Narrative:

We were on a return flight to dab 5 mi north of omn VOR. I received radar contact from approach. As pilot I observed an aircraft fly x-wind and enter downwind about 600' below and to the left of our position. As we approached and were crossing perpendicular to the downwind I scanned to the left side of the aircraft again and observed a twin aircraft slightly lower than our position and about 100' to the left. Evasive action involved a quick immediate climb to avoid collision. It appeared the small aircraft Y climbed 600' while on downwind. The aircraft continued on and landed at ormond. I contacted approach and queried the controller if he had been talking to the aircraft. The answer was negative. From the position the multi-aircraft was in, he should have been in contact with the arsa controling agency.

Related reports:

Google
 

Original NASA ASRS Text

Title: LIGHT ACFT HAS NMAC WITH ANOTHER LIGHT TWIN NOT COMMUNICATING WITH ATC WHILE IN ARSA.

Narrative: WE WERE ON A RETURN FLT TO DAB 5 MI N OF OMN VOR. I RECEIVED RADAR CONTACT FROM APCH. AS PLT I OBSERVED AN ACFT FLY X-WIND AND ENTER DOWNWIND ABOUT 600' BELOW AND TO THE LEFT OF OUR POSITION. AS WE APCHED AND WERE XING PERPENDICULAR TO THE DOWNWIND I SCANNED TO THE LEFT SIDE OF THE ACFT AGAIN AND OBSERVED A TWIN ACFT SLIGHTLY LOWER THAN OUR POSITION AND ABOUT 100' TO THE LEFT. EVASIVE ACTION INVOLVED A QUICK IMMEDIATE CLIMB TO AVOID COLLISION. IT APPEARED THE SMA Y CLIMBED 600' WHILE ON DOWNWIND. THE ACFT CONTINUED ON AND LANDED AT ORMOND. I CONTACTED APCH AND QUERIED THE CTLR IF HE HAD BEEN TALKING TO THE ACFT. THE ANSWER WAS NEGATIVE. FROM THE POSITION THE MULTI-ACFT WAS IN, HE SHOULD HAVE BEEN IN CONTACT WITH THE ARSA CTLING AGENCY.

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.