Air taxi flight crew with C90 TRACON experienced TCAS RA event at 5000 ft with issued traffic; subse...

Narrative:

Received a traffic advisory from TRACON regarding traffic identified at 400 ft above and converging from approximately 1130-1200 o'clock position. The controller also issued a vector upon reaching the next fix on our route. About 10 seconds later TCAS generated a 'traffic' alert followed which was soon followed by a 'descend' command. I did not visually acquire the target prior to the 'descend' command. Upon receiving the 'descend' RA I disconnected the autopilot and simultaneously began a descent as commanded on my vsi. The descent resulted in an approximate 300-400 foot altitude loss. I then received a 'clear of conflict' and I returned the aircraft to the assigned altitude. In the meanwhile; the first officer; as soon as there was a break in other ATC radio communications announced that our aircraft was descending for TCAS. Upon arrival into mdw I was asked to call TRACON. The controller that I spoke to at TRACON asked for my pilot certificate information and address and stated that they understood we responded to a TCAS RA; but had to document the situation since there was a loss of separation. Being aware of the potential conflict and the busy radio I would like to have had the vector prior to the next fix; I believe this would have remedied the RA in advance. We were going to make that request when it appeared evident that the traffic would be a conflict; but were not able to get a break in the radio in those few moments.

Original NASA ASRS Text

Title: Air taxi flight crew with C90 TRACON experienced TCAS RA event at 5000 FT with issued traffic; subsequent descent resulted in an ATC loss of separation.

Narrative: Received a traffic advisory from TRACON regarding traffic identified at 400 FT above and converging from approximately 1130-1200 o'clock position. The Controller also issued a vector upon reaching the next fix on our route. About 10 seconds later TCAS generated a 'TRAFFIC' alert followed which was soon followed by a 'DESCEND' command. I did not visually acquire the target prior to the 'DESCEND' command. Upon receiving the 'DESCEND' RA I disconnected the autopilot and simultaneously began a descent as commanded on my VSI. The descent resulted in an approximate 300-400 foot altitude loss. I then received a 'CLEAR OF CONFLICT' and I returned the aircraft to the assigned altitude. In the meanwhile; the First Officer; as soon as there was a break in other ATC radio communications announced that our aircraft was descending for TCAS. Upon arrival into MDW I was asked to call TRACON. The Controller that I spoke to at TRACON asked for my pilot certificate information and address and stated that they understood we responded to a TCAS RA; but had to document the situation since there was a loss of separation. Being aware of the potential conflict and the busy radio I would like to have had the vector prior to the next fix; I believe this would have remedied the RA in advance. We were going to make that request when it appeared evident that the traffic would be a conflict; but were not able to get a break in the radio in those few moments.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	839146
Time
Date	200906
Local Time Of Day	1201-1800
Place
Locale Reference	C90.TRACON
State Reference	IL
Environment
Light	Daylight
Aircraft 1
Make Model Name	Light Transport
Operating Under FAR Part	Part 135
Flight Phase	Descent
Route In Use	STAR GSH
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor
Experience	Flight Crew Last 90 Days 70 Flight Crew Total 6800 Flight Crew Type 85
Events
Anomaly	Conflict NMAC
Miss Distance	Horizontal 0 Vertical 400

Air taxi flight crew with C90 TRACON experienced TCAS RA event at 5000 ft with issued traffic; subsequent descent resulted in an ATC loss of separation.