Narrative:

After canceling my IFR clearance and quickly descending on a slam dunk descent to moore county airport; my copilot announced on 122.7 our intention to enter a l-hand pattern on a left crosswind leg for full stop landing on runway 23; which I did. There was a 3 KT wind favoring runway 23. Shortly after turning left downwind; my copilot let out an expletive and grabbed the yoke to take evasive action to turn the airplane to the right. I immediately looked up and saw a piston twin engine airplane just to the left of us very close to our altitude; and I also assisted in the evasive action to turn our airplane to the right. The twin was in a slight left bank. We barely missed hitting that airplane head-on. After landing; we discovered that the other plane had landed on runway 5; apparently from a r-hand pattern. That airplane quickly departed before we had a chance to talk to the pilot. We asked the airport lineman if 122.7 was the correct CTAF; and he indicated it is 123.05. I then assumed that the approach plate from which I got the frequency was not current due to an error in posting terminal plate revisions. Later investigation yielded the fact that I was most likely looking at the approach plate for the wrong airport; that of monroe county; nc; instead of moore county; nc. The facts that the airport names are very close in the alphabet; sound; and appearance; they both have a single runway oriented 5/23; they both have a GPS 23 approach; and the runways are nearly the same in length made the error less apparent. My copilot questioned whether or not the airport name was correct; for the approach controller had referred to the airport as southern pines. When I looked up the airport in my flight guide during preflight planning; I remembered that the airport had 2 names; southern pines/moore county (remembered incorrectly as monroe county); so I felt assured the airport name on the plate was correct. As a result; we had transmitted our announcement to enter the pattern on the wrong frequency; and hence the other plane did not hear us; and we did not hear whatever xmissions they made either. On our next flight leg; we looked in the GNS530 database on board and found the correct frequency to be 123.05. After talking more to my copilot later; he indicated to me he saw the other plane enter the pattern from a 45 degree to the right downwind for runway 5 and it turned to the left right to intercept the right downwind directly in front of us. Neither myself nor my copilot remember seeing a segmented circle. Published data online and in air guide pubs 'flight guide' indicate l-hand patterns at SOP.

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Original NASA ASRS Text

Title: PILOT OF SMA REPORTS NMAC WITH LIGHT TWIN IN TRAFFIC PATTERN AT SOP. REPORTER IS USING WRONG CTAF FREQUENCY.

Narrative: AFTER CANCELING MY IFR CLRNC AND QUICKLY DSNDING ON A SLAM DUNK DSCNT TO MOORE COUNTY ARPT; MY COPLT ANNOUNCED ON 122.7 OUR INTENTION TO ENTER A L-HAND PATTERN ON A L XWIND LEG FOR FULL STOP LNDG ON RWY 23; WHICH I DID. THERE WAS A 3 KT WIND FAVORING RWY 23. SHORTLY AFTER TURNING L DOWNWIND; MY COPLT LET OUT AN EXPLETIVE AND GRABBED THE YOKE TO TAKE EVASIVE ACTION TO TURN THE AIRPLANE TO THE R. I IMMEDIATELY LOOKED UP AND SAW A PISTON TWIN ENG AIRPLANE JUST TO THE L OF US VERY CLOSE TO OUR ALT; AND I ALSO ASSISTED IN THE EVASIVE ACTION TO TURN OUR AIRPLANE TO THE R. THE TWIN WAS IN A SLIGHT L BANK. WE BARELY MISSED HITTING THAT AIRPLANE HEAD-ON. AFTER LNDG; WE DISCOVERED THAT THE OTHER PLANE HAD LANDED ON RWY 5; APPARENTLY FROM A R-HAND PATTERN. THAT AIRPLANE QUICKLY DEPARTED BEFORE WE HAD A CHANCE TO TALK TO THE PLT. WE ASKED THE ARPT LINEMAN IF 122.7 WAS THE CORRECT CTAF; AND HE INDICATED IT IS 123.05. I THEN ASSUMED THAT THE APCH PLATE FROM WHICH I GOT THE FREQ WAS NOT CURRENT DUE TO AN ERROR IN POSTING TERMINAL PLATE REVISIONS. LATER INVESTIGATION YIELDED THE FACT THAT I WAS MOST LIKELY LOOKING AT THE APCH PLATE FOR THE WRONG ARPT; THAT OF MONROE COUNTY; NC; INSTEAD OF MOORE COUNTY; NC. THE FACTS THAT THE ARPT NAMES ARE VERY CLOSE IN THE ALPHABET; SOUND; AND APPEARANCE; THEY BOTH HAVE A SINGLE RWY ORIENTED 5/23; THEY BOTH HAVE A GPS 23 APCH; AND THE RWYS ARE NEARLY THE SAME IN LENGTH MADE THE ERROR LESS APPARENT. MY COPLT QUESTIONED WHETHER OR NOT THE ARPT NAME WAS CORRECT; FOR THE APCH CTLR HAD REFERRED TO THE ARPT AS SOUTHERN PINES. WHEN I LOOKED UP THE ARPT IN MY FLT GUIDE DURING PREFLT PLANNING; I REMEMBERED THAT THE ARPT HAD 2 NAMES; SOUTHERN PINES/MOORE COUNTY (REMEMBERED INCORRECTLY AS MONROE COUNTY); SO I FELT ASSURED THE ARPT NAME ON THE PLATE WAS CORRECT. AS A RESULT; WE HAD XMITTED OUR ANNOUNCEMENT TO ENTER THE PATTERN ON THE WRONG FREQ; AND HENCE THE OTHER PLANE DID NOT HEAR US; AND WE DID NOT HEAR WHATEVER XMISSIONS THEY MADE EITHER. ON OUR NEXT FLT LEG; WE LOOKED IN THE GNS530 DATABASE ON BOARD AND FOUND THE CORRECT FREQ TO BE 123.05. AFTER TALKING MORE TO MY COPLT LATER; HE INDICATED TO ME HE SAW THE OTHER PLANE ENTER THE PATTERN FROM A 45 DEG TO THE R DOWNWIND FOR RWY 5 AND IT TURNED TO THE L RIGHT TO INTERCEPT THE R DOWNWIND DIRECTLY IN FRONT OF US. NEITHER MYSELF NOR MY COPLT REMEMBER SEEING A SEGMENTED CIRCLE. PUBLISHED DATA ONLINE AND IN AIR GUIDE PUBS 'FLT GUIDE' INDICATE L-HAND PATTERNS AT SOP.

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.