Air carrier B737-300 given descent clearance by one sector and then handed off to reporter. Reporter saw unknown traffic below the air carrier and tried to stop his descent. Took reporter 3 calls to stop air carrier who stated he saw the traffic below, however separation had already been lost.

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Attributes
ACN	331809
Time
Date	199603
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dvv
State Reference	CO
Altitude	msl bound lower : 32200 msl bound upper : 33000
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 15
ASRS Report	331809
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 1200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X was given descent clearance with unknown traffic Y below. Could have been avoided if proper coordination at ZDV was used. Also pilot of air carrier X reported lower traffic in sight on previous frequency and should have questioned descent clearance. Also pilot was called 3 times to maintain an altitude and did not respond. The frequency was not busy at the time, pilot just having good time.

Original NASA ASRS Text

Title: ACR B737-300 GIVEN DSCNT CLRNC BY ONE SECTOR AND THEN HANDED OFF TO RPTR. RPTR SAW UNKNOWN TFC BELOW THE ACR AND TRIED TO STOP HIS DSCNT. TOOK RPTR 3 CALLS TO STOP ACR WHO STATED HE SAW THE TFC BELOW, HOWEVER SEPARATION HAD ALREADY BEEN LOST.

Narrative: ACR X WAS GIVEN DSCNT CLRNC WITH UNKNOWN TFC Y BELOW. COULD HAVE BEEN AVOIDED IF PROPER COORD AT ZDV WAS USED. ALSO PLT OF ACR X RPTED LOWER TFC IN SIGHT ON PREVIOUS FREQ AND SHOULD HAVE QUESTIONED DSCNT CLRNC. ALSO PLT WAS CALLED 3 TIMES TO MAINTAIN AN ALT AND DID NOT RESPOND. THE FREQ WAS NOT BUSY AT THE TIME, PLT JUST HAVING GOOD TIME.

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.