Narrative:

Air carrier X, an MD80, was a departure off of stl en route to sat. I climbed the aircraft to FL310, where they leveled for a few mins. Mode C readout showed FL310. I then climbed the aircraft to FL330 and heard the pilot read back FL330. I entered a temporary altitude in the data block of FL330. I placed a 'halo' on the FL350 traffic (air carrier Y) to facilitate the climbing of air carrier X to their requested altitude of FL350, once lateral separation was ensured. I observed air carrier X data block readout of FL332 and attributed it to being within +/-300 ft. Once I observed a mode C readout of FL334, I asked the pilot to verify level at FL330. He responded 'we thought we were given FL350.' I replied, 'negative, your clearance was FL330, descend and maintain FL330, traffic 12 O'clock, 1 1/2 mi at FL350.' he responded 'roger, leveling at FL330.' his data block showed FL339 at this time, then FL336, then FL331. The traffic management supervisor interviewed the pilot via phone, rptedly asked the pilot if he ever left FL330, and supposedly the pilot said no, that possibly they had a mode C problem. The traffic management supervisor determined it was a non occurrence and no pilot deviation was filed.

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Original NASA ASRS Text

Title: ZKC CTLR CLBS AN MD80 FROM FL310 TO FL330. CTLR OBSERVES ACFT'S MODE C CLB CRESTING AT FL339, ISSUING CONFLICTING TFC AT FL350. PLT CALLS FACILITY STATING HE DID NOT REACH CONFLICT ALERT POSTED ALT. NO PLTDEV FILED.

Narrative: ACR X, AN MD80, WAS A DEP OFF OF STL ENRTE TO SAT. I CLBED THE ACFT TO FL310, WHERE THEY LEVELED FOR A FEW MINS. MODE C READOUT SHOWED FL310. I THEN CLBED THE ACFT TO FL330 AND HEARD THE PLT READ BACK FL330. I ENTERED A TEMPORARY ALT IN THE DATA BLOCK OF FL330. I PLACED A 'HALO' ON THE FL350 TFC (ACR Y) TO FACILITATE THE CLBING OF ACR X TO THEIR REQUESTED ALT OF FL350, ONCE LATERAL SEPARATION WAS ENSURED. I OBSERVED ACR X DATA BLOCK READOUT OF FL332 AND ATTRIBUTED IT TO BEING WITHIN +/-300 FT. ONCE I OBSERVED A MODE C READOUT OF FL334, I ASKED THE PLT TO VERIFY LEVEL AT FL330. HE RESPONDED 'WE THOUGHT WE WERE GIVEN FL350.' I REPLIED, 'NEGATIVE, YOUR CLRNC WAS FL330, DSND AND MAINTAIN FL330, TFC 12 O'CLOCK, 1 1/2 MI AT FL350.' HE RESPONDED 'ROGER, LEVELING AT FL330.' HIS DATA BLOCK SHOWED FL339 AT THIS TIME, THEN FL336, THEN FL331. THE TFC MGMNT SUPVR INTERVIEWED THE PLT VIA PHONE, RPTEDLY ASKED THE PLT IF HE EVER LEFT FL330, AND SUPPOSEDLY THE PLT SAID NO, THAT POSSIBLY THEY HAD A MODE C PROB. THE TFC MGMNT SUPVR DETERMINED IT WAS A NON OCCURRENCE AND NO PLTDEV WAS FILED.

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.