Narrative:

En route from nevada co airport to livermore (lvk) requested and received flight following from sac approach. We were level 4500', 125 KTS. Controller directed a commuter flight to maintain 4000' to clear an small aircraft at 4500. I maintained my altitude of 4500 and saw the aircraft lights approximately 5 mi at 2 O'clock below our altitude. The pilot acknowledged 'hold at 4000' and I think I see him'. We were told by the controller 'small aircraft...traffic 1 mi at 4500', I acknowledged and the controller told the commuter flight to maintain visual clearance. As the aircraft on our right came closer we saw no course change on his side. When he made no heading nor altitude changes I made a right turning rapid descent of 250-300'. The other aircraft proceeded to climb to higher assigned altitude. I climbed back to 4500' proceeding to lvk. In retrospect, the other aircraft was assigned a hold altitude and told to maintain visual clearance. The other aircraft did not positively acknowledge that he had us in sight. The other aircraft apparently did not see us since they did not inform the controller of the 1 mi distance call that they had us positively in sight. I should probably have told the controller that we were on a collision course and told him that I would take evasive action by descending. From our point of view the other pilot was too casual about his flying as well as his communication. The controller should probably have provided vectors for clearance especially after the other aircraft violated its assigned altitude.

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Original NASA ASRS Text

Title: SMA PLT TOOK EVASIVE ACTION TO AVOID COLLISION WITH COMMUTER ACFT CLIMBING. TRAFFIC CALLED BY ATC.

Narrative: ENRTE FROM NEVADA CO ARPT TO LIVERMORE (LVK) REQUESTED AND RECEIVED FLT FOLLOWING FROM SAC APCH. WE WERE LEVEL 4500', 125 KTS. CTLR DIRECTED A COMMUTER FLT TO MAINTAIN 4000' TO CLEAR AN SMA AT 4500. I MAINTAINED MY ALT OF 4500 AND SAW THE ACFT LIGHTS APPROX 5 MI AT 2 O'CLOCK BELOW OUR ALT. THE PLT ACKNOWLEDGED 'HOLD AT 4000' AND I THINK I SEE HIM'. WE WERE TOLD BY THE CTLR 'SMA...TFC 1 MI AT 4500', I ACKNOWLEDGED AND THE CTLR TOLD THE COMMUTER FLT TO MAINTAIN VISUAL CLRNC. AS THE ACFT ON OUR RIGHT CAME CLOSER WE SAW NO COURSE CHANGE ON HIS SIDE. WHEN HE MADE NO HDG NOR ALT CHANGES I MADE A RIGHT TURNING RAPID DSCNT OF 250-300'. THE OTHER ACFT PROCEEDED TO CLIMB TO HIGHER ASSIGNED ALT. I CLIMBED BACK TO 4500' PROCEEDING TO LVK. IN RETROSPECT, THE OTHER ACFT WAS ASSIGNED A HOLD ALT AND TOLD TO MAINTAIN VISUAL CLRNC. THE OTHER ACFT DID NOT POSITIVELY ACKNOWLEDGE THAT HE HAD US IN SIGHT. THE OTHER ACFT APPARENTLY DID NOT SEE US SINCE THEY DID NOT INFORM THE CTLR OF THE 1 MI DISTANCE CALL THAT THEY HAD US POSITIVELY IN SIGHT. I SHOULD PROBABLY HAVE TOLD THE CTLR THAT WE WERE ON A COLLISION COURSE AND TOLD HIM THAT I WOULD TAKE EVASIVE ACTION BY DESCENDING. FROM OUR POINT OF VIEW THE OTHER PLT WAS TOO CASUAL ABOUT HIS FLYING AS WELL AS HIS COM. THE CTLR SHOULD PROBABLY HAVE PROVIDED VECTORS FOR CLRNC ESPECIALLY AFTER THE OTHER ACFT VIOLATED ITS ASSIGNED ALT.

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.