Narrative:

Bna TRACON was providing radar vectors to the ILS runway 20R approach. ATC cleared our flight for the ILS approach approximately 12 mi northeast of bna at an altitude of 4000 ft MSL. About 10 seconds later, ATC canceled our approach clearance and directed us to turn right to a heading of 270 degrees. We noted on our TCASII traffic at our 12 O'clock position less than 2 mi at 3000 ft and concluded that was the reason for our canceled approach. Shortly after turning to a 270 degree heading, ATC directed us to turn to a heading of 360 degrees. While established on a 360 degree heading at an altitude of 4000 ft, our TCASII alerted us to traffic at our 12 O'clock position altitude of 3800 ft and less than a mi. We responded to the TCASII RA by climbing to 4500 ft. Frequency congestion prevented us of informing ATC of our climb by 10 seconds. ATC then directed us to turn to a heading of 110 degrees. After turning, the TCASII advised us that we were clear of the threatening traffic and we returned to our assigned altitude of 4000 ft. The controller's sequencing plans falling through took our aircraft out of the normal flow. Moderate to heavy workload for the controller diverted his attention away from our flight. No TA was provided by ATC, and due to the fact that we were in IMC, we had to completely rely on the TCASII to avoid a mid air collision.

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Original NASA ASRS Text

Title: TCASII ALERT AND FLC FOLLOWED RESOLUTION COMMAND, DEVIATED FROM ASSIGNED ALT, THEN RETURNED.

Narrative: BNA TRACON WAS PROVIDING RADAR VECTORS TO THE ILS RWY 20R APCH. ATC CLRED OUR FLT FOR THE ILS APCH APPROX 12 MI NE OF BNA AT AN ALT OF 4000 FT MSL. ABOUT 10 SECONDS LATER, ATC CANCELED OUR APCH CLRNC AND DIRECTED US TO TURN R TO A HDG OF 270 DEGS. WE NOTED ON OUR TCASII TFC AT OUR 12 O'CLOCK POS LESS THAN 2 MI AT 3000 FT AND CONCLUDED THAT WAS THE REASON FOR OUR CANCELED APCH. SHORTLY AFTER TURNING TO A 270 DEG HDG, ATC DIRECTED US TO TURN TO A HDG OF 360 DEGS. WHILE ESTABLISHED ON A 360 DEG HDG AT AN ALT OF 4000 FT, OUR TCASII ALERTED US TO TFC AT OUR 12 O'CLOCK POS ALT OF 3800 FT AND LESS THAN A MI. WE RESPONDED TO THE TCASII RA BY CLBING TO 4500 FT. FREQ CONGESTION PREVENTED US OF INFORMING ATC OF OUR CLB BY 10 SECONDS. ATC THEN DIRECTED US TO TURN TO A HDG OF 110 DEGS. AFTER TURNING, THE TCASII ADVISED US THAT WE WERE CLR OF THE THREATENING TFC AND WE RETURNED TO OUR ASSIGNED ALT OF 4000 FT. THE CTLR'S SEQUENCING PLANS FALLING THROUGH TOOK OUR ACFT OUT OF THE NORMAL FLOW. MODERATE TO HVY WORKLOAD FOR THE CTLR DIVERTED HIS ATTN AWAY FROM OUR FLT. NO TA WAS PROVIDED BY ATC, AND DUE TO THE FACT THAT WE WERE IN IMC, WE HAD TO COMPLETELY RELY ON THE TCASII TO AVOID A MID AIR COLLISION.

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.