SMT X LATER STATED TROUBLE WAS A BLOWN CYLINDER HEAD IN LEFT ENGINE.

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.