Air carrier on approach has near midair collision with a traffic watch helicopter. Gets TCASII RA.

Attributes
ACN	323295
Time
Date	199511
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mdw
State Reference	IL
Altitude	msl bound lower : 2500 msl bound upper : 2500
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tower : mdw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Helicopter
Flight Phase	cruise other
Flight Plan	None
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 14000 flight time type : 3600
ASRS Report	323295
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	conflict : nmac non adherence : far other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action none taken : unable
Consequence	Other
Miss Distance	horizontal : 0 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

Cleared to fly ILS runway 31C circle to land runway 22L (GS inoperative). At approximately 2800 ft on approach, we were advised that 2000 ft helicopter traffic had us in sight and would avoid us. Traffic observed on TCASII (no visual contact) -700 ft TCASII traffic was on converging course and it continued to decrease (separation). We stopped our descent at 2500 ft. Helicopter continued above 2000 ft. Subsequent RA 'climb, climb.' visual contact made with helicopter. Shortly after RA, passed directly under us -300 ft on TCASII. Had we not checked our descent at 2500 ft collision would have occurred. Midway tower failed to provide separation (radar environment).

Original NASA ASRS Text

Title: ACR ON APCH HAS NMAC WITH A TFC WATCH HELI. GETS TCASII RA.

Narrative: CLRED TO FLY ILS RWY 31C CIRCLE TO LAND RWY 22L (GS INOP). AT APPROX 2800 FT ON APCH, WE WERE ADVISED THAT 2000 FT HELI TFC HAD US IN SIGHT AND WOULD AVOID US. TFC OBSERVED ON TCASII (NO VISUAL CONTACT) -700 FT TCASII TFC WAS ON CONVERGING COURSE AND IT CONTINUED TO DECREASE (SEPARATION). WE STOPPED OUR DSCNT AT 2500 FT. HELI CONTINUED ABOVE 2000 FT. SUBSEQUENT RA 'CLB, CLB.' VISUAL CONTACT MADE WITH HELI. SHORTLY AFTER RA, PASSED DIRECTLY UNDER US -300 FT ON TCASII. HAD WE NOT CHKED OUR DSCNT AT 2500 FT COLLISION WOULD HAVE OCCURRED. MIDWAY TWR FAILED TO PROVIDE SEPARATION (RADAR ENVIRONMENT).

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.