Narrative:

Approached sonoma, ca, airport in santa rosa, ca, from southeast VFR at 4500 ft. ZOA was providing flight following and I had a discrete transponder code. As I got within 15 NM of the airport I asked for a lower altitude (start my descent). Center informed me of a helicopter on a practice instrument approach for runway 32. I was told to stay at the higher altitude. Finally, the controller let me descend, but not lower than 2500 ft MSL until I had the helicopter in sight. He also instructed me to contact sonoma company tower. I began a 1000 FPM descent and contacted the tower. The controller told me to enter downwind left traffic runway 14 and inform her when I was abeam the tower. The helicopter was told to break off his approach and follow me. My attention to keeping visual contact with the helicopter did not allow much time to looking forward. As I approached the downwind leg abeam the tower I looked forward to turn downwind and call the tower. I spotted a piper arrow climbing toward me and immediately began an evasive maneuver after the arrow pilot pulled up hard and smoked left. I pushed down hard to provide more separation. I informed the tower of our near miss and began to ask why I was not informed of the arrow crossing my flight path. I realized then the pattern was not the place to ask questions and went on with my landing. The controller never followed up, nor did the arrow pilot. As we know, accidents are brought on by several events or factors. The factors leading up to this incident are my arrival to the downwind leg high due to a late descent because of the helicopter traffic on instrument approach, my attention to this helicopter trying to maintain visual contact as he moved in behind me, the controller not informing the arrow pilot or myself of the relative position of our aircraft, the arrow crossing the field through the airspace in close proximity to the downwind leg of the active runway. I have always instructed my students to never arrive in the pattern at an altitude higher than pattern altitude. The circumstances warranted me doing just the opposite. In the future, however, I will request a vector away from the airport to descend to the appropriate altitude. As a side note, the following day I contacted oakland FSDO to ask about filing an incident report. The inspector discouraged me from doing so. Instead he recommended sending in the ASRS.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 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.