Narrative:

I approached the airport from the south to enter the left downwind for runway 20. I made my first advisory on 122.8 about 9.5 NM south of the airport. As I cancelled my IFR flight plan with cak approach, the controller informed me of traffic off my right from westbound. Also, I was informed by the controller of traffic located west of the airport by about 4 mi at 3400'. There was no indication of the 3400' traffic descending. However, as I proceeded toward the airport, I determined the westbound traffic would be no factor, but the 3400' eastbound traffic appeared to be descending. I made radio calls on 122.8 5 mi out, 2 southeast and on each leg of the traffic pattern. At mid field on downwind the descending aircraft, which by this time had increased its speed and descent rate dramatically, passed directly in front of us at exactly our altitude while still descending and was approximately no more than 200' ahead (passing left to right). I made a hard left to avoid a critical conflict with the aircraft. I continued my traffic pattern and completed an uneventful landing. Of course, all of my anti-collision and position lights were on as I descended past 5000' MSL (my personal policy). As I taxied back to my hangar an aircraft came on the radio and announced short final for runway 20 at wadsworth. After talking with the pilot on the radio he said he was above the pattern altitude and had me in sight. The pilot was in small aircraft X.

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Original NASA ASRS Text

Title: SMT ON DOWNWIND AT NIGHT EXECUTED A HARD LEFT AVOIDANCE MANEUVER TO MISS SMA ENTERING PATTERN IN NON STANDARD ENTRY.

Narrative: I APCHED THE ARPT FROM THE S TO ENTER THE LEFT DOWNWIND FOR RWY 20. I MADE MY FIRST ADVISORY ON 122.8 ABOUT 9.5 NM S OF THE ARPT. AS I CANCELLED MY IFR FLT PLAN WITH CAK APCH, THE CTLR INFORMED ME OF TFC OFF MY RIGHT FROM WBND. ALSO, I WAS INFORMED BY THE CTLR OF TFC LOCATED W OF THE ARPT BY ABOUT 4 MI AT 3400'. THERE WAS NO INDICATION OF THE 3400' TFC DSNDING. HOWEVER, AS I PROCEEDED TOWARD THE ARPT, I DETERMINED THE WBND TFC WOULD BE NO FACTOR, BUT THE 3400' EBND TFC APPEARED TO BE DSNDING. I MADE RADIO CALLS ON 122.8 5 MI OUT, 2 SE AND ON EACH LEG OF THE TFC PATTERN. AT MID FIELD ON DOWNWIND THE DSNDING ACFT, WHICH BY THIS TIME HAD INCREASED ITS SPD AND DSCNT RATE DRAMATICALLY, PASSED DIRECTLY IN FRONT OF US AT EXACTLY OUR ALT WHILE STILL DSNDING AND WAS APPROX NO MORE THAN 200' AHEAD (PASSING LEFT TO RIGHT). I MADE A HARD LEFT TO AVOID A CRITICAL CONFLICT WITH THE ACFT. I CONTINUED MY TFC PATTERN AND COMPLETED AN UNEVENTFUL LNDG. OF COURSE, ALL OF MY ANTI-COLLISION AND POS LIGHTS WERE ON AS I DSNDED PAST 5000' MSL (MY PERSONAL POLICY). AS I TAXIED BACK TO MY HANGAR AN ACFT CAME ON THE RADIO AND ANNOUNCED SHORT FINAL FOR RWY 20 AT WADSWORTH. AFTER TALKING WITH THE PLT ON THE RADIO HE SAID HE WAS ABOVE THE PATTERN ALT AND HAD ME IN SIGHT. THE PLT WAS IN SMA X.

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.