ZTL controller described near midair collision event when IFR traffic level at FL240 climbed into IFR crossover traffic level at FL250; climbing traffic alleging aircraft pitch problems.

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Attributes
ACN	812717
Time
Date	200811
Place
Locale Reference	navaid : clt.vortac
State Reference	NC
Altitude	msl bound lower : 24000 msl bound upper : 25000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	general aviation : corporate
Make Model Name	Beechjet 400
Operating Under FAR Part	Part 91
Flight Phase	climbout : vacating altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	EMB ERJ 145 ER&LR
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller military : 4 controller non radar : 20 controller radar : 20
ASRS Report	812717
Events
Anomaly	conflict : nmac
Independent Detector	atc equipment : conflict alert aircraft equipment : tcas other controllera
Resolutory Action	controller : issued alert controller : issued new clearance flight crew : took evasive action
Miss Distance	horizontal : 0 vertical : 200
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Ambiguous

Narrative:

I was working a high altitude sector 43 ZTL. Aircraft X was level at FL240 awaiting climb until passing traffic. Air carrier Y was level at FL250 crossing traffic in level flight. Aircraft X started a climb on its own into air carrier Y. I called to confirm level and pilot stated level. The aircraft still indicated climb so I questioned aircraft X again; he stated standby. I immediately issued a traffic alert. Aircraft X reported traffic in sight and started descending back to FL240. The E145 responded to a TCAS alert and climbed to FL255. The pilot of the BE40 reported he had a pitch problem and said he was going to put the aircraft in service as soon as he landed. The falcon replay at ZTL showed 200 ft vertical and merging lateral. My only question is; were there 2 pilots in the aircraft. Why didn't the pilot recognize he was climbing; and if I didn't notice the climb in a timely manner could a possible collision have occurred.

Original NASA ASRS Text

Title: ZTL CONTROLLER DESCRIBED NMAC EVENT WHEN IFR TRAFFIC LEVEL AT FL240 CLIMBED INTO IFR CROSSOVER TRAFFIC LEVEL AT FL250; CLIMBING TRAFFIC ALLEGING AIRCRAFT PITCH PROBLEMS.

Narrative: I WAS WORKING A HIGH ALT SECTOR 43 ZTL. ACFT X WAS LEVEL AT FL240 AWAITING CLB UNTIL PASSING TFC. ACR Y WAS LEVEL AT FL250 XING TFC IN LEVEL FLT. ACFT X STARTED A CLB ON ITS OWN INTO ACR Y. I CALLED TO CONFIRM LEVEL AND PLT STATED LEVEL. THE ACFT STILL INDICATED CLB SO I QUESTIONED ACFT X AGAIN; HE STATED STANDBY. I IMMEDIATELY ISSUED A TFC ALERT. ACFT X RPTED TFC IN SIGHT AND STARTED DSNDING BACK TO FL240. THE E145 RESPONDED TO A TCAS ALERT AND CLBED TO FL255. THE PLT OF THE BE40 RPTED HE HAD A PITCH PROB AND SAID HE WAS GOING TO PUT THE ACFT IN SVC AS SOON AS HE LANDED. THE FALCON REPLAY AT ZTL SHOWED 200 FT VERT AND MERGING LATERAL. MY ONLY QUESTION IS; WERE THERE 2 PLTS IN THE ACFT. WHY DIDN'T THE PLT RECOGNIZE HE WAS CLBING; AND IF I DIDN'T NOTICE THE CLB IN A TIMELY MANNER COULD A POSSIBLE COLLISION HAVE OCCURRED.

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.