Narrative:

I was flying small aircraft X into san diego international on an IFR flight plan. During the whole route on V23/V363, no discrepancies were noted by any of the ATC's. However, after switching to san diego approach, I was told my transponder was not being received. I had begun a descent at this time, and in a few mins, approach said my transponder was working again, but squawking xyxx, instead of the XXXX it was set on and which I had been assigned. I confirmed the setting to the controller and reset it, but never heard whether it was correct or not after that. I assumed it was ok, and recalled this particular plane had minor problems in the past with its transponder. I took off the following morning on an IFR flight plan to poc, and was initially cleared to 2000' on a 310 degree heading. After switching from tower to departure, the controller confirmed receiving my transponder and didn't note any problems. I leveled off at 2000', and shortly thereafter, the controller said I should be lower, but I confirmed I was at the assigned altitude and altimeter setting. According to their scopes, apparently I was out of limits on altitude clearance. I was directed to make an immediate turn to avoid the traffic, which was small aircraft Y at 2500' MSL. I had no visual contact with the aircraft. ATC said small aircraft Y was indicating 2500', i.e., its transponder return. Given the problems with my transponder, and the potential errors in other aircraft xponders and ATC radar equipment, I am concerned that ATC would put me on a converging heading with traffic and only a 500' cushion. What I am suggesting is that even with the 500' altitude difference, converging aircraft should also be given lateral separation of at least 2000'. I've tried to remedy my situation by squawking the aircraft's transponder.

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Original NASA ASRS Text

Title: AIRBORNE CONFLICT LESS SEVERE.

Narrative: I WAS FLYING SMA X INTO SAN DIEGO INTL ON AN IFR FLT PLAN. DURING THE WHOLE ROUTE ON V23/V363, NO DISCREPANCIES WERE NOTED BY ANY OF THE ATC'S. HOWEVER, AFTER SWITCHING TO SAN DIEGO APCH, I WAS TOLD MY XPONDER WAS NOT BEING RECEIVED. I HAD BEGUN A DSCNT AT THIS TIME, AND IN A FEW MINS, APCH SAID MY XPONDER WAS WORKING AGAIN, BUT SQUAWKING XYXX, INSTEAD OF THE XXXX IT WAS SET ON AND WHICH I HAD BEEN ASSIGNED. I CONFIRMED THE SETTING TO THE CTLR AND RESET IT, BUT NEVER HEARD WHETHER IT WAS CORRECT OR NOT AFTER THAT. I ASSUMED IT WAS OK, AND RECALLED THIS PARTICULAR PLANE HAD MINOR PROBLEMS IN THE PAST WITH ITS XPONDER. I TOOK OFF THE FOLLOWING MORNING ON AN IFR FLT PLAN TO POC, AND WAS INITIALLY CLRED TO 2000' ON A 310 DEG HDG. AFTER SWITCHING FROM TWR TO DEP, THE CTLR CONFIRMED RECEIVING MY XPONDER AND DIDN'T NOTE ANY PROBLEMS. I LEVELED OFF AT 2000', AND SHORTLY THEREAFTER, THE CTLR SAID I SHOULD BE LOWER, BUT I CONFIRMED I WAS AT THE ASSIGNED ALT AND ALTIMETER SETTING. ACCORDING TO THEIR SCOPES, APPARENTLY I WAS OUT OF LIMITS ON ALT CLRNC. I WAS DIRECTED TO MAKE AN IMMEDIATE TURN TO AVOID THE TFC, WHICH WAS SMA Y AT 2500' MSL. I HAD NO VISUAL CONTACT WITH THE ACFT. ATC SAID SMA Y WAS INDICATING 2500', I.E., ITS XPONDER RETURN. GIVEN THE PROBLEMS WITH MY XPONDER, AND THE POTENTIAL ERRORS IN OTHER ACFT XPONDERS AND ATC RADAR EQUIPMENT, I AM CONCERNED THAT ATC WOULD PUT ME ON A CONVERGING HDG WITH TFC AND ONLY A 500' CUSHION. WHAT I AM SUGGESTING IS THAT EVEN WITH THE 500' ALT DIFFERENCE, CONVERGING ACFT SHOULD ALSO BE GIVEN LATERAL SEPARATION OF AT LEAST 2000'. I'VE TRIED TO REMEDY MY SITUATION BY SQUAWKING THE ACFT'S XPONDER.

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.