Narrative:

During cruise flight as an altitude in the mfd 20's (FL200-FL290). I was in level flight when a B737 cruising 2000 ft above me stated he was executing an evasive pull-up for a TCASII warning he had received about my aircraft. Then, seconds later, he told center that if we were 2000 ft apart again. I did not change altitude. Then with the next controller, we were given a climb to FL330. When I leveled at FL330, the ATC controller said he had me at FL337 and climbing. My copilot said we are level at FL330. The controller questioned our altitude again, and my copilot said we are descending. What he meant was we were 150 ft high and correcting are altitude to level at FL330. Shortly after this happened, I switched to our secondary transponder and no other problems occurred with our altitude reporting, because there was an airbus cruising at FL350 within 3 NM of our position. ZKC is investigating this incident. Later that day, on a different leg on ZFW, I switched back to our primary transponder. They said it was working good. When this loss of radar separation occurred with ZKC, my aircraft was not more than 150 ft off altitude, and that was only for the level off. Either the center radar had a problem or my primary transponder was reporting mode C incorrectly. Either way, actual physical loss of separation between my aircraft (lear jet 25) and the airbus cruising at FL350 above us was never lost. Callback conversation with reporter revealed the following information: reporter was unsure who's equipment problem it was. Controller supervisor advised that they were 'looking into the event.' reporter has not been advised of any further resolution from ATC.

Related reports:

Google
 

Original NASA ASRS Text

Title: LJ25 FLC ADVISED BY PLT AN ATC THAT A B737, THEN AN AIRBUS HAD INITIATED A TCASII MANEUVER DUE TO A MODE C READOUT. AFTER CHANGING XPONDERS TWICE, NO ADDITIONAL BAD HITS WERE OBSERVED.

Narrative: DURING CRUISE FLT AS AN ALT IN THE MFD 20'S (FL200-FL290). I WAS IN LEVEL FLT WHEN A B737 CRUISING 2000 FT ABOVE ME STATED HE WAS EXECUTING AN EVASIVE PULL-UP FOR A TCASII WARNING HE HAD RECEIVED ABOUT MY ACFT. THEN, SECONDS LATER, HE TOLD CTR THAT IF WE WERE 2000 FT APART AGAIN. I DID NOT CHANGE ALT. THEN WITH THE NEXT CTLR, WE WERE GIVEN A CLB TO FL330. WHEN I LEVELED AT FL330, THE ATC CTLR SAID HE HAD ME AT FL337 AND CLBING. MY COPLT SAID WE ARE LEVEL AT FL330. THE CTLR QUESTIONED OUR ALT AGAIN, AND MY COPLT SAID WE ARE DSNDING. WHAT HE MEANT WAS WE WERE 150 FT HIGH AND CORRECTING ARE ALT TO LEVEL AT FL330. SHORTLY AFTER THIS HAPPENED, I SWITCHED TO OUR SECONDARY XPONDER AND NO OTHER PROBS OCCURRED WITH OUR ALT RPTING, BECAUSE THERE WAS AN AIRBUS CRUISING AT FL350 WITHIN 3 NM OF OUR POS. ZKC IS INVESTIGATING THIS INCIDENT. LATER THAT DAY, ON A DIFFERENT LEG ON ZFW, I SWITCHED BACK TO OUR PRIMARY XPONDER. THEY SAID IT WAS WORKING GOOD. WHEN THIS LOSS OF RADAR SEPARATION OCCURRED WITH ZKC, MY ACFT WAS NOT MORE THAN 150 FT OFF ALT, AND THAT WAS ONLY FOR THE LEVEL OFF. EITHER THE CTR RADAR HAD A PROB OR MY PRIMARY XPONDER WAS RPTING MODE C INCORRECTLY. EITHER WAY, ACTUAL PHYSICAL LOSS OF SEPARATION BTWN MY ACFT (LEAR JET 25) AND THE AIRBUS CRUISING AT FL350 ABOVE US WAS NEVER LOST. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS UNSURE WHO'S EQUIP PROB IT WAS. CTLR SUPVR ADVISED THAT THEY WERE 'LOOKING INTO THE EVENT.' RPTR HAS NOT BEEN ADVISED OF ANY FURTHER RESOLUTION FROM ATC.

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.