Less than standard separation between 2 air carrier. Pilot deviation or operational error.

Attributes
ACN	95730
Time
Date	198807
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cgt airport : ord
State Reference	IL
Altitude	msl bound lower : 10000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau tracon : ord
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other other
Route In Use	enroute airway : ord
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 220 flight time total : 13000 flight time type : 1200
ASRS Report	95730
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 270 flight time total : 4000 flight time type : 1500
ASRS Report	95735
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : insufficient time
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error Inter Facility Coordination Failure

Narrative:

Issued/flew holding at cgt VOR to maintain 11000'. During outbnd turn to right (as published) told by ATC to 'descend immediately to 10000',' saw widebody transport air carrier Y approaching from east at 11000'. Closed throttles, disconnected autoplt, deployed spoilers and rapidly descended to 10000'. A conflict would have resulted from anything less than an immediate and rapid descent. Because of the very rapid change in altitude by us--no near miss occurred. Tried to call air carrier Y captain at his operations after landing to determine how it happened, but he had left operations area. Ord approach?/center? (Frequency 125.7?) seemed rattled and confused about the air carrier Y's entry into cgt area at 11000'. Callback conversation with reporter revealed the following: reporter did not talk with any ATC personnel after landing and has not had any contact with FAA since incident. Sep was less than 3 mi at first sighting of widebody transport air carrier Y at same altitude. Had about 500-600' vertical sep when 1 mi latitude. Reporter on approach frequency and shortly after passing he heard air carrier Y on same frequency. Does not know if ATC error or if flight crew of air carrier Y busted their altitude.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. PLT DEVIATION OR OPERATIONAL ERROR.

Narrative: ISSUED/FLEW HOLDING AT CGT VOR TO MAINTAIN 11000'. DURING OUTBND TURN TO RIGHT (AS PUBLISHED) TOLD BY ATC TO 'DSND IMMEDIATELY TO 10000',' SAW WDB ACR Y APCHING FROM E AT 11000'. CLOSED THROTTLES, DISCONNECTED AUTOPLT, DEPLOYED SPOILERS AND RAPIDLY DSNDED TO 10000'. A CONFLICT WOULD HAVE RESULTED FROM ANYTHING LESS THAN AN IMMEDIATE AND RAPID DSCNT. BECAUSE OF THE VERY RAPID CHANGE IN ALT BY US--NO NEAR MISS OCCURRED. TRIED TO CALL ACR Y CAPT AT HIS OPS AFTER LNDG TO DETERMINE HOW IT HAPPENED, BUT HE HAD LEFT OPS AREA. ORD APCH?/CENTER? (FREQ 125.7?) SEEMED RATTLED AND CONFUSED ABOUT THE ACR Y'S ENTRY INTO CGT AREA AT 11000'. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR DID NOT TALK WITH ANY ATC PERSONNEL AFTER LNDG AND HAS NOT HAD ANY CONTACT WITH FAA SINCE INCIDENT. SEP WAS LESS THAN 3 MI AT FIRST SIGHTING OF WDB ACR Y AT SAME ALT. HAD ABOUT 500-600' VERT SEP WHEN 1 MI LAT. RPTR ON APCH FREQ AND SHORTLY AFTER PASSING HE HEARD ACR Y ON SAME FREQ. DOES NOT KNOW IF ATC ERROR OR IF FLT CREW OF ACR Y BUSTED THEIR ALT.

Data retrieved from NASA's ASRS site as of August 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.