PA28 AND C120 HAD NMAC IN THE ARPT PATTERN AT ARB.

Narrative

AFTER SEVERAL CIRCUITS AROUND THE PATTERN DOING TOUCH- AND-GOES; WE WERE ONCE AGAIN CLBING AFTER TKOF. EITHER WELL INTO THE TURN TO XWIND OR JUST AS WE ROLLED OUT ONTO THE XWIND HDG; THE TWR INSTRUCTED US '...RESUME UPWIND HDG; TFC IS A CESSNA JOINING THE DOWNWIND AHEAD AND TO YOUR L.' I ACKNOWLEDGED AND ROLLED INTO A R TURN. DURING THE TURN BACK TO THE UPWIND HDG; I AND MY PAX SIMULTANEOUSLY IDENTED CESSNA TFC PASSING ON OUR L; WHERE WE WOULD EXPECT IT TO BE FROM THE TWR'S DESCRIPTION. WE WOULD MOMENTARILY DISCOVER THAT THIS WAS NOT THE TFC IN QUESTION; WHICH WAS BY NOW LIKELY HIDDEN UNDER OUR NOSE AS WE CONTINUED THE CLB IN THE TURN BACK TO UPWIND. UPON SPOTTING THE TFC; I ROLLED BACK INTO A L TURN TO FOLLOW; AND AS I RECALL; RPTED VISUAL SIGHTING TO THE TWR. A MOMENT LATER THE TWR INSTRUCTED THE OTHER ACFT TO MAKE A R 360 DEG TURN. NOW ALERTED TO SOME ANOMALY; I LOWERED THE NOSE; REVEALING THE CESSNA TFC AHEAD; APPARENTLY SLIGHTLY ABOVE; AND TO OUR R A BIT. THE CESSNA WAS ROLLING INTO A R TURN. I IMMEDIATELY INITIATED A R TURN TO AVOID COLLISION; AND ADVISED THE TWR OF OUR TURN. THE TWR THEN INSTRUCTED US TO FLY R TFC THIS CIRCUIT; AND ON THE NEXT TIME AROUND DIRECTED US BACK INTO THE L PATTERN. HUMAN FACTORS/FUTURE AVOIDANCE: THIS INCIDENT OCCURRED AT A VERY BUSY TIME. THERE WERE A LOT OF ACFT IN THE PATTERN; FLYING BOTH L AND R TFC. THE TWR FREQ WAS CONGESTED. AGAINST THAT BACKGND; I SEE SEVERAL FACTORS CONTRIBUTING TO THIS INCIDENT. CHIEF AMONG THESE IS THE TWR'S INITIAL DESCRIPTION OF THE CONFLICTING TFC'S LOCATION AS 'AHEAD AND TO YOUR L.' THE CTLR; WHILE AWARE OF OUR LOCATION; MIGHT NOT HAVE BEEN AWARE THAT OUR HDG WAS WELL OFF THE UPWIND AND APCHING THE XWIND HDG. THE RESULT WAS THAT OUR SEARCH FOR THE TFC WAS DIRECTED TO THE WRONG AREA. UNFORTUNATELY; THERE WAS ALSO CESSNA TFC IN THE AREA WHERE WE WERE LOOKING. WHILE THE TRUE CONFLICTING TFC MIGHT AT TIMES HAVE BEEN VISIBLE HAD WE LOOKED IN THE RIGHT DIRECTION; WE WERE ALSO HANDICAPPED BY BEING IN A CLB. WITH THE NOSE HIGH; THE CONFLICTING CESSNA WOULD LIKELY HAVE BEEN HIDDEN FROM VIEW BENEATH THE NOSE MUCH OF THE TIME. OF COURSE; IT IS NOT THE TWR'S USUAL PROC TO INDIVIDUALLY DIRECT EACH ACFT WHEN TO MAKE EACH TURN IN THE PATTERN. IT'S GENERALLY EXPECTED THAT UPON IDENTING THE ACFT AHEAD OF US WE ARE TO FOLLOW IN SEQUENCE WITHOUT FURTHER INSTRUCTION. I TOOK THE TWR'S INSTRUCTION TO RESUME THE UPWIND HDG; FOLLOWED BY THE TFC CALLOUT; AS IMPLICIT INSTRUCTIONS TO DO JUST THAT. IN RETROSPECT; I WISH I'D TAKEN THAT INSTRUCTION TO MEAN 'RESUME UPWIND HDG UNTIL FURTHER NOTICE; I WILL CALL YOUR XWIND; TFC IS....' IT WOULD HAVE BEEN BETTER STILL IF THE CTLR HAD SAID JUST THAT. IT MAY BE WORTH NOTING THAT SUBSEQUENT TO THIS INCIDENT THE TWR DID FREQUENTLY CALL TURNS TO XWIND OR BASE; BOTH FOR US AND OTHER ACFT. IDEALLY; HAD THE TWR BEEN AWARE OF THE POTENTIAL CONFLICT; INSTRUCTIONS DURING THE INITIAL CLBOUT TO MAINTAIN RWY HDG UNTIL FURTHER NOTICE WOULD HAVE COMPLETELY AVOIDED SETTING THE STAGE FOR THIS INCIDENT. AS NOTED EARLIER; HOWEVER; THE TWR FREQ WAS VERY CONGESTED. THE CTLR'S DIRECTIONS MAY HAVE BEEN AS TIMELY AS WAS POSSIBLE UNDER THE CIRCUMSTANCES.