Cpr Y descent to occupied altitude had less than standard separation from cpr X. System error.

Attributes
ACN	247024
Time
Date	199307
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ewo
State Reference	KY
Altitude	msl bound lower : 10000 msl bound upper : 10000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct enroute airway : zid
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 12
ASRS Report	247024
Person 2
Affiliation	Other
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
Resolutory Action	none taken : anomaly accepted
Consequence	faa : investigated
Miss Distance	horizontal : 24000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Operational error was at the ewo lo sector. About 5 aircraft on frequency with 8 data blocks on scope. Traffic was decreasing. I was operating on a 75 mi scope. This is a smaller range than the other sectors operate in the area. Thus, 5 mi looks much larger on the 750 mi range than the 100 mi range. Cpr X was swbound at 1000 ft proceeding from over ewo-pah landing. Cpr Y was nebound from about bwg. Ewo-iiu-sdf at 11000 ft. A jet was following cpr Y by 20-25 mi and was also landing sdf. I cleared the jet to descent to 11000. I then cleared cpr Y to descend to 10000. I felt that I had 5 mi at the time of clearance and that it would not decrease. After the descent clearance, I called sdf approach to appreq 10000 for cpr Y per LOA. As sdf approach answered, the adep alarm sounded. At that point I looked at cpr X and assumed that it was set off because of cpr Y and cpr X. I told cpr Y to climb and maintain 11000. However, I re-evaluated the situation and decided that there was no reason for cpr Y to climb. I reclred cpr Y to 10000.

Original NASA ASRS Text

Title: CPR Y DSCNT TO OCCUPIED ALT HAD LTSS FROM CPR X. SYS ERROR.

Narrative: OPERROR WAS AT THE EWO LO SECTOR. ABOUT 5 ACFT ON FREQ WITH 8 DATA BLOCKS ON SCOPE. TFC WAS DECREASING. I WAS OPERATING ON A 75 MI SCOPE. THIS IS A SMALLER RANGE THAN THE OTHER SECTORS OPERATE IN THE AREA. THUS, 5 MI LOOKS MUCH LARGER ON THE 750 MI RANGE THAN THE 100 MI RANGE. CPR X WAS SWBOUND AT 1000 FT PROCEEDING FROM OVER EWO-PAH LNDG. CPR Y WAS NEBOUND FROM ABOUT BWG. EWO-IIU-SDF AT 11000 FT. A JET WAS FOLLOWING CPR Y BY 20-25 MI AND WAS ALSO LNDG SDF. I CLRED THE JET TO DSCNT TO 11000. I THEN CLRED CPR Y TO DSND TO 10000. I FELT THAT I HAD 5 MI AT THE TIME OF CLRNC AND THAT IT WOULD NOT DECREASE. AFTER THE DSCNT CLRNC, I CALLED SDF APCH TO APPREQ 10000 FOR CPR Y PER LOA. AS SDF APCH ANSWERED, THE ADEP ALARM SOUNDED. AT THAT POINT I LOOKED AT CPR X AND ASSUMED THAT IT WAS SET OFF BECAUSE OF CPR Y AND CPR X. I TOLD CPR Y TO CLB AND MAINTAIN 11000. HOWEVER, I RE-EVALUATED THE SIT AND DECIDED THAT THERE WAS NO REASON FOR CPR Y TO CLB. I RECLRED CPR Y TO 10000.

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.