Narrative:

We received a momentary TCASII TA. TCASII idented the intruder at 2 O'clock, 11-12 mi, plus 1300 ft descending. The first officer and I searched the sector visually and were unable to acquire the intruder visually and were unable to acquire the intruder visually. On TCASII, we observed the intruder pass our right wing. Shortly after the intruder passed us, about 1-2 mins after the TA, ATC gave us a 'descend immediately' followed by 'correction, climb to FL330' followed by 'disregard' and shortly thereafter, 'say your altitude.' we complied with all ATC instructions showing altitude variances of a 100 ft descent immediately followed by a 400 ft climb, then descending back to FL310. My first officer and I were somewhat concerned and confused by the conflicting ATC instructions without any follow-up from ATC as to what the problem was. In our opinion, the ATC instructions were too late if at all necessary. As I said, it was only a momentary TA, there was no RA. From our observations on TCASII, the closest the intruder came was 2 O'clock, high at 1300 ft at 12 mi moving to 6 O'clock, plus 1800 ft at 8-9 mi. At the time of the incident, radio traffic on ZID frequency 133.05 was quite heavy. Complicating matters, apparently another controller who had access to the frequency was inadvertently transmitting on it, blocking radio communication. This could very well be one of the reasons for the late ATC instructions. However, I'm still unsure as to the logic of the conflicting ATC instructions. Also, where was the ATC supervisor? Supplemental information from acn 250024: the frequency 133.05 was busy and to add to the problem was another controller that didn't realize he was transmitting on this frequency and talking personal business on this frequency.

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Original NASA ASRS Text

Title: ACR FLC ISSUED CONFLICTING SET OF CLRNCS FROM ARTCC RADAR CTLR. UNAUTH USE OF FREQ ASSIGNED TO SECTOR BY UNKNOWN CTLR.

Narrative: WE RECEIVED A MOMENTARY TCASII TA. TCASII IDENTED THE INTRUDER AT 2 O'CLOCK, 11-12 MI, PLUS 1300 FT DSNDING. THE FO AND I SEARCHED THE SECTOR VISUALLY AND WERE UNABLE TO ACQUIRE THE INTRUDER VISUALLY AND WERE UNABLE TO ACQUIRE THE INTRUDER VISUALLY. ON TCASII, WE OBSERVED THE INTRUDER PASS OUR R WING. SHORTLY AFTER THE INTRUDER PASSED US, ABOUT 1-2 MINS AFTER THE TA, ATC GAVE US A 'DSND IMMEDIATELY' FOLLOWED BY 'CORRECTION, CLB TO FL330' FOLLOWED BY 'DISREGARD' AND SHORTLY THEREAFTER, 'SAY YOUR ALT.' WE COMPLIED WITH ALL ATC INSTRUCTIONS SHOWING ALT VARIANCES OF A 100 FT DSCNT IMMEDIATELY FOLLOWED BY A 400 FT CLB, THEN DSNDING BACK TO FL310. MY FO AND I WERE SOMEWHAT CONCERNED AND CONFUSED BY THE CONFLICTING ATC INSTRUCTIONS WITHOUT ANY FOLLOW-UP FROM ATC AS TO WHAT THE PROB WAS. IN OUR OPINION, THE ATC INSTRUCTIONS WERE TOO LATE IF AT ALL NECESSARY. AS I SAID, IT WAS ONLY A MOMENTARY TA, THERE WAS NO RA. FROM OUR OBSERVATIONS ON TCASII, THE CLOSEST THE INTRUDER CAME WAS 2 O'CLOCK, HIGH AT 1300 FT AT 12 MI MOVING TO 6 O'CLOCK, PLUS 1800 FT AT 8-9 MI. AT THE TIME OF THE INCIDENT, RADIO TFC ON ZID FREQ 133.05 WAS QUITE HVY. COMPLICATING MATTERS, APPARENTLY ANOTHER CTLR WHO HAD ACCESS TO THE FREQ WAS INADVERTENTLY XMITTING ON IT, BLOCKING RADIO COM. THIS COULD VERY WELL BE ONE OF THE REASONS FOR THE LATE ATC INSTRUCTIONS. HOWEVER, I'M STILL UNSURE AS TO THE LOGIC OF THE CONFLICTING ATC INSTRUCTIONS. ALSO, WHERE WAS THE ATC SUPVR? SUPPLEMENTAL INFO FROM ACN 250024: THE FREQ 133.05 WAS BUSY AND TO ADD TO THE PROB WAS ANOTHER CTLR THAT DIDN'T REALIZE HE WAS XMITTING ON THIS FREQ AND TALKING PERSONAL BUSINESS ON THIS FREQ.

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.