Narrative:

VFR small aircraft X requested TCA clearance at 5500. Was issued clearance and reported level at 5500. IFR small transport Y was level at 60. VFR small aircraft X climbed without advising ATC, apparently to maintain clear of clouds. Climb was made in such close proximity to radar antenna that mode C was lost on radar. IFR small transport X reported near midair with VFR that was at his altitude. Traffic had been issued to both aircraft several mins prior to incident. IFR small transport Y reported sighting small aircraft X just seconds before overtaking him. The situation could have been avoided if the VFR pilot had advised he was going to need a climb to maintain VFR. Supplemental information from acn 196019: traffic was issued and acknowledged. Over the atl VOR the aircraft merged. Small transport Y requested a verification of small aircraft X altitude. Small aircraft X replied he was at 6000 to remain VFR. Small transport Y said he was at 6100 and had only 1 second to avoid the small aircraft X. It appears small aircraft X was predisposed to comply with FARS for VFR flight, but he seemed to disregard the FARS for operating VFR while in the TCA.

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Original NASA ASRS Text

Title: SMA X NON ADHERENCE TO ATC CLRNC IN TCA UNAUTHORIZED CLB TO OCCUPIED ALT HAD LTSS FROM SMT Y. PLTDEV.

Narrative: VFR SMA X REQUESTED TCA CLRNC AT 5500. WAS ISSUED CLRNC AND RPTED LEVEL AT 5500. IFR SMT Y WAS LEVEL AT 60. VFR SMA X CLBED WITHOUT ADVISING ATC, APPARENTLY TO MAINTAIN CLR OF CLOUDS. CLB WAS MADE IN SUCH CLOSE PROX TO RADAR ANTENNA THAT MODE C WAS LOST ON RADAR. IFR SMT X RPTED NEAR MIDAIR WITH VFR THAT WAS AT HIS ALT. TFC HAD BEEN ISSUED TO BOTH ACFT SEVERAL MINS PRIOR TO INCIDENT. IFR SMT Y RPTED SIGHTING SMA X JUST SECONDS BEFORE OVERTAKING HIM. THE SITUATION COULD HAVE BEEN AVOIDED IF THE VFR PLT HAD ADVISED HE WAS GOING TO NEED A CLB TO MAINTAIN VFR. SUPPLEMENTAL INFO FROM ACN 196019: TFC WAS ISSUED AND ACKNOWLEDGED. OVER THE ATL VOR THE ACFT MERGED. SMT Y REQUESTED A VERIFICATION OF SMA X ALT. SMA X REPLIED HE WAS AT 6000 TO REMAIN VFR. SMT Y SAID HE WAS AT 6100 AND HAD ONLY 1 SECOND TO AVOID THE SMA X. IT APPEARS SMA X WAS PREDISPOSED TO COMPLY WITH FARS FOR VFR FLT, BUT HE SEEMED TO DISREGARD THE FARS FOR OPERATING VFR WHILE IN THE TCA.

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.