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

Attributes
ACN	145091
Time
Date	199004
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ord
State Reference	IL
Altitude	msl bound lower : 4000 msl bound upper : 4000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 6700 flight time type : 1550
ASRS Report	145091
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	other flight crewa
Resolutory Action	none taken : insufficient time
Consequence	faa : reviewed incident with flight crew Other
Miss Distance	horizontal : 1500 vertical : 200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X were being radar vectored for approach to localizer 27R at ord level at 4000' heading 180 degrees 170 KIAS when from our right front, heading eastbound, came air carrier medium large transport Y which descended from above through our assigned altitude as it passed within 1/4-1/3 mi of our nose. When the first officer asked approach, 'what about that air carrier Y that just passed in front of us?', ord approach replied, 'he should have passed behind you.' then he gave us a turn to intercept the localizer 27R and frequency change to a final controller. We were in and out of the clouds at the time and had visibility contact with air carrier Y for only a few seconds.

Original NASA ASRS Text

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

Narrative: ACR X WERE BEING RADAR VECTORED FOR APCH TO LOC 27R AT ORD LEVEL AT 4000' HDG 180 DEGS 170 KIAS WHEN FROM OUR RIGHT FRONT, HDG EBND, CAME ACR MLG Y WHICH DSNDED FROM ABOVE THROUGH OUR ASSIGNED ALT AS IT PASSED WITHIN 1/4-1/3 MI OF OUR NOSE. WHEN THE F/O ASKED APCH, 'WHAT ABOUT THAT ACR Y THAT JUST PASSED IN FRONT OF US?', ORD APCH REPLIED, 'HE SHOULD HAVE PASSED BEHIND YOU.' THEN HE GAVE US A TURN TO INTERCEPT THE LOC 27R AND FREQ CHANGE TO A FINAL CTLR. WE WERE IN AND OUT OF THE CLOUDS AT THE TIME AND HAD VIS CONTACT WITH ACR Y FOR ONLY A FEW SECS.

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.