Narrative:

Reported 3 NM northeast rnm. Rnm tower instructed me to circumnav to a position for 4 NM straight-in; runway 27. During transit downwind; I heard tower ask a cessna to turn base r-hand runway 27. At 4 NM final; I reported position and was asked to do a 360 degree r-hand turn for spacing. During the turn; I noticed a C172 heading downwind. At the same time overheard a transmission from the tower; 'cessna XXXX I told you to turn base a while ago. Turn base #2 runway 27.' at this point I lost sight of the C172 and assumed that he would turn base; putting him ahead of me when I completed my turn. Reported 4 mi final after completing 360 degrees. Was cleared to land #3 runway 27. I saw a C172 in front of me but could not find the C172 on base; to my right. A C172 reported visual with very close traffic on his right. On looking left and aft; I saw the C172 approximately 30 ft at same altitude. I immediately initiated a r-hand 360 degree turn and positioned behind the C172. Tower was informed of the shuffle. This was the C172 instructed to turn base; but apparently did not.

Google
 

Original NASA ASRS Text

Title: SMA PLT EXPERIENCED NMAC AT 2500 FT DURING PATTERN ENTRY AT RNM INDICATING PLT ERROR ON THE PART OF THE CONFLICTING ACFT.

Narrative: RPTED 3 NM NE RNM. RNM TWR INSTRUCTED ME TO CIRCUMNAV TO A POS FOR 4 NM STRAIGHT-IN; RWY 27. DURING TRANSIT DOWNWIND; I HEARD TWR ASK A CESSNA TO TURN BASE R-HAND RWY 27. AT 4 NM FINAL; I RPTED POS AND WAS ASKED TO DO A 360 DEG R-HAND TURN FOR SPACING. DURING THE TURN; I NOTICED A C172 HEADING DOWNWIND. AT THE SAME TIME OVERHEARD A XMISSION FROM THE TWR; 'CESSNA XXXX I TOLD YOU TO TURN BASE A WHILE AGO. TURN BASE #2 RWY 27.' AT THIS POINT I LOST SIGHT OF THE C172 AND ASSUMED THAT HE WOULD TURN BASE; PUTTING HIM AHEAD OF ME WHEN I COMPLETED MY TURN. RPTED 4 MI FINAL AFTER COMPLETING 360 DEGS. WAS CLRED TO LAND #3 RWY 27. I SAW A C172 IN FRONT OF ME BUT COULD NOT FIND THE C172 ON BASE; TO MY R. A C172 RPTED VISUAL WITH VERY CLOSE TFC ON HIS R. ON LOOKING L AND AFT; I SAW THE C172 APPROX 30 FT AT SAME ALT. I IMMEDIATELY INITIATED A R-HAND 360 DEG TURN AND POSITIONED BEHIND THE C172. TWR WAS INFORMED OF THE SHUFFLE. THIS WAS THE C172 INSTRUCTED TO TURN BASE; BUT APPARENTLY DID NOT.

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