Fgt flight replied to clearance to small aircraft. Aircraft descended and had less than standard separation with small aircraft. Controller missed incorrect readback.

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Attributes
ACN	168223
Time
Date	199101
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : hec
State Reference	CA
Altitude	msl bound lower : 14000 msl bound upper : 14100
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other descent other
Route In Use	enroute airway : zla
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Fighter
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 2 controller radar : 6
ASRS Report	168223
Person 2
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence : clearance non adherence : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	other
Consequence	faa : investigated
Miss Distance	horizontal : 9000 vertical : 100
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Pilot Deviation Operational Error

Narrative:

I was working sector 19 between the time of xa:40 UTC-xb:25 UTC. At approximately xb:19:40 I issued descent clearance to small aircraft X from 14000' to 12000' with the ontario altimeter 3011. I heard a readback of 'ontario 3011 descend to 12000'.' at this time fgt Y (flight of two) at 16000' was 2 1/2 mi behind small aircraft X with no mode C being reported. At approximately xb:20 I noticed fgt Y altitude show 14000' and was 1 1/2 mi to the east of small aircraft X. I asked fgt Y his altitude and he stated he was out of 14000' to 12000' with the traffic in sight. I then asked fgt Y where he received clearance to 12000' and there was no reply. When listening to the tapes of this incident, fgt Y does readback clearance that was issued to small aircraft X, but as required there is no call sign in the readback, but just the 'ontario altimeter and out of 16000' to 12000'. This error was processed as an operational error since I did not catch the readback stating out of '16000' to 12000',' but there is also a pilot deviation being filed on fgt Y for accepting and executing a clearance meant for another aircraft.

Original NASA ASRS Text

Title: FGT FLT REPLIED TO CLRNC TO SMA. ACFT DESCENDED AND HAD LESS THAN STANDARD SEPARATION WITH SMA. CTLR MISSED INCORRECT READBACK.

Narrative: I WAS WORKING SECTOR 19 BTWN THE TIME OF XA:40 UTC-XB:25 UTC. AT APPROX XB:19:40 I ISSUED DSNT CLRNC TO SMA X FROM 14000' TO 12000' WITH THE ONTARIO ALTIMETER 3011. I HEARD A READBACK OF 'ONTARIO 3011 DSND TO 12000'.' AT THIS TIME FGT Y (FLT OF TWO) AT 16000' WAS 2 1/2 MI BEHIND SMA X WITH NO MODE C BEING RPTED. AT APPROX XB:20 I NOTICED FGT Y ALT SHOW 14000' AND WAS 1 1/2 MI TO THE E OF SMA X. I ASKED FGT Y HIS ALT AND HE STATED HE WAS OUT OF 14000' TO 12000' WITH THE TFC IN SIGHT. I THEN ASKED FGT Y WHERE HE RECEIVED CLRNC TO 12000' AND THERE WAS NO REPLY. WHEN LISTENING TO THE TAPES OF THIS INCIDENT, FGT Y DOES READBACK CLRNC THAT WAS ISSUED TO SMA X, BUT AS REQUIRED THERE IS NO CALL SIGN IN THE READBACK, BUT JUST THE 'ONTARIO ALTIMETER AND OUT OF 16000' TO 12000'. THIS ERROR WAS PROCESSED AS AN OPERATIONAL ERROR SINCE I DID NOT CATCH THE READBACK STATING OUT OF '16000' TO 12000',' BUT THERE IS ALSO A PLT DEV BEING FILED ON FGT Y FOR ACCEPTING AND EXECUTING A CLRNC MEANT FOR ANOTHER ACFT.

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.