Narrative:

It was a typical first day of spring flying. There was plenty of radio traffic on the CTAF (used by several airports). I was released from approach to advisory frequency 4 mi south at 3500 ft. I announced my position and requested advisories on the CTAF. I spotted an airplane on the runway and heard a mooney who announced several mi to the west of the airport. I announced my entry to the downwind at about 2 mi and 2000 ft MSL (pattern altitude 1800 ft MSL). The mooney was spotted at my 9 O'clock position. He announced a downwind entry and the small tail dragger that was on the runway was crosswind to downwind. So; the southeast corner of the pattern had 3 aircraft within 500 ft of each other. I announced that there were 3 aircraft stacked on top of each other in the downwind. A fourth pilot acknowledged witnessing the event. The tail dragger departed; direction unknown. I maneuvered eastward past the freeway heading north and descending to about 1000 ft MSL. The mooney continued his approach. We were flying parallel in the downwind. I was outside; he was inside the pattern. The mooney landed; I extended my downwind to provide separation and landed without incident.

Related reports:

Google
 

Original NASA ASRS Text

Title: GA8 PILOT REPORTS CRITICAL CONFLICT WITH TWO OTHER ACFT IN TRAFFIC PATTERN AT UNCONTROLLED ARPT.

Narrative: IT WAS A TYPICAL FIRST DAY OF SPRING FLYING. THERE WAS PLENTY OF RADIO TFC ON THE CTAF (USED BY SEVERAL ARPTS). I WAS RELEASED FROM APCH TO ADVISORY FREQ 4 MI S AT 3500 FT. I ANNOUNCED MY POS AND REQUESTED ADVISORIES ON THE CTAF. I SPOTTED AN AIRPLANE ON THE RWY AND HEARD A MOONEY WHO ANNOUNCED SEVERAL MI TO THE W OF THE ARPT. I ANNOUNCED MY ENTRY TO THE DOWNWIND AT ABOUT 2 MI AND 2000 FT MSL (PATTERN ALT 1800 FT MSL). THE MOONEY WAS SPOTTED AT MY 9 O'CLOCK POS. HE ANNOUNCED A DOWNWIND ENTRY AND THE SMALL TAIL DRAGGER THAT WAS ON THE RWY WAS XWIND TO DOWNWIND. SO; THE SE CORNER OF THE PATTERN HAD 3 ACFT WITHIN 500 FT OF EACH OTHER. I ANNOUNCED THAT THERE WERE 3 ACFT STACKED ON TOP OF EACH OTHER IN THE DOWNWIND. A FOURTH PLT ACKNOWLEDGED WITNESSING THE EVENT. THE TAIL DRAGGER DEPARTED; DIRECTION UNKNOWN. I MANEUVERED EASTWARD PAST THE FREEWAY HDG N AND DSNDING TO ABOUT 1000 FT MSL. THE MOONEY CONTINUED HIS APCH. WE WERE FLYING PARALLEL IN THE DOWNWIND. I WAS OUTSIDE; HE WAS INSIDE THE PATTERN. THE MOONEY LANDED; I EXTENDED MY DOWNWIND TO PROVIDE SEPARATION AND LANDED WITHOUT INCIDENT.

Data retrieved from NASA's ASRS site as of May 2009 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.