Controller descended air carrier X to occupied altitude had less than standard separation from air c...

Attributes
ACN	234525
Time
Date	199302
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lou
State Reference	KY
Altitude	msl bound lower : 26000 msl bound upper : 26000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 7 controller radar : 5
ASRS Report	234525
Person 2
Affiliation	government : faa
Function	controller : flight data
Qualification	controller : radar
Experience	controller radar : 2
ASRS Report	235548
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	faa : investigated
Miss Distance	horizontal : 24000 vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier Y on frequency northbound FL260 approximately 40 mi northwest lou. Air carrier X checked on frequency approximately 55 mi northwest lou descending FL280, eastbound. I intended to clear air carrier X to FL270 but inadvertently cleared air carrier X to FL260. Traffic was issued to air carrier X with no reply. I again issued traffic to air carrier X with a clearance to maintain FL270 with no reply again. Air carrier Y advised they were descending due to an RA on TCASII. I cleared air carrier X to climb and maintain FL270 and again no reply, however, air carrier X executed an immediate climb to FL270. At this point, separation is lost. At the time of this incident, I believed this to be a mode 'C' swap because the targets merged and air carrier X rapid mode C change with no reply, as well as TCASII RA. Why didn't air carrier X question his clearance to FL260 after being told his traffic is at FL260. Why didn't air carrier X answer the 3 clearance that could have potentially avoided this problem. Supplemental information from acn 235548: the radar controller issued traffic to air carrier X again saying the traffic was 'at FL260 maintain FL270.' again, the air carrier X did not respond. When conflict alert activated, the radar controller told air carrier X to climb and maintain FL270. Still, air carrier X did not respond. Supplemental information from acn 234545: air carrier X on ZID cleared from FL280 to FL260, copilot read back clearance to descend to FL260. While descending through FL270, a TCASII warning TA then immediately to RA was presented at about the same time controller told us to climb to FL270. We immediately initiated climb to FL270. Conflict was with air carrier Y who was at FL260. This aircraft was passing at approximately right angles to our flight path. They also received a TCASII warning and descended. After conflict was resolved, we asked the controller what the problem had been. He responded, 'no problem, no big deal, switch to frequency.'

Original NASA ASRS Text

Title: CTLR DSNDED ACR X TO OCCUPIED ALT HAD LTSS FROM ACR Y. SYS ERROR. ACR X TCASII TA RA CLB. ACR Y TCASII RA DSND. EVASIVE ACTION TAKEN.

Narrative: ACR Y ON FREQ NBOUND FL260 APPROX 40 MI NW LOU. ACR X CHKED ON FREQ APPROX 55 MI NW LOU DSNDING FL280, EBOUND. I INTENDED TO CLR ACR X TO FL270 BUT INADVERTENTLY CLRED ACR X TO FL260. TFC WAS ISSUED TO ACR X WITH NO REPLY. I AGAIN ISSUED TFC TO ACR X WITH A CLRNC TO MAINTAIN FL270 WITH NO REPLY AGAIN. ACR Y ADVISED THEY WERE DSNDING DUE TO AN RA ON TCASII. I CLRED ACR X TO CLB AND MAINTAIN FL270 AND AGAIN NO REPLY, HOWEVER, ACR X EXECUTED AN IMMEDIATE CLB TO FL270. AT THIS POINT, SEPARATION IS LOST. AT THE TIME OF THIS INCIDENT, I BELIEVED THIS TO BE A MODE 'C' SWAP BECAUSE THE TARGETS MERGED AND ACR X RAPID MODE C CHANGE WITH NO REPLY, AS WELL AS TCASII RA. WHY DIDN'T ACR X QUESTION HIS CLRNC TO FL260 AFTER BEING TOLD HIS TFC IS AT FL260. WHY DIDN'T ACR X ANSWER THE 3 CLRNC THAT COULD HAVE POTENTIALLY AVOIDED THIS PROB. SUPPLEMENTAL INFO FROM ACN 235548: THE RADAR CTLR ISSUED TFC TO ACR X AGAIN SAYING THE TFC WAS 'AT FL260 MAINTAIN FL270.' AGAIN, THE ACR X DID NOT RESPOND. WHEN CONFLICT ALERT ACTIVATED, THE RADAR CTLR TOLD ACR X TO CLB AND MAINTAIN FL270. STILL, ACR X DID NOT RESPOND. SUPPLEMENTAL INFO FROM ACN 234545: ACR X ON ZID CLRED FROM FL280 TO FL260, COPLT READ BACK CLRNC TO DSND TO FL260. WHILE DSNDING THROUGH FL270, A TCASII WARNING TA THEN IMMEDIATELY TO RA WAS PRESENTED AT ABOUT THE SAME TIME CTLR TOLD US TO CLB TO FL270. WE IMMEDIATELY INITIATED CLB TO FL270. CONFLICT WAS WITH ACR Y WHO WAS AT FL260. THIS ACFT WAS PASSING AT APPROX R ANGLES TO OUR FLT PATH. THEY ALSO RECEIVED A TCASII WARNING AND DSNDED. AFTER CONFLICT WAS RESOLVED, WE ASKED THE CTLR WHAT THE PROB HAD BEEN. HE RESPONDED, 'NO PROB, NO BIG DEAL, SWITCH TO FREQ.'

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.

Controller descended air carrier X to occupied altitude had less than standard separation from air carrier Y. System error. Air carrier X TCASII TA RA climb. Air carrier Y TCASII RA descend. Evasive action taken.