Narrative:

Dfw jan/tue/94, air carrier X had near miss of 400 ft vertical and 0 ft horizontal. We took evasive action. The WX was about 2000 ft overcast with better than 5 mi visibility. TCASII was placed in traffic only (no RA) mode per guidance from company when in the traffic pattern. As we crossed the 36L OM, I twice checked on dfw tower frequency but received no answer. I mentioned our position by calling out the name of the 36L OM on one of the calls. Neither call was acknowledged although 2 controller voices were constantly talking on the frequency, mostly to aircraft lined up to take off on the inside runway. There were many targets on the TCASII and one of them turned yellow accompanied by the aural warning of 'traffic, traffic.' the intruder was at 11 O'clock and about 500 ft below us. I ordered the first officer to arrest the descent, and so we went above the GS in an effort to avoid the intruder Y. We were above the GS about 2 1/2 mi from the end of the runway and about 900 ft AGL when the TCASII indicated the intruder going under us at 400 ft below us. The intruder would have been closer if we had been on or slightly below (normal bracketing maneuvers) the GS. We never visually acquired the intruder. While we were busy with TCASII and evasive action, I heard the controller voice I took to be a trainer or supervisor speak our call sign. He said something about a helicopter, but it was not at all clear to me that the intruder we observed was the one he was mentioning. I was simply too busy to answer him until after the intruder encounter was successfully resolved. I'm rethinking the wisdom of selecting away from the TCASII RA mode. I believe we would have gotten better protection and evasive guidance if we had had the TCASII fully armed. After landing I asked the ground controller for a phone number. I called tower supervisor and he stated the traffic was a helicopter who was being handled by another controller on a different frequency and that the helicopter was being operated in accordance with a tower LOA. He further stated that the helicopter saw us. I asked the separation standard, and he replied that all the helicopter had to do was not hit us! Supervisor stated that they (dfw tower) hadn't had these problems until TCASII was installed.

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Original NASA ASRS Text

Title: ACR X TCASII TA HAD NMAC WITH VFR HELI ON FINAL APCH. EVASIVE ACTION TAKEN.

Narrative: DFW JAN/TUE/94, ACR X HAD NEAR MISS OF 400 FT VERT AND 0 FT HORIZ. WE TOOK EVASIVE ACTION. THE WX WAS ABOUT 2000 FT OVCST WITH BETTER THAN 5 MI VISIBILITY. TCASII WAS PLACED IN TFC ONLY (NO RA) MODE PER GUIDANCE FROM COMPANY WHEN IN THE TFC PATTERN. AS WE CROSSED THE 36L OM, I TWICE CHKED ON DFW TWR FREQ BUT RECEIVED NO ANSWER. I MENTIONED OUR POS BY CALLING OUT THE NAME OF THE 36L OM ON ONE OF THE CALLS. NEITHER CALL WAS ACKNOWLEDGED ALTHOUGH 2 CTLR VOICES WERE CONSTANTLY TALKING ON THE FREQ, MOSTLY TO ACFT LINED UP TO TAKE OFF ON THE INSIDE RWY. THERE WERE MANY TARGETS ON THE TCASII AND ONE OF THEM TURNED YELLOW ACCOMPANIED BY THE AURAL WARNING OF 'TFC, TFC.' THE INTRUDER WAS AT 11 O'CLOCK AND ABOUT 500 FT BELOW US. I ORDERED THE FO TO ARREST THE DSCNT, AND SO WE WENT ABOVE THE GS IN AN EFFORT TO AVOID THE INTRUDER Y. WE WERE ABOVE THE GS ABOUT 2 1/2 MI FROM THE END OF THE RWY AND ABOUT 900 FT AGL WHEN THE TCASII INDICATED THE INTRUDER GOING UNDER US AT 400 FT BELOW US. THE INTRUDER WOULD HAVE BEEN CLOSER IF WE HAD BEEN ON OR SLIGHTLY BELOW (NORMAL BRACKETING MANEUVERS) THE GS. WE NEVER VISUALLY ACQUIRED THE INTRUDER. WHILE WE WERE BUSY WITH TCASII AND EVASIVE ACTION, I HEARD THE CTLR VOICE I TOOK TO BE A TRAINER OR SUPVR SPEAK OUR CALL SIGN. HE SAID SOMETHING ABOUT A HELI, BUT IT WAS NOT AT ALL CLR TO ME THAT THE INTRUDER WE OBSERVED WAS THE ONE HE WAS MENTIONING. I WAS SIMPLY TOO BUSY TO ANSWER HIM UNTIL AFTER THE INTRUDER ENCOUNTER WAS SUCCESSFULLY RESOLVED. I'M RETHINKING THE WISDOM OF SELECTING AWAY FROM THE TCASII RA MODE. I BELIEVE WE WOULD HAVE GOTTEN BETTER PROTECTION AND EVASIVE GUIDANCE IF WE HAD HAD THE TCASII FULLY ARMED. AFTER LNDG I ASKED THE GND CTLR FOR A PHONE NUMBER. I CALLED TWR SUPVR AND HE STATED THE TFC WAS A HELI WHO WAS BEING HANDLED BY ANOTHER CTLR ON A DIFFERENT FREQ AND THAT THE HELI WAS BEING OPERATED IN ACCORDANCE WITH A TWR LOA. HE FURTHER STATED THAT THE HELI SAW US. I ASKED THE SEPARATION STANDARD, AND HE REPLIED THAT ALL THE HELI HAD TO DO WAS NOT HIT US! SUPVR STATED THAT THEY (DFW TWR) HADN'T HAD THESE PROBS UNTIL TCASII WAS INSTALLED.

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.