Air carrier X TCASII RA with VFR aircraft 500 ft below.

Attributes
ACN	247003
Time
Date	199303
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 8
ASRS Report	247003
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : private
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Traffic was issued 3 times to air carrier X on the VFR at 10500 ft. Verified altitude being worked by another position. On the 3RD traffic call, air carrier X advised he was descending back to 11000 ft after responding to RA. There was a clearance deviation by the aircraft of 600 ft. Communication was after the maneuver had been accomplished. There was no reason for the aircraft to climb. The traffic was at a verified altitude and in no way was a factor.

Original NASA ASRS Text

Title: ACR X TCASII RA WITH VFR ACFT 500 FT BELOW.

Narrative: TFC WAS ISSUED 3 TIMES TO ACR X ON THE VFR AT 10500 FT. VERIFIED ALT BEING WORKED BY ANOTHER POS. ON THE 3RD TFC CALL, ACR X ADVISED HE WAS DSNDING BACK TO 11000 FT AFTER RESPONDING TO RA. THERE WAS A CLRNC DEV BY THE ACFT OF 600 FT. COM WAS AFTER THE MANEUVER HAD BEEN ACCOMPLISHED. THERE WAS NO REASON FOR THE ACFT TO CLB. THE TFC WAS AT A VERIFIED ALT AND IN NO WAY WAS A FACTOR.

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.