Narrative:

On jul/thu/04 at approximately XA40, separation was lost between my C210 and another in class D airspace at apa airport. I contacted the tower about 10 NM from the field and was instructed to 'report parker road, straight-in runway 28.' this point is 2.5 NM from the threshold of runway 28. As I approached the call-in point, another C210 passed me about 75 yards off of my right wing at the same altitude. As he flew in front of me, he called the tower and reported that he had passed another C210. The tower instructed him to land, and I was given a right 360 'for spacing.' after landing, I decided to call the tower to see what had happened. They informed me that separation was lost because they received an intermittent transponder signal from me and only had a 'primary return.' this caused them to 'lose track' of me. I've since had my transponder checked, and it was on the edge of the appropriate transmitting frequency. The avionics shop made an adjustment and has assured me that it will report normally. He stated that on the bench the transponder checked out normally, but in the plane, it was out of frequency. I had just had the 24 month transponder certification done a week ago by another avionics shop. They said that it tested fine after they installed it in the plane. I will have the transponder checked again for 'drift' every couple of months instead of waiting for the mandatory 2 yr check, and will also be extra alert for traffic no matter where I am.

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Original NASA ASRS Text

Title: WHILE ON A STRAIGHT-IN VFR APCH INTO APA ARPT, A C210 PLT OBSERVED A SECOND C210 CROSS HIS PATH BY APPROX 75 YARDS.

Narrative: ON JUL/THU/04 AT APPROX XA40, SEPARATION WAS LOST BTWN MY C210 AND ANOTHER IN CLASS D AIRSPACE AT APA ARPT. I CONTACTED THE TWR ABOUT 10 NM FROM THE FIELD AND WAS INSTRUCTED TO 'RPT PARKER ROAD, STRAIGHT-IN RWY 28.' THIS POINT IS 2.5 NM FROM THE THRESHOLD OF RWY 28. AS I APCHED THE CALL-IN POINT, ANOTHER C210 PASSED ME ABOUT 75 YARDS OFF OF MY R WING AT THE SAME ALT. AS HE FLEW IN FRONT OF ME, HE CALLED THE TWR AND RPTED THAT HE HAD PASSED ANOTHER C210. THE TWR INSTRUCTED HIM TO LAND, AND I WAS GIVEN A R 360 'FOR SPACING.' AFTER LNDG, I DECIDED TO CALL THE TWR TO SEE WHAT HAD HAPPENED. THEY INFORMED ME THAT SEPARATION WAS LOST BECAUSE THEY RECEIVED AN INTERMITTENT XPONDER SIGNAL FROM ME AND ONLY HAD A 'PRIMARY RETURN.' THIS CAUSED THEM TO 'LOSE TRACK' OF ME. I'VE SINCE HAD MY XPONDER CHKED, AND IT WAS ON THE EDGE OF THE APPROPRIATE XMITTING FREQ. THE AVIONICS SHOP MADE AN ADJUSTMENT AND HAS ASSURED ME THAT IT WILL RPT NORMALLY. HE STATED THAT ON THE BENCH THE XPONDER CHKED OUT NORMALLY, BUT IN THE PLANE, IT WAS OUT OF FREQ. I HAD JUST HAD THE 24 MONTH XPONDER CERTIFICATION DONE A WK AGO BY ANOTHER AVIONICS SHOP. THEY SAID THAT IT TESTED FINE AFTER THEY INSTALLED IT IN THE PLANE. I WILL HAVE THE XPONDER CHKED AGAIN FOR 'DRIFT' EVERY COUPLE OF MONTHS INSTEAD OF WAITING FOR THE MANDATORY 2 YR CHK, AND WILL ALSO BE EXTRA ALERT FOR TFC NO MATTER WHERE I AM.

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.