Narrative:

A TA advisory was received while on radar vectors at 9000 ft. The advisory was level at +300 ft at 1 O'clock. The TA was immediately followed by an RA advisory to descend, still showing traffic level +300 ft. As soon as the descent was started, the advisory cancelled and the target disappeared. No targets were showing prior to the TA. No traffic was sighted visually. The first officer advised mke approach of the alert and descent as we leveled at 8500 ft. Approach said there was no traffic in our area. He then cleared us to 7000 ft for the handoff to ord approach. As we leveled at 7000 ft we received another TA and RA advisory at 12 O'clock -2500 ft climbing. This traffic was spotted visually. It was a high performance single pulling into a loop. No deviation was made and the advisory cancelled as he started down the back side of the loop. I have no idea if the aircraft doing aerobatics could have triggered the advisory at 9000 MSL. Judging by his speed and performance, he may have. Perhaps the rapid altitude and position changes of his aerobatics caused the TCASII computer to issue a false advisory. My experience with TCASII has been positive. It gives fast, accurate traffic information. Plus it gives you some insight and respect for the controllers.

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Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION DURING PLT FLC RESPONSE TO TCASII RA. EVASIVE ACTION DSCNT.

Narrative: A TA ADVISORY WAS RECEIVED WHILE ON RADAR VECTORS AT 9000 FT. THE ADVISORY WAS LEVEL AT +300 FT AT 1 O'CLOCK. THE TA WAS IMMEDIATELY FOLLOWED BY AN RA ADVISORY TO DSND, STILL SHOWING TFC LEVEL +300 FT. AS SOON AS THE DSCNT WAS STARTED, THE ADVISORY CANCELLED AND THE TARGET DISAPPEARED. NO TARGETS WERE SHOWING PRIOR TO THE TA. NO TFC WAS SIGHTED VISUALLY. THE FO ADVISED MKE APCH OF THE ALERT AND DSCNT AS WE LEVELED AT 8500 FT. APCH SAID THERE WAS NO TFC IN OUR AREA. HE THEN CLRED US TO 7000 FT FOR THE HDOF TO ORD APCH. AS WE LEVELED AT 7000 FT WE RECEIVED ANOTHER TA AND RA ADVISORY AT 12 O'CLOCK -2500 FT CLBING. THIS TFC WAS SPOTTED VISUALLY. IT WAS A HIGH PERFORMANCE SINGLE PULLING INTO A LOOP. NO DEV WAS MADE AND THE ADVISORY CANCELLED AS HE STARTED DOWN THE BACK SIDE OF THE LOOP. I HAVE NO IDEA IF THE ACFT DOING AEROBATICS COULD HAVE TRIGGERED THE ADVISORY AT 9000 MSL. JUDGING BY HIS SPD AND PERFORMANCE, HE MAY HAVE. PERHAPS THE RAPID ALT AND POS CHANGES OF HIS AEROBATICS CAUSED THE TCASII COMPUTER TO ISSUE A FALSE ADVISORY. MY EXPERIENCE WITH TCASII HAS BEEN POSITIVE. IT GIVES FAST, ACCURATE TFC INFO. PLUS IT GIVES YOU SOME INSIGHT AND RESPECT FOR THE CTLRS.

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.