Atx X had less than standard separation from air carrier Y. System error.

Attributes
ACN	132559
Time
Date	199001
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : ftz
State Reference	MO
Altitude	msl bound lower : 8700 msl bound upper : 9000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zkc
Operator	common carrier : air taxi
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 17
ASRS Report	132559
Person 2
Affiliation	company : air taxi
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Miss Distance	horizontal : 27000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I cleared atx X to cross 20 west ftz at 8000. Some mins later I cleared atx X to descend and maintain 9000. According to the tape the pilot read back, 'roger, descend right on down to 9000 and cross 20 out at 8'. All I heard on the readback was descend to 9000. Callback conversation with reporter revealed the following: reporter was vectoring atx X for spacing behind air carrier Y. He had issued a clearance to atx X to descend to cross 20 west ftz at and maintain 8000. He then instructed atx X to descend and maintain 9000. Reporter observed atx X leaving 8700, conflict alert activated, and he instructed atx X to climb back to 9000.

Original NASA ASRS Text

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

Narrative: I CLRED ATX X TO CROSS 20 W FTZ AT 8000. SOME MINS LATER I CLRED ATX X TO DSND AND MAINTAIN 9000. ACCORDING TO THE TAPE THE PLT READ BACK, 'ROGER, DSND RIGHT ON DOWN TO 9000 AND CROSS 20 OUT AT 8'. ALL I HEARD ON THE READBACK WAS DSND TO 9000. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: REPORTER WAS VECTORING ATX X FOR SPACING BEHIND ACR Y. HE HAD ISSUED A CLRNC TO ATX X TO DSND TO CROSS 20 W FTZ AT AND MAINTAIN 8000. HE THEN INSTRUCTED ATX X TO DSND AND MAINTAIN 9000. REPORTER OBSERVED ATX X LEAVING 8700, CONFLICT ALERT ACTIVATED, AND HE INSTRUCTED ATX X TO CLIMB BACK TO 9000.

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.