MDT HAS TCASII TA; RA DURING CLB.

Narrative

FLT WAS APPROX 30 NM WSW OF HMV ON A VECTOR TO INTERCEPT THE SWEED 2 ARR NW OF HMV. THE FLT WAS CLBING AT APPROX 1000 FPM THROUGH FL260 WITH A CLRNC TO FL290 WHEN WE RECEIVED A 'TFC' AURAL WARNING WITH A RED 'TFC' MESSAGE ON THE IVSI AND A 2000 FPM MINIMUM CLB COMMAND. I DISCONNECTED THE AUTOPLT AND INITIATED AN IMMEDIATE CLB WHILE THE FO INFORMED ATC. I SELECTED MY TCASII DISPLAY AND IT SHOWED A RED -07 TARGET IN THE 8 O'CLOCK POS; MERGING WITH THE ACFT SYMBOL. PASSING APPROX FL280 THE RA ENDED AND I CONTINUED A NORMAL CLB TO FL290. AFTER THE RA ENDED I EXPANDED THE RANGE AND ENVELOPE OF THE TCASII DISPLAY AND WAS UNABLE TO REACQUIRE THE TARGET. THERE WAS NO DEV FROM AN ATC CLRNC OR ASSIGNED ALT BECAUSE WE WERE ALREADY CLBING TO A HIGHER ASSIGNED ALT. DURING THE RA THE FO NOTIFIED ATC THAT WE WERE FOLLOWING A TCASII RA AND INQUIRED ABOUT ANY TFC IN OUR IMMEDIATE VICINITY. ATC ADVISED US THAT ALL THEY HAD WAS A FLT OF 4 KC-135 TANKER ACFT UNDERNEATH US AT APPROX FL220 (OR 230). DURING THE RA; PRIOR TO ATC'S MESSAGE I SAW 2 ACFT (LIGHTS ONLY) IN A LOOSE FORMATION; IN MY 8 O'CLOCK AND SEVERAL THOUSAND FT BELOW US. THE FO RPTED TO ATC THAT WE HAD AN ACFT PASS UNDER US BY A COUPLE OF HUNDRED FT. THE FO SAW THE THREAT ACFT PASS BEHIND AND TO OUR R WITHIN 400-500 FT VERT SEPARATION. ATC DIDN'T SEE ANYTHING IN OUR IMMEDIATE AREA BUT THEY ASKED US IF THE TCASII COMMANDED A CLB OR A DSCNT. WE INFORMED THEM THAT WE RECEIVED A CLB COMMAND. LACK OF ADVANCED WARNING: THE FIRST THING I RECALL WAS HEARING THE 'TFC' AURAL WARNING. I IMMEDIATELY LOOKED DOWN AT THE IVSI AND IT WAS ALREADY IN THE RA MODE WITH A RED 'TFC' MESSAGE AND A VERT COMMAND. WE NEVER HEARD OR SAW A TA. I DID NOT HEAR A CLB OR DSND AURAL WARNING. LATER THE FO SAID THAT HE THOUGHT HE HEARD THE TCASII SAY SOMETHING; POSSIBLY A 'MONITOR VERT SPD' OR A 'CLB' MESSAGE; BUT HE WASN'T SURE. HE ALSO SAID THAT THE AURAL MESSAGE CAME FROM THE L SIDE SPEAKER; NOT THROUGH HIS HEADSET. AFTER LNDG IN CVG; I RAN THE TCASII THROUGH SEVERAL TEST CYCLES AND IT TESTED OK EXCEPT THE ONLY AUDIO I COULD HEAR WAS A WEAK 'TCASII TEST OK' THROUGH THE L SPEAKER. I COULD NOT HEAR THE AURAL WARNING THROUGH MY HEADSET. (NOTE: INFLT I WAS USING THE TELEX.) ON THE GND I GOT OUT MY DAVID CLARKS AND STILL COULDN'T HEAR THE AURAL WARNING THROUGH THE HEADSET.) I THEN WROTE UP THE TCASII AURAL WARNING AND LEFT THE ACFT AT THE MAINT HANGAR SO I DON'T KNOW WHAT AVIONICS DID TO FIX THE PROB. POSSIBLE SCENARIOS: 1) ERRONEOUS TCASII INDICATION. 2) A MIL ACFT PASSING UNDERNEATH US INITIATED A VERY STEEP VERT CLB; POSSIBLY AFTER REFUELING FROM ONE OF THE KC-135 ACFT. A RAPID VERT MANEUVER MAY HAVE TAKEN THE THREAT ACFT RAPIDLY THROUGH THE NORMAL TA RANGE SO THAT IT BECAME AN RA BEFORE THE TCASII COULD DISPLAY IT AS A TA. 3) TCASII DIDN'T DETECT THE THREAT ACFT UNTIL IT WAS WELL WITHIN THE RA ENVELOPE. IT HAS BEEN NOTED THAT THE TCASII SYS INSTALLED IN THE CL-65 DOES NOT ALWAYS DISPLAY TFC WITHIN THE SELECTED ENVELOPE. WE HAVE RPTS OF THE TCASII TAKING AS LONG AS 10-15 MINS TO DISPLAY A TARGET THAT IS OBVIOUSLY WITHIN THE SELECTED RANGE. OTHER TIMES A TARGET; WELL WITHIN THE SELECTED RANGE; WILL DROP ON AND OFF THE TCASII DISPLAY. IT IS NOT KNOWN WHETHER OR NOT THIS IS A DISPLAY PROB OR THE TCASII ACTUALLY IS NOT AWARE OF THE OTHER ACFT. UPDATE: COMMERCIAL RADIO IS LOOKING INTO THIS TOO; ZTL QUALITY CTL RPTED NO LOSS OF SEPARATION. THERE HAVE BEEN RPTS OF ERRONEOUS TCASII RA'S DUE TO ANOMALIES WITH MIL XPONDERS; PARTICULARLY KC-135'S.