ALTDEV ALT EXCURSION BY ACR IN FLC RESPONSE TO TCASII RA.

Narrative

ACR FLT X PROCEEDING DIRECT TO OMA VOR AT FL280; AUTOPLT ON; FO FLYING ACFT IN CLOUDS WITH SOME TSTM ACTIVITY IN LCL AREA. TCASII ON WITH SWITCH PLACED IN TA/RA. HEARD CTR TALK TO ACR FLT Y; PROCEEDING FROM MKC TO MSP AS IT WAS CLBING AND HE WAS ASKED ABOUT TSTMS. ACR Y CLRED TO FL270 UNTIL HE WAS CLR OF US. TARGET CAME ON OUR TCASII AT ABOUT 7 O'CLOCK POS AND SHOWED THAT IT WAS CLBING AND ABOUT 2000 FT BELOW US. ASSUMED THIS WAS ACR Y. AS TARGET APCHED OUR 2 MI RANGE; ALT DIFFERENCE WAS 1100 FT; THEN 1000 FT; THEN 900 FT THEN 800 FT BELOW US. WHEN THIS REACHED 500 FT; OUR TCASII GAVE CONFLICT ALERT AND SAID TO CLB; WHICH FO DID IMMEDIATELY AND ADDED FULL PWR. AT THIS TIME; APPARENTLY ACR Y RECEIVED A TCASII WARNING TO DSND; WHICH IT DID. WE THEN RECEIVED 'MONITOR VERT SPD' AND THEN 'CLR OF CONFLICT' AS TARGET PASSED BY US. NO VISUAL SIGHTING. WE THEN RETURNED TO FL280. DISCUSSION THEN HELD ON FREQ BTWN ACR X; ACR Y; AND CTR CTLR. ACR Y SAID HE WAS LEVEL AT FL270 WHEN ALERT OCCURRED. ALL 3 OF US SAID WE WOULD FILE A RPT ON THIS EVENT. ACR X THEN CONTINUED TO OMA WITHOUT FURTHER INCIDENT.