CIRRUS SR22 WAS INVOLVED IN AN NMAC WHILE ESTABLISHED ON DOWNWIND IN A VFR TFC PATTERN.

Narrative

I WAS FLYING WITH A CIRRUS FLT INSTRUCTOR NEAR WINCHESTER; VA. WE ENTERED THE TFC PATTERN ON A 45 DEG TO MID-FIELD DOWNWIND. WE HAD BEEN MONITORING CTAF FROM AT LEAST 15 NM OUT. THERE WERE ACFT IN THE PATTERN AND ONE ON AN INST APCH. WHEN WE WERE APPROX 4.5 NM OUT A CESSNA RPTED ON DOWNWIND; I HAD AN ACFT ON DOWNWIND IN SIGHT AND ANNOUNCED THAT WE WOULD ENTER ON THE 45 DEGS AND FOLLOW. WHILE ON THE DOWNWIND THE ACFT AHEAD BEGAN TO TURN BASE AND A PIPER RPTED TURNING BASE ON CTAF. SOMEONE ON THE GND BROADCAST THAT AN ACFT IN THE PATTERN HAD AN UNREADABLE RADIO. THE INSTRUCTOR VERIFIED THAT IT WAS NOT MY RADIO. WE WERE LOOKING FOR THE ACFT ON THE INST APCH TO DETERMINE IF WE HAD SPACE TO LAND OR WOULD NEED TO EXTEND THE DOWNWIND. SHORTLY THEREAFTER WE SAW THE CESSNA BELOW AND TO OUR R. I IMMEDIATELY TURNED BASE AND HELD PATTERN ALT WITH THE INTENT OF MANEUVERING AWAY FROM THE CESSNA AND ENTERING THE UPWIND. THE INSTRUCTOR RPTED TURNING BASE WITH THE INTENT TO ENTER THE UPWIND ON CTAF. SHORTLY THEREAFTER THE CESSNA RPTED TURNING BASE (WE BELIEVE THAT HE DID NOT KNOW OUR POS). WE ENTERED THE UPWIND; REMAINED IN THE PATTERN AND THEN LANDED WITHOUT INCIDENT. CONTRIBUTING FACTORS TO THIS INCIDENT WAS: THE HIGH WING VERSUS LOW WING IN THE TFC PATTERN.