Narrative:

Our aircraft (DC9) was on a heading, 250 degrees as I recall, descending to 4000 ft assigned at 210 KTS. I heard a transmission from the controller the first of which was blocked that ended in '5000.' I picked up the microphone to transmit the word 'blocked.' before I could transmit 2 other aircraft transmitted 'blocked' very plain on the frequency (125.15). The frequency was very congested and the controller very busy. The controller never replied nor acknowledged the 'blocked' xmissions. In short order we got a TCASII RA to descend. At about the same time I saw the other aircraft (DC9) ahead and to our left in a right turning climb for avoidance. I think that the blocked '5000' transmission had been for him as he had probably been previously cleared below '5000 ft.' in the moments of disruption that followed we were not given clearance to intercept the localizer and flew through it (runway 21L dtw) and ended up on or slightly west of centerline of runway 21R. The situation was tense for a moment until we were able to recover to our proper position on centerline of runway 21L. I don't think there were any other conflicts as there were no other TCASII RA messages. The situation would have been avoided had the controller responded to the 'blocked' xmissions regarding his issued clearance. In his defense he was very busy, probably overloaded. I noticed no other faults and discrepancies in his performance. Also he did not seem to panic or let his operation fall apart.

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Original NASA ASRS Text

Title: POTENTIAL CONFLICT LTSS FOR 2 ARR ACFT DURING A PERIOD OF FREQ CONGESTION, SIMULTANEOUS XMISSIONS.

Narrative: OUR ACFT (DC9) WAS ON A HDG, 250 DEGS AS I RECALL, DSNDING TO 4000 FT ASSIGNED AT 210 KTS. I HEARD A XMISSION FROM THE CTLR THE FIRST OF WHICH WAS BLOCKED THAT ENDED IN '5000.' I PICKED UP THE MIKE TO XMIT THE WORD 'BLOCKED.' BEFORE I COULD XMIT 2 OTHER ACFT XMITTED 'BLOCKED' VERY PLAIN ON THE FREQ (125.15). THE FREQ WAS VERY CONGESTED AND THE CTLR VERY BUSY. THE CTLR NEVER REPLIED NOR ACKNOWLEDGED THE 'BLOCKED' XMISSIONS. IN SHORT ORDER WE GOT A TCASII RA TO DSND. AT ABOUT THE SAME TIME I SAW THE OTHER ACFT (DC9) AHEAD AND TO OUR L IN A R TURNING CLB FOR AVOIDANCE. I THINK THAT THE BLOCKED '5000' XMISSION HAD BEEN FOR HIM AS HE HAD PROBABLY BEEN PREVIOUSLY CLRED BELOW '5000 FT.' IN THE MOMENTS OF DISRUPTION THAT FOLLOWED WE WERE NOT GIVEN CLRNC TO INTERCEPT THE LOC AND FLEW THROUGH IT (RWY 21L DTW) AND ENDED UP ON OR SLIGHTLY W OF CTRLINE OF RWY 21R. THE SIT WAS TENSE FOR A MOMENT UNTIL WE WERE ABLE TO RECOVER TO OUR PROPER POS ON CTRLINE OF RWY 21L. I DON'T THINK THERE WERE ANY OTHER CONFLICTS AS THERE WERE NO OTHER TCASII RA MESSAGES. THE SIT WOULD HAVE BEEN AVOIDED HAD THE CTLR RESPONDED TO THE 'BLOCKED' XMISSIONS REGARDING HIS ISSUED CLRNC. IN HIS DEFENSE HE WAS VERY BUSY, PROBABLY OVERLOADED. I NOTICED NO OTHER FAULTS AND DISCREPANCIES IN HIS PERFORMANCE. ALSO HE DID NOT SEEM TO PANIC OR LET HIS OP FALL APART.

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.