Narrative:

Working clthi sector ZTL (FL240-FL340); I accepted handoff on aircraft #2 eastbound at FL250. I accepted handoff on aircraft #1 northbound departure from clt climbing to FL230. I climbed aircraft #2 to FL240. As aircraft #2 leveled FL240; I issued traffic to both aircraft. Both aircraft advised 'traffic in sight.' both aircraft were near sector boundary; I coordinated with next sector; 'aircraft #2 has aircraft #1 in sight; your control to climb aircraft #1 reference aircraft #2.' I xferred communications of aircraft #2 to the next sector. Moments later I notice aircraft #2's mode C readout at FL243. I call the next sector to advise. The controller says the pilot is reporting a pitch problem as the mode C indicates FL246 while aircraft #1 is announcing a climb in response to an RA. The targets merged on the scope. Aircraft #1 returned to FL250 and asked what happened. I told him the other pilot reported a pitch problem. I was not removed from the sector as is customary (and mandatory) when an incident occurs that is controller error. I was visibly shaken having seen the proximity of the 2 aircraft and I requested a break from the sector.

Related reports:

Google
 

Original NASA ASRS Text

Title: ZTL CONTROLLER DESCRIBED LOSS OF SEPARATION EVENT NEAR FL250; CAUSED WHEN ONE AIRCRAFT LOST PITCH CONTROL; CLIMBED; RESULTING IN TCAS RA EVENT.

Narrative: WORKING CLTHI SECTOR ZTL (FL240-FL340); I ACCEPTED HDOF ON ACFT #2 EBOUND AT FL250. I ACCEPTED HDOF ON ACFT #1 NBOUND DEP FROM CLT CLBING TO FL230. I CLBED ACFT #2 TO FL240. AS ACFT #2 LEVELED FL240; I ISSUED TFC TO BOTH ACFT. BOTH ACFT ADVISED 'TFC IN SIGHT.' BOTH ACFT WERE NEAR SECTOR BOUNDARY; I COORDINATED WITH NEXT SECTOR; 'ACFT #2 HAS ACFT #1 IN SIGHT; YOUR CTL TO CLB ACFT #1 REF ACFT #2.' I XFERRED COMS OF ACFT #2 TO THE NEXT SECTOR. MOMENTS LATER I NOTICE ACFT #2'S MODE C READOUT AT FL243. I CALL THE NEXT SECTOR TO ADVISE. THE CTLR SAYS THE PLT IS RPTING A PITCH PROB AS THE MODE C INDICATES FL246 WHILE ACFT #1 IS ANNOUNCING A CLB IN RESPONSE TO AN RA. THE TARGETS MERGED ON THE SCOPE. ACFT #1 RETURNED TO FL250 AND ASKED WHAT HAPPENED. I TOLD HIM THE OTHER PLT RPTED A PITCH PROB. I WAS NOT REMOVED FROM THE SECTOR AS IS CUSTOMARY (AND MANDATORY) WHEN AN INCIDENT OCCURS THAT IS CTLR ERROR. I WAS VISIBLY SHAKEN HAVING SEEN THE PROX OF THE 2 ACFT AND I REQUESTED A BREAK FROM THE SECTOR.

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.