Operational error. Air carrier X had less than standard separation from air carrier Y system error.

Attributes
ACN	289282
Time
Date	199411
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : tth
State Reference	IN
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other descent other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 11 controller radar : 9
ASRS Report	289282
Person 2
Affiliation	government : faa
Function	controller : radar other personnel other
Qualification	controller : developmental controller : non radar
Events
Anomaly	non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	none taken : unable
Consequence	Other
Miss Distance	horizontal : 24600 vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was observing/instructing a developmental at a high altitude radar sector, moderately busy. He had cleared an aircraft, air carrier X (DC9) from FL350 to FL310 and I had not noticed this clearance. There was opposite direction traffic at FL330 air carrier Y (B737). When the first aircraft started down and I realized the error, I at first prompted my trainee to initiate vectors, then took over the frequency and continued attempted separation, but it was too late.

Original NASA ASRS Text

Title: OPERROR. ACR X HAD LTSS FROM ACR Y SYS ERROR.

Narrative: I WAS OBSERVING/INSTRUCTING A DEVELOPMENTAL AT A HIGH ALT RADAR SECTOR, MODERATELY BUSY. HE HAD CLRED AN ACFT, ACR X (DC9) FROM FL350 TO FL310 AND I HAD NOT NOTICED THIS CLRNC. THERE WAS OPPOSITE DIRECTION TFC AT FL330 ACR Y (B737). WHEN THE FIRST ACFT STARTED DOWN AND I REALIZED THE ERROR, I AT FIRST PROMPTED MY TRAINEE TO INITIATE VECTORS, THEN TOOK OVER THE FREQ AND CONTINUED ATTEMPTED SEPARATION, BUT IT WAS TOO LATE.

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.