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

Attributes
ACN	134122
Time
Date	199001
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bdf
State Reference	IL
Altitude	msl bound lower : 24000 msl bound upper : 24000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
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 : 1 controller radar : 7
ASRS Report	134122
Person 2
Affiliation	company : air carrier
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	none taken : anomaly accepted
Consequence	faa : investigated
Miss Distance	horizontal : 9000 vertical : 800
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Scenario: air carrier X inbound to mdw via J64-bdf-jot-mdw at FL290. Air carrier Y proceeding direct irk (from vorin intersection) at FL240. Problem: how to get the air carrier X down west/O hitting air carrier Y. Possible solution: the computer (at the center) says that 3 mins can elapse before the aircraft are within 10 mi of each other--therefore, if air carrier X can vacate FL230 in 3 mins, everything will be ok, right? So, let's ask air carrier X if that's possible. More scenario: 'air carrier X, can you be out of FL230 in 3 mins?' 'air carrier X, uh, affirmative center.' 'roger, air carrier X descend and maintain FL200, no delays through FL230.' 'air carrier X, roger (reads back clearance).' end result: the aircraft pass with 800' sep and 1.5 mi, an operational error. What went wrong: I (the controller) accepted the air carrier X statement that he could do something as meaning he would do it. I did not ensure that he would. Meanwhile air carrier X set the plane up for a 3-MIN descent (computerized) through FL230, which took time that I had counted on and didn't do what I expected. Final comment: you know, I've read NASA's bulletins religiously for several yrs now, and seen this type of incident reported time and time again. I only wish that I had paid more attention to them at the time I was reading. I intend to rectify this now, albeit too late to prevent an entirely preventable (and stupid) error.

Original NASA ASRS Text

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

Narrative: SCENARIO: ACR X INBND TO MDW VIA J64-BDF-JOT-MDW AT FL290. ACR Y PROCEEDING DIRECT IRK (FROM VORIN INTXN) AT FL240. PROB: HOW TO GET THE ACR X DOWN W/O HITTING ACR Y. POSSIBLE SOLUTION: THE COMPUTER (AT THE CENTER) SAYS THAT 3 MINS CAN ELAPSE BEFORE THE ACFT ARE WITHIN 10 MI OF EACH OTHER--THEREFORE, IF ACR X CAN VACATE FL230 IN 3 MINS, EVERYTHING WILL BE OK, RIGHT? SO, LET'S ASK ACR X IF THAT'S POSSIBLE. MORE SCENARIO: 'ACR X, CAN YOU BE OUT OF FL230 IN 3 MINS?' 'ACR X, UH, AFFIRMATIVE CENTER.' 'ROGER, ACR X DSND AND MAINTAIN FL200, NO DELAYS THROUGH FL230.' 'ACR X, ROGER (READS BACK CLRNC).' END RESULT: THE ACFT PASS WITH 800' SEP AND 1.5 MI, AN OPERROR. WHAT WENT WRONG: I (THE CTLR) ACCEPTED THE ACR X STATEMENT THAT HE COULD DO SOMETHING AS MEANING HE WOULD DO IT. I DID NOT ENSURE THAT HE WOULD. MEANWHILE ACR X SET THE PLANE UP FOR A 3-MIN DSCNT (COMPUTERIZED) THROUGH FL230, WHICH TOOK TIME THAT I HAD COUNTED ON AND DIDN'T DO WHAT I EXPECTED. FINAL COMMENT: YOU KNOW, I'VE READ NASA'S BULLETINS RELIGIOUSLY FOR SEVERAL YRS NOW, AND SEEN THIS TYPE OF INCIDENT RPTED TIME AND TIME AGAIN. I ONLY WISH THAT I HAD PAID MORE ATTN TO THEM AT THE TIME I WAS READING. I INTEND TO RECTIFY THIS NOW, ALBEIT TOO LATE TO PREVENT AN ENTIRELY PREVENTABLE (AND STUPID) ERROR.

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.