MD80 experiences multiple TCAS RA events with unsighted target in both VMC and IMC conditions.

Attributes
ACN	786026
Time
Date	200805
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl single value : 11500
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude ground : maintenance
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	786026
Events
Anomaly	conflict : nmac
Independent Detector	aircraft equipment : tcas
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 0 vertical : 300
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

On climb out of ord; our flight was being vectored by ZAU. We were climbing to 13000 ft MSL out of 10000 ft MSL when we got a TCAS TA and was advised by center of a VFR target at 11500 ft MSL. We soon got a TCAS RA advising us to descend. We complied with the RA and notified center. Shortly thereafter; we got a second RA to monitor vertical speed. Then; as we closed on the VFR target; we got a third RA telling us to climb. As we complied; we went IMC at 11000 ft MSL and no visual on the VFR target. As we closed on the VFR target; we climbed over him in IMC somewhere between 100-500 ft. It was hard to tell if those were the exact distances. We were climbing at 3500 FPM and the TCAS was clicking off the distances. We were directly overhead the VFR target. We reported to center that the VFR target was IMC. Unknown whether any action was taken.

Original NASA ASRS Text

Title: MD80 EXPERIENCES MULTIPLE TCAS RA EVENTS WITH UNSIGHTED TARGET IN BOTH VMC AND IMC CONDITIONS.

Narrative: ON CLB OUT OF ORD; OUR FLT WAS BEING VECTORED BY ZAU. WE WERE CLBING TO 13000 FT MSL OUT OF 10000 FT MSL WHEN WE GOT A TCAS TA AND WAS ADVISED BY CTR OF A VFR TARGET AT 11500 FT MSL. WE SOON GOT A TCAS RA ADVISING US TO DSND. WE COMPLIED WITH THE RA AND NOTIFIED CTR. SHORTLY THEREAFTER; WE GOT A SECOND RA TO MONITOR VERT SPD. THEN; AS WE CLOSED ON THE VFR TARGET; WE GOT A THIRD RA TELLING US TO CLB. AS WE COMPLIED; WE WENT IMC AT 11000 FT MSL AND NO VISUAL ON THE VFR TARGET. AS WE CLOSED ON THE VFR TARGET; WE CLBED OVER HIM IN IMC SOMEWHERE BTWN 100-500 FT. IT WAS HARD TO TELL IF THOSE WERE THE EXACT DISTANCES. WE WERE CLBING AT 3500 FPM AND THE TCAS WAS CLICKING OFF THE DISTANCES. WE WERE DIRECTLY OVERHEAD THE VFR TARGET. WE RPTED TO CTR THAT THE VFR TARGET WAS IMC. UNKNOWN WHETHER ANY ACTION WAS TAKEN.

Data retrieved from NASA's ASRS site as of May 2009 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.