NMAC.

Narrative

APCHED SONOMA; CA; ARPT IN SANTA ROSA; CA; FROM SE VFR AT 4500 FT. ZOA WAS PROVIDING FLT FOLLOWING AND I HAD A DISCRETE XPONDER CODE. AS I GOT WITHIN 15 NM OF THE ARPT I ASKED FOR A LOWER ALT (START MY DSCNT). CTR INFORMED ME OF A HELI ON A PRACTICE INST APCH FOR RWY 32. I WAS TOLD TO STAY AT THE HIGHER ALT. FINALLY; THE CTLR LET ME DSND; BUT NOT LOWER THAN 2500 FT MSL UNTIL I HAD THE HELI IN SIGHT. HE ALSO INSTRUCTED ME TO CONTACT SONOMA COMPANY TWR. I BEGAN A 1000 FPM DSCNT AND CONTACTED THE TWR. THE CTLR TOLD ME TO ENTER DOWNWIND L TFC RWY 14 AND INFORM HER WHEN I WAS ABEAM THE TWR. THE HELI WAS TOLD TO BREAK OFF HIS APCH AND FOLLOW ME. MY ATTN TO KEEPING VISUAL CONTACT WITH THE HELI DID NOT ALLOW MUCH TIME TO LOOKING FORWARD. AS I APCHED THE DOWNWIND LEG ABEAM THE TWR I LOOKED FORWARD TO TURN DOWNWIND AND CALL THE TWR. I SPOTTED A PIPER ARROW CLBING TOWARD ME AND IMMEDIATELY BEGAN AN EVASIVE MANEUVER AFTER THE ARROW PLT PULLED UP HARD AND SMOKED L. I PUSHED DOWN HARD TO PROVIDE MORE SEPARATION. I INFORMED THE TWR OF OUR NEAR MISS AND BEGAN TO ASK WHY I WAS NOT INFORMED OF THE ARROW XING MY FLT PATH. I REALIZED THEN THE PATTERN WAS NOT THE PLACE TO ASK QUESTIONS AND WENT ON WITH MY LNDG. THE CTLR NEVER FOLLOWED UP; NOR DID THE ARROW PLT. AS WE KNOW; ACCIDENTS ARE BROUGHT ON BY SEVERAL EVENTS OR FACTORS. THE FACTORS LEADING UP TO THIS INCIDENT ARE MY ARR TO THE DOWNWIND LEG HIGH DUE TO A LATE DSCNT BECAUSE OF THE HELI TFC ON INST APCH; MY ATTN TO THIS HELI TRYING TO MAINTAIN VISUAL CONTACT AS HE MOVED IN BEHIND ME; THE CTLR NOT INFORMING THE ARROW PLT OR MYSELF OF THE RELATIVE POS OF OUR ACFT; THE ARROW XING THE FIELD THROUGH THE AIRSPACE IN CLOSE PROX TO THE DOWNWIND LEG OF THE ACTIVE RWY. I HAVE ALWAYS INSTRUCTED MY STUDENTS TO NEVER ARRIVE IN THE PATTERN AT AN ALT HIGHER THAN PATTERN ALT. THE CIRCUMSTANCES WARRANTED ME DOING JUST THE OPPOSITE. IN THE FUTURE; HOWEVER; I WILL REQUEST A VECTOR AWAY FROM THE ARPT TO DSND TO THE APPROPRIATE ALT. AS A SIDE NOTE; THE FOLLOWING DAY I CONTACTED OAKLAND FSDO TO ASK ABOUT FILING AN INCIDENT RPT. THE INSPECTOR DISCOURAGED ME FROM DOING SO. INSTEAD HE RECOMMENDED SENDING IN THE ASRS.