ZMA controller experienced operational error at 3000 ft when incomplete readback was not recognized.

Attributes
ACN	682820
Time
Date	200601
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : vrb.airport
State Reference	FL
Altitude	msl single value : 3000
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zma.artcc tower : zzz.tower
Operator	general aviation : corporate
Make Model Name	Citation Excel
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zma.artcc
Operator	general aviation : corporate
Make Model Name	BAe 125 Series 800
Operating Under FAR Part	Part 91
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 22 controller time certified in position1 : 3
ASRS Report	682820
Person 2
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera
Resolutory Action	controller : issued alert controller : issued new clearance flight crew : took evasive action
Consequence	faa : investigated
Miss Distance	horizontal : 9960 vertical : 600
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I issued aircraft Y an approach clearance. When he did not read it back; I sought confirmation of the clearance from the pilot. He acknowledged the clearance but never began the descent. I took evasive action with aircraft X to maintain separation. Upon reviewing the tapes; it became apparent that aircraft Y never read back the descent portion of the clearance.

Original NASA ASRS Text

Title: ZMA CTLR EXPERIENCED OPERROR AT 3000 FT WHEN INCOMPLETE READBACK WAS NOT RECOGNIZED.

Narrative: I ISSUED ACFT Y AN APCH CLRNC. WHEN HE DID NOT READ IT BACK; I SOUGHT CONFIRMATION OF THE CLRNC FROM THE PLT. HE ACKNOWLEDGED THE CLRNC BUT NEVER BEGAN THE DSCNT. I TOOK EVASIVE ACTION WITH ACFT X TO MAINTAIN SEPARATION. UPON REVIEWING THE TAPES; IT BECAME APPARENT THAT ACFT Y NEVER READ BACK THE DSCNT PORTION OF THE CLRNC.

Data retrieved from NASA's ASRS site as of January 2009 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.