Less than standard separation between GA-small aircraft and corp jet. Operational error.

Attributes
ACN	85782
Time
Date	198804
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dtw airport : yip
State Reference	MI
Altitude	msl bound lower : 6000 msl bound upper : 6500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Retractable Gear
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller non radar : 2 controller radar : 5
ASRS Report	85782
Person 2
Function	flight crew : single pilot
Qualification	pilot : instrument
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Small aircraft X was eastbound at 6000' corp Y was nwbnd 7000'. Y said he had willow run airport in sight several times. I, being the controller working the 2 aircraft, told corp Y, 'roger, maintain 6000'.' slip of the tongue. Y readback, 'roger, 6000,' was not caught by me. After I switched Y to another frequency, I noticed him leaving 6900'. I checked my frequency, but he wasn't there and the other controller wasn't talking to him yet either. I gave aircraft X traffic and he had corp Y in sight. I just misspoke myself by saying maintain 6000' instead of 7000'. The radar scope was being used by 2 controllers, one working north traffic, one working south traffic. So, the map display is very small and hard to judge distance. The ARTS system has had a history of coasting when aircraft are at level flight. This coasting blocks out their mode C readout, which happened in this case.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN GA-SMA AND CORP JET. OPERATIONAL ERROR.

Narrative: SMA X WAS EBND AT 6000' CORP Y WAS NWBND 7000'. Y SAID HE HAD WILLOW RUN ARPT IN SIGHT SEVERAL TIMES. I, BEING THE CTLR WORKING THE 2 ACFT, TOLD CORP Y, 'ROGER, MAINTAIN 6000'.' SLIP OF THE TONGUE. Y READBACK, 'ROGER, 6000,' WAS NOT CAUGHT BY ME. AFTER I SWITCHED Y TO ANOTHER FREQ, I NOTICED HIM LEAVING 6900'. I CHKED MY FREQ, BUT HE WASN'T THERE AND THE OTHER CTLR WASN'T TALKING TO HIM YET EITHER. I GAVE ACFT X TFC AND HE HAD CORP Y IN SIGHT. I JUST MISSPOKE MYSELF BY SAYING MAINTAIN 6000' INSTEAD OF 7000'. THE RADAR SCOPE WAS BEING USED BY 2 CTLRS, ONE WORKING N TFC, ONE WORKING S TFC. SO, THE MAP DISPLAY IS VERY SMALL AND HARD TO JUDGE DISTANCE. THE ARTS SYS HAS HAD A HISTORY OF COASTING WHEN ACFT ARE AT LEVEL FLT. THIS COASTING BLOCKS OUT THEIR MODE C READOUT, WHICH HAPPENED IN THIS CASE.

Data retrieved from NASA's ASRS site as of August 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.