Air carrier X had less than standard separation from small aircraft Y. System error.

Attributes
ACN	181292
Time
Date	199106
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : mcn
State Reference	GA
Altitude	msl bound lower : 9000 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : mcn
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 2 Eng, Retractable Gear
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 270 flight time total : 9000 flight time type : 4000
ASRS Report	181292
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew faa : investigated
Miss Distance	horizontal : 12000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error
Situations
ATC Facility	procedure or policy : unspecified

Narrative:

Air carrier X inbound to atl at 10000' on vectors for intrail sep by mcn approach control. Crossing mcn 340 degree right (V323) northwest mcn cleared direct naliz intersection to cross at 8000' (naliz mcn 340 degree right/30 NM). Transitioned to descent, passing 9500' another controller changed clearance to climb and maintain 10000'. We started our climb and I verified the clearance. It was repeated as climb immediately to 10000', which we were doing. After a pause, I requested a traffic advisory which was then issued (reluctantly?). We observed a light twin, assigned 9000', pass at 1 O'clock and approximately 1 mi. Nothing further was said. Controller admitted that the other aircraft was known traffic. Upon investigation by my flight control, mcn approach control admitted the system error which they said was caused by a trnee which was working the traffic on that frequency.

Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM SMA Y. SYSTEM ERROR.

Narrative: ACR X INBND TO ATL AT 10000' ON VECTORS FOR INTRAIL SEP BY MCN APCH CTL. XING MCN 340 DEG R (V323) NW MCN CLRED DIRECT NALIZ INTXN TO CROSS AT 8000' (NALIZ MCN 340 DEG R/30 NM). TRANSITIONED TO DSNT, PASSING 9500' ANOTHER CTLR CHANGED CLRNC TO CLB AND MAINTAIN 10000'. WE STARTED OUR CLB AND I VERIFIED THE CLRNC. IT WAS REPEATED AS CLB IMMEDIATELY TO 10000', WHICH WE WERE DOING. AFTER A PAUSE, I REQUESTED A TFC ADVISORY WHICH WAS THEN ISSUED (RELUCTANTLY?). WE OBSERVED A LIGHT TWIN, ASSIGNED 9000', PASS AT 1 O'CLOCK AND APPROX 1 MI. NOTHING FURTHER WAS SAID. CTLR ADMITTED THAT THE OTHER ACFT WAS KNOWN TFC. UPON INVESTIGATION BY MY FLT CTL, MCN APCH CTL ADMITTED THE SYS ERROR WHICH THEY SAID WAS CAUSED BY A TRNEE WHICH WAS WORKING THE TFC ON THAT FREQ.

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.